If the duplexers for each system are only 50 ohms at each
receiver and transmitter, then I should see 4 frequencies
where there is a 50 ohm load, and they are all different. Why
would I need more than some sort of phasing harness to
connect the two duplexers to the single transmission
Perhaps a little off topic subject Does anyone know of a
source for
25 Ohm, 0.10 diameter flexible coax cable? I am in the process of
converting a 500 Watt Quintron QT-7095 station to 10 Meters. The RF
amplifier uses four 28V MOSFET's matched to 50 Ohms with a
Guanella 4:1
ps: It's a Canadian Market Mitrek so in addition to being
a bit different... the CTCSS encoder also says eh at the
end of every transmission... :-)
Canadian reverse-burst!
Back in the 80's, one of the local repeaters here used DVR tracks for
courtesy tones. One of the
Couple of questions. It looks like between dipoles #2 and #3 it is
31. Is this going to be the same if it is setup for omni?
It may change a bit depending on how much slack there is in the harness. In
reality, there will be little change in gain (on the horizon) if the spacing
is varied
Maybe a little off topic, but since we always seem to meet up with a bunch
of other repeater-builder denizens every year at Dayton, maybe not...
Has everyone else received their annual package from the Dayton Hamvention
folks this year for flea market spaces? Seems to me that I usually received
No package here, so I went on line and found that we had to
send for our spaces by February 15th for them to guarantee us
the spaces we had last year. I went on line and sent them my
vendor ticket request and 2008 Dayton Hamvention Flea Market
Agreement I downloaded and signed, along with
We have a 222 MHz repeater comprised of a converted Micor
mobile, Telewave TPRD-2254 BpBr duplexer, AM-6155 PA modified
for class C operation at 250W, and a DB-264JJ antenna at 80
ft. fed by 1/2' Heliax on a commercial FM broadcast tower .
With the duplexer terminated into a load, we
The MSR2000 Tx multiplier is 12x the channel element frequency if I remember
right, so the crystal fundamental would be 14.279167. 157.071 would be the
11x product if that's the case. Look for a similiar spur on the other side
of carrier. The exciter may be bad or not properly tuned, or it
-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Paul Plack
Sent: Sunday, January 13, 2008 6:22 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Revisiting Shorted 1/2-wave Traps
Paul,
Curious who
One of the initial proposals
was an open, 1/4-wave stub tuned for the FM broadcast
frequency, fed on a coaxial T-connector. This is, indeed, a
common method to trap a particular frequency.
I set forth that this wouldn't work, as the desired pass
frequency was too near the 9th harmonic
My coax is RG-8M, similar to RG-8X. I couldn't find a
published velocity factor for M, but thought I remembered
.87. RG-8X is .84 (not .66). I cut a piece off an old scrap
cable (with connector) to 41 inches, measured from the tip of
the PL-259's center pin to the cut point, as a
Guy's, anyone know what the current hourly wage that tower
maintenance types charge?
73 de Jack - N7OO
Like everything else, it varies a whole lot.
For a well-equipped and competent crew, figure $75 to $125 an hour depending
on what area you're in. Usually that rate is only good for 8
Their current license is for 100 watts ERP omni Cpol. 240 watts TPO would
be about right for 100 watts ERP for a 1-bay Cpol antenna.
They have a CP to go directional with 1.5 kW Vpol, 1 watt Hpol. I didn't
look at the application but most likely they went with almost all Vpol power
due to a
The question for Amateurs is a good one though -- lots of people run
lots of power and don't ever do even a cursory bit of math on their
particular station (let alone their repeaters) to see if
they're in any
danger.
OET 65 is the RFR bible as far as the FCC is concerned. Supplement B
A couple of basic things come to mind:
1. Do you have the PL encoder plugged into the exciter? If not, did you
install the jumper in the exciter board?
2. Did the station originally have the F1-PL card? It provides one (or
more) keying voltages, but I'm not in the office and I don't
The above sheet states that the TX leg on a TX-below-RX cable
should be
about 1/4 wavelength, and the RX leg should be about 5/4 wavelength.
I'm not sure why it would matter whether the Tx freq was above or below the
Rx freq given the minor (and generally negligible) differences in length for
I am well aware of the Delta tees used on Sinclair duplexers,
but those
incorporate one or more N plugs. My comment clearly stated
that a three-way
crimp tee (that is, crimp-crimp-crimp) was not readily
available.
I misunderstood. I thought you meant you were looking for a three-way
My understanding of the current rules is that would be classified
as broadcasting also. Announcements of any sort, including IDs,
must be associated with repeater receiver activity. If the receiver
has been inactive, the transmitter should be as well.
That seems to be the FCC's view. Note
After spending so much time chasing the DB-224JJ information down
I'd probably buy and use something else, which I have done. I'll
keep the JJ Model in my mind as I pull down a few more of the
Nationwide 220 ACSB Trunking Systems in the spring time.
Knowing full well that Skipp may fight
Other's haven't mentioned this, since you're working on
the PA issues
here... but when you get done with that PA, something's not
right in an
exciter that won't put out at least 200mW.
I don't often measure them, but I was under the impression
that they barely
made 200 mW. One I did
I'm slowly going through all my repeater stuff here and have
a problem
with the 100 watt UHF PA PL19d424895g32. No output. I checked the
exciter into another identical PA and it works fine. Drive is
a little
low, 100mw, but it drives the other identical amp just fine.
The bad PA
Has anyone on the list adapted a modern controller for
frequency-shift keying?
I've taken a CWID'er and, combined with an LM386 audio amp, did collector
modulated CW for link ID'ing by AC-coupling the CW audio into the power
control circuitry. In broadcast we do FSK ID'ing, as well as MCW/AM,
If you read part 97.119 CW can be used for IDing, not MCW as
most all repeaters use.
97.119(b)(2) says you can use a phone emission (i.e. voice), in English, to
identify.
97.3(c)(5) is the definition for phone, which explicitly specifies MCW for
the purposes of performing station
Very true; I know some who swore off the 4066 as unreliable poorly
performing because of their lack of consideration of the
above. Use it
within its limits it works great.
I have a priority-based receiver selector board that I designed many moons
ago for my inbound link concentrator
Lookee here:
http://www.repeater-builder.com/badconn/
-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Steve
S. Bosshard (NU5D)
Sent: Wednesday, November 21, 2007 2:13 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re:
OK, I'm blowing smoke, but I'm afraid of white smoke in
cabinet! I would like to get this drive back to 1.5 -2 watts
(protect the GM300 and prevent spurs) and get this PA back
down to 70 watts
Any easy way to control the control line?
Why not skip the first two stages in the Micor amp
Looking for a 7K autopatch board. Will buy or have lots of stuff to trade.
Thanks.
--- Jeff WN3A
My last few crystal orders went to West Crystal (www.westcrystal.com) in BC,
Canada. In the 80's and early 90's I ordered from Bomar exclusively, and
then started running into problems and switched to ICM. I was very happy
with ICM for the next ten years or so, but their prices started to get
Again, the circulator will produce intermod when external strong
signals enter the antenna port when used as a switch for the duplexer
and there is transmitter power also going through it. 50 Watts or
47dBm to -116dBm receiver sensitivity is 163dBm dynamic range. The
device is not linear
You have to read carefully -- I said capable of gain. Not
designed into the circuit in such a way that they EXHIBIT gain.
Thank you.
I can tune an otherwise-functional transmitter such that it takes in several
kW of DC power and gives me practically zero RF output. That doesn't make
the tube
Beta is the current gain of a transistor, HFE and Hfe.
Finally something we can agree on. But the way you used beta was
referring to the net gain of a *circuit* using a transistor in
emitter-follower
configuration, which I don't think is the correct use for the term, and
which is why I put
Total isolation = 97 to 127db (as good or better than most
stock duplexer setups)
That's for carrier attenuation only. Aside from the passive losses in the
system, you've done nothing to attenuate transmitter noise, which is going
to be a bigger enemy in your close-spaced frequency
An isolator is linear except with frequency just as a cap or
inductor or feedline are.
No, it's not linear. First off, it doesn't satisfy the superposition
principle since it will produce harmonic when fed by a pure sinusoid carrier
(hopefully we can agree to that without added discussion),
Not sure why isolator cause harmonics for it has no
non-linear components. It might cause tx to generate
harmonics. Isolators are on the output of many repeater
transmitters including my UHF Micor and it is built to work
directly into an antenna although most applications use a
duplexer
Jeff,
A diode is most certainly an active device. Its properities
change with exciting voltage and follow many parameters just
as a transistor.
A diode is NOT an active device. It's properties changing with applied
voltage do not define whether or not it's active. Whether or not it is
OK - Here are my requirements for the transmit chain. minimal
physical space and minimal insertion loss :-) (ok - too
bloody obvious) Tuning simplicity is also a factor. I'm
combining 3 transmitters at 144.39, 145.05 +/- 0.04 and 145.25
Before we get to what hardware to use, we still need
If I do two antennas, the best I can do is about 30db
isolation (30ft separation, 6db multi-bay folded dipole
antenna on bottom, 9db 2m/440 base station antenna on top),
If you can get 30 feet of separation, you'll get more than 30 dB of
isolation. More like 50 dB on VHF, 60 dB or more on
Sorry, but I totally disagree about a diode not being active.
If having to have gain then many devices such as a transistor
emitter follower with a beta of 1 would not be an active device.
I assume you're using the term beta to really mean current gain of the
stage. On my planet, an
Transmit and receive paths will be separate with 30db of
isolation (either split antennas, or a 30db isolation
circulator just before the feed to the antenna)
I posted a followup to one of your previous messages regarding using
isolators as a makeshift way of getting more Tx to Rx isolation,
This isn't guessing - its called RESEARCH
When I said guessing, I was talking about quantifying the performance of
your radios rather than guessing how much isolation you need. In other
words, make measurements to actually determine how much noise supression and
carrier attenuation you need
I am not sure why an isolator would cause intermod. Usually
there are not active or non-linear components in them
An isolator IS a non-linear device.
and
they are often used to prevent intermod by preventing outside
signals from coming in thru the feedline into the transmitter.
As a
An isolator wont cause intermod, but it may cause harmonics.
How so? What phenomenon occurs in a ferrite circulator that creates
harmonics but won't generate IMD?
Commercial installations usually use either a harmonic filter
and 3db hybrid coupler, or a special type of band pass cavity
Is anyone running a Samlex 12V supply in a situation
where they can measure the voltage regulation from
minimal load to something near half load?
After a catastrophic failure of a Samlex SEC-1223, I won't use them ever
again.
I had one that was powering a stack of 7 SpectraTAC receivers, an
Also could use the 5 Pin male connector used for Micors.
You mean 7 pin?
The easiest place to find those is in a SpectraTAC receiver chassis - there
is a little jumper with one of those connectors on each end that connects
the receiver to the interconnect board for use with the metering module.
Jeff you just gave away all the secrets... Good, concise job!
Well, I've fixed more than a few. The Micor amps were a helluva lot more
reliable and easier to service than the M2 UHF PA's ever were...
--- Jeff
The coupling cap between stages that is at the end of the semi-rigid coax
can develop a bad connection as Tom said. Usually if it does, the pitting
that occurs due to the arcing renders the cap's end plate too damaged to
re-solder reliably, so replacing it is a good idea.
The 25.5 pF caps
repeater owners in the New York City metro found that they
had fewer issues with desense and overload if they flipped to a
negative offset (i.e. get the ham repeater Rx further away from
the 450-455 commercial repeater Tx's).
... which is not really a valid reason. Probably a
From what I've been told, when 70cm first started to take off for FM
repeaters, repeater owners in the New York City metro found that they had
fewer issues with desense and overload if they flipped to a negative offset
(i.e. get the ham repeater Rx further away from the 450-455 commercial
Real world loss using a hybrid is over 4dB per leg... of which I'm
not a fan about space heating a radio vault with terminated rf power.
The quadrature hybrid itself should only be 3 dB theoretically, typically
around 3.2 dB in the real world. It's the external circulators that need to
be
Now that's a neat idea... I'll file that in my head and claim
local credit for it when no one here is paying close attention.
Unless someone is really trying or just gets really lucky... it's
my opinion the nulls from a side mounted omni shouldn't be that
deep if it's properly offset
I would have interest in this also as I need to combine 443.150 and
462.600 to 1 ant
thank you
Merrill
KG4IDD
I'm just addressing the two-port project above-- would not an ordinary
duplexer work just fine?
Laryn K8TVZ
Yep, do it all the time.
When combining transmitters,
restoration compound (liquid).
If it works for you... fan'tas'toe If it doesn't fix the problem
pot you will find it helps most pots work mucho betta'
chow for now
skipp
cheers,
skipp
Jeff DePolo [EMAIL PROTECTED] wrote:
Skipp sed:
I've got a few Kenwood TM-331 radios
What is the allowable deviation for a two meter digipeater in
amateur service? Is 15 kHz excessive?
Lord, yes, 15 kHz is excessive. The occupied bandwidth would be on the
order of 35 kHz for Bell 202 tones. You'd be clobbering both adjacent
channels.
5 kHz is typically considered the
But if it's a repeater AT ALL, it is PROHIBITED in the 145.5 - 145.8
sub-band!
I wasn't commenting on the frequencies in use and the legality therein; I
was just commenting that it can be serving two different functions
concurrently.
5. According to one of the postings on Icom's D-Star forums, the
developer(s) of D-Star have ALWAYS envisioned and called it
a repeater
system, as does the current sole vendor, Icom.
Yes it may be a repeater, but it's also an auxiliary station.
There's no reason why a particular piece
Adding or removing cable lengths between the transmitter and
duplexer also
does not change the VSWR as seen by the transmitter (minimal
cable loss
effects notwithstanding).
--- Jeff
True but only if everything (tx out, cable and duplexer) is
One can see there becomes a point where the coax will not
look like coax at low frequencies or atleast have a
characteristic impedance of something other than it normal value.
Most of this is true (although I don't know what you mean by coax will not
look like coax), and I already
The question is way off base. No one said one cannot carry
DC or any other signal on coax. The question was what was
the impedance of a coax at given frequencies.
You said coax has a low-frequency cutoff. I'm asking about that
specifically. I didn't ask about about impedance.
At DC I
Impedance refers to both R and X, resistance and reactance. Impedance
affects all current flow, DC and AC. X affects AC only.
Impedance is specific to AC. There's no such thing as impedance at DC, only
resistance. Look up in the definition of impedance in any engineering text
and you'll find
I don't know where the confusion is...all coax and feedline
has a upper and lower freq limit. Might try to learn
something about this.
If what you say is true, can you tell me, using sound engineering and math,
why you can carry DC on coax if it has a low-frequency cutoff?
When I replace my DB224 I am going to a SuperStation Master
fiber glass pole. It is obvious the exposed dipoles have a
survival problem in this salt air.
Have you looked at the heavy-duty Sinclair folded-dipoles? They seem
better built than the DB's.
10 years is starting to push it
Sorry, I just assumed that a repeater coordinator's
technical standards
would be a bit above the mess you describe above. I know
we (TASMA)
wouldn't coordinate such a system.
Bob NO6B
You guys have control of the quality level of the equipment used when
issuing
There's a capacitor hidden in in my coax? Where? I can't
find it, and now
I've ruined my cable looking for it :-)
Yep, whenever one has two conductors with spacing between
them you got a cap. For a cap in coax might try looking for
the conductors of center and shield...looks like
It doesn t matter where the min and max are on the line. The
same amount
of reflected power will be seen at any point. Reflected
power does NOT get
back into the transmitter. It gets re-reflected back towards
the antenna
when it reaches the transmitter circuits.
I don't buy into
The 300 Ohm or 50 Ohm is not part of the R in IR losses.
No, but the Z (300 or 50 or whatever) is what determines the *I* for a given
amount of power. The actual losses are due to that I squared, and the R of
the conductors themselves. Z is impedance. R is resistance.
I think we are
If your coax is the same impedance as your transmitter, but
different than your load, can it still be a transformer
though?
It will ALWAYS act as a transformer when the cable's Z does not match the
LOAD Z. The SOURCE device (transmitter) plays NO part in the transformation
that happens.
Jesse,
Then why do twin feeders have much less loss than coax???
Skin affect is even more of a factor there due to the
differences in the area of the outer shield in coax vs the
twin feeders wire.
The current in a 50 ohm cable is higher as compared to a 300 ohm cable for a
given power
it for other purposes and was
so disappointed I hadpurchased such a cable with so little shield.
Guess works for CB and Ham HF bands, but really not good
forVHF/UHF. The same can be said for many PL259 connectors
and adapters.
73, ron, n9ee/r
From: Jeff DePolo [EMAIL PROTECTED]
Date
It appears that the instant discussion has overlooked that
there are three factors in the attenuation of transmission
lines. They are the conductor losses, the dielectric losses, and
also the optimum ratio of b/a = 3.6 for a coaxial line, which
corresponds to a characteristic impedance of
The length of coax doesn't effect impedance.
That statement is misleading, if not totally wrong. If there is anything
other than a perfect match at the load (in other words, if the VSWR on the
line is not a perfect 1:1), the coax behaves as a transformer. The
resulting Z, as measured at the
I have heard this point argued for years. Does trimming the
coax affect the SWR?
The answer is NO!!
If the length of coax has an affect on
impedance, then how could it not affect power out?
Changing the length of the line changes IMPEDANCE at the source end
(assuming the VSWR isn't
The whole problem here is the comparison between high
impedance twin lead and low impedance coax. Is the
difference of impedance really coax attenuation?
Maybe I'm not understanding the question. In the most general terms, loss
has no direct correlation to impedance because there are
As a side note for this discussion, I think Jeff's doing a
great job of
explaining how transmission line theory works...
I try...
For those that want to dive in a lot further (e.g. Do the math), the
ARRL Antenna Book has a whole section dedicated to this
topic, and it's
written well
Ya you should be able to trim your coax so the transmitter
sees 50 ohms, which should be every 1/2 wave. All this
does it protect the transmitter, the standing waves are still
there, they just gets dissipated/radiated by the coax.
No, no, no, no, no (thumping head on desk).
If the VSWR
as transformers when their characteristic Z is different than
the termination Z.
--- Jeff
-
Jeff DePolo - [EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030
Wait a minute Jeff... what about that crappy low cost silver jacket
Super-flex Columbia branded coax I bought back in the 70's during
the CB boom...
Coax leakage is different than currents flowing on the shield though...
I remember having some RG8 from Radio Shack with braid openings that
I recently purchased a Mastr II VHF station and it has a PLL
Tx exciter.
Is it feasible to change that out with a normal P.M. Xtal
type exciter.
Yes, it's straightforward, just swap them out. But why would you want to do
that? If you are going to use this station on 2m, you're MUCH
Bob
That doesn't square with the large body of repeater owners
who have used Wacom cavities. Their UHF products used RG-142.
However, their VHF products used a proprietary cable which
had: MODIFIED RG-214 DOUBLE SHIELDED which was nothing more
or less than RG-214 without silver
Your test equipment is unquestionably more sophisticated than
my tracker but I wonder about the figure you recorded for the
BP BR pass attenuation at .0953. That seems awfully low. I
would expect to see something in the whereabouts of .5 db.
I noticed that too, and verified it twice. It
Allen Crites correctly pointed out that I had fat-fingered the wavelength of
the factory cable I had in the original version of the text - I fixed it.
Also, I had previously estimated the physical length of the type N elbows to
be about 1.5 inches, or 0.12 wavelength. For the heck of it, I
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.
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.
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
According to Lloyd, the cable length between a duplexer and
an inline
cavity filter and the receiver makes little or no difference.
Steve,
Was the question posed (or probably misunderstood as being) whether the
cable length between the receiver and the filter being critical, or the
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.
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
...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
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
Rather than having to add on an airflow sensor of some ilk, there are two
other options that might be easier:
1. Use fans that have a fail indication lead. Most fans, especially the PC
variety, have a third wire that is used as a tachometer. Most give two
squarewave pulses per rotation. If
If the blower is used to cool a tube pa the thermostat detection
hardware is probably way to slow.
I was assuming a SS PA, but maybe that was a mis-assumption.
Many vane indicators are of the long arm micro switch type. Easy
enough to make your own but you can probably find them through
Sure, a UHF isolator will not protect the transmitter from
VHF transmitter junk. But isn't the flip side that out of
band VHF junk is less likely to produce UHF transmitter
intermod than in band transmitter junk?
Not necessarily. If it were the other way around (UHF coming back down the
Do you have any thoughts on why or how a well designed Z
match could produce cable
radiation?
For the feedline to radiate, there would have to be currents flowing
on the
shield. It would seem to me the only way to get that to happen would
be if
there was an imperfect shield
The other ways to correct the problem, other than using a different
transmitter that is not bothered by reactive loads as much,
is to use a Z
match or try different length cables that make the
transmitter happier.
But if the transmitter is bothered by the bad Z at frequencies outside of
Doesn't the isolator typically installed at the transmitter
output spin off any anything reflected from the duplexer (or
the feedline) into it's load?
The generic answer is yes, but the qualified answer is that isolators,
like everything else, have a finite bandwidth, so if the energy is
If your duplexer presents 50+j0 at its input at the operating
frequency and
you are using 50 ohm cable to connect it to the transmitter then the
transmitter is always going to see 50+j0 at the operating frequency no
matter what the cable length is. But at some off frequency
that is not
Hi Steve,
I don't recall ever seeing that done. What was the purpose of using an
isolator there?
Steve will probably reply too, but I'll give you the quick answer. UHF
Micor mobiles all came stock with an isolator in the antenna network, just
like their big brother base/repeater stations.
You can't convert to a perfect 50 ohms using cable lengths
if the load isn't already 50 ohms. I've said before, and I'm
saying it again. If your duplexer 50 ohms load, you can pull
all of the 50 ohm cables you want out of your bag and you'll
never get it back to 50 ohms at the PA.
Boy,
However, the load impedance of most PAs
will vary
significantly with the drive level,
I think you meant source impedance.
and the input impedance
of a duplexer
cavity is always reactive
Not necessarily. You can tune a duplexer very close to 50+j0 at the pass
frequency. It's at
I don't think the cable cares whether the source and load
impedances are 50 ohms
resistive. I think the cable is indifferent to whether the
load and source values are
resistive or whether they present a complex impedance
involving +/- J. as long as the
composite value looks like 50
OK so you have a reel of cable and two connectors to make up
the jumper between transmitter and duplexer.
The duplexer is tuned using 50 ohm test gear and the
transmitter has been optimised into a 50 ohm load.
Unfortunatley the output impedance of the transmitter is not
50 ohms and
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