subject:"\[Repeater\-Builder\] Coax length"


 Hi Kevin:

Regarding temperature, our club has a site, no A/C or heat, where 
temperatures inside the shelter can get below +20 deg F in winter, and 
well over 130 deg F in the summer heat.  I can't imagine filter tuning 
not changing under such conditions, Invar or not.  I can see over time 
where tuning might walk off the reservation.  But I bow to your 
greater experience with cavity duplexers.


Another chance?  Which part, erroneous readings, don't directly measure 
power, or the voltmeter part?  Sure, what the heck. ;-)


I've had Bird 43's, and calibrated line sections with matched elements 
for that matter, give erroneous reflected power readings depending upon 
what was going on with the transmission line.  By erroneous, I mean it 
was usually a reading that was, for example, excessively high versus 
what we knew was going on, such as a straight piece of rigid line or 
coax terminated into a known good load.  On rare occasion, we found we 
slipped a bullet or had a bad connector.  More often, relocating the 
instrument somewhere else along the line resolved those bad readings.


RF calorimeters can measure power directly.  But unless they've one 
hidden in them somewhere, ThruLine meters can not.  Just because the 
Commission might accept wattmeter readings, or Bird says so, doesn't 
make it so.


As for the voltmeter part, check out page 6 of the Bird 43 manual (page 
18 of the PDF), a copy of which you'll recall is here:


http://www.repeater-builder.com/bird/pdf/bird-43-wattmeter-2004.pdf

I respectfully submit what is shown is a schematic/diagram of a 
directional coupler attached to a voltmeter as an indicator.  An induced 
RF voltage sample is rectified, filtered and applied through a dropping 
resistor to a shunt-connected ammeter.


By definition, a voltmeter is the shunt-connected ammeter with series 
resistor part.  But don't take my word for it.  Take a peek at Chapter 
25 in any recent ARRL Handbook (this works for my 2007 copy anyway).


Is it less a voltmeter because the induced voltage tracks current on the 
line?  Want to call it an ammeter or current meter then, after all 
that's what the actual meter movement is?


I submit this particular voltmeter happens to be calibrated to read 
average power at 50 ohms impedance, and it does this quite well within 
its limitations.


I now await your thrashing.  Please be gentle. ;-)

Like the manual says, the Bird 43 is fast, convenient and accurate.  I 
agree it's fast and convenient.  I'll agree it's accurate with the 
caveats expressed.  It beats lugging a slotted line around, and it beats 
every other meter like it, IMHO, including my old Daiwa dual-metered POS 
wattmeter. ;-)


Oh, BTW, the emperor has no clothes either. :-P

73, Russ WB8ZCC


On 8/14/2010 10:11 PM, Kevin Custer wrote:


Russ Hines wrote:


Some related comments, if you don't mind.

Temperature changes seem to be the biggest detuner of largely 
mechanical devices like cavity duplexers.  We often send our 
repeaters off to live in less-than-ideal environments, then expect 
cavity input/output impedances to remain as we measured them in the 
shop?  Don't think so.


I largely disagree.  Most modern duplexer designs (within the last 25 
years or so) use compensating elements to make the duplexer or cavity 
temperature stable.  Invar is a nickel-steel alloy that exhibits about 
1/10 the thermal expansion as a common carbon steel counterpart.  
Invar is used to make the tuning rod - many times it's threaded.  The 
rest of the duplexer or cavity is usually made of similar metals and 
generally thermal expansion occurs across these components equally, 
resulting in extremely low frequency drift over its rated operating 
temperature.





Our in-line power meters, like our trusted Bird 43, do not directly 
measure power.  They're really voltage meters calibrated in watts at 
a specific impedance.  That's why they can be fooled into displaying 
an erroneous reflected power reading, perhaps lulling us into a sense 
of security that the VSWR on the line is acceptable when it may not be.


What?  Maybe you would like to have another chance at that one

Kevin Custer

Re: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread Joe

I don't know about that.  Anritsu SiteMaster and CellMaster test sets 
are fairly common test equipment available to cell techs here in 
Connecticut.  Whether they use them (or know how) is another thing.

Joe

On 8/15/2010 2:59 AM, Nate Duehr wrote:
 What's up with the RF industry not buying these things by the truckload?  Too 
 spendy?

RE: [Repeater-Builder] Coax length, etc.

 But why? If all of the power (or, let's hope, at least 
 99.99% of it)
  is
  on-channel, *should* a properly-designed and properly-functioning
  transmitter misbehave due to the poor match a duplexer presents at
  frequencies far removed from the channel center?
 
 Well yes, properly designed transmitter. But how much do you 
 want to pay for
 it? 

Me personally?  I'll pay for a transmitter that works, and works right.  

The way I see it, repeaters are like cars.  You have to get your car
inspected for safety.  Your car doesn't pass safety inspection?  You can't
drive it on the public roads, lest you'd be putting other people at risk.
Same with a repeater transmitter.  If it's unstable and has the potential
for causing interference other systems (ham repeaters, public safety,
aviation, etc.), it shouldn't be on the air.  Either fix it, or if you can't
afford to fix it, take it down.  I don't want some scmuck driving a beat-up
1972 pickup down the interstate in front of me and having his rear bumper
fall off any more than I want somebody putting some clunker up on a
mountantop and having it go spurious and interfering with EMS or ATC. That's
just the way I see it, sorry if that rubs some people the wrong way.

 A built in isolator will solve all of those problems as 
 an example.

Maybe.  An isolator will help flatten the load on, and around, the carrier
frequency, but isolators, too, have a finite VSWR bandwidth, they won't
provide a perfect load across the entire spectrum.  And if you can afford an
isolator, you can probably afford a better PA.

 It is almost impossible for a high Q cavity to not present 
 some reactance
 away from the tuned frequency. 

It's not almost impossible, it's definately impossible.

 If it didn't then it would not have any
 selectivity. 

Right.

 The random length cable of course transforms 
 that reactance to
 something that the transmitter may or may not be comfortable with as
 discussed above.

Just to clarify, the complex Z is being transformed (both R and jX), not
just the reactive component.

The thing with random-length cables is just that - they're random.  How do
we know what cable length is going to make the transmitter happy?  Does the
transmitter like more XL or more XC, or bigger R's or smaller R's, and at
what frequency, because as I'm sure you know, the complex Z is going vary
wildly at different frequencies, due to the duplexer's Z, its behavior as a
transformer with respect to the load Z at the antenna port, the antenna
feedline acting as a transformer with respect to the antenna feedpoint Z,
and the cable between the PA and the duplexer also acting as a transformer,
so you end up with this complex system of cascaded transformers.  Chances
are if the PA is that picky, its behavior may also change with temperature,
voltage, who knows what else.  

Antenna feedpoint Z's change with environmental conditions (precipitation,
icing, etc.).  Feedline electrical lengths (phase) change with temperature,
so the resulting Z at the duplexer antenna port is also going to change.
There are *so many variables* that will constantly be changing over time
that what may seem to work when you walk off the site may fail miserably
months, days, maybe even hours later after you think you've found that magic
cable length.  At least with an isolator we've taken the bulk of those
external variables out of the equation - I can agree with that.  But, call
me a fundamentalist, I still believe that a PA should work, and work right,
when it sees 50 ohms on-channel no matter what's happening off-channel.

--- Jeff WN3A

RE: [Repeater-Builder] Coax length, etc.

 Actually I think that even though Service Monitors have 
 finally become *relatively* commonplace in the Ham Shack, the 
 VNA is not something most hams have seen or know how to use.

For $100, Rick's (Amtronix) return loss bridge is a must-have for anyone
that has a SM with a SA/TG.  With it, there's no longer any excuse for not
being able to tune cavities properly for maximum return loss.

 Like Service Monitors used to be before the flood of HPs on 
 eBay in the last few years, I hear rumors of great deals on 
 VNAs, and yet never see them in any way plentiful, easy to 
 acquire, or affordable, but then again I'm also not 
 exactly looking that hard, and perhaps I'm missing one of 
 those everyone knows about Bob's VNA Warehouse! kinds of 
 sources for such things.

Hey, I didn't say they were cheap, nor that everybody can or should own one.

There's nothing more enjoyable than tuning up a $100 duplexer from Dayton on
a $50,000 network analyzer, especially when it's a 3-porter and you don't
even have to swap cables around  :-)

--- Jeff WN3A

RE: Properly designed PAs (was: Re: [Repeater-Builder] Coax length, etc.)

 Jeff, out of all the PAs you've seen out there, both commonly 
 used and not-so-common... which ones (in your opinion) are 
 properly designed (when working right)?

I think a lot of them, generally speaking, are properly designed.  That's
not to say that some of them don't have some downsides or specific,
recurring points of failure (to wit: the beloved Mastr II output strap
connection failure).  I'd name manufacturers that are on my $^!+ list, but
I'd rather not do that here, but I will say that most of them are the
made-for-amateur brands.  I've had great luck with just about anything Micor
(and, I have to say, significantly better long-term results with Micor over
M2, sorry GE fans).  Crescend and *newer* TPL amps have been good to me.
EFJ CR1010 PA's have also been workhorses.

 I have this feeling that most, if not all, have various 
 problems... but you've seen a heck of a lot more of them 
 in-service than I have. 

Well, I dunno, there are probably others on this list in the two-way
business that have seen more than me.  I do broadcast for a living; I'm
generally an RF guy, my interest in repeaters is just a subset of that.  I
have a bunch of ham repeaters (20-some I think), and maintain a bunch for
other individuals/clubs, and have built or maintained many for others over
the years, but I'm sure there are others that do two-way on a daily basis
that can give more points of reference as far as recurring problems with
other brands/models that I'm not as familiar with.
 
 I ask, because this is always the kind of mature, 
 well-developed tech I'm looking for. Price is still a factor, 
 but when you find something that just works... it's truly 
 grand in the tech world, for all sorts of reasons that tend 
 to degrade what something was intended to be, vs. what it 
 really ended up being.

To me, the cost of the radio hardware is the least of my worries.  I'm not
saying that to sound like an alpha-hotel.  I look at it this way.  I've got
all of these repeaters to deal with.  I have no free time the way it is.
When one breaks, that means I have to take a day off work (or away from
family, or away from something else) to go deal with it.  It probably means
a few hundred miles of driving.  And, more than likely, if it's a major
failure, I'm probably going to have to make a return trip, doubling the
time/cost.  So do I really want to take a chance on low-grade hardware up
front?  No way.

Whoever said time is money was an idiot.  Time is worth inifinitely times
more than money.  You can make more money.  You can even borrow money.
Hell, if you were desparate you could even steal money.  You can't do any of
those things with time.  Time is the one resource you can't make more of.
And, for me, I've never had enough time to get everything done that I want
to get done.  Life's too short to waste time on high-maintenance equipment.
 
 I'm also curious to see if your recommendations are new gear, 
 or 20+ year old gear. 

Both.  While I still believe the glory days of two-way turned out the best
damned equipment ever made, there is still some decent stuff being made
today.

 I really like MASTR II Stations, but I will admit to some 
 consternation over how the PAs *sometimes* act. We've had 'em 
 run for a decade, and we've had 'em pop like light bulbs 
 every few months. 

With the exception of the PA's, they generally just run.  100 watt UHF M2
PA's have been rather disappointing for me, both with and without matching
networks, with or without isolators.  75 watters seem to run forever.
Highband and lowband, much fewer problems.  I have a bunch of the 200 watt
solid state M2 stations, and have pulled them all out (except for one, which
is coming out in a week or two), they're just a nightmare to keep all three
PA's working all the time.

 Is the answer to this question the Crescend amps perhaps? 

I've been happy with them.  I have 7 or 8 of the previous-vintage UHF
Crescend/Milcoms (the gold-alodined ones that you're probably familiar with)
on the air, and they've been fine, running in the 150-175 watt range.  I
ordered a couple 100 watt highband amps for a local club about a year ago,
they seem OK.  I have a bunch of their 900 MHz linear amps in use on STL's
and they've been solid.  I wouldn't hesitate to buy them.

 How 
 did their acquisition of Vocom affect their quality? 

They did change their design, and talking to their engineers a few months
ago, they're doing some re-designs due to some of the devices they had been
using going on EOL, so more changes will be forthcoming.

Some of the older pre-Crescend Vocom amps weren't very good.

 I 
 haven't looked lately, did they mix up the model line and 
 keep the Vocom stuff? 

They still have the Vocom line which they market as a lower-cost
alternative.

I like the TPL RXR series because they are extremely simple.  They also have
one device per board, so in the event that you have a device fail or burn up
a collector trace or something, you only have

RE: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread JOHN MACKEY

I've brought that issue up a few times, and usually get the blank radio shack
salesman type of stare.

-- Original Message --
Received: Sat, 14 Aug 2010 08:45:47 PM PDT
From: Jeff DePolo j...@broadsci.com
 
 There is no simple rule of thumb, and if anybody tells you that there is,
 ask them how do you account for the unknown-length of coax that's *inside*
 your transmitter/amplifier before it gets to the antenna jack.
 
   --- Jeff WN3A

RE: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread Gary Schafer

Russ,

 

Of course the Bird 43 does not measure power directly. But it does sample
voltage AND current on the line in amounts that are combined to indicate
power.

It is a directional coupler. The only time you will have a problem with it
deviating from its accuracy is when the directivity becomes too low such as
when the line impedance is way off from its design 50 ohms.

As I said before it will read power accurately even if the transmission line
is no a 50 ohm line.

 

The manual even tells you that you can use it to measure line loss with an
open at the far end of the line.

 

Please read chapter 2 theory of operation of the Bird manual that you show
the reference  to. 

Then read it again!

 

73

Gary K4FMX

 


Another chance?  Which part, erroneous readings, don't directly measure
power, or the voltmeter part?  Sure, what the heck. ;-) 

I've had Bird 43's, and calibrated line sections with matched elements for
that matter, give erroneous reflected power readings depending upon what was
going on with the transmission line.  By erroneous, I mean it was usually a
reading that was, for example, excessively high versus what we knew was
going on, such as a straight piece of rigid line or coax terminated into a
known good load.  On rare occasion, we found we slipped a bullet or had a
bad connector.  More often, relocating the instrument somewhere else along
the line resolved those bad readings.  

RF calorimeters can measure power directly.  But unless they've one hidden
in them somewhere, ThruLine meters can not.  Just because the Commission
might accept wattmeter readings, or Bird says so, doesn't make it so.

As for the voltmeter part, check out page 6 of the Bird 43 manual (page 18
of the PDF), a copy of which you'll recall is here:

http://www.repeater-builder.com/bird/pdf/bird-43-wattmeter-2004.pdf

I respectfully submit what is shown is a schematic/diagram of a directional
coupler attached to a voltmeter as an indicator.  An induced RF voltage
sample is rectified, filtered and applied through a dropping resistor to a
shunt-connected ammeter.  

By definition, a voltmeter is the shunt-connected ammeter with series
resistor part.  But don't take my word for it.  Take a peek at Chapter 25 in
any recent ARRL Handbook (this works for my 2007 copy anyway).

Is it less a voltmeter because the induced voltage tracks current on the
line?  Want to call it an ammeter or current meter then, after all that's
what the actual meter movement is?  

I submit this particular voltmeter happens to be calibrated to read average
power at 50 ohms impedance, and it does this quite well within its
limitations. 

I now await your thrashing.  Please be gentle. ;-) 

Like the manual says, the Bird 43 is fast, convenient and accurate.  I
agree it's fast and convenient.  I'll agree it's accurate with the caveats
expressed.  It beats lugging a slotted line around, and it beats every other
meter like it, IMHO, including my old Daiwa dual-metered POS wattmeter. ;-) 

Oh, BTW, the emperor has no clothes either. :-P 

73, Russ WB8ZCC

RE: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread Mark

Agreed!!

Mark - N9WYS

-Original Message-
From: Repeater-Builder@yahoogroups.com On Behalf Of Eric Lemmon

(major snippage)

This discussion is both informative and quite entertaining!

73, Eric Lemmon WB6FLY

Re: [Repeater-Builder] Coax length, etc.


 I see some folks are heading for the Advil.  My apologies.

Thanks, Gary, for admitting the 43 doesn't measure power directly.  One 
myth down.


Of course, it is a directional coupler, no argument.  That makes it a 
reflectometer, it enables the instrument to isolate forward/reflected 
samples to some degree of reliability.  What's the rest of the circuit? ;-)


IMHO, what makes the 43 better than most (if not all) meters of its 
type, is the directional coupler is a true transmission line coupler, 
not a ferrite transformer, directly connected capacitor, etc.


As far as rereading the manual, I have been.  Bird's explanation 
requires the reader to suspend a standing wave viewpoint of 
transmission line theory, and buy into their traveling wave 
viewpoint.  Uh, okay.  But that kind of thing sends up red flags for 
me.  I shouldn't have to suspend accepted transmission line theory to 
understand how their meter works.


As it turns out, I don't.  When line impedances get away from 50 ohms, 
accuracy falls and the meter behaves like you'd expect.  It tracks 
whatever current is on the line at that (the meter's) point in the line 
without regard for impedance.  Since it's just not calibrated for 
whatever that impedance might be, how can it be accurate?


If the meter did as you suggest, then it would show what the voltage and 
current are at any point in the line, and therefore be able to tell you 
what the impedance is at that point, all with some level of accuracy.  
It simply can't do all that.


Yes, Bird describes what happens when using 70 ohm lines with the meter 
under less-than-perfect conditions.  IMHO, it's really messy.  It can't 
tell the difference between a 1:1 VSWR and a 2:1 VSWR (both will 
calculate out to 1.4:1) on a 70 ohm line.  That's not accuracy, that's 
nearly useless.


BTW, my POS Daiwa can show me a 100% reflected condition, just like the 
Bird.  And just like the Bird, it doesn't indicate if that's an open or 
a short.


I believe Bird wants us to believe that their meter is faster and more 
convenient (it is) yet as accurate as a slotted line and calorimeter 
(sorry, nope).  It's a calibrated voltmeter, not a network analyzer.


For most everyday, mundane RF chores, it's just dandy as we don't really 
need high accuracy.  And as long as line impedances stay reasonably 
close to 50 ohms, it turns out accuracy is pretty good, too.


Certainly not bad for a portable instrument, and that's the point.  If 
we remember what its limitations are, we should be good to go.  That's 
why I own one and want more.


Okay, I'm done picking nits.  It's the next yahoo's turn. ;-)

73, Russ WB8ZCC


On 8/15/2010 2:08 PM, Gary Schafer wrote:


Russ,

Of course the Bird 43 does not measure power directly. But it does 
sample voltage AND current on the line in amounts that are combined to 
indicate power.


It is a directional coupler. The only time you will have a problem 
with it deviating from its accuracy is when the directivity becomes 
too low such as when the line impedance is way off from its design 50 
ohms.


As I said before it will read power accurately even if the 
transmission line is no a 50 ohm line.


The manual even tells you that you can use it to measure line loss 
with an open at the far end of the line.


Please read chapter 2 theory of operation of the Bird manual that 
you show the reference  to.


Then read it again!

73

Gary K4FMX


Another chance?  Which part, erroneous readings, don't directly 
measure power, or the voltmeter part?  Sure, what the heck. ;-)


I've had Bird 43's, and calibrated line sections with matched elements 
for that matter, give erroneous reflected power readings depending 
upon what was going on with the transmission line.  By erroneous, I 
mean it was usually a reading that was, for example, excessively high 
versus what we knew was going on, such as a straight piece of rigid 
line or coax terminated into a known good load.  On rare occasion, we 
found we slipped a bullet or had a bad connector.  More often, 
relocating the instrument somewhere else along the line resolved those 
bad readings.


RF calorimeters can measure power directly.  But unless they've one 
hidden in them somewhere, ThruLine meters can not.  Just because the 
Commission might accept wattmeter readings, or Bird says so, doesn't 
make it so.


As for the voltmeter part, check out page 6 of the Bird 43 manual 
(page 18 of the PDF), a copy of which you'll recall is here:


http://www.repeater-builder.com/bird/pdf/bird-43-wattmeter-2004.pdf

I respectfully submit what is shown is a schematic/diagram of a 
directional coupler attached to a voltmeter as an indicator.  An 
induced RF voltage sample is rectified, filtered and applied through a 
dropping resistor to a shunt-connected ammeter.


By definition, a voltmeter is the shunt-connected ammeter with series 
resistor part.  But don't take my word for it.  Take a peek at Chapter 
25 in any recent ARRL Handbook (this works

RE: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread Gary Schafer

Hi again Russ,

 

 

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Russ Hines
Sent: Sunday, August 15, 2010 4:54 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length, etc.

 



I see some folks are heading for the Advil.  My apologies.

Thanks, Gary, for admitting the 43 doesn't measure power directly.  One myth
down.

Of course, it is a directional coupler, no argument.  That makes it a
reflectometer, it enables the instrument to isolate forward/reflected
samples to some degree of reliability.  What's the rest of the circuit?  ;-)


IMHO, what makes the 43 better than most (if not all) meters of its type, is
the directional coupler is a true transmission line coupler, not a ferrite
transformer, directly connected capacitor, etc.  

 

But it works the same way.



As far as rereading the manual, I have been.  Bird's explanation requires
the reader to suspend a standing wave viewpoint of transmission line
theory, and buy into their traveling wave viewpoint.  Uh, okay.  But that
kind of thing sends up red flags for me.  I shouldn't have to suspend
accepted transmission line theory to understand how their meter works.

 

There are no standing waves that you can measure directly with the Bird
meter. In order to truly measure standing waves you need to have a line
length greater than a half  wave length and measure where the nulls are
along the line.

Swr is calculated from forward and reflected power at one point on the line
with a Bird type of meter.



As it turns out, I don't.  When line impedances get away from 50 ohms,
accuracy falls and the meter behaves like you'd expect.  It tracks whatever
current is on the line at that (the meter's) point in the line without
regard for impedance.  Since it's just not calibrated for whatever that
impedance might be, how can it be accurate? 

The Bird is set up so that the ratio of voltage and current that are
detected work out to the power at 50 ohms. When the line is not 50 ohms that
voltage/current ratio change that the meter detects. So you can no longer
simply look at the scale on the meter and directly read power.

For ANY reflected power reading you must subtract the reflected power shown
from the forward power shown to find the true power delivered to the load.
This holds true no matter what the impedance of the line is.


If the meter did as you suggest, then it would show what the voltage and
current are at any point in the line, and therefore be able to tell you what
the impedance is at that point, all with some level of accuracy.  It simply
can't do all that.

With the Bird meter you don't care what the  impedance is because it
measures voltage (by way of capacitive coupling) and current (by way of
inductive coupling). Both create voltages that add together in the proper
ratio to give the meter reading that represents power level for that
combination of voltage and current. 



Yes, Bird describes what happens when using 70 ohm lines with the meter
under less-than-perfect conditions.  IMHO, it's really messy.  It can't tell
the difference between a 1:1 VSWR and a 2:1 VSWR (both will calculate out to
1.4:1) on a 70 ohm line.  That's not accuracy, that's nearly useless.

Yes it gets a little tricky to find VSWR with a non 50 ohm line. But most of
the time we really don't care what it is. I say we don't care because it is
rare that the 50 ohm Bird meter gets used in a non 50 ohm transmission line.
With a 50 ohm line things work out nicely to find power and VSWR no matter
what kind of reflection the load presents.


BTW, my POS Daiwa can show me a 100% reflected condition, just like the
Bird.  And just like the Bird, it doesn't indicate if that's an open or a
short.

So what? If you need to know that then you are using the wrong instrument.


I believe Bird wants us to believe that their meter is faster and more
convenient (it is) yet as accurate as a slotted line and calorimeter (sorry,
nope).  It's a calibrated voltmeter, not a network analyzer.

Try doing the same thing with a voltmeter. :)  

No one claims it to be anything other than a simple wattmeter. It is not a
super accurate at measuring power either. It is claimed to be 5% of full
scale reading. That means with a 100 watt slug the best accuracy that you
can depend on is +- 5 watts anywhere on the scale. So at 25 watts on the
meter scale it could be as low as 20 watts or as much as 30 watts. But for
what it is it works very well.


For most everyday, mundane RF chores, it's just dandy as we don't really
need high accuracy.  And as long as line impedances stay reasonably close to
50 ohms, it turns out accuracy is pretty good, too.

Again, line impedance doesn't matter for power measurement.

  73

Gary  K4FMX


Certainly not bad for a portable instrument, and that's the point.  If we
remember what its limitations are, we should be good to go.  That's why I
own one and want more.

Okay, I'm done picking

Re: [Repeater-Builder] Coax length, etc.


 Last round.  Hi again, Gary.  ;-)


On 8/15/2010 7:09 PM, Gary Schafer wrote:


Hi again Russ,



*From:* Repeater-Builder@yahoogroups.com 
[mailto:repeater-buil...@yahoogroups.com] *On Behalf Of *Russ Hines

*Sent:* Sunday, August 15, 2010 4:54 PM
*To:* Repeater-Builder@yahoogroups.com
*Subject:* Re: [Repeater-Builder] Coax length, etc.



I see some folks are heading for the Advil.  My apologies.

Thanks, Gary, for admitting the 43 doesn't measure power directly.  
One myth down.


Of course, it is a directional coupler, no argument.  That makes it a 
reflectometer, it enables the instrument to isolate forward/reflected 
samples to some degree of reliability.  What's the rest of the 
circuit? ;-)


IMHO, what makes the 43 better than most (if not all) meters of its 
type, is the directional coupler is a true transmission line coupler, 
not a ferrite transformer, directly connected capacitor, etc.


But it works the same way.


Yeah, and?  The Bird does it better.




As far as rereading the manual, I have been.  Bird's explanation 
requires the reader to suspend a standing wave viewpoint of 
transmission line theory, and buy into their traveling wave 
viewpoint.  Uh, okay.  But that kind of thing sends up red flags for 
me.  I shouldn't have to suspend accepted transmission line theory to 
understand how their meter works.


There are no standing waves that you can measure directly with the 
Bird meter. In order to truly measure standing waves you need to have 
a line length greater than a half  wave length and measure where the 
nulls are along the line.


Swr is calculated from forward and reflected power at one point on the 
line with a Bird type of meter.



That's correct.  As I said, the 43 isn't a slotted line.

Regarding VSWR, all in-line meters make an attempt at this, some have 
fancy cross-needle indicators where VSWR is represented at the 
intersection of the needles.  How else would you do determine VSWR with 
such a device?  That was a rhetorical question. ;-)




As it turns out, I don't.  When line impedances get away from 50 ohms, 
accuracy falls and the meter behaves like you'd expect.  It tracks 
whatever current is on the line at that (the meter's) point in the 
line without regard for impedance.  Since it's just not calibrated for 
whatever that impedance might be, how can it be accurate?


The Bird is set up so that the ratio of voltage and current that are 
detected work out to the power at 50 ohms. When the line is not 50 
ohms that voltage/current ratio change that the meter detects. So you 
can no longer simply look at the scale on the meter and directly read 
power.


For ANY reflected power reading you must subtract the reflected power 
shown from the forward power shown to find the true power delivered to 
the load. This holds true no matter what the impedance of the line is.


Thanks, Gary, that's right.  The meter is calibrated at 50 ohms 
impedance.  When the line impedance isn't 50 ohms, you can't just look 
at the meter, the meter scale is no longer accurate, is it?


Subtracting reflected from forward is a given, and never at issue here.

Well, impedance does matter.  At the characteristic impedance of the 
meter, line, load, etc., seems a waste of time to subtract nothing, 
you'll see right away there's no reflected power. ;-)



If the meter did as you suggest, then it would show what the voltage 
and current are at any point in the line, and therefore be able to 
tell you what the impedance is at that point, all with some level of 
accuracy.  It simply can't do all that.


With the Bird meter you don't care what the  impedance is because it 
measures voltage (by way of capacitive coupling) and current (by way 
of inductive coupling). Both create voltages that add together in the 
proper ratio to give the meter reading that represents power level for 
that combination of voltage and current.


Gary, you seem to be contradicting yourself.  A paragraph ago you said 
the ratio of voltage and current work out to the power at 50 ohms. Now 
we don't care what the impedance is?  We either do or don't.


As for me, I choose to care 'cuz that's the kind of guy I am. ;-)

I understand the coupling, both are present, agreed.  But if impedance 
didn't matter, then the meter would indicate power accurately regardless 
of line impedance.  That's simply not so.  The Bird manual even says 
it's not so.  It's limited by its own line section.




Yes, Bird describes what happens when using 70 ohm lines with the 
meter under less-than-perfect conditions.  IMHO, it's really messy.  
It can't tell the difference between a 1:1 VSWR and a 2:1 VSWR (both 
will calculate out to 1.4:1) on a 70 ohm line.  That's not accuracy, 
that's nearly useless.


Yes it gets a little tricky to find VSWR with a non 50 ohm line. But 
most of the time we really don't care what it is. I say we don't care 
because it is rare that the 50

Re: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread Kevin Custer


Russ Hines wrote:


Hi Kevin:

Regarding temperature, our club has a site, no A/C or heat, where 
temperatures inside the shelter can get below +20 deg F in winter, and 
well over 130 deg F in the summer heat.  I can't imagine filter tuning 
not changing under such conditions, Invar or not.  I can see over time 
where tuning might walk off the reservation.  But I bow to your 
greater experience with cavity duplexers. 


Duplexer tuning is not the only thing you'd need to worry about with 
temperature extremes you reference.  The radio set might have a hard 
time with +130 shelter temp.  That could easily relate to radio 
temperatures exceeding the ability of some equipment manufacturers to 
remain stable. 

Filters will change with temperature - it's a fact.  The amount they 
change is, I suppose, what's under question.  Most commercially made 
units have a temperature rating of -30 to +60 degrees C.  This means the 
duplexer will remain within its ratings between those extremes.  Most of 
us engineer our repeater systems to have some amount of isolation 
headroom.  Headroom is necessary for several reasons, temperature 
variations are likely the biggest reason, along with icing of the antenna.


I have a site using a Wacom WP-641 and 250 watt transmitter.  This site 
sees -25 degree F temperatures in the winter and +85 degree F 
temperatures in the summer - outside shelter.  The shelter is not 
climate controlled.  The duplexer loss is 1.5 dB or 29%.  This relates 
to 72.5 watts going up as heat.  If the repeater is in transmit for a 
long time, the temperature in the building can approach +100 degrees 
ambient.  Now, add the heat generated by the loss of the duplexer, and 
the duplexer becomes very hot to the touch.  Even at these temperature 
extremes, the repeater is completely happy with the isolation provided 
by the duplexer.


You state that over time the tuning might walk off the reservation.  
This seems to allude to the duplexer changing tuning and not coming back 
to its settings after it has returned to the temperature it was tuned 
at.  If this is the case, the duplexer design is faulty - period.





Another chance?  Which part, erroneous readings, don't directly 
measure power, or the voltmeter part?  Sure, what the heck. ;-)


I've had Bird 43's, and calibrated line sections with matched elements 
for that matter, give erroneous reflected power readings depending 
upon what was going on with the transmission line.  By erroneous, I 
mean it was usually a reading that was, for example, excessively high 
versus what we knew was going on, such as a straight piece of rigid 
line or coax terminated into a known good load.  On rare occasion, we 
found we slipped a bullet or had a bad connector.  More often, 
relocating the instrument somewhere else along the line resolved those 
bad readings.


If you were able to move the meter and have differing determined power 
readings, something IS/WAS very wrong.  But, maybe you aren't using the 
instrument correctly?  To paraphrase the manual, the reflected power 
must be subtracted from the forward power to determine the actual power 
delivered to the load.  If you move the meter about the line, it is 
possible that the power shown on the meter will change, but, if you read 
the reflected at the same spot, and determine the power - it should 
always subtract to the same determined power reading.




RF calorimeters can measure power directly.  But unless they've one 
hidden in them somewhere, ThruLine meters can not.  Just because the 
Commission might accept wattmeter readings, or Bird says so, doesn't 
make it so.


While I'll agree that the Bird doesn't measure power directly, it still 
measures power, quite accurately, no matter the impedance of the 
connected line.  Bird claims the meter to be accurate within 5% of full 
scale reading.  While it might not be as accurate as a VNA, it doesn't 
cost as much either.


Let's revisit what you originally wrote:

/Our in-line power meters, like our trusted Bird 43, do not directly 
measure power./


No argument here...

/  They're really voltage meters calibrated in watts at a specific 
impedance.

/


When you were reading the manual, you missed something - read on...



As for the voltmeter part, check out page 6 of the Bird 43 manual 
(page 18 of the PDF), a copy of which you'll recall is here:

http://www.repeater-builder.com/bird/pdf/bird-43-wattmeter-2004.pdf

I respectfully submit what is shown is a schematic/diagram of a 
directional coupler attached to a voltmeter as an indicator.  An 
induced RF voltage sample is rectified, filtered and applied through a 
dropping resistor to a shunt-connected ammeter. 
By definition, a voltmeter is the shunt-connected ammeter with series 
resistor part.  But don't take my word for it.  Take a peek at Chapter 
25 in any recent ARRL Handbook (this works for my 2007 copy anyway).
Is it less a voltmeter because the induced voltage tracks current on 
the line?  Want

RE: [Repeater-Builder] Coax length, etc.

2010-08-15 Thread Gary Schafer

I don't know if you really don't get it or you are just trying to be
controversial. I tend to think a little of both.

Either way, I give up.

 

73

Gary K4FMX

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Russ Hines
Sent: Sunday, August 15, 2010 7:37 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length, etc.

 



Last round.  Hi again, Gary. ;-) 


On 8/15/2010 7:09 PM, Gary Schafer wrote: 

  

Hi again Russ,

 

 

 

  _  

From:  mailto:Repeater-Builder@yahoogroups.com
Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com]
On Behalf Of Russ Hines
Sent: Sunday, August 15, 2010 4:54 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length, etc.

 



I see some folks are heading for the Advil.  My apologies.

Thanks, Gary, for admitting the 43 doesn't measure power directly.  One myth
down.

Of course, it is a directional coupler, no argument.  That makes it a
reflectometer, it enables the instrument to isolate forward/reflected
samples to some degree of reliability.  What's the rest of the circuit?  ;-)


IMHO, what makes the 43 better than most (if not all) meters of its type, is
the directional coupler is a true transmission line coupler, not a ferrite
transformer, directly connected capacitor, etc.  

 

But it works the same way.

Yeah, and?  The Bird does it better.





As far as rereading the manual, I have been.  Bird's explanation requires
the reader to suspend a standing wave viewpoint of transmission line
theory, and buy into their traveling wave viewpoint.  Uh, okay.  But that
kind of thing sends up red flags for me.  I shouldn't have to suspend
accepted transmission line theory to understand how their meter works.

 

There are no standing waves that you can measure directly with the Bird
meter. In order to truly measure standing waves you need to have a line
length greater than a half  wave length and measure where the nulls are
along the line.

Swr is calculated from forward and reflected power at one point on the line
with a Bird type of meter.

That's correct.  As I said, the 43 isn't a slotted line.

Regarding VSWR, all in-line meters make an attempt at this, some have fancy
cross-needle indicators where VSWR is represented at the intersection of the
needles.  How else would you do determine VSWR with such a device?  That was
a rhetorical question. ;-) 





As it turns out, I don't.  When line impedances get away from 50 ohms,
accuracy falls and the meter behaves like you'd expect.  It tracks whatever
current is on the line at that (the meter's) point in the line without
regard for impedance.  Since it's just not calibrated for whatever that
impedance might be, how can it be accurate? 

The Bird is set up so that the ratio of voltage and current that are
detected work out to the power at 50 ohms. When the line is not 50 ohms that
voltage/current ratio change that the meter detects. So you can no longer
simply look at the scale on the meter and directly read power.

For ANY reflected power reading you must subtract the reflected power shown
from the forward power shown to find the true power delivered to the load.
This holds true no matter what the impedance of the line is.

Thanks, Gary, that's right.  The meter is calibrated at 50 ohms impedance.
When the line impedance isn't 50 ohms, you can't just look at the meter, the
meter scale is no longer accurate, is it?

Subtracting reflected from forward is a given, and never at issue here.

Well, impedance does matter.  At the characteristic impedance of the meter,
line, load, etc., seems a waste of time to subtract nothing, you'll see
right away there's no reflected power. ;-) 




If the meter did as you suggest, then it would show what the voltage and
current are at any point in the line, and therefore be able to tell you what
the impedance is at that point, all with some level of accuracy.  It simply
can't do all that.

With the Bird meter you don't care what the  impedance is because it
measures voltage (by way of capacitive coupling) and current (by way of
inductive coupling). Both create voltages that add together in the proper
ratio to give the meter reading that represents power level for that
combination of voltage and current.

Gary, you seem to be contradicting yourself.  A paragraph ago you said the
ratio of voltage and current work out to the power at 50 ohms.  Now we
don't care what the impedance is?  We either do or don't.  

As for me, I choose to care 'cuz that's the kind of guy I am.  ;-) 

I understand the coupling, both are present, agreed.  But if impedance
didn't matter, then the meter would indicate power accurately regardless of
line impedance.  That's simply not so.  The Bird manual even says it's not
so.  It's limited by its own line section.





Yes, Bird describes what happens when using 70 ohm lines with the meter
under less-than-perfect conditions.  IMHO

RE: [Repeater-Builder] Coax length, etc.

I know I'm going to regret stepping into this one, but since when has that
stopped me before... 

 Thanks, Gary, for admitting the 43 doesn't measure power 
 directly.  

What do you mean by measure power directly?  If you're talking about
comparing a thruline measurement against absorptive/calorimetric techniques,
then that's apples and oranges, one is measuring power in a transmission
line (either with or without reflections present), the other is measuring
power absorbed into a load, big difference.

Please clarify what you mean by measuring power directly so at least we're
all on the same page.

 Of course, it is a directional coupler, no argument.  That 
 makes it a reflectometer

No, it's not a reflectometer, it can't do forward and reverse measurements
concurrently.

 If the meter did as you suggest, then it would show what the 
 voltage and current are at any point in the line, and 
 therefore be able to tell you what the impedance is at that 
 point

Not without knowing the phase between the two it couldn't.

 BTW, my POS Daiwa can show me a 100% reflected condition, 
 just like the Bird.  And just like the Bird, it doesn't 
 indicate if that's an open or a short.

A Bird isn't a VSWR bridge, it's a directional wattmeter.  Yes, it can be
used in a roundabout way to measure/calculate VSWR, but it's not a VSWR
meter.  

Sidebar.  I grit my teeth when I hear someone on the radio say my SWR meter
shows I'm putting out 100 watts.  Since when does a SWR meter measure
power!???!  Do you use your bathroom scale to check your blood pressure?
Egads.

I'm not taking a stance here (at least not yet) on the relative merits of
the Bird 43 or other thruline-type wattmeter line sections or elements, I'm
just trying to get a handle on the matter that is the subject of debate...

--- Jeff WN3A

Re: [Repeater-Builder] Coax length, etc.

 Sorry, Gary.  I have a bad tendency to question what's put in front of 
me.  That includes what I call the girl copy I read in product manuals 
and brochures.


FWIW, girl copy refers to the rarely-true supposed personal 
information about the particular lady-of-the-month in certain men's 
magazines. ;-)


I appreciated the banter, take care, Gary.

73, Russ WB8ZCC

On 8/15/2010 9:20 PM, Gary Schafer wrote:


I don't know if you really don't get it or you are just trying to be 
controversial. I tend to think a little of both.


Either way, I give up.

73

Gary K4FMX



*From:* Repeater-Builder@yahoogroups.com 
[mailto:repeater-buil...@yahoogroups.com] *On Behalf Of *Russ Hines

*Sent:* Sunday, August 15, 2010 7:37 PM
*To:* Repeater-Builder@yahoogroups.com
*Subject:* Re: [Repeater-Builder] Coax length, etc.



Last round.  Hi again, Gary. ;-)


On 8/15/2010 7:09 PM, Gary Schafer wrote:

Hi again Russ,



*From:* Repeater-Builder@yahoogroups.com 
mailto:Repeater-Builder@yahoogroups.com 
[mailto:Repeater-Builder@yahoogroups.com 
mailto:Repeater-Builder@yahoogroups.com] *On Behalf Of *Russ Hines

*Sent:* Sunday, August 15, 2010 4:54 PM
*To:* Repeater-Builder@yahoogroups.com 
mailto:Repeater-Builder@yahoogroups.com

*Subject:* Re: [Repeater-Builder] Coax length, etc.



I see some folks are heading for the Advil.  My apologies.

Thanks, Gary, for admitting the 43 doesn't measure power directly.  
One myth down.


Of course, it is a directional coupler, no argument.  That makes it a 
reflectometer, it enables the instrument to isolate forward/reflected 
samples to some degree of reliability.  What's the rest of the 
circuit? ;-)


IMHO, what makes the 43 better than most (if not all) meters of its 
type, is the directional coupler is a true transmission line coupler, 
not a ferrite transformer, directly connected capacitor, etc.


But it works the same way.

Yeah, and?  The Bird does it better.



As far as rereading the manual, I have been.  Bird's explanation 
requires the reader to suspend a standing wave viewpoint of 
transmission line theory, and buy into their traveling wave 
viewpoint.  Uh, okay.  But that kind of thing sends up red flags for 
me.  I shouldn't have to suspend accepted transmission line theory to 
understand how their meter works.


There are no standing waves that you can measure directly with the 
Bird meter. In order to truly measure standing waves you need to have 
a line length greater than a half  wave length and measure where the 
nulls are along the line.


Swr is calculated from forward and reflected power at one point on the 
line with a Bird type of meter.


That's correct.  As I said, the 43 isn't a slotted line.

Regarding VSWR, all in-line meters make an attempt at this, some have 
fancy cross-needle indicators where VSWR is represented at the 
intersection of the needles.  How else would you do determine VSWR 
with such a device?  That was a rhetorical question. ;-)




As it turns out, I don't.  When line impedances get away from 50 ohms, 
accuracy falls and the meter behaves like you'd expect.  It tracks 
whatever current is on the line at that (the meter's) point in the 
line without regard for impedance.  Since it's just not calibrated for 
whatever that impedance might be, how can it be accurate?


The Bird is set up so that the ratio of voltage and current that are 
detected work out to the power at 50 ohms. When the line is not 50 
ohms that voltage/current ratio change that the meter detects. So you 
can no longer simply look at the scale on the meter and directly read 
power.


For ANY reflected power reading you must subtract the reflected power 
shown from the forward power shown to find the true power delivered to 
the load. This holds true no matter what the impedance of the line is.


Thanks, Gary, that's right.  The meter is calibrated at 50 ohms 
impedance.  When the line impedance isn't 50 ohms, you can't just look 
at the meter, the meter scale is no longer accurate, is it?


Subtracting reflected from forward is a given, and never at issue here.

Well, impedance does matter.  At the characteristic impedance of the 
meter, line, load, etc., seems a waste of time to subtract nothing, 
you'll see right away there's no reflected power. ;-)



If the meter did as you suggest, then it would show what the voltage 
and current are at any point in the line, and therefore be able to 
tell you what the impedance is at that point, all with some level of 
accuracy.  It simply can't do all that.


With the Bird meter you don't care what the  impedance is because it 
measures voltage (by way of capacitive coupling) and current (by way 
of inductive coupling). Both create voltages that add together in the 
proper ratio to give the meter reading that represents power level for 
that combination of voltage and current.


Gary, you

RE: [Repeater-Builder] Coax length, etc.

 Because the impedance is not matched between the transmitter 
 and duplexer, the 'apparent' loss of the duplexer is greater 
 than the manufacturers stated loss of the duplexer.  Changing 
 the cable length is not changing the loss of the duplexer, 
 it's changing the power that is accepted at the transmitter 
 port of the duplexer by matching the output impedance of the 
 transmitter to the input impedance of the transmitter port of 
 the duplexer.

But if the duplexer is tuned to 50 ohms, and the cable is 50 ohms, varying
the cable length isn't going to change the Z seen by the transmitter.  Or
are you suggesting the duplexer is purposely de-tuned from 50 ohms?

 And also that by varying the cable length between the 
 transmitter and the duplexer that you can vary the reflected
   power on that same line?
 
 
 Yes.

With all due respect, that's not possible, regardless of what the Z is of
the duplexer.  The only time it could have an effect on the reflected power
would be if the transmitter/PA were spurious, and the amplitude/frequency of
the spurs changed with varying load Z, and I think we can both agree that if
that's the case, we have bigger fish to fry.

Not to belabor the point, but whatever the VSWR is on a length of
transmission line, that's the VSWR that's on the line *regardless of
length*.  You can't change the VSWR by changing the length of the line.  As
you vary the length, you go round n' round the Smith Chart in a constant
VSWR circle, with the Z repeating cyclicly every half-wavelength, but you've
still got a complex Z that nets a 1:5:1 VSWR relative to 50 ohms at the end
of whatever length of line you choose (cable loss effects notwithstanding).
There are an infinite number of complex Z's that yield a 1.5:1 VSWR - cut
the line to any random length and you'll hit one of them.

 In a situation where the duplexer and transmitter have 
 differing impedances, and a cable optimized in length matches 
 these impedances, the mismatch at the duplexer is minimized, 
 therefore the power reflected by the duplexer is minimized.  

I think what you're really saying is that the mismatch at the *input to the
matching section* (i.e. the cable between the PA and the duplexer), NOT the
mismatch at the duplexer, is minimized.  The duplexer's input Z isn't
changing; you can't change that unless you re-tune the cavities or change
the load at the antenna port.  Whether or that the transmitter
likes/dislikes the different Z it sees as you change cable lengths is, I
guess, what's up for debate...

 I have found that when you get a transmitter that is 'picky' 
 about the length of interconnecting cable, power being read 
 at the output port of the duplexer is low and you cannot 
 alter the tuning of the cavity closest to the transmitter to 
 make things right.  In other words, the place where lowest 
 VSWR and maximum power transfer occurs is at two completely 
 different places, and power transfer is not up where it 
 should be (transmitter makes 100 watts into a dummy load but 
 only shows 50 watts on the output port of the duplexer that 
 has a stated 1.5 dB loss (29 %)).  

That would imply that either duplexer is presenting a load Z substantially
far removed from 50+j0, OR the transmitter doesn't like a 50 ohm load, or
something inbetween, would it not?

 As you get close to the 
 'optimum' cable length, the lowest VSWR and maximum power 
 transfer occur near the same place when tuning the cavity 
 closest to the transmitter.

But again, *you're NOT changing the VSWR*!  You can't change the VSWR by
varying the length of the line!  I just want to make sure we're on the same
page - the VSWR on a transmission line doesn't vary with length (loss
notwithstanding).
 
 I usually pay more attention to what is coming out the 
 antenna port of the duplexer - first.  Then, when things are 
 right, comparing forward power going to the duplexer and 
 power going to a good dummy load will be very close the same, 
 since matching the impedance of the transmitter to the 
 impedance of the duplexer was accomplished by some means.

Can you give me some real-world examples of what combinations of duplexers
and transmitters you've run across that just didn't want to play nice
without having to resort to changing cable lengths?  Like a highband Micor
110 watt H split paired with a Q2220E or whatever.  I'm just curious if I've
done any of the same combinations.

I think you know me well enough by now Kevin that I'm not looking to pick a
fight, I'm just a hard-ass when it comes to basing technique on solid
engineering foundation.  I can't say I've ever had to play with cable
lengths to either get a transmitter/PA to make rated power, or to get the
apparent loss of a duplexer to meet spec.  Have I just been lucky?  Maybe.
But if I'm *that* lucky, I'm in the wrong business, I shouldn't be sitting a
hotel room in Harrisburg on a Saturday waiting for a tower crew to show up,
I should be living the good life in Vegas

Re: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Chuck Kelsey

FWIW,

TX/RX Systems talks about adverse length cable between the transmitter and 
the duplexer in their technical papers.

Chuck
WB2EDV



- Original Message - 
From: Jeff DePolo j...@broadsci.com
To: Repeater-Builder@yahoogroups.com
Sent: Saturday, August 14, 2010 8:44 AM
Subject: RE: [Repeater-Builder] Coax length, etc.


 Because the impedance is not matched between the transmitter
 and duplexer, the 'apparent' loss of the duplexer is greater
 than the manufacturers stated loss of the duplexer.  Changing
 the cable length is not changing the loss of the duplexer,
 it's changing the power that is accepted at the transmitter
 port of the duplexer by matching the output impedance of the
 transmitter to the input impedance of the transmitter port of
 the duplexer.

 But if the duplexer is tuned to 50 ohms, and the cable is 50 ohms, varying
 the cable length isn't going to change the Z seen by the transmitter.  Or
 are you suggesting the duplexer is purposely de-tuned from 50 ohms?

   And also that by varying the cable length between the
 transmitter and the duplexer that you can vary the reflected
 power on that same line?


 Yes.

 With all due respect, that's not possible, regardless of what the Z is of
 the duplexer.  The only time it could have an effect on the reflected 
 power
 would be if the transmitter/PA were spurious, and the amplitude/frequency 
 of
 the spurs changed with varying load Z, and I think we can both agree that 
 if
 that's the case, we have bigger fish to fry.

 Not to belabor the point, but whatever the VSWR is on a length of
 transmission line, that's the VSWR that's on the line *regardless of
 length*.  You can't change the VSWR by changing the length of the line. 
 As
 you vary the length, you go round n' round the Smith Chart in a constant
 VSWR circle, with the Z repeating cyclicly every half-wavelength, but 
 you've
 still got a complex Z that nets a 1:5:1 VSWR relative to 50 ohms at the 
 end
 of whatever length of line you choose (cable loss effects 
 notwithstanding).
 There are an infinite number of complex Z's that yield a 1.5:1 VSWR - cut
 the line to any random length and you'll hit one of them.

 In a situation where the duplexer and transmitter have
 differing impedances, and a cable optimized in length matches
 these impedances, the mismatch at the duplexer is minimized,
 therefore the power reflected by the duplexer is minimized.

 I think what you're really saying is that the mismatch at the *input to 
 the
 matching section* (i.e. the cable between the PA and the duplexer), NOT 
 the
 mismatch at the duplexer, is minimized.  The duplexer's input Z isn't
 changing; you can't change that unless you re-tune the cavities or change
 the load at the antenna port.  Whether or that the transmitter
 likes/dislikes the different Z it sees as you change cable lengths is, I
 guess, what's up for debate...

 I have found that when you get a transmitter that is 'picky'
 about the length of interconnecting cable, power being read
 at the output port of the duplexer is low and you cannot
 alter the tuning of the cavity closest to the transmitter to
 make things right.  In other words, the place where lowest
 VSWR and maximum power transfer occurs is at two completely
 different places, and power transfer is not up where it
 should be (transmitter makes 100 watts into a dummy load but
 only shows 50 watts on the output port of the duplexer that
 has a stated 1.5 dB loss (29 %)).

 That would imply that either duplexer is presenting a load Z substantially
 far removed from 50+j0, OR the transmitter doesn't like a 50 ohm load, or
 something inbetween, would it not?

 As you get close to the
 'optimum' cable length, the lowest VSWR and maximum power
 transfer occur near the same place when tuning the cavity
 closest to the transmitter.

 But again, *you're NOT changing the VSWR*!  You can't change the VSWR by
 varying the length of the line!  I just want to make sure we're on the 
 same
 page - the VSWR on a transmission line doesn't vary with length (loss
 notwithstanding).

 I usually pay more attention to what is coming out the
 antenna port of the duplexer - first.  Then, when things are
 right, comparing forward power going to the duplexer and
 power going to a good dummy load will be very close the same,
 since matching the impedance of the transmitter to the
 impedance of the duplexer was accomplished by some means.

 Can you give me some real-world examples of what combinations of duplexers
 and transmitters you've run across that just didn't want to play nice
 without having to resort to changing cable lengths?  Like a highband Micor
 110 watt H split paired with a Q2220E or whatever.  I'm just curious if 
 I've
 done any of the same combinations.

 I think you know me well enough by now Kevin that I'm not looking to pick 
 a
 fight, I'm just a hard-ass when it comes to basing technique on solid
 engineering foundation.  I can't say I've ever had to play

Re: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Joe

  On 8/14/2010 8:44 AM, Jeff DePolo wrote:
 But if the duplexer is tuned to 50 ohms, and the cable is 50 ohms, varying
 the cable length isn't going to change the Z seen by the transmitter.  Or
 are you suggesting the duplexer is purposely de-tuned from 50 ohms?
I use a Network Analyzer to tune duplexers.  Although I can usually get 
an impedance of 50 ohms, many times the L or C reactance is not 
perfect.  Maybe the transmitter is responding more to the reactance 
mismatch rather than the impedance mismatch.

This area of RF black magic very quickly gets me lost in the ether.

73, Joe, k1ike

Re: [Repeater-Builder] Coax length, etc.


Jeff DePolo wrote:
Because the impedance is not matched between the transmitter 
and duplexer, the 'apparent' loss of the duplexer is greater 
than the manufacturers stated loss of the duplexer.  Changing 
the cable length is not changing the loss of the duplexer, 
it's changing the power that is accepted at the transmitter 
port of the duplexer by matching the output impedance of the 
transmitter to the input impedance of the transmitter port of 
the duplexer.



But if the duplexer is tuned to 50 ohms, and the cable is 50 ohms, varying
the cable length isn't going to change the Z seen by the transmitter.  Or
are you suggesting the duplexer is purposely de-tuned from 50 ohms?
  


Purposely, accidentally, by lack of good design - people not having the 
right equipment to tune it correctly - whatever.
  
	  And also that by varying the cable length between the 
transmitter and the duplexer that you can vary the reflected

power on that same line?


Yes.



With all due respect, that's not possible, regardless of what the Z is of
the duplexer.  The only time it could have an effect on the reflected power
would be if the transmitter/PA were spurious, and the amplitude/frequency of
the spurs changed with varying load Z, and I think we can both agree that if
that's the case, we have bigger fish to fry.
  


And this is where I believe the duplexer manufacturers are covering 
their butt.  They don't want the problem with complex reactance 
presented by the duplexer to be their problem.  Not that I don't agree, 
because it's usually the transmitter that is really at fault. 

Joe Ham buys a new duplexer and hooks it up to his 110 Watt MASTR II 
repeater and gets 50 watts out the antenna port.  He does his homework 
and realizes that he should only be loosing 29% with the 1.5 dB of 
insertion loss stated in the paperwork - but he's loosing over 50%.  The 
duplexer manufacturer supposedly engineered and tuned it for a 50 Ohm 
system.  He knows that the cable he connected to the transmitter is 
good, because when he disconnects the end going to the transmitter port 
of the duplexer and connects it to his Bird 43 terminated with a good 
load - it reads 110 watts.


Now, is the transmitter becoming spurious and the cable length being 
changed in length satisfies the match between the duplexer and 
transmitter - I don't know...   All I can tell you is I have followed 
the suggestions written in the WACOM manual and it has worked.  I had 
one instance of a ham radio club loosing PA's left and right on their 2M 
machine.  They told me of the situation and I offered to do a little 
testing.  The 110 watt PA would put out 110 watts into a Bird and dummy, 
but only 45 watts was coming out the antenna port of the duplexer.  At 
the time I didn't own a spectrum analyzer.  The repeater wouldn't duplex 
without desense.  I changed the length of the line between the PA and 
duplexer until I got the power to read about 75 Watts as I remember.  
That was 13 years and they still have the same PA - no desense either.




Not to belabor the point, but whatever the VSWR is on a length of
transmission line, that's the VSWR that's on the line *regardless of
length*.  You can't change the VSWR by changing the length of the line.  As
you vary the length, you go round n' round the Smith Chart in a constant
VSWR circle, with the Z repeating cyclicly every half-wavelength, but you've
still got a complex Z that nets a 1:5:1 VSWR relative to 50 ohms at the end
of whatever length of line you choose (cable loss effects notwithstanding).
There are an infinite number of complex Z's that yield a 1.5:1 VSWR - cut
the line to any random length and you'll hit one of them.

  
In a situation where the duplexer and transmitter have 
differing impedances, and a cable optimized in length matches 
these impedances, the mismatch at the duplexer is minimized, 
therefore the power reflected by the duplexer is minimized.  



I think what you're really saying is that the mismatch at the *input to the
matching section* (i.e. the cable between the PA and the duplexer), NOT the
mismatch at the duplexer, is minimized.


Sorry - that is what I meant to say.  Many of us use converted 
commercial gear in the ham band.  Many don't take the time to properly 
convert the receiver and especially the transmitter to properly operate 
in the adjacent ham band.  So, when you run a 150.8 to 174 MHz amplifier 
in the 2M ham band or a 450 to 470 MHz amplifier in the UHF ham band is 
it going to represent a good 50 Ohm impedance?  Likely not...


We need to realize that most duplexer manufacturers know what they are 
doing and their products are presenting a 50 ohm match on its intended 
frequencies - unless somebody has adjusted on it.  But, because the 
duplexer is not a perfect load, it creates reactance and the 
transmitter/PA may not like it.  If it doesn't like it, it may become 
spurious.  If it becomes spurious, it isn't putting out all of its power

Re: [Repeater-Builder] Coax length, etc.


Kevin Custer wrote:


Joe Ham buys a new duplexer and hooks it up to his 110 Watt MASTR II 
repeater and gets 50 watts out the antenna port.  He does his homework 
and realizes that he should only be loosing 29%


Wow -* loosing -*  that should have been losing - that's what I get for 
being in a hurry

Re: [Repeater-Builder] Coax length, etc.


Kevin Custer wrote:
I had one instance of a ham radio club loosing PA's left and right on 
their 2M machine.


Indeed - I am loosing my mind - grin

K

RE: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Eric Lemmon

Kevin,

Don't feel bad- look at the number of postings that use you instead of your,
your instead of you're, mhz instead of MHz, Khz instead of kHz, it's instead
of its... the list is endless!

But, back to the thread... it's refreshing to see that more than a few list
members know that a dummy load is purely resistive, while a duplexer cavity
is reactive- explaining why a transmitter that works perfectly when feeding
a dummy load can be unstable when connected to a duplexer.  This discussion
is both informative and quite entertaining!

73, Eric Lemmon WB6FLY
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Kevin Custer
Sent: Saturday, August 14, 2010 10:15 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length, etc.

 Kevin Custer wrote: 

Joe Ham buys a new duplexer and hooks it up to his 110 Watt MASTR II
repeater and gets 50 watts out the antenna port.  He does his homework and
realizes that he should only be loosing 29% 

Wow - loosing -  that should have been losing - that's what I get for being
in a hurry

RE: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Ross Johnson

So will someone post a simple rule of thumb. If you have the option of
optimizing cable length from PA to first cavity, IE you haven't made
them yet what's the best simple rule of thumb to follow to build them
to avoid reactance. 1/2wl if allowed minus coupling loop depth? Or is
that past a simple thumb. Also, This will obviously not work well for
220 or 440 or a most vhf repeater setups. So what would the next ideal
cable wl be? And so forth. The reason I ask, if your building new cables
why not? Answers on here seem to range a lot.
 
Ross kc7rjk

RE: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Ross Johnson

FORGOT to multiply cable VF then subtract coupling loop depth!!! Forgive
me :-)

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Ross Johnson
Sent: Saturday, August 14, 2010 11:59 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Coax length, etc.

So will someone post a simple rule of thumb. If you have the option of
optimizing cable length from PA to first cavity, IE you haven't made
them yet what's the best simple rule of thumb to follow to build them
to avoid reactance. 1/2wl if allowed minus coupling loop depth? Or is
that past a simple thumb. Also, This will obviously not work well for
220 or 440 or a most vhf repeater setups. So what would the next ideal
cable wl be? And so forth. The reason I ask, if your building new cables
why not? Answers on here seem to range a lot.

Ross kc7rjk

Re: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Russ Hines


 That's because there are as many rules as there are thumbs.  ;-)

I don't know about anyone else, but I can tell you about the highly 
scientific method I use.


I start with a multiple of 1/2 electrical wavelength and trim as 
necessary.  I'd stay away from an odd-multiple of 1/4 wavelength in this 
application... no good reason, just because (black magic and all that).


Try cutting the transmitter-to-duplexer line using the receive frequency 
length, and vice versa.  If that doesn't work out, you can swap them.


I know, on a 2m amateur system, the length difference is about 1/4.  In 
that case, make a cable 1-2 shorter and see what happens.


An alternative is to use multiple short lengths of coax connected 
together to find a happy length, then replace with a single coax cut 
to that length.


As I said, highly scientific. :-P

73, Russ WB8ZCC


On 8/14/2010 2:59 PM, Ross Johnson wrote:


So will someone post a simple rule of thumb... If you have the option 
of optimizing cable length from PA to first cavity, IE you haven't 
made them yet what's the best simple rule of thumb to follow to 
build them to avoid reactance. 1/2wl if allowed minus coupling loop 
depth? Or is that past a simple thumb. Also, This will obviously not 
work well for 220 or 440 or a most vhf repeater setups. So what would 
the next ideal cable wl be? And so forth... The reason I ask, if your 
building new cables why not? Answers on here seem to range a lot...


Ross kc7rjk

Re: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Russ Hines


 Some related comments, if you don't mind.

Temperature changes seem to be the biggest detuner of largely 
mechanical devices like cavity duplexers.  We often send our repeaters 
off to live in less-than-ideal environments, then expect cavity 
input/output impedances to remain as we measured them in the shop?  
Don't think so.


IMHO, we're making the same mistake I made in a post the other day, 
saying VSWR when what we really mean is reflected power as indicated 
on a meter.


Jeff is correct, VSWR along a transmission line doesn't change if 
source, load and line impedances are stable, the ratio remains the 
same.  What does change, and what is affected by line length, are actual 
impedances along the line under not-so-perfect-or-stable conditions; the 
actual impedances along the line change but the ratio does not.  For 
example, 100+j0, 25+j0, 40+j30, and 40-j30, are different impedances yet 
all exhibit a VSWR of 2:1 in a 50-ohm impedance system.


Voltage is proportional to impedance.  We can't really have a voltage 
standing wave ratio greater than 1:1 without a voltage differential, and 
that really can't happen if impedances along the line remain the same.


Our friends at Agilent have put together a Java applet demonstrating 
what happens along a transmission line. Maybe you're aware of it, it's 
really kind of cool.  The applet allows you to change the load impedance 
of the model and see the changes, so have fun with it.


http://education.tm.agilent.com/index.cgi?CONTENT_ID=6

Our in-line power meters, like our trusted Bird 43, do not directly 
measure power.  They're really voltage meters calibrated in watts at a 
specific impedance.  That's why they can be fooled into displaying an 
erroneous reflected power reading, perhaps lulling us into a sense of 
security that the VSWR on the line is acceptable when it may not be.


With most transmitters I'm familiar with, a high VSWR condition is 
detected from a reflected RF sample from a directional coupler at the 
transmitter's output, so it's not a real VSWR measurement per se, it's 
a voltage measurement.  Worse, these couplers tend not to be very 
selective, so out-of-channel and even out-of-band energy can cause high 
VSWR trips even when our measurements indicate all is well on our 
frequency of interest.


Great discussion, keep it going.  If I repeated what was already 
mentioned, my apologies.


73, Russ WB8ZCC


On 8/14/2010 12:53 PM, Kevin Custer wrote:


Jeff DePolo wrote:


Because the impedance is not matched between the transmitter
and duplexer, the 'apparent' loss of the duplexer is greater
than the manufacturers stated loss of the duplexer.  Changing
the cable length is not changing the loss of the duplexer,
it's changing the power that is accepted at the transmitter
port of the duplexer by matching the output impedance of the
transmitter to the input impedance of the transmitter port of
the duplexer.
 


But if the duplexer is tuned to 50 ohms, and the cable is 50 ohms, varying
the cable length isn't going to change the Z seen by the transmitter.  Or
are you suggesting the duplexer is purposely de-tuned from 50 ohms?
   


Purposely, accidentally, by lack of good design - people not having 
the right equipment to tune it correctly - whatever.
   

And also that by varying the cable length between the
transmitter and the duplexer that you can vary the reflected
power on that same line?


Yes.
 


With all due respect, that's not possible, regardless of what the Z is of
the duplexer.  The only time it could have an effect on the reflected power
would be if the transmitter/PA were spurious, and the amplitude/frequency of
the spurs changed with varying load Z, and I think we can both agree that if
that's the case, we have bigger fish to fry.
   


And this is where I believe the duplexer manufacturers are covering 
their butt.  They don't want the problem with complex reactance 
presented by the duplexer to be their problem.  Not that I don't 
agree, because it's usually the transmitter that is really at fault.


Joe Ham buys a new duplexer and hooks it up to his 110 Watt MASTR II 
repeater and gets 50 watts out the antenna port.  He does his homework 
and realizes that he should only be loosing 29% with the 1.5 dB of 
insertion loss stated in the paperwork - but he's loosing over 50%.  
The duplexer manufacturer supposedly engineered and tuned it for a 50 
Ohm system.  He knows that the cable he connected to the transmitter 
is good, because when he disconnects the end going to the transmitter 
port of the duplexer and connects it to his Bird 43 terminated with a 
good load - it reads 110 watts.


Now, is the transmitter becoming spurious and the cable length being 
changed in length satisfies the match between the duplexer and 
transmitter - I don't know...   All I can tell you is I have followed 
the suggestions written in the WACOM manual and it has worked.  I had 
one instance of a ham radio club

RE: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Gary Schafer

One correction here; the Bird power meter is not just a voltage measuring
meter. It does in fact measure voltage and current to calculate power. It
will give true power even if used in a non 50 ohm circuit. But you must
always subtract reflected power from indicated forward power to find true
power delivered to the load.

 

When measuring SWR you must always calculate it (or use the chart) and
compare reflected to forward indicated on the meter. It is easy to be fooled
as indicated forward power also drops as reflected power drops.

 

73

Gary  K4FMX

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Russ Hines
Sent: Saturday, August 14, 2010 4:30 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length, etc.73

 

 



Some related comments, if you don't mind.

Temperature changes seem to be the biggest detuner of largely mechanical
devices like cavity duplexers.  We often send our repeaters off to live in
less-than-ideal environments, then expect cavity input/output impedances to
remain as we measured them in the shop?  Don't think so.

IMHO, we're making the same mistake I made in a post the other day, saying
VSWR when what we really mean is reflected power as indicated on a
meter.  

Jeff is correct, VSWR along a transmission line doesn't change if source,
load and line impedances are stable, the ratio remains the same.  What does
change, and what is affected by line length, are actual impedances along the
line under not-so-perfect-or-stable conditions; the actual impedances along
the line change but the ratio does not.  For example, 100+j0, 25+j0, 40+j30,
and 40-j30, are different impedances yet all exhibit a VSWR of 2:1 in a
50-ohm impedance system.  

Voltage is proportional to impedance.  We can't really have a voltage
standing wave ratio greater than 1:1 without a voltage differential, and
that really can't happen if impedances along the line remain the same.

Our friends at Agilent have put together a Java applet demonstrating what
happens along a transmission line. Maybe you're aware of it, it's really
kind of cool.  The applet allows you to change the load impedance of the
model and see the changes, so have fun with it.

http://education.tm.agilent.com/index.cgi?CONTENT_ID=6

Our in-line power meters, like our trusted Bird 43, do not directly measure
power.  They're really voltage meters calibrated in watts at a specific
impedance.  That's why they can be fooled into displaying an erroneous
reflected power reading, perhaps lulling us into a sense of security that
the VSWR on the line is acceptable when it may not be.

With most transmitters I'm familiar with, a high VSWR condition is
detected from a reflected RF sample from a directional coupler at the
transmitter's output, so it's not a real VSWR measurement per se, it's a
voltage measurement.  Worse, these couplers tend not to be very selective,
so out-of-channel and even out-of-band energy can cause high VSWR trips
even when our measurements indicate all is well on our frequency of
interest.

Great discussion, keep it going.  If I repeated what was already mentioned,
my apologies.

73, Russ WB8ZCC


_._,___

Re: [Repeater-Builder] Coax length, etc.


Russ Hines wrote:



Some related comments, if you don't mind.

Temperature changes seem to be the biggest detuner of largely 
mechanical devices like cavity duplexers.  We often send our repeaters 
off to live in less-than-ideal environments, then expect cavity 
input/output impedances to remain as we measured them in the shop?  
Don't think so.


I largely disagree.  Most modern duplexer designs (within the last 25 
years or so) use compensating elements to make the duplexer or cavity 
temperature stable.  Invar is a nickel-steel alloy that exhibits about 
1/10 the thermal expansion as a common carbon steel counterpart.  Invar 
is used to make the tuning rod - many times it's threaded.  The rest of 
the duplexer or cavity is usually made of similar metals and generally 
thermal expansion occurs across these components equally, resulting in 
extremely low frequency drift over its rated operating temperature.





Our in-line power meters, like our trusted Bird 43, do not directly 
measure power.  They're really voltage meters calibrated in watts at a 
specific impedance.  That's why they can be fooled into displaying an 
erroneous reflected power reading, perhaps lulling us into a sense of 
security that the VSWR on the line is acceptable when it may not be.


What?  Maybe you would like to have another chance at that one

Kevin Custer

Re: [Repeater-Builder] Coax length, etc.


Ross Johnson wrote:



So will someone post a simple rule of thumb... If you have the option 
of optimizing cable length from PA to first cavity, IE you haven't 
made them yet what's the best simple rule of thumb to follow to 
build them to avoid reactance. 1/2wl if allowed minus coupling loop 
depth? Or is that past a simple thumb.




Simple rule - there is none.  The length can be determined 
experimentally as outlined in several publications of various duplexer 
manufacturers.


I use the length I need to do a good job - then, if the transmitter is 
unhappy, I build a cable long enough to do the job and satisfy the 
transmitter.


Kevin

RE: [Repeater-Builder] Coax length, etc.

 Jeff, you aren't stepping on my toes at all. Glad to see your 
 comments.

OK, good.  Since you've never met me, I can assure you, you definately DO
NOT want me stepping on your toes, it would be painful.

 I do have to agree with Kevin that most duplexer 
 manufacturers recommend different cable length trials between 
 the transmitter and the duplexer when full power can not be 
 reached into the duplexer.

Ah, but the crux of the matter is that we're not changing the performance of
the duplexer, we're just getting the transmitter to transfer more power into
the line.

  Over the years I have been a manufacturers rep for TX-RX, 
 Sinclair and Telewave. All of them recommend the same thing.

Again, it's a CYA measure as Kevin pointed out.  PA won't make power?  Don't
blame us, try mucking with the cable length, see if that helps.

 I am not a transmitter expert but it is my understanding that 
 the problem is not one of the duplexer not presenting 50 ohms 
 at the wanted frequency but the impedance that it presents 
 off frequency to the transmitter finals. Some solid state 
 devices do not like to see high reactance, even off 
 frequency. 

But why?  If all of the power (or, let's hope, at least 99.99% of it) is
on-channel, *should* a properly-designed and properly-functioning
transmitter misbehave due to the poor match a duplexer presents at
frequencies far removed from the channel center?

 For one thing the reactance causes them to draw 
 more current than normal. 

Again, why?

 This may be why you find that 
 tuning for minimum pa current and maximum power out don't 
 exactly agree with one another. 

I can promise you they almost never do, but that's not any great mystery.

 You are probably finding a 
 balance between the off frequency reactance and the on 
 frequency wanted load that the finals see.

No, that's not it.  The off-frequency Z issue is a totally separate topic
from the efficiency vs maximum output subject.  Let's keep those two topics
separate for the sake of this discussion.

 If you have the duplexer properly tuned to provide 50 ohms at 
 its input port, the transmitter may still not be happy 
 because of the off frequency reactance presented by the duplexer.

I disagree.  I would accept the notion that the transmitter may not be
happy (and I put that in quotes not to mock you, but becuase I can't come
up with a better word either) because it is not *properly matched* when
looking into a 50+j0 load.  This indicates a deficiency in the amplifier; if
it were designed and working right, it *should* make rated power when
terminated in a 50 ohm load on-channel.

 Changing the cable length in this case really does nothing 
 for the  on frequency load between the duplexer and 
 transmitter, when the duplexer is presenting 50 ohms, but it 
 can change the off frequency impedance transformation that 
 the transmitter sees. 

Yes, but again, I argue that this all points back to a PA problem.  Or the
input Z of the duplexer really isn't 50 ohms and the line is acting as a
transformer.

 Detuning the duplexer and or changing 
 cable length to get the transmitter power up is the wrong way 
 to go here. First the transmitter should be optimized into a 
 50 ohm load. Then optimize the duplexer input for 50 ohms input.

Yes, yes, yes, amen!

 Someone asked about a rule of thumb for transmitter to 
 duplexer cable length. There is none! 

Yes there is. You take out a tape measure and the distance from the
transmitter to the duplexer.  You make the cable at least that length.

 The cable length between multiple cavities is predictable. As 
 an example between two notch cavities; the first notch 
 presents a very low impedance. With a quarter wave line to 
 the next cavity that low impedance is transformed to a high 
 impedance at the input to the next cavity. That high 
 impedance is then presented with a very low impedance of the 
 second cavity. This critical length cable increases the 
 ultimate notch depth because the high impedance that the 
 cable presents and the low impedance of the cavity form a 
 voltage divider. The greater the ratio the better the rejection.


'zactly.  When done right, you can pick up close to 6 dB additional net
notch depth when cascading notch (or pass/notch) cavities when the
intra-cavity cables are cut this way.

 Jeff WN3A

RE: [Repeater-Builder] Coax length, etc.

 So will someone post a simple rule of thumb. If you have the 
 option of optimizing cable length from PA to first cavity, IE 
 you haven't made them yet what's the best simple rule of 
 thumb to follow to build them to avoid reactance. 1/2wl if 
 allowed minus coupling loop depth? Or is that past a simple 
 thumb. Also, This will obviously not work well for 220 or 440 
 or a most vhf repeater setups. So what would the next ideal 
 cable wl be? And so forth. The reason I ask, if your building 
 new cables why not? Answers on here seem to range a lot.

There is no simple rule of thumb, and if anybody tells you that there is,
ask them how do you account for the unknown-length of coax that's *inside*
your transmitter/amplifier before it gets to the antenna jack.

--- Jeff WN3A

RE: [Repeater-Builder] Coax length, etc.


OK, I think, for the most part, we're on the same page.  I'm cuttin' and
trimmin' a lot here...
 
 And this is where I believe the duplexer manufacturers are 
 covering their butt.  They don't want the problem with 
 complex reactance presented by the duplexer to be their 
 problem.  Not that I don't agree, because it's usually the 
 transmitter that is really at fault.  

I think that last sentence speaks volumes on the matter.
 
 Joe Ham buys a new duplexer and hooks it up to his 110 Watt 
 MASTR II repeater and gets 50 watts out the antenna port.  He 
 does his homework and realizes that he should only be loosing 
 29% with the 1.5 dB of insertion loss stated in the paperwork 
 - but he's loosing over 50%.  

Ah, but is he really *losing* 50 percent in the duplexer, or is transmitter
not making the full 110 watts output to start with?  Maybe his transmitter
is really only delivering 70 watts to the duplexer.  Is it an issue of the
duplexer's loss being high, or is the problem the transmitter's not making
power?  Seems to me it's really the latter.  

 The duplexer manufacturer 
 supposedly engineered and tuned it for a 50 Ohm system.  

Well, kinda.  Many duplexers are spec'ed for 1.5:1 (14 dB RL) input VSWR
max.  Fortunately, I rarely see any that are that bad.  I'll gladly trade
off a tenth of a dB of insertion loss for several (if not 10 or more) dB of
return loss improvement when I'm tuning on the VNA, but some hams are greedy
and don't think along those lines when they're tuning...

 He 
 knows that the cable he connected to the transmitter is good, 
 because when he disconnects the end going to the transmitter 
 port of the duplexer and connects it to his Bird 43 
 terminated with a good load - it reads 110 watts.

Yes, but did he have a second Bird between the Tx and the duplexer when he
was measuring power output?  That would have told the real story.

 Now, is the transmitter becoming spurious 

Now all bets are off.

 and the cable 
 length being changed in length satisfies the match between 
 the duplexer and transmitter - I don't know...   All I can 
 tell you is I have followed the suggestions written in the 
 WACOM manual and it has worked.  I had one instance of a ham 
 radio club loosing PA's left and right on their 2M machine.  
 They told me of the situation and I offered to do a little 
 testing.  The 110 watt PA would put out 110 watts into a Bird 
 and dummy, but only 45 watts was coming out the antenna port 
 of the duplexer.  At the time I didn't own a spectrum 
 analyzer.  The repeater wouldn't duplex without desense.  I 
 changed the length of the line between the PA and duplexer 
 until I got the power to read about 75 Watts as I remember.  
 That was 13 years and they still have the same PA - no desense either.

Out of morbid curiosity, what kind of PA was it?

 You are changing the VSWR when tuning the cavity closest to 
 the transmitter.   

Yes, but once you've adjusted that cavity, from that point on, changing the
cable length doesn't vary the VSWR.  That was my point - changing the cable
length doesn't change VSWR.  

 I realize that impedance transformation 
 cannot occur when you have a 50 Ohm cable (of any length) and 
 a perfect 50 Ohm load - but I think you will agree that a 
 duplexer doesn't, in any way shape or form, present a nice 50 
 Ohm load.  

Well, it can get pretty damn close.  I can send you some VNA plots of
duplexers with input Z's well in excess of 30 dB return loss, some
approaching the limits of my test equipment.  Of course, when hooked up to
an antenna instead of being terminated in a precision load, all bets are
off, but hey, that's not the fault of the duplexer...

 Some transmitters just cannot deal with it without 
 some form of matching after the fact - like a Z-Matcher, 
 Isolator, Circulator, or even a critical cable length.

I don't like those transmitters  :-)

 GE MASTR II 110 watt 150.8 to 174 MHz PA and WACOM WP-641.  

Thinking...thinking...no, haven't done that one.

 Motorola MICOR 150.8 to 162 MHz PA and WACOM WP-641.  

Yes, have done that combo, several times that I can think of.  Actually, one
of the repeaters was low-split from the factory (out of Canada) now that I
think about it, so that doesn't count, the others were all H split with no
PA mods.  Didn't do anything special with cable lengths.

 Hamtronics 45 Watt 2M PA and Sinclair Q-202.

Haven't done any Hamtronics.

 Well, I cannot believe that I'm the only person on this list 
 that has had success with optimizing the length of cable 
 between the duplexer and transmitter/PA.  

I don't doubt that others have seen positive (or negative) effects from
varying cable lengths - I just said I've never had to resort to doing it,
using the equipment that I've used, with the equipment tuned the way I've
tuned it.

 I'll get us some tickets for Vegas - Jeff.

I think ZZU has the right idea.  He's down in MX-land right now, probably
sitting on a beach laughing at us working

RE: [Repeater-Builder] Coax length, etc.

2010-08-14 Thread Gary Schafer

 -Original Message-
 From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
 buil...@yahoogroups.com] On Behalf Of Jeff DePolo
 Sent: Saturday, August 14, 2010 10:45 PM
 To: Repeater-Builder@yahoogroups.com
 Subject: RE: [Repeater-Builder] Coax length, etc.

  Jeff, you aren't stepping on my toes at all. Glad to see your
  comments.

 OK, good.  Since you've never met me, I can assure you, you definately DO
 NOT want me stepping on your toes, it would be painful.

  I do have to agree with Kevin that most duplexer
  manufacturers recommend different cable length trials between
  the transmitter and the duplexer when full power can not be
  reached into the duplexer.

 Ah, but the crux of the matter is that we're not changing the performance
 of
 the duplexer, we're just getting the transmitter to transfer more power
 into
 the line.

Yes! I fully agree.

   Over the years I have been a manufacturers rep for TX-RX,
  Sinclair and Telewave. All of them recommend the same thing.

 Again, it's a CYA measure as Kevin pointed out.  PA won't make power?
 Don't
 blame us, try mucking with the cable length, see if that helps.

But it is not necessarily the duplexer's problem.

  I am not a transmitter expert but it is my understanding that
  the problem is not one of the duplexer not presenting 50 ohms
  at the wanted frequency but the impedance that it presents
  off frequency to the transmitter finals. Some solid state
  devices do not like to see high reactance, even off
  frequency.

 But why?  If all of the power (or, let's hope, at least 99.99% of it)
 is
 on-channel, *should* a properly-designed and properly-functioning
 transmitter misbehave due to the poor match a duplexer presents at
 frequencies far removed from the channel center?

Well yes, properly designed transmitter. But how much do you want to pay for
it? A built in isolator will solve all of those problems as an example.

  For one thing the reactance causes them to draw
  more current than normal.

 Again, why?

Not sure why. I have been told by device engineers that is a characteristics
of some devices.

  This may be why you find that
  tuning for minimum pa current and maximum power out don't
  exactly agree with one another.

 I can promise you they almost never do, but that's not any great mystery.

  You are probably finding a
  balance between the off frequency reactance and the on
  frequency wanted load that the finals see.

 No, that's not it.  The off-frequency Z issue is a totally separate topic
 from the efficiency vs maximum output subject.  Let's keep those two
 topics
 separate for the sake of this discussion.

If what you find in tuning happens directly into a 50 ohm load I agree.

  If you have the duplexer properly tuned to provide 50 ohms at
  its input port, the transmitter may still not be happy
  because of the off frequency reactance presented by the duplexer.

 I disagree.  I would accept the notion that the transmitter may not be
 happy (and I put that in quotes not to mock you, but becuase I can't
 come
 up with a better word either) because it is not *properly matched* when
 looking into a 50+j0 load.  This indicates a deficiency in the amplifier;
 if
 it were designed and working right, it *should* make rated power when
 terminated in a 50 ohm load on-channel.

Yes it would be a transmitter problem. Maybe as designed.

  Changing the cable length in this case really does nothing
  for the  on frequency load between the duplexer and
  transmitter, when the duplexer is presenting 50 ohms, but it
  can change the off frequency impedance transformation that
  the transmitter sees.

 Yes, but again, I argue that this all points back to a PA problem.  Or the
 input Z of the duplexer really isn't 50 ohms and the line is acting as a
 transformer.

Again I agree. In this instance I was describing a duplexer that did
present 50 ohms at the operating frequency and still the transmitter was not
happy. Because of the off frequency impedance being transformed to
something that the transmitter does not like.

It is almost impossible for a high Q cavity to not present some reactance
away from the tuned frequency. If it didn't then it would not have any
selectivity. The random length cable of course transforms that reactance to
something that the transmitter may or may not be comfortable with as
discussed above.

  Detuning the duplexer and or changing
  cable length to get the transmitter power up is the wrong way
  to go here. First the transmitter should be optimized into a
  50 ohm load. Then optimize the duplexer input for 50 ohms input.

Of course I am talking about when the duplexer is presenting a good 50 ohm
input impedance at the operating frequency.

 Yes, yes, yes, amen!

  Someone asked about a rule of thumb for transmitter to
  duplexer cable length. There is none!

 Yes there is. You take out a tape measure and the distance from the
 transmitter to the duplexer.  You make

RE: [Repeater-Builder] Coax length, etc.

2010-08-13 Thread Jeff DePolo


I must have missed some posts - my inbox ran out of space (I'm on the road
and not checking email as often as I usually do), so my apologies if I'm
asking questions that have already been answered... 

  Allan Crites and I are currently in discussion which will 
 be used as the basis of a RB web article that will explain 
 exactly what is happening, why it happens, and why an 
 'optimized' cable length can be used to transfer power ending 
 up with the stated loss of the duplexer and have little 
 reflected power toward the transmitter - so long as the 
 duplexer is tuned properly and exhibits good return loss on 
 the frequency it's designed to pass.

Maybe I'm not understanding right.  Are you saying that by varying the cable
length between the transmitter and the duplexer that you can affect the
insertion loss of the duplexer?  And also that by varying the cable length
between the transmitter and the duplexer that you can vary the reflected
power on that same line?  Please tell me I'm reading this wrong...I've been
on the road a long time and working a lot of long hours, so it's quite
possible...

--- Jeff WN3A

Re: [Repeater-Builder] Coax length, etc.

2010-08-13 Thread Kevin Custer


Jeff DePolo wrote:


Maybe I'm not understanding right.  Are you saying that by varying the cable
length between the transmitter and the duplexer that you can affect the
insertion loss of the duplexer?


No. 

Because the impedance is not matched between the transmitter and 
duplexer, the 'apparent' loss of the duplexer is greater than the 
manufacturers stated loss of the duplexer.  Changing the cable length is 
not changing the loss of the duplexer, it's changing the power that is 
accepted at the transmitter port of the duplexer by matching the output 
impedance of the transmitter to the input impedance of the transmitter 
port of the duplexer.



  And also that by varying the cable length between the transmitter and the 
duplexer that you can vary the reflected
power on that same line?


Yes.

In a situation where the duplexer and transmitter have differing 
impedances, and a cable optimized in length matches these impedances, 
the mismatch at the duplexer is minimized, therefore the power reflected 
by the duplexer is minimized. 


  Please tell me I'm reading this wrong...I've been
on the road a long time and working a lot of long hours, so it's quite
possible...

--- Jeff WN3A


I have found that when you get a transmitter that is 'picky' about the 
length of interconnecting cable, power being read at the output port of 
the duplexer is low and you cannot alter the tuning of the cavity 
closest to the transmitter to make things right.  In other words, the 
place where lowest VSWR and maximum power transfer occurs is at two 
completely different places, and power transfer is not up where it 
should be (transmitter makes 100 watts into a dummy load but only shows 
50 watts on the output port of the duplexer that has a stated 1.5 dB 
loss (29 %)).  As you get close to the 'optimum' cable length, the 
lowest VSWR and maximum power transfer occur near the same place when 
tuning the cavity closest to the transmitter.


I usually pay more attention to what is coming out the antenna port of 
the duplexer - first.  Then, when things are right, comparing forward 
power going to the duplexer and power going to a good dummy load will be 
very close the same, since matching the impedance of the transmitter to 
the impedance of the duplexer was accomplished by some means.


I use a compensation cable along with my Bird so that the samplers 
transmission line length is nullified in the line under test.  This 
compensation cable results in exactly 1/2 WL including the samplers 
transmission line.  Compensation cable lengths are outlined in the 
manual for the Bird 43.


Kevin

RE: [Repeater-Builder] Coax length, etc.

2010-08-06 Thread Jeff DePolo


 The cable length issue is a brother to if you don't like 
 your VSWR, change the point along the transmission line where 
 you're measuring it.  

I don't know what that's supposed to mean.  The VSWR on the line is the same
no matter where along the line you measure it.  If you're using a meter that
reads a different VSWR depending where on the line you put it, you need a
new meter...

--- Jeff WN3A

Re: [Repeater-Builder] Coax length, etc.

2010-08-06 Thread allan crites

And a new perspective on transmission lines.
I didn't think it was worth responding to, Jeff.
AC   WA9ZZU.

From: Jeff DePolo j...@broadsci.com
To: Repeater-Builder@yahoogroups.com
Sent: Fri, August 6, 2010 8:23:09 AM
Subject: RE: [Repeater-Builder] Coax length, etc.

 The cable length issue is a brother to if you don't like 
 your VSWR, change the point along the transmission line where 
 you're measuring it. 

I don't know what that's supposed to mean. The VSWR on the line is the same
no matter where along the line you measure it. If you're using a meter that
reads a different VSWR depending where on the line you put it, you need a
new meter...

--- Jeff WN3A

Re: [Repeater-Builder] Coax length, etc.

2010-08-06 Thread Steven M Hodell

Grab your Smith chart!  LOL

  - Original Message - 
  From: allan crites 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Friday, August 06, 2010 12:46 PM
  Subject: Re: [Repeater-Builder] Coax length, etc.

  And a new perspective on transmission lines.
  I didn't think it was worth responding to, Jeff.
  AC   WA9ZZU.

--
  From: Jeff DePolo j...@broadsci.com
  To: Repeater-Builder@yahoogroups.com
  Sent: Fri, August 6, 2010 8:23:09 AM
  Subject: RE: [Repeater-Builder] Coax length, etc.

   The cable length issue is a brother to if you don't like 
   your VSWR, change the point along the transmission line where 
   you're measuring it. 

  I don't know what that's supposed to mean. The VSWR on the line is the same
  no matter where along the line you measure it. If you're using a meter that
  reads a different VSWR depending where on the line you put it, you need a
  new meter...

  --- Jeff WN3A

Re: [Repeater-Builder] Coax length, etc.

2010-08-06 Thread Russ Hines

 Jeff was correct to question.  I was vague.  What I should have said 
was indicated reflected power, not VSWR.


But good luck trying to determine an accurate VSWR based on erroneous 
reflected readings.


Let the boo birds squawk.  Keep questioning, Jeff.

73, Russ WB8ZCC


On 8/6/2010 1:07 PM, Steven M Hodell wrote:




Grab your Smith chart!  LOL

- Original Message -
*From:* allan crites mailto:wa9...@arrl.net
*To:* Repeater-Builder@yahoogroups.com
mailto:Repeater-Builder@yahoogroups.com
*Sent:* Friday, August 06, 2010 12:46 PM
*Subject:* Re: [Repeater-Builder] Coax length, etc.

And a new perspective on transmission lines.
I didn't think it was worth responding to, Jeff.
AC   WA9ZZU.


*From:* Jeff DePolo j...@broadsci.com mailto:j...@broadsci.com
*To:* Repeater-Builder@yahoogroups.com
mailto:Repeater-Builder@yahoogroups.com
*Sent:* Fri, August 6, 2010 8:23:09 AM
*Subject:* RE: [Repeater-Builder] Coax length, etc.


 The cable length issue is a brother to if you don't like
 your VSWR, change the point along the transmission line where
 you're measuring it.

I don't know what that's supposed to mean. The VSWR on the line is
the same
no matter where along the line you measure it. If you're using a
meter that
reads a different VSWR depending where on the line you put it, you
need a
new meter...

--- Jeff WN3A

Re: [Repeater-Builder] Coax length

2010-08-05 Thread Doug Hutchison

Hi Kevin and all who responded to my question.

Thank you, good info in the link provided by Kevin along with other 
interesting guidelines. More for the file.

Regards,
Doug - GM7SVK




On 04/08/2010 11:04 PM, Kevin Custer wrote:
 Doug Hutchison wrote:

 Does the length of coax connecting cable between repeater and filters
 matter?
  

 Yes - and no.

 Please read the note about cabling lengths between the repeater and the
 duplexer in the section on page 4 of the following document:
 http://www.repeater-builder.com/wacom/wp6xx-vhf-tuning-instructions-remec.pdf

 Watch for word wrap...

 Kevin Custer



 



 Yahoo! Groups Links

Re: [Repeater-Builder] Coax length, etc.

2010-08-05 Thread Russ Hines

 Thanks, guys, a good topic and one that always seems to come up.  And 
it sparks more questions and comments, of course.


The cable length issue is a brother to if you don't like your VSWR, 
change the point along the transmission line where you're measuring 
it.  By changing the length of the line, we're creating a transmission 
line transformer (a good thing) but we're limited by its length (not so 
good).  It seems to me the mentioned circulator/isolator at the output 
of the xmtr is a better fix, as reflections coming back from the 
duplexer is absorbed by the circulator's load, the xmtr is generally 
happy, and we're no longer limited where we can put things in a rack or 
elsewhere.


For amateurs, coming up with usable VHF circulators seems to be 
difficult and usually expensive, and coax always seems to be cheaper.  
Has anyone had luck finding a source for reasonbly priced VHF 
circulators, or success in rolling their own?


Also, I noted in the pamphlet Kevin referenced that the unused duplexer 
port was left open (Figs. 1  2).  I guess if the isolation is already 
greater than the load's return loss, it doesn't matter, at least at the 
reject frequency.  But it seems to me one could possibly create problems 
for oneself by not terminating the unused open port.  Just a thought.


Maybe I work better knowing there's a load there. ;-)

Your comments, please.

73, Russ WB8ZCC


On 8/5/2010 10:19 AM, Doug Hutchison wrote:


Hi Kevin and all who responded to my question.

Thank you, good info in the link provided by Kevin along with other
interesting guidelines. More for the file.

Regards,
Doug - GM7SVK

On 04/08/2010 11:04 PM, Kevin Custer wrote:
 Doug Hutchison wrote:

 Does the length of coax connecting cable between repeater and filters
 matter?


 Yes - and no.

 Please read the note about cabling lengths between the repeater and the
 duplexer in the section on page 4 of the following document:
 
http://www.repeater-builder.com/wacom/wp6xx-vhf-tuning-instructions-remec.pdf


 Watch for word wrap...

 Kevin Custer



 



 Yahoo! Groups Links

Re: [Repeater-Builder] Coax length, etc.

2010-08-05 Thread Kevin Custer


Russ Hines wrote:


Thanks, guys, a good topic and one that always seems to come up.  And 
it sparks more questions and comments, of course.


The cable length issue is a brother to if you don't like your VSWR, 
change the point along the transmission line where you're measuring 
it.  By changing the length of the line, we're creating a 
transmission line transformer (a good thing) but we're limited by its 
length (not so good).  It seems to me the mentioned 
circulator/isolator at the output of the xmtr is a better fix, as 
reflections coming back from the duplexer is absorbed by the 
circulator's load, the xmtr is generally happy, and we're no longer 
limited where we can put things in a rack or elsewhere. 

For amateurs, coming up with usable VHF circulators seems to be 
difficult and usually expensive, and coax always seems to be cheaper.  
Has anyone had luck finding a source for reasonbly priced VHF 
circulators, or success in rolling their own?


Also, I noted in the pamphlet Kevin referenced that the unused 
duplexer port was left open (Figs. 1  2).  I guess if the isolation 
is already greater than the load's return loss, it doesn't matter, at 
least at the reject frequency.  But it seems to me one could possibly 
create problems for oneself by not terminating the unused open port.  
Just a thought.


Maybe I work better knowing there's a load there. ;-)

Your comments, please. 


73, Russ WB8ZCC




I think we all agree that a real impedance matching device is the best 
approach, but hams (generally speaking) are cheap.  Many will spend two 
days hacking on a piece of RG-214 before spending fifty or a hundred 
bucks on a different (better?) solution.


Allan Crites and I are currently in discussion which will be used as the 
basis of a RB web article that will explain exactly what is happening, 
why it happens, and why an 'optimized' cable length can be used to 
transfer power ending up with the stated loss of the duplexer and have 
little reflected power toward the transmitter - so long as the duplexer 
is tuned properly and exhibits good return loss on the frequency it's 
designed to pass. 


Kevin Custer

Re: [Repeater-Builder] Coax length, etc.

2010-08-05 Thread Russ Hines


 Thanks for the reply, Kevin.  I'm looking forward to seeing the article.

73, Russ WB8ZCC

On 8/5/2010 1:20 PM, Kevin Custer wrote:


Russ Hines wrote:

Thanks, guys, a good topic and one that always seems to come up.  And 
it sparks more questions and comments, of course.


The cable length issue is a brother to if you don't like your VSWR, 
change the point along the transmission line where you're measuring 
it.  By changing the length of the line, we're creating a 
transmission line transformer (a good thing) but we're limited by its 
length (not so good).  It seems to me the mentioned 
circulator/isolator at the output of the xmtr is a better fix, as 
reflections coming back from the duplexer is absorbed by the 
circulator's load, the xmtr is generally happy, and we're no longer 
limited where we can put things in a rack or elsewhere.


For amateurs, coming up with usable VHF circulators seems to be 
difficult and usually expensive, and coax always seems to be 
cheaper.  Has anyone had luck finding a source for reasonbly priced 
VHF circulators, or success in rolling their own?


Also, I noted in the pamphlet Kevin referenced that the unused 
duplexer port was left open (Figs. 1  2).  I guess if the isolation 
is already greater than the load's return loss, it doesn't matter, at 
least at the reject frequency.  But it seems to me one could possibly 
create problems for oneself by not terminating the unused open port.  
Just a thought.


Maybe I work better knowing there's a load there. ;-)

Your comments, please.

73, Russ WB8ZCC




I think we all agree that a real impedance matching device is the best 
approach, but hams (generally speaking) are cheap.  Many will spend 
two days hacking on a piece of RG-214 before spending fifty or a 
hundred bucks on a different (better?) solution.


Allan Crites and I are currently in discussion which will be used as 
the basis of a RB web article that will explain exactly what is 
happening, why it happens, and why an 'optimized' cable length can be 
used to transfer power ending up with the stated loss of the duplexer 
and have little reflected power toward the transmitter - so long as 
the duplexer is tuned properly and exhibits good return loss on the 
frequency it's designed to pass.


Kevin Custer

[Repeater-Builder] Coax length

2010-08-04 Thread Doug Hutchison

Does the length of coax connecting cable between repeater and filters 
matter?

Doug

Re: [Repeater-Builder] Coax length

2010-08-04 Thread n5sxq.0


 Doug Hutchison specialq@ntlworld.com wrote: 
 Does the length of coax connecting cable between repeater and filters 
 matter?
 
 Doug
 
As long as the filters are working correctly, the cable length  from the 
duplexers to the radios tx and rx does not matter. Having said that, remember 
that the shortest length of double shielded coax or HELIAX cable that will 
reach without kinks or physcial loads (binds) on the connectors should be used. 
This has nothing to do with impedeance matching, but rather cross talk thru 
cable leakage. On this same note (and knowing I'm going to stur up a hornets 
nest) I strongly advise against using the LMR type cables for ANY full duplex 
system. Any double sheilded cable which uses dissimular metals in the 2 (or 
more) shields will eventually cause rf noise .
Jeff N5SXQ

Re: [Repeater-Builder] Coax length

2010-08-04 Thread Kevin Custer

Doug Hutchison wrote:
 Does the length of coax connecting cable between repeater and filters 
 matter?


Yes - and no.

Please read the note about cabling lengths between the repeater and the
duplexer in the section on page 4 of the following document:
http://www.repeater-builder.com/wacom/wp6xx-vhf-tuning-instructions-remec.pdf

Watch for word wrap...

Kevin Custer

Re: [Repeater-Builder] Coax length

2010-08-04 Thread Doug Hutchison

I will do sir, thank you Kevin.

Doug

On 04/08/2010 23:04:07, Kevin Custer (kug...@kuggie.com) wrote:
  Doug Hutchison wrote:
   Does the length of coax connecting cable between repeater and filters
   matter?
 
 
  Yes - and no.
 
  Please read the note about cabling lengths between the repeater and the
  duplexer in the section on page 4 of the following document:
  
http://www.repeater-builder.com/wacom/wp6xx-vhf-tuning-instructions-remec.
  pdf
 
  Watch for word wrap...
 
  Kevin Custer
 
 
 
  
 
 
 
  Yahoo! Groups Links

Re: [Repeater-Builder] Coax length

2010-08-04 Thread no6b

At 8/4/2010 14:37, you wrote:

 Doug Hutchison specialq@ntlworld.com wrote:
  Does the length of coax connecting cable between repeater and filters
  matter?
 
  Doug
 
As long as the filters are working correctly, the cable length  from the 
duplexers to the radios tx and rx does not matter. Having said that, 
remember that the shortest length of double shielded coax or HELIAX cable 
that will reach without kinks or physcial loads (binds) on the connectors 
should be used. This has nothing to do with impedeance matching, but 
rather cross talk thru cable leakage.

Double-shielded cables aren't going to leak enough to be a concern.  You do 
want to keep the length short to minimize loss.

BTW, I once measured the isolation between a pair of ordinary RG-58 cables 
on a VNA from 50 to 500 MHz.  Unless the cables were twisted together, I 
didn't see any coupling between them down to at least -90 dB.  When they 
were twisted together, I think there was ONE frequency around 500 MHz where 
there was -65 dB coupling.

  On this same note (and knowing I'm going to stur up a hornets nest) I 
 strongly advise against using the LMR type cables for ANY full duplex 
 system. Any double sheilded cable which uses dissimular metals in the 2 
 (or more) shields will eventually cause rf noise .

No argument here.

Bob NO6B

Re: [Repeater-Builder] Coax length

2010-08-04 Thread Chuck Kelsey

Keep in mind that duplexer manufacturers used to routinely use single 
shielded (RG-213) cables to make up harnesses. They worked. So Bob's testing 
doesn't surprise me.

Chuck
WB2EDV


- Original Message - 
From: n...@no6b.com
To: Repeater-Builder@yahoogroups.com
Sent: Wednesday, August 04, 2010 10:22 PM
Subject: Re: [Repeater-Builder] Coax length


 At 8/4/2010 14:37, you wrote:

 Doug Hutchison specialq@ntlworld.com wrote:
  Does the length of coax connecting cable between repeater and filters
  matter?
 
  Doug
 
As long as the filters are working correctly, the cable length  from the
duplexers to the radios tx and rx does not matter. Having said that,
remember that the shortest length of double shielded coax or HELIAX cable
that will reach without kinks or physcial loads (binds) on the connectors
should be used. This has nothing to do with impedeance matching, but
rather cross talk thru cable leakage.

 Double-shielded cables aren't going to leak enough to be a concern.  You 
 do
 want to keep the length short to minimize loss.

 BTW, I once measured the isolation between a pair of ordinary RG-58 cables
 on a VNA from 50 to 500 MHz.  Unless the cables were twisted together, I
 didn't see any coupling between them down to at least -90 dB.  When they
 were twisted together, I think there was ONE frequency around 500 MHz 
 where
 there was -65 dB coupling.

  On this same note (and knowing I'm going to stur up a hornets nest) I
 strongly advise against using the LMR type cables for ANY full duplex
 system. Any double sheilded cable which uses dissimular metals in the 2
 (or more) shields will eventually cause rf noise .

 No argument here.

 Bob NO6B

RE: [Repeater-Builder] coax length

2008-09-24 Thread Mike Besemer (WM4B)

Collin,

 

I found a nice commercial-quality load (the type that looks like a big
heat-sink) on the e-place quite cheap.  I'm really happy with it.  The guy
who was selling it had a bunch of them, so you might give it a shot.

 

Also, check with Dan. he may have something he can at least loan you.

 

Mike

WM4B

 

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
Sent: Wednesday, September 24, 2008 12:14 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] coax length

 

John,
Very well then, I guess I need to be shopping for a good load. Any 
suggestions? Any under an arm and a leg? What do the good loads use for 
a resistor? I was under the impression that a non inductive resistor 
was the purest resistance you could get. I have been wrong many times 
in the past.
Thanks, Collin

-Original Message-
From: John J. Riddell [EMAIL PROTECTED] mailto:ve3amz%40earthlink.net

To: Repeater-Builder@yahoogroups.com
mailto:Repeater-Builder%40yahoogroups.com 
Sent: Tue, 23 Sep 2008 9:08 pm
Subject: Re: [Repeater-Builder] coax length

Colin, Non inductive resistors are quite inductive above 30 Mhz.
The Cantenna is also a poor load at VHF / UHF.

John VE3AMZ

- Original Message -
From: [EMAIL PROTECTED] mailto:n4tua%40aol.com 
To: Repeater-Builder@yahoogroups.com
mailto:Repeater-Builder%40yahoogroups.com 
Sent: Tuesday, September 23, 2008 8:25 PM
Subject: Re: [Repeater-Builder] coax length

I am not sure what would make a good or not good load resistor. I am
 using a pair of non inductive 100 ohm 100 watt resistors in parallel,
 air cooled. I also use a cantenna. Are these not good or fair?
 Thanks, Collin


 -Original Message-
 From: wd8chl [EMAIL PROTECTED] mailto:wd8chl%40gmail.com 
 To: Repeater-Builder@yahoogroups.com
mailto:Repeater-Builder%40yahoogroups.com 
 Sent: Wed, 24 Sep 2008 8:26 am
 Subject: Re: [Repeater-Builder] coax length






 [EMAIL PROTECTED] mailto:n4tua%40aol.com  wrote:
 Dear RP,
 I am doing some testing and have the 145.410 repeater connected to a
 dummy load. To get an accurate output indication in watts is it
 critical to have 1/2 wavelength cables? I have used an 18 cable from
 TX to wattmeter and then a 72 cable from wattmeter to load 
resistor.
 I
 have noticed a big difference in wattmeter indication between using
 the
 72 cable and connecting the load right to the wattmeter. Also the
 same
 indication with a cable 144 long. I am making some cables 1/2
 wavelength long for tuning use. Am I doing right?
 Thanks, Collin


 If you have a good dummy load, it WILL NOT matter what length coax you
 use. In fact, I try to make sure my cables are NOT resonant. If 
there's
 a significant difference when you go from a resonant cable to a
 non-resonant one, or from a 1/4-wave to a 1/2-wave, there is a problem
 with the load.





 



 Yahoo! Groups Links





 

image001.jpgimage002.jpg

RE: [Repeater-Builder] coax length

2008-09-24 Thread n9wys

Collin,

A guy local to me (WD9HSY) sells them - rated at 200W - on a certain auction
site.  Normal cost is about $59.00.  If you do a search for dummy load it
will pop up for you.  Although not costing an arm and a leg these might
qualify for a finger or two...  ;-)

They are very nice loads...

NOTE: I have no pecuniary interest in his business - just answering an
inquiry regarding a source for dummy loads.

73,
Mark - N9WYS

-Original Message-
From: Repeater-Builder@yahoogroups.com  On Behalf Of [EMAIL PROTECTED]

John,
Very well then, I guess I need to be shopping for a good load. Any 
suggestions? Any under an arm and a leg? What do the good loads use for 
a resistor? I was under the impression that a non inductive resistor 
was the purest resistance you could get. I have been wrong many times 
in the past.
Thanks, Collin

Re: [Repeater-Builder] coax length

2008-09-24 Thread Ralph Mowery

--- On Wed, 9/24/08, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote:

 From: [EMAIL PROTECTED] [EMAIL PROTECTED]
 Subject: Re: [Repeater-Builder] coax length
 To: Repeater-Builder@yahoogroups.com
 Date: Wednesday, September 24, 2008, 12:14 AM
 John,
 Very well then, I guess I need to be shopping for a good
 load. Any 
 suggestions? Any under an arm and a leg? What do the good
 loads use for 
 a resistor? I was under the impression that a non inductive
 resistor 
 was the purest resistance you could get. I have been wrong
 many times 
 in the past.
 Thanks, Collin

Most of the non inductive resistors are only that way around audio frequencies. 
 At RF they turn very reactive.  You need a dummy load that is RF rated.  If 
you don't run too much power for the coax to handle it, 100 feet of rg58 and 
the cantenna would make a good dummy load for 140 MHz and up.  The losser the 
coax is (but good coax) the better the dummy load it will be.  If you have 
around 400 to 500 feet of rg58 you can just short the end and have a better 
match than most commercial dummy loads at 140 MHz and up.

Some of the good dummy loads are made similar to the Heath-kit but the 
'shielding tube' is formed to be a better match to 50 ohms.  Sometimes it is 
not a straight pipe,but it is curved so it will match 50 ohms over a broad 
range of frequencies.

[Repeater-Builder] coax length

2008-09-23 Thread n4tua

Dear RP,
I am doing some testing and have the 145.410 repeater connected to a 
dummy load. To get an accurate output indication in watts is it 
critical to have 1/2 wavelength cables? I have used an 18 cable from 
TX to wattmeter and then a 72 cable from wattmeter to load resistor. I 
have noticed a big difference in wattmeter indication between using the 
72 cable and connecting the load right to the wattmeter. Also the same 
indication with a cable 144 long. I am making some cables 1/2 
wavelength long for tuning use. Am I doing right?
Thanks, Collin

Re: [Repeater-Builder] coax length

2008-09-23 Thread Mike Dietrich

If you can find a manual for a bird wattmeter, they had a chart in the back of 
how long to make cables to go with the meter for different freqs.
With this setup, you could insert it in a system and after tuning remove the 
meter setup and still have it balanced.
Mike

  - Original Message - 
  From: [EMAIL PROTECTED] 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Tuesday, September 23, 2008 4:45 AM
  Subject: [Repeater-Builder] coax length

  Dear RP,
  I am doing some testing and have the 145.410 repeater connected to a 
  dummy load. To get an accurate output indication in watts is it 
  critical to have 1/2 wavelength cables? I have used an 18 cable from 
  TX to wattmeter and then a 72 cable from wattmeter to load resistor. I 
  have noticed a big difference in wattmeter indication between using the 
  72 cable and connecting the load right to the wattmeter. Also the same 
  indication with a cable 144 long. I am making some cables 1/2 
  wavelength long for tuning use. Am I doing right?
  Thanks, Collin

Re: [Repeater-Builder] coax length

2008-09-23 Thread n4tua

I am not sure what would make a good or not good load resistor. I am 
using a pair of non inductive 100 ohm 100 watt resistors in parallel, 
air cooled. I also use a cantenna. Are these not good or fair?
Thanks, Collin

-Original Message-
From: wd8chl [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Wed, 24 Sep 2008 8:26 am
Subject: Re: [Repeater-Builder] coax length

[EMAIL PROTECTED] wrote:
 Dear RP,
 I am doing some testing and have the 145.410 repeater connected to a
 dummy load. To get an accurate output indication in watts is it
 critical to have 1/2 wavelength cables? I have used an 18 cable from
 TX to wattmeter and then a 72 cable from wattmeter to load resistor. 
I
 have noticed a big difference in wattmeter indication between using 
the
 72 cable and connecting the load right to the wattmeter. Also the 
same
 indication with a cable 144 long. I am making some cables 1/2
 wavelength long for tuning use. Am I doing right?
 Thanks, Collin

If you have a good dummy load, it WILL NOT matter what length coax you
use. In fact, I try to make sure my cables are NOT resonant. If there's
a significant difference when you go from a resonant cable to a
non-resonant one, or from a 1/4-wave to a 1/2-wave, there is a problem
with the load.

Re: [Repeater-Builder] coax length

2008-09-23 Thread John J. Riddell

Colin,  Non inductive resistors are quite inductive above 30 Mhz.
The Cantenna is also a poor load at VHF / UHF.

John VE3AMZ

- Original Message - 
From: [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Tuesday, September 23, 2008 8:25 PM
Subject: Re: [Repeater-Builder] coax length

I am not sure what would make a good or not good load resistor. I am 
 using a pair of non inductive 100 ohm 100 watt resistors in parallel, 
 air cooled. I also use a cantenna. Are these not good or fair?
 Thanks, Collin

 -Original Message-
 From: wd8chl [EMAIL PROTECTED]
 To: Repeater-Builder@yahoogroups.com
 Sent: Wed, 24 Sep 2008 8:26 am
 Subject: Re: [Repeater-Builder] coax length

 [EMAIL PROTECTED] wrote:
 Dear RP,
 I am doing some testing and have the 145.410 repeater connected to a
 dummy load. To get an accurate output indication in watts is it
 critical to have 1/2 wavelength cables? I have used an 18 cable from
 TX to wattmeter and then a 72 cable from wattmeter to load resistor. 
 I
 have noticed a big difference in wattmeter indication between using 
 the
 72 cable and connecting the load right to the wattmeter. Also the 
 same
 indication with a cable 144 long. I am making some cables 1/2
 wavelength long for tuning use. Am I doing right?
 Thanks, Collin

 If you have a good dummy load, it WILL NOT matter what length coax you
 use. In fact, I try to make sure my cables are NOT resonant. If there's
 a significant difference when you go from a resonant cable to a
 non-resonant one, or from a 1/4-wave to a 1/2-wave, there is a problem
 with the load.

 Yahoo! Groups Links

Re: [Repeater-Builder] coax length

2008-09-23 Thread n4tua

John,
Very well then, I guess I need to be shopping for a good load. Any 
suggestions? Any under an arm and a leg? What do the good loads use for 
a resistor? I was under the impression that a non inductive resistor 
was the purest resistance you could get. I have been wrong many times 
in the past.
Thanks, Collin


-Original Message-
From: John J. Riddell [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Tue, 23 Sep 2008 9:08 pm
Subject: Re: [Repeater-Builder] coax length






Colin, Non inductive resistors are quite inductive above 30 Mhz.
The Cantenna is also a poor load at VHF / UHF.

John VE3AMZ

- Original Message -
From: [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Tuesday, September 23, 2008 8:25 PM
Subject: Re: [Repeater-Builder] coax length

I am not sure what would make a good or not good load resistor. I am
 using a pair of non inductive 100 ohm 100 watt resistors in parallel,
 air cooled. I also use a cantenna. Are these not good or fair?
 Thanks, Collin


 -Original Message-
 From: wd8chl [EMAIL PROTECTED]
 To: Repeater-Builder@yahoogroups.com
 Sent: Wed, 24 Sep 2008 8:26 am
 Subject: Re: [Repeater-Builder] coax length






 [EMAIL PROTECTED] wrote:
 Dear RP,
 I am doing some testing and have the 145.410 repeater connected to a
 dummy load. To get an accurate output indication in watts is it
 critical to have 1/2 wavelength cables? I have used an 18 cable from
 TX to wattmeter and then a 72 cable from wattmeter to load 
resistor.
 I
 have noticed a big difference in wattmeter indication between using
 the
 72 cable and connecting the load right to the wattmeter. Also the
 same
 indication with a cable 144 long. I am making some cables 1/2
 wavelength long for tuning use. Am I doing right?
 Thanks, Collin


 If you have a good dummy load, it WILL NOT matter what length coax you
 use. In fact, I try to make sure my cables are NOT resonant. If 
there's
 a significant difference when you go from a resonant cable to a
 non-resonant one, or from a 1/4-wave to a 1/2-wave, there is a problem
 with the load.





 



 Yahoo! Groups Links

RE: [Repeater-Builder] Coax length between added cavities

 So my take is that there are critical cable lengths involved 
 for adding a pure pass cavity to a BP BR duplexer, but I 
 would be interested to hear from anyone aboard who has the 
 necessary hardware kicking around to repeat that experiment 
 and either replicate or refute the results I got. 

As Bob and others have said, the cable length is not critical from a
Z-matching standpoint if both cavities are tuned for 50 ohms at the pass
frequency, but the cable length will affect the reject response.

 As I said, 
 my sole cavity experience has been with Wacoms, but I find it 
 difficult to believe that this parameter is OEM specific.

I'm doing some RD work today and have the VNA (Agilent E5070B) lit up, so
I'll do some real-world tests and post the results.  Taking a quick look
around here, I see some Wacom 900 MHz pass/reject and pass-only cavities, so
those will be my test subjects.

--- Jeff

Re: [Repeater-Builder] Coax length between added cavities

2007-07-27 Thread FHS

To All: Over the past 50 years I have worked with most all Cavity mfg's on 
special and standard product applications. Let me assure you that the 
interconnecting cables are critical. Some applications more so than others.
Msg for Nate; Before you try shot-gunning the symptoms, please spend the needed 
time to identify the problem, then a cure can be better established. Yes, this 
will take more time, but it will be well worth it in the end!
Fred W5VAY (Retired Engineer) 
  - Original Message - 
  From: [EMAIL PROTECTED] 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Friday, July 27, 2007 12:03 AM
  Subject: [Repeater-Builder] Coax length between added cavities

  Can we wind our way back to addressing the original query which asked if 
there is a critical length for the interconnect between a BP BR duplexer and 
added pure pass cavities? I can't speak for all bottle manufacturers, but I own 
8 Wacom BP BR duplexer + pass cavity arrays some of which go back to the early 
eighties. Lloyd Alcorn was kind enough and patient enough to give me a pretty 
good nuts and bolts education on cavity characteristics. He said in no 
uncertain terms that there were optimum cable lengths
  for both the interconnects between the duplexer cavities and also an optimum 
length for any pure pass cavities added to the chain.  For the added pure pass 
cavity, the optimum interconnect length would ensure that the pure pass curve 
would superimpose over the duplexer curve. When I did some experimenting with 
the pure pass cable length, it validated his point. If I significantly 
lengthened or shortened this cable, the tracking generator would indicate that 
the pass curve was no longer superimposed on the duplexer curve. It would 
either lead or lag the duplexer curve producing two results: 1) the composite 
curve began to show some distortion and 2) the total attenuation at the desired 
frequency was higher than when the optimum cable length (supplied by Lloyd) was 
used.

  So my take is that there are critical cable lengths involved for adding a 
pure pass cavity to a BP BR duplexer, but I would be interested to hear from 
anyone aboard who has the necessary hardware kicking around to repeat that 
experiment and either replicate or refute the results I got. As I said, my sole 
cavity experience has been with Wacoms, but I find it difficult to believe that 
this parameter is OEM specific.

  K7IJ 

--
  Get a sneak peek of the all-new AOL.com.

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-27 Thread Jim

Ron Wright wrote:
 Nate,
 
 A local, in Tampa, FL, high profile repeater has a similar problem.
 They are on 2 meters along side a 800 MHz repeater which gives them
 interference.  They have to live with it.  However, it is weak and
 they PL'd their repeater.  Since weak the users can over ride and the
 PL only allows the users to bring up the machine.

Wow-an 800 repeater is giving a 2M rx problems? Must be a really crappy 
rx! Or the antennas are REALLY close!
-- 
Jim Barbour
WD8CHL

Re: [Repeater-Builder] Coax length between added cavities

2007-07-27 Thread WD7F - John in Tucson

Repeating the experiment?  Hmmm.  We were re-cabling a set of Sinclair 
duplexers for a 2-meter machine and had access to a high quality vector 
voltmeter.  It took three of us Keystone Cops over 3 hours to make a set of 
1/4, 1/2 and even a couple of 1 wavelength cables.  Later, we repeated the 
process for a 220 machine and even though we had experience, it took about the 
same amount of time.  My point?  It ain't easy !  We just weren't ready to use 
the time and materials to add an inch to a set of cables and then make another 
set of short ones.

In both cases, things worked out great.  Many hams who are delving in cavity 
alignment don't have a vector voltmeter, so we were in good shape.  Plus, you 
have a warm fuzzy comfort factor if you know your cables are the right length 
when you start the job.  If alignment ain't happening, you can say I know it 
ain't the cables!...right ! And I got some ocean front property here in 
western Arizona

de WD7F
John in Tucson




So my take is that there are critical cable lengths involved for adding a pure 
pass cavity to a BP BR duplexer, but I would be interested to hear from anyone 
aboard who has the necessary hardware kicking around to repeat that experiment 
and either replicate or refute the results I got. As I said, my sole cavity 
experience has been with Wacoms, but I find it difficult to believe that this 
parameter is OEM specific.

K7IJ 









Get a sneak peek of the all-new AOL.com.
 





No virus found in this incoming message.
Checked by AVG Free Edition. 
Version: 7.5.476 / Virus Database: 269.10.20/919 - Release Date: 7/26/2007 9:56 
AM

Re: Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-27 Thread Ron Wright

Nate,

A local, in Tampa, FL, high profile repeater has a similar problem.  They are 
on 2 meters along side a 800 MHz repeater which gives them interference.  They 
have to live with it.  However, it is weak and they PL'd their repeater.  Since 
weak the users can over ride and the PL only allows the users to bring up the 
machine.

As so many of us Hams do, getting on sites for free, we have to put up with 
some problems.  Of course it does depend on the survarity of the problem.

73, ron, n9ee/r



From: Nate Bargmann [EMAIL PROTECTED]
Date: 2007/07/26 Thu PM 01:09:56 CDT
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer

  
* Steve S. Bosshard (NU5D) [EMAIL PROTECTED] [2007 Jul 26 13:05 -0500]:
 You could always try and scrap the front end from a thrashed M2 mobile - 
 kinda lossy but can be used as a preselector - Also even a 3 dB. 
 attenuator might help against overload at the cost of 3dB. in RX sen.
 
 Out of curiosity, what kind of repeater are you using?  Probably said in 
 an earlier post - don't remember. 

It is a TKR-720.  Probably not the best choice for this site.  ;-)

Again, it's not my system and there are some politics with getting
involved to much that I'd rather avoid.  So, at this point we're
helping as we can.

Thanks for all the ideas.  Many I've seen or even tried in the pastand
perhaps forgot.  :-D

73, de Nate 

-- 
 Wireless | Amateur Radio Station N0NB  |  Successfully Microsoft
  Amateur radio exams; ham radio; Linux info @  | free since January 1998.
 http://www.qsl.net/n0nb/   |  Debian, the choice of
 My Kawasaki KZ-650 SR @| a GNU generation!
http://www.networksplus.net/n0nb/   |   http://www.debian.org



Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

Re: Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-27 Thread Ron Wright

That would be intermod, but not intermod generated inside ones own equipment.

If there is intermod mixing on a different or far away commerical site finding 
it would be hard, but getting it solved might be even harder.  Depends on the 
owner of the other system.  300 W pager txs for years have caused problems, but 
since no problem to the pager company they often don't care.  It is just 
spending money to solve someone elses problem.  

73, ron, n9ee/r



From: [EMAIL PROTECTED]
Date: 2007/07/26 Thu PM 01:38:13 CDT
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer

  
And if theÂ mixing is someone else's PA with some outside RF energy - that's 
notproperly characterized as intermod when it ends up on your input?Â Â In a 
message dated 7/26/2007 11:30:47 A.M. Pacific Daylight Time, [EMAIL PROTECTED] 
writes:---Intermod means there is mixing in YOUR PA with some outside RF   
energy. Could be, could be not. You need to run all the frequencies   
used at your site in order to identify any possible 2nd, 3rd, 4th and   
so on products. Or it might be a straight mix. BTW, what do you mean   
by interference? Are you hearing other signals or is is something   
else? (knowing the 'sound' of the interference generally goes a long   
way at identifying it)

Â 


Get a sneak peek of the all-new AOL.com.


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

RE: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-27 Thread Eric Lemmon

Jim,

I agree that the 800 MHz repeater's carrier frequency is probably too far
from the 2m repeater's input to cause a problem, but there is also the
possibility that the 800MHz transmitter's exciter is causing the problem.  A
case in point:  An older 800 MHz repeater was turned on at the same site as
a local 2m repeater, and immediately caused major interference.  It turned
out that the exciter was radiating at 1/6 of the 868 MHz carrier, since that
model transmitter used a VHF exciter followed by a doubler and a tripler.
The exciter leakage was just a few kHz away from the 2m input, and it
severely interfered with the 2m repeater's reception.  The leakage occurred
because a careless tech left off one shield and did not install all of the
screws in another shield.  Once the 800MHz machine was properly buttoned up,
the problem went away.

73, Eric Lemmon WB6FLY
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jim
Sent: Friday, July 27, 2007 8:34 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length between added cavity and
duplexer

SNIP

Wow-an 800 repeater is giving a 2M rx problems? Must be a really crappy 
rx! Or the antennas are REALLY close!
-- 
Jim Barbour
WD8CHL

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-27 Thread Steve S. Bosshard (NU5D)

W5AC at Texas AM has a 2M repeater on 146.820 co-located with an 800 
Mhz PST.  The 146.820 transmitter mixes with one of the 800 mhz 
transmitters and has a direct hit on 146.220.  They use split channel 
guard tones because if in and out tone were the same, the transmitter 
mix would open the receiver.  They could have left tone off the 
transmitter, but then the co-channel 82 repeaters would be an issue to 
folks listening.  The ham repeater is a MastrII.  Seems like they moved 
the 2M repeater from Kyle Stadium to Rudder Hall and the problem 
lessened but did not entirely go away. 

PS - I called Lloyd Alcorn this morning but got his answering machine - 
will call back later in the day. 

Steve NU5D.

Jim wrote:
 Ron Wright wrote:
   
 Nate,

 A local, in Tampa, FL, high profile repeater has a similar problem.
 They are on 2 meters along side a 800 MHz repeater which gives them
 interference.  They have to live with it.  However, it is weak and
 they PL'd their repeater.  Since weak the users can over ride and the
 PL only allows the users to bring up the machine.
 

 Wow-an 800 repeater is giving a 2M rx problems? Must be a really crappy 
 rx! Or the antennas are REALLY close!
   

-- 
Ham Radio Spoken Here !!!  NU5D EM11
http://www.qrz.com/callsign/NU5D
Nickel Under 5 Dollars

[Repeater-Builder] Coax length between added cavity and duplexer - test results


I performed an experiment per previous discussion.  The results are
available at:

http://www.broadsci.com/900.pdf

Apologies in advance for the terse verbage and any typos; I was trying to
get it done quickly between real work projects.

Feedback would be greatly appreciated.

--- Jeff

RE: [Repeater-Builder] Coax length between added cavities

 We just 
 weren't ready to use the time and materials to add an inch to 
 a set of cables and then make another set of short ones.

Connector savers can be incrementally added to a cable when experimenting
to find the optimum length.  Connector savers are male-to-famale adapters of
the same connector type.  They are frequently installed on test equipment to
save wear and tear on the built-in connector, hence their nickname.  They
are about the shortest length you can add from a mechanical standpoint to
cables that use type N connectors.  A line stretcher is the best way to do
it, but connector savers are quick and dirty, and their incremental
electrical length is small enough to make them effective for this purpose at
the frequencies we normally deal with below 1 GHz.

High-quality elbow adapters can be used in a pinch instead, but there are
some caveats with respect to the impedence bump they can create (see the
blurb I put together earlier today that touches on this subject).  They are
also electrically longer than connector savers, typically making them useful
only below about 500 MHz in many cases.

If you do this kind of work on a regular basis like we do, you end up with a
few dozen test cables of varying lengths (nominally 1/2 incremental
difference in length) to use when building a system.  Once the optimum cable
lengths are found, new cables are made for the final installation.

BTW, when making up cables based on manufacturers' recommend cable lengths,
make sure you know whether the cable length they specify is the cut length
or whether it's tip-to-tip.  Some manufacturers, like TX-RX, specify their
cable lengths based on the cut length before the connectors are installed,
so the overall tip-to-tip length ends up being about 1.25 longer when type
N crimp connectors are installed.

--- Jeff

Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r...

2007-07-27 Thread cruising7388

 
Jeff
 
Just a dynamite presentation. Thanks for the effort. BTW, where are you  
(The analysis is dated July 29)
 
 
Bruce K7IJ
 
 
 
In a message dated 7/27/2007 10:19:02 A.M. Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

I  performed an experiment per previous discussion. The results are
available  at:

_http://www.broadscihttp://wwhtt_ (http://www.broadsci.com/900.pdf) 

Apologies  in advance for the terse verbage and any typos; I was trying to
get it done  quickly between real work projects.

Feedback would be greatly  appreciated.

--- Jeff







** Get a sneak peek of the all-new AOL at 
http://discover.aol.com/memed/aolcom30tour

Re: [Repeater-Builder] Coax length between added cavity and duplexer - test results

2007-07-27 Thread George Henry

Very nicely done, Jeff!  At least as good as some manufacturers' reports, 
and color too!

George

- Original Message - 
From: Jeff DePolo [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Friday, July 27, 2007 11:54 AM
Subject: [Repeater-Builder] Coax length between added cavity and duplexer - 
test results

 I performed an experiment per previous discussion.  The results are
 available at:

 http://www.broadsci.com/900.pdf

 Apologies in advance for the terse verbage and any typos; I was trying to
 get it done quickly between real work projects.

 Feedback would be greatly appreciated.

 --- Jeff

Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r...

2007-07-27 Thread George Henry

Maybe his computer is running on UTC?

  - Original Message - 
  From: [EMAIL PROTECTED] 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Friday, July 27, 2007 5:16 PM
  Subject: Re: [Repeater-Builder] Coax length between added cavity and duplexer 
- test r...

  Jeff

  Just a dynamite presentation. Thanks for the effort. BTW, where are you 
(The analysis is dated July 29)

  Bruce K7IJ

RE: [Repeater-Builder] Coax length between added cavity and duplexer - test r...


 Just a dynamite presentation. Thanks for the effort. BTW, 
 where are you (The analysis is dated July 29)

I'm caught in a time warp in Philadelphia.

Re: [Repeater-Builder] Coax length between added cavity and duplexer - test r...

2007-07-27 Thread cruising7388

 
Understood. But take comfort. You're not alone. Report is that everybody in  
Philadelphia is warped.
 
In a message dated 7/27/2007 6:05:10 P.M. Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

  Just a dynamite presentation. Thanks for the effort. BTW, 
 where are  you (The analysis is dated July 29)

I'm caught in a time warp in  Philadelphia.







** Get a sneak peek of the all-new AOL at 
http://discover.aol.com/memed/aolcom30tour

Re: [Repeater-Builder] Coax length between added cavity and duplexer - test results

2007-07-27 Thread Chuck Kelsey

Cannot display the webpage is what I get.

Chuck

- Original Message - 
From: Jeff DePolo [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Friday, July 27, 2007 12:54 PM
Subject: [Repeater-Builder] Coax length between added cavity and duplexer - 
test results

 I performed an experiment per previous discussion.  The results are
 available at:

 http://www.broadsci.com/900.pdf

 Apologies in advance for the terse verbage and any typos; I was trying to
 get it done quickly between real work projects.

 Feedback would be greatly appreciated.

 --- Jeff

 Yahoo! Groups Links

Re: [Repeater-Builder] Coax length between added cavity and duplexer

* [EMAIL PROTECTED] [EMAIL PROTECTED] [2007 Jul 26 12:14 -0500]:
 
Thanks for all of your input.  I'm learning more as I go along.

I did not get a chance to performance check the RX on site.  It just
happened that we were able to stop by the site a week ago and see what
we were up against.

 Having said that, I think Skipp's point is well taken -  if the junk is on
 channel,  an additional pass cavity
 isn't going to eliminate it.  BTW, are you using an isolator on the TX?

Right now, no.  There isn't one handy and since there are only a couple
of active hams in the county, I don't know whether they're willing to
plop down a few hundred bucks to try.  But, you never know!

There is also some amount of politics involved here as the repeater is
actually owned by the county, as I understand it now.

Fortunately, the interference is not constant nor really consistent. 
Hopefully, we can arrange a meet out there again and I can gather more
information and do some tests.

73, de Nate 

-- 
 Wireless | Amateur Radio Station N0NB  |  Successfully Microsoft
  Amateur radio exams; ham radio; Linux info @  | free since January 1998.
 http://www.qsl.net/n0nb/   |  Debian, the choice of
 My Kawasaki KZ-650 SR @| a GNU generation!
http://www.networksplus.net/n0nb/   |   http://www.debian.org

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Jim

Gary Schafer wrote:
 Intermod IS the result of mixing. The mixing can take place in your receiver
 (commonly called receiver intermod). 
 Mixing can take place in your own transmitter, which generates a product
 that falls on your receive frequency(or on someone else's) or the mixing can
 take place in someone else's transmitter with the resulting product falling
 on your receive frequency. It is all intermodulation. i.e. the result of
 mixing of two or more frequencies in a non linear device.
 

...like a rusty joint on a tower...
...or a guy wire...
...or a fence...

-- 
Jim Barbour
WD8CHL

RE: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Jeff DePolo

 Now, from a perspective of impedance matching, wouldn't it 
 make sense to 
 use a circulator at the input of the reciever so that it is 
 also matched 
 to 50-ohms?

At first glance it might seem like a good idea, until you consider that
circulators aren't linear devices; they can produce mix products and
harmonics within.  At low receive signal levels this isn't a problem because
the IM products are substantially lower in amplitude than the fundamentals,
but in the presence of one or more strong signals, it could be an issue...

--- Jeff

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Kris Kirby

On Thu, 26 Jul 2007, Ken Arck wrote:
 Firstly, in the case of your additional bandpass cavity - if cavities 
 are properly tuned to 50 ohms, the length of 50 ohm coax between them 
 doesn't make one bit of difference. The problem most people have with 
 proper cavity/duplexer tuning is that they don't maintain a 50 ohm 
 load on ALL ports when they tune 'em. So when they're placed into 
 service, the port impedances are different and the tuning of the 
 cavity/duplexer changes. Which is why you should NEVER EVER tune 
 either without at least a 3 dB 50 ohm pad on each of the ports. From 
 your description, I'm willing to bet you didn't use pads :-)

Now, from a perspective of impedance matching, wouldn't it make sense to 
use a circulator at the input of the reciever so that it is also matched 
to 50-ohms?


rf - circulator - rx
  |
  - dummy load

?

Since we know that some RXs aren't 50-ohms, nor are some TXs.
 
I'm looking at this strictly from the point of view of matched 
impedances.

--
Kris Kirby, KE4AHR  [EMAIL PROTECTED]
* WAR IS PEACE *  FREEDOM IS SLAVERY *
* IGNORANCE IS STRENGTH * KETCHUP IS *
  * A VEGETABLE *

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread George Henry

- Original Message - 
From: Jeff DePolo [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Thursday, July 26, 2007 8:50 PM
Subject: RE: [Repeater-Builder] Coax length between added cavity and 
duplexer



[snip]

 But that doesn't even compare to the side-arm I saw made out of pine
 2x4's...

 --- Jeff


I've never seen the joints between 2x4's act as diodes;-)



George

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Vincent Caruso


Hey, I thought I was the only one that ran in to the 2X4 cross arms.

RE: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Jeff DePolo

 
 ...like a rusty joint on a tower...
 ...or a guy wire...
 ...or a fence...

One of my favorites comes to mind.  I was working a tower (somewhere in
Virginia if I remember right), and there was a side-arm mount that had
hardware on it that was too big for the tower legs, so as shims, the tower
crew had stuck a crescent wrench behind the upper U-bolt and a pair of vice
grips behind the lower U-bolt to make up the difference.  I don't know how
long they were up there, but the rust stains ran about 20' down the tower
leg...

But that doesn't even compare to the side-arm I saw made out of pine
2x4's...

--- Jeff

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Dave Baughn

Nate, I see you received a lot of answers to your question, and I have not taken the time to read them all, but my answer is that it will probably not matter how long the coax is. Also, what you are doing sounds like a very reasonable approach to the problem and may very well fix it. Good luck.

Dave BaughnDirector of EngineeringThe University of AlabamaCenter for Public Television and RadioWVUA/WUOA-TV WUAL/ WQPR/ WAPR FMBox 870150195 Reese Phifer Hall, 901 University Blvd.Tuscaloosa, Alabama 35487205.348.8622 cell 205.310.8798[EMAIL PROTECTED] KX4I Nate Bargmann [EMAIL PROTECTED] 7/26/2007 7:09 AM

I'm helping a club in the next county get their repeater workingbetter. A couple of weeks ago they brought the RF unit (TKR-720) overand we (KC0MLS, K0BYK, and myself) checked it out. The PA transistorrequired soldering and after that everything checked out well.Next we checked out the duplexer, a Wacom BpBr set. Lacking a trackinggenerator, we used our ancient IFR-1200 and a reprogrammed Spectramobile radio and tuned the pass filters for best SINAD and the notchfilters for the poorest SINAD for their respective frequencies.After they put everything back on site, it all works well except thatthe local public safety is getting into the receiver intermintently. My first thought was intermod, but the various programs don't turn up amatch for the receiver's frequency.A week ago we were able to visit the site and tightened several looseconnectors on the other hardware in the site. Since then theinterference does seem to be less but is still present on occasion.Observations of the site revealed that the public safety and the club'srepeater antennas (DB-224 style, unsure of exact models) both share thetop of the tower and are broadside to each other and are maybe fourfeet apart at most. So now our thinking is that the problem may bereceiver overload. We set up a spare Celwave bandpass cavity that has about 2 dB ofinsertion loss and offers about 45 dB of insertion loss at the publicsafety's transmitter frequency. My question is whether the coax lengthis critical between the RX port of the Wacom duplexer and the inputport of the Celwave cavity? I plan to send along a length of RG-393(double shielded teflon coax) with the cavity. As far as I know, it isa random length. Should I cut it to something closer to 1/2wavelength? 3/4 WL?Thanks!73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully MicrosoftAmateur radio exams; ham radio; Linux info @ | free since January 1998.http://wwwqsl.net/n0nb/ | "Debian, the choice ofMy Kawasaki KZ-650 SR @ | a GNU generation!"http://www.networksplus.net/n0nb/ | http://www.debian.orgimage/gifimage/xxx

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread cruising7388

 
What do you think a half wave interconnect at some unwanted frequency is  
going to to the pass curve at the desired frequency?  If your sole concern  is 
rejection of an unwanted frequency, hey, there is even
a more effective way to do it - cut the cable in half.
 
 
 
n a message dated 7/26/2007 10:32:39 A.M. Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

So ideally if you  want the most rejection a cable that provides a half wave 
length at the  unwanted frequency will reflect that low impedance provided by 
the cavity  skirt to the next port in the system at that  frequency.


 



** Get a sneak peek of the all-new AOL at 
http://discover.aol.com/memed/aolcom30tour

RE: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Gary Schafer

Cable lengths sometimes are critical and sometimes not, depending what you
are trying to accomplish with the particular setup. In the case of
interconnecting cables between notch cavities a critical length cable will
provide more notch depth because it unloads the next cavity.

In the case of using pass band cavities to make a combiner into a common
junction the cable lengths are critical even though everything is running at
50 ohms. The off frequency skirt of the cavity provides a short at some
frequency and that short needs to be transformed to a high impedance at the
junction so as not to load the other devices.

 

DUPLEXER TUNING: 

In this case proper duplexer tuning should make little if any difference in
the interference problem noted. As long as there is no desense from his own
transmitter the duplexer is doing what it can. A bp-br duplexer has little
off frequency rejection (pass band rejection) compared to a pass cavity. The
bp-br duplexer does provide a little pass band help but not as much as some
people like to believe. The frequencies between the transmit and receive
frequencies have the most rejection from pass band effects but outside of
them there is little. 

As was stated he is getting interference from a public safety transmitter so
it would fall outside the more protected part of the duplexer. An additional
pass filter on the receiver would indeed provide more protection but 45 db
sounds like a lot to expect from a pass filter unless the frequency is a
long ways away. As Skip noted a notch cavity at that point may well provide
more protection.

 

More to the point of cable length, a pass filter actually looks like a notch
filter at the unwanted frequency i.e. a low impedance at that frequency. So
ideally if you want the most rejection a cable that provides a half wave
length at the unwanted frequency will reflect that low impedance provided by
the cavity skirt to the next port in the system at that frequency.

In this case the difference will probably not be noticed for the trouble
involved.

 

With the public safety antenna right beside the repeater antenna there can
be fundamental overload of the receiver so some form of additional
protection may help.

 

73

Gary  K4FMX

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Ken Arck
Sent: Thursday, July 26, 2007 9:40 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Coax length between added cavity and
duplexer

 

Hi Nate

Firstly, in the case of your additional bandpass cavity - if cavities are
properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't
make one bit of difference. The problem most people have with proper
cavity/duplexer tuning is that they don't maintain a 50 ohm load on ALL
ports when they tune 'em. So when they're placed into service, the port
impedances are different and the tuning of the cavity/duplexer changes.
Which is why you should NEVER EVER tune either without at least a 3 dB 50
ohm pad on each of the ports. From your description, I'm willing to bet you
didn't use pads :-)

My other comment (and in my humble opinion) is that if you're using a
properly tuned BpBr duplexer on a low power repeater (the 720 is 25 watts,
yes?) and you need additional cavities in the receive side, you've got
bigger issue than simply needing an additional cavity. You didn't specify
what the inteference is but have you done an intermod study of the site? 

IMHO, the additional cavity is a waste of time and effort until you identify
the source of the interference (and made sure your duplexer is first
properly tuned)

Ken


At 05:09 AM 7/26/2007, you wrote:




I'm helping a club in the next county get their repeater working
better. A couple of weeks ago they brought the RF unit (TKR-720) over
and we (KC0MLS, K0BYK, and myself) checked it out. The PA transistor
required soldering and after that everything checked out well.

Next we checked out the duplexer, a Wacom BpBr set. Lacking a tracking
generator, we used our ancient IFR-1200 and a reprogrammed Spectra
mobile radio and tuned the pass filters for best SINAD and the notch
filters for the poorest SINAD for their respective frequencies.

After they put everything back on site, it all works well except that
the local public safety is getting into the receiver intermintently. 
My first thought was intermod, but the various programs don't turn up a
match for the receiver's frequency.

A week ago we were able to visit the site and tightened several loose
connectors on the other hardware in the site. Since then the
interference does seem to be less but is still present on occasion.

Observations of the site revealed that the public safety and the club's
repeater antennas (DB-224 style, unsure of exact models) both share the
top of the tower and are broadside to each other and are maybe four
feet apart at most. So now our thinking is that the problem may be
receiver overload. 

We set up a spare Celwave

RE: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Gary Schafer

Intermod IS the result of mixing. The mixing can take place in your receiver
(commonly called receiver intermod). 
Mixing can take place in your own transmitter, which generates a product
that falls on your receive frequency(or on someone else's) or the mixing can
take place in someone else's transmitter with the resulting product falling
on your receive frequency. It is all intermodulation. i.e. the result of
mixing of two or more frequencies in a non linear device.

73
Gary  K4FMX

 -Original Message-
 From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
 [EMAIL PROTECTED] On Behalf Of Ken Arck
 Sent: Thursday, July 26, 2007 1:29 PM
 To: Repeater-Builder@yahoogroups.com
 Subject: Re: [Repeater-Builder] Coax length between added cavity and
 duplexer
 
 At 11:06 AM 7/26/2007, you wrote:
 
 
 
 Intermod means there is mixing in YOUR PA with some outside RF energy.
 
 I should probably clarify that intermod is an often misused
 term that has become a generic terms used to describe just about any
 type of received interference. Ya know, kinda like Klenex has become
 the name for any tissue.
 
 Intermod is a very specific type of phenomenon and for accuracy,
 should only be used to describe intermodulation issues and not mixes,
 adjacent channel interference, etc.
 
 (more of my 2 cents)
 
 Ken
 
 
 
 
 
 
 Yahoo! Groups Links

Re: [Repeater-Builder] Coax length between added cavity and duplexer

At 11:06 AM 7/26/2007, you wrote:



Intermod means there is mixing in YOUR PA with some outside RF energy.

I should probably clarify that intermod is an often misused 
term that has become a generic terms used to describe just about any 
type of received interference. Ya know, kinda like Klenex has become 
the name for any tissue.

Intermod is a very specific type of phenomenon and for accuracy, 
should only be used to describe intermodulation issues and not mixes, 
adjacent channel interference, etc.

(more of my 2 cents)

Ken

Re: [Repeater-Builder] Coax length between added cavity and duplexer

At 11:06 AM 7/26/2007, you wrote:


No, we didn't. The IFR does have a pad built into its generator output
and the Motorola Spectra mobile is probably fairly close to 50 ohms.


I have yet to see a receiver from anyone that is 50 ohms. 
Besides, you know what they say about close but no cigar, yes? :-)





The interference is that the repeater is receiving the public safety
transmitter very clearly which has led me to think intermod. This
TKR-720 is running about 40 Watts.

---Intermod means there is mixing in YOUR PA with some outside RF 
energy. Could be, could be not. You need to run all the frequencies 
used at your site in order to identify any possible 2nd, 3rd, 4th and 
so on products. Or it might be a straight mix. BTW, what do you mean 
by interference? Are you hearing other signals or is is something 
else? (knowing the 'sound' of the interference generally goes a long 
way at identifying it)

Ken

Re: [Repeater-Builder] Coax length between added cavity and duplexer

* Ken Arck [EMAIL PROTECTED] [2007 Jul 26 09:44 -0500]:
 Hi Nate
 
 Firstly, in the case of your additional bandpass cavity - if cavities are
 properly tuned to 50 ohms, the length of 50 ohm coax between them doesn't make
 one bit of difference. The problem most people have with proper 
 cavity/duplexer
 tuning is that they don't maintain a 50 ohm load on ALL ports when they tune
 'em. So when they're placed into service, the port impedances are different 
 and
 the tuning of the cavity/duplexer changes. Which is why you should NEVER EVER
 tune either without at least a 3 dB 50 ohm pad on each of the ports. From your
 description, I'm willing to bet you didn't use pads :-)

No, we didn't.  The IFR does have a pad built into its generator output
and the Motorola Spectra mobile is probably fairly close to 50 ohms. 

We did check the Celwave cavity this morning using pads and noted no
change in its tuing.  Admittedly, the Celwave is a much different
device than the Wacom BpBr.

 My other comment (and in my humble opinion) is that if you're using a properly
 tuned BpBr duplexer on a low power repeater (the 720 is 25 watts, yes?) and 
 you
 need additional cavities in the receive side, you've got bigger issue than
 simply needing an additional cavity. You didn't specify what the inteference 
 is
 but have you done an intermod study of the site?

The interference is that the repeater is receiving the public safety
transmitter very clearly which has led me to think intermod.  This
TKR-720 is running about 40 Watts.

 IMHO, the additional cavity is a waste of time and effort until you identify
 the source of the interference (and made sure your duplexer is first properly
 tuned)

Right now it's the easiest approach to try and be installed by the ham
over there on his schedule.  See one of my other posts for the details
of the site.

73, de Nate 

-- 
 Wireless | Amateur Radio Station N0NB  |  Successfully Microsoft
  Amateur radio exams; ham radio; Linux info @  | free since January 1998.
 http://www.qsl.net/n0nb/   |  Debian, the choice of
 My Kawasaki KZ-650 SR @| a GNU generation!
http://www.networksplus.net/n0nb/   |   http://www.debian.org

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Steve S. Bosshard (NU5D)

You could always try and scrap the front end from a thrashed M2 mobile - 
kinda lossy but can be used as a preselector - Also even a 3 dB. 
attenuator might help against overload at the cost of 3dB. in RX sen.

Out of curiosity, what kind of repeater are you using?  Probably said in 
an earlier post - don't remember. 

73,

Steve
www.bosshardradio.com


Nate Bargmann wrote:
 * [EMAIL PROTECTED] [EMAIL PROTECTED] [2007 Jul 26 12:14 -0500]:
  
 Thanks for all of your input.  I'm learning more as I go along.

 I did not get a chance to performance check the RX on site.  It just
 happened that we were able to stop by the site a week ago and see what
 we were up against.
   

-- 
Ham Radio Spoken Here !!!  NU5D EM11
http://www.qrz.com/callsign/NU5D
Nickel Under 5 Dollars

RE: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread Jeff DePolo

  But that doesn't even compare to the side-arm I saw made out of pine
  2x4's...
 
  --- Jeff
 
 
 I've never seen the joints between 2x4's act as diodes;-)

Yeah, but just try explaining to your insurance carrier that the reason your
antenna came through the roof of the transmitter shelter was because of
termites...

Re: [Repeater-Builder] Coax length between added cavity and duplexer


Hi Nate

Firstly, in the case of your additional bandpass cavity - if cavities 
are properly tuned to 50 ohms, the length of 50 ohm coax between them 
doesn't make one bit of difference. The problem most people have with 
proper cavity/duplexer tuning is that they don't maintain a 50 ohm 
load on ALL ports when they tune 'em. So when they're placed into 
service, the port impedances are different and the tuning of the 
cavity/duplexer changes. Which is why you should NEVER EVER tune 
either without at least a 3 dB 50 ohm pad on each of the ports. From 
your description, I'm willing to bet you didn't use pads :-)


My other comment (and in my humble opinion) is that if you're using a 
properly tuned BpBr duplexer on a low power repeater (the 720 is 25 
watts, yes?) and you need additional cavities in the receive side, 
you've got bigger issue than simply needing an additional cavity. You 
didn't specify what the inteference is but have you done an intermod 
study of the site?


IMHO, the additional cavity is a waste of time and effort until you 
identify the source of the interference (and made sure your duplexer 
is first properly tuned)


Ken


At 05:09 AM 7/26/2007, you wrote:


I'm helping a club in the next county get their repeater working
better. A couple of weeks ago they brought the RF unit (TKR-720) over
and we (KC0MLS, K0BYK, and myself) checked it out. The PA transistor
required soldering and after that everything checked out well.

Next we checked out the duplexer, a Wacom BpBr set. Lacking a tracking
generator, we used our ancient IFR-1200 and a reprogrammed Spectra
mobile radio and tuned the pass filters for best SINAD and the notch
filters for the poorest SINAD for their respective frequencies.

After they put everything back on site, it all works well except that
the local public safety is getting into the receiver intermintently.
My first thought was intermod, but the various programs don't turn up a
match for the receiver's frequency.

A week ago we were able to visit the site and tightened several loose
connectors on the other hardware in the site. Since then the
interference does seem to be less but is still present on occasion.

Observations of the site revealed that the public safety and the club's
repeater antennas (DB-224 style, unsure of exact models) both share the
top of the tower and are broadside to each other and are maybe four
feet apart at most. So now our thinking is that the problem may be
receiver overload.

We set up a spare Celwave bandpass cavity that has about 2 dB of
insertion loss and offers about 45 dB of insertion loss at the public
safety's transmitter frequency. My question is whether the coax length
is critical between the RX port of the Wacom duplexer and the input
port of the Celwave cavity? I plan to send along a length of RG-393
(double shielded teflon coax) with the cavity. As far as I know, it is
a random length. Should I cut it to something closer to 1/2
wavelength? 3/4 WL?

Thanks!

73, de Nate 

--
Wireless | Amateur Radio Station N0NB | Successfully Microsoft
Amateur radio exams; ham radio; Linux info @ | free since January 1998.
http://www.qsl.net/n0nb/http://www.qsl.net/n0nb/ | Debian, the choice of
My Kawasaki KZ-650 SR @ | a GNU generation!
http://www.networksplus.net/n0nb/http://www.networksplus.net/n0nb/ 
| http://www.debian.org




--
President and CTO - Arcom Communications
Makers of repeater controllers and accessories.
http://www.arcomcontrollers.com/
Authorized Dealers for Kenwood and Telewave and
we offer complete repeater packages!
AH6LE/R - IRLP Node 3000
http://www.irlp.net
We don't just make 'em. We use 'em!

Re: [Repeater-Builder] Coax length between added cavity and duplexer

2007-07-26 Thread cruising7388

 
And if the mixing is someone else's PA with some outside RF energy -  that's 
not
properly characterized as intermod when it ends up on your input?
 
 
In a message dated 7/26/2007 11:30:47 A.M. Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

---Intermod means there is mixing in YOUR PA with some outside RF  
energy. Could be, could be not. You need to run all the frequencies  
used at your site in order to identify any possible 2nd, 3rd, 4th and  
so on products. Or it might be a straight mix. BTW, what do you mean  
by interferenceby interferenceWBR? Are you hearing other signals o
else? (knowing the 'sound' of the interference generally goes a long  
way at identifying it)








** Get a sneak peek of the all-new AOL at 
http://discover.aol.com/memed/aolcom30tour

Re: [Repeater-Builder] Coax length between added cavity and duplexer

* Steve S. Bosshard (NU5D) [EMAIL PROTECTED] [2007 Jul 26 13:05 -0500]:
 You could always try and scrap the front end from a thrashed M2 mobile - 
 kinda lossy but can be used as a preselector - Also even a 3 dB. 
 attenuator might help against overload at the cost of 3dB. in RX sen.
 
 Out of curiosity, what kind of repeater are you using?  Probably said in 
 an earlier post - don't remember. 

It is a TKR-720.  Probably not the best choice for this site.  ;-)

Again, it's not my system and there are some politics with getting
involved to much that I'd rather avoid.  So, at this point we're
helping as we can.

Thanks for all the ideas.  Many I've seen or even tried in the pastand
perhaps forgot.  :-D

73, de Nate 

-- 
 Wireless | Amateur Radio Station N0NB  |  Successfully Microsoft
  Amateur radio exams; ham radio; Linux info @  | free since January 1998.
 http://www.qsl.net/n0nb/   |  Debian, the choice of
 My Kawasaki KZ-650 SR @| a GNU generation!
http://www.networksplus.net/n0nb/   |   http://www.debian.org

Re: [Repeater-Builder] Coax length between added cavity and duplexer


At 11:38 AM 7/26/2007, you wrote:

And if the mixing is someone else's PA with some outside RF energy - 
that's not

properly characterized as intermod when it ends up on your input?



---Good point, although I meant more it happening at that site than 
specifically in his PA. I guess technically it would intermod based 
but not necessarily being generated in his equipment.


My main point was explained later - in that intermod seems to have 
become a generic term for all sorts of interference, from external 
mixes to front-end overloading.


Ken

[Repeater-Builder] Coax length between added cavity and duplexer