> There are 7 stubs, 4 are on the pass cans, 3 in-between the 4
> resonators. Adjusting any of the 3 stubs (between each of the 4
> resonators) has little effect on the skirt.
The between adjust the size of the aperature (coupling) between filters.
You won't find a whole lot of change in the passb
Ed,
I have a new Telewave single-stage high-power (300 watt I believe) isolator.
What frequency do you need? I can put it on the network analyzer to make
sure it meets spec at your frequency. I'd sell it for half of whatever
Telewave list price is, and again, it's brand new, still in the orig
Sorry, that last message was supposed to be direct...
--- Jeff
--------
Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant
> Call or write to Celwave (now RFSystems) and ask them
> for the cutting chart for units using RG400. Last time
> I tried that, every technician I spoke with told me,
> in no certain terms, that they NEVER used RG400 or
> RG142, yet I have seen photos and one actual unit that
> was factory fresh a
I'm not sure if you were looking for constructive criticism or not. If you
were, here's mine. If not, the delete key is within finger's reach...
> 1 TKR-750 VHF Kenwood Repeater - $1350
> 1 KPG-91D Repeater Programming Kit - $119
> 1 TKR-PS1223 Kenwood Internal Power Supply - $169
> 1 PC24-NN P
The easiest way is to use the Micor battery backup power supply.
You can't run a Micor on 12V alone; it requires 9.6V as well. If you only
hooked up the 12V to your battery, the station won't work as you found out.
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto
I think I see how Steve's logic is leaning, and I agree - I don't see any
logical mix here until you include a user's transmission on one of the
repeater's inputs. Fred - do you hear ALL 147.33 transmitter activity
coming in on the 147.765 input, or just when there is actually a user keyed
up on
> As
> soon as the 33
> subscriber unkeys the interfering signal on 165 goes away.
I'd bet a box of isolators that the problems at the 165 site, NOT at the 33
site.
> Is it valid to add 600 kHz to the intermod calculator? I get
> an interesting
> fifth order when I do.
Just add the mobile f
> Some one heard the owner of 165 talk about having to keep the
> power down
> because of desense.
A perfect example of bandaidsmanship.
> What about a band pass on 147.765?
Nah, it would only buy you a couple of dB of attenuation at 147.93.
> It may take a crystal
> filter or just
> paddi
> I'm setting up a Mastr II VHF station for a 2 meter repeater
> and when I
> got to the power amp to check everything I can only get about
> 86 watts
> out of the 110watt PA. I noticed that the power supply
> starts to fold
> over at about 20 watts out and when I get to 80 watts the supply
.
--- Jeff
> Hi Jeff!
>
> Thanks for the reply.
>
> The no load voltage is about 14.1 volts.
>
> Bill...
>
> -Original message-
> From: "Jeff DePolo" [EMAIL PROTECTED]
> Date: Mon, 05 Feb 2007 16:28:07 -0800
> To: Repeater-Builder@y
> I notice in the below referenced article on antenna
> separation that it is stated that the "graphs are misleading
> and no where near accurate for modern day solid state equipment".
> That is not correct as the graphs for antenna isolation show
> approximately how much isolation can be expect
> I have a mastr II station that has me wondering...
> No matter what I do it will not unkey. Tried swapping out all the
> cards and it didn't make a difference. I can get it to unkey by
> pushing I think it's the ptt remote switch.
My shot-in-the-dark guess would be jumpers set wrong on the 10V
> As another note on the tx-rx isolation curves, a synthesized
> transmitter is
> not always worse than a crystal controlled transmitter as far
> as broad band
> noise output. If I remember right There are somewhere some
> curves showing
> that a certain model GE synthesized transmitter has less
> Agreed, but my main point was that newer receivers even
> though wide band may be as good as older narrow band
> receivers. No question that additional filtering makes them
> even better.
Do you have a particular wide-band receiver in mind?
--- Jeff
Are you doing these tests while using an outboard controller?
Does it do it with the PA output connected directly to a dummy load? I'm
wondering if you have excessive RF floating around that's somehow getting
into the logic circuitry.
Does it do it with PA disconnected from the exciter? I'm won
> I'm suspecting the ferro cap after looking at it.
Seems to me last time I ordered one I got it from either Newark or Allied.
It might have been classified under motor-start capacitors or the like. I
believe I was able to cross-ref the part number off the failed unit and get
an exact replacemen
Has anyone else looked at the input return loss on their ARR preamp? I had
one that, when put in place, was throwing off the tuning of a two-cavity
bandpass filter I had ahead of it. I swept it and found the return loss to
only be about 5 dB. I put an Angle Linear preamp in its place and all wa
> For those who are inquiring minds and not up to all of the
> terminology, what
> is a "golden screwdriver"?
Using the "golden screwdriver" means somebody went and diddled with
something that they shouldn't have diddled with, and probably did so without
using any test equipment.
I don't know
> <---I swear by my last breath that I will *never* use anything other
> than Chip's stuff - there is simply *nothing* on the planet that
> comes close. I've been using his preamps and multicouplers for close
> to 20 years now and have *never* been disappointed (nor have I ever
> been disappoin
> or
> large amounts of wiring bundled with jap-wrap (cheap vinyl electrical
> tape)
Hey, thanks, I learned a new term today! That one will come in handy!
--- Jeff
> The better question is... have you looked at the input section of
> the circuit diagram? Looks like a high Z input doesn't it... :-)
Don't think I've seen an ARR schematic, but most GaAsFET preamp designs I've
evaluated will tend to produce least noise figure with an input Z quite a
ways away
> If you really want to isolate the preamp from the duplexer,
> you need to put
> an isolator ahead of it.
>
> Bob NO6B
>From a matching standpoint, yeah, but now the NF goes up due to the added
losses of the isolator. You might come out ahead by modifying/retuning the
preamp's input network
> True, but the original question was if the noise figure of a
> preamp was
> degraded by the poor input match looking into the preamp
> itself, & the
> answer is no.
Bob,
Actually, my question wasn't in regard to the NF of the preamp itself,
but rather the resulting NF (system NF) due to th
> Your math looks sound, Jeff, except I thought 1/2" Heliax
> wasn't quite so
> lossy @ 450 MHz (~1.5 dB/100 ft IIRC?).
> >Scenario 1: Preamp = 0.5 dB NF, antenna feeding 200' of
> 1/2" Heliax (3
> >dB loss @ 450 MHz @ 1:1 VSWR)
1.5 dB per 100 ft versus 3 dB for 200'. I think we're in agre
> Question: The only way I see this happening is due to some AM
> component on radio station's transmitter.
>
> Thoughts?
Virtually all FM transmitters have some residual/undesirable AM components.
If the AM follows the applied FM modulation, it's referred to as synchronous
AM, and is usually ca
> If "Joe Ham" were serious about weak signal reception, he'd mount the
> preamp at the antenna. Otherwise, 3 dB is already a lot of loss to
> tolerate for weak signal work; what's another dB?
Us northeastern Joe Ham types don't like climbing the tower during the
middle of the January contest w
> Any idea what kind of bandwidth a full size station master would have?
> VHF marked 153.XX...should it go down into the 2 meter band or are
> they very narrow?
>
> Ben
Depends on which model. A PD200 Stationmaster is narrowband; about 1.5 MHz.
A PD220 is wider, typically 8 MHz.Both are 20'
> > Measured on their range-they used to be based in Cleveland, and my
> > father was one of the designers.
> > (anybody here remember the PRO-27JR 27Mhz antenna? Or the
> original 4BTV?)
> > --
> > Jim Barbour
> > WD8CHL
> >
>
> With all due respect to your father Jim, I think that 4 db of gain
> Oh, and 'mag mounts' didn't really exist much then...you
> either mounted
> the antenna in a hole, or you didn't have an antenna.
Ah, the gold old days, when men armed with a drill and Greenlee punch
thought nothing of putting holes in their roofs, fearing not the Wrath of
Wife.
> I'm presently setting up 4 Delta SX UHF Transceivers as Tx'ters for a
> repeater system. I have completed the mod and am presently trying to
> tune radios. The problem I'm having is that my dev is up to about 9.8
> kHz. My service manual says to adjust R237 (Dev Adj). The
> radio that I
> am
> There is also a pot for modulating the VCO ...
Sorry. That should have been "a pot for modulating the reference
oscillator".
> I never suggested that the cable between the TX and the
> duplexer had to be an exact length and if the TX output is a
> true 50 ohms then any cable length produces no consequence at
> the cavity input. But if the TX impedance is not 50 ohms, I
> think any cable length other than half wave w
> Bypassing the relay shouldn't have an effect on the TX output
> Z when not
> TXing, as the final RF output transistor is going to look
> like an open too.
> Bob NO6B
But the "open" transistors would be at a different electrical distance away
from the duplexer than the open T/R relay was.
Skipp sed:
> Well...
> Normally I wouldn't post this type of thing here... but it might
> come in really handy for some of you.
> The $825 cost might seem a bit high... but man it's worth the money.
> The Seller is fluent on the Product and provides all the proper cal
> data.
The seller is
DB408's hang upside-down quite nicely, and work just as well too. You do
have to drill new weep holes in the elements - put them in the same location
as they would be if the antenna were right side up. Whatever you do, DON'T
drill weep holes in the very bottom of the element as it will split onc
Manufacturer = RF Industries, Vendor = Tessco.
--- Jeff
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of wd0ekr
> Sent: Saturday, March 10, 2007 7:31 AM
> To: Repeater-Builder@yahoogroups.com
> Subject:
I've got 220 isolators if anyone is interested, relatively cheap (figure 20%
of what they would typically go for as a ballpark). Email direct.
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Scott
> Overstreet
> Sent: Monday, Marc
> Correct. Instead of "flat audio", a term such as "unshaped",
> "unprocessed"
> and/or "direct FM" should be used instead.
>
> Bob NO6B
Right.
An FM discriminator is always "flat" - the discriminator doesn't do anything
to alter the frequency response. It's only purpose is to recover the au
> Real world transmitters always have limiters. Those DO change
> flatness. Just look at the EIA/TIA specication for testing
> transmitter pre-emphasis. The test is not run at system deviation.
> It is not even run at 60% of system deviation. It is run at 20% of
> system deviation. [that's
> Most two-way radio people never use the term flat audio repeater. We
> would assume most standard voice audio repeaters operate as the
> mentioned so the "flat audio repeater" has never really been applied
> by Industry as a real description. Some Amateurs seem to want to
> apply the label a
> >> Real world transmitters always have limiters. Those DO change
> >> flatness.
>
> That keeps throwing me. I hear 'limiter' and I go towards the
> receiver.
Actually, it wasn't me that said "Real world transmitters always have
limiters." I know it was just a cut n' paste mistake, no off
> I've stayed out of the debate so far, but even Amphenol claims
> "nominal 50 ohm impedance" for their 50 ohm BNC connectors up to 4
> GHz. On their N-connector they drop the "nominal" but they don't
> elaborate.
BNC's are rated for a lower MUF because the mechanics of the bayonet lock
aren't id
> One of the reasons you see UHF connectors on VHF and UHF
> mobile radios,
> including commercial radios, is because it is a lot harder to
> screw a UHF
> connector.
DOH! That should have said "screw up" a UHF connector. Blame Freud, and
Ken with his Anna Nicole comment...
I have a Brady ID-Pro and a Brady TLS2200, the former of which has seen
better days. Unless you have a financially-viable reason to spend the money
on a wire labeler, you're probably better off buying sheets of
laser-printable wire labels. They come in regular 8.5x11" sheets. You can
get differe
There's no easy answer to that question. The two biggest factors to
consider when selecting the right value are:
a) What frequency range are you trying to filter out? If your problem is
keeping an AM broadcast station out, you'll need larger values as compared
to targeting your own VHF/UHF emis
A linear translator for something like D-Star wouldn't work out real well
since you are dealing with mobile users. The first issue to overcome is the
constantly-varying amplitude of the incoming signal - on the order of tens
of dB's in level change doezens of times per second at highway speeds (6
> There's good reason a "hot air" alarm probably went off for many
> of you when reading the article.
I'm trying to figure out what his closing paragraph is trying to say:
"A duplexer is working correctly when the sensitivity of the receiver is not
degraded when the transmitter becomes active.
OH! He's talking about the "oscillation" of the repeater keying up and
down. I guess he's making a major assumption that the repeater hangtime is
0.5 to 1 second? Kind of a gross over-generalization in my opinion. When I
think "oscillation" I think of it in terms of AF or AF, not duty cycle...
It started out as a stock six-cavity notch duplexer (I have one of these in
storage - I think it's a DB-4021?). Let me explain that part (the stock
duplexer) first.
Before I get into it, realize that some notch cavities are asymmetrical in
terms of the notch response - they have somewhat of a
I bought my last rolls of filament tape and aluminum tape from Tessco. They
were OEM'ed by 3M but sold as Decibel products. If you can't find them,
I'll see if I can get a 3M part number off them.
--- Jeff
> -Original Message-
> From: Repeater-
> Nope, because like you said, they would draw the feedline into the
> strut, smashing it all up...
I regularly use cushioned clamps for attaching rigid feedline to unistrut.
I usually buy them from McMaster-Carr, but I'm sure they're available
elsewhere. McMaster-Carr has them available in "tub
I think this is, or should be, a repeater-builder FAQ.
Foil+braid cables like 9913, LMR-series, etc. should generally NOT be used
in duplex environments. Although a few may report results to the contrary,
braid-over-foil cables produce noise due to the dissimilar metal contact,
particularly as
I don't have a control shelf manual ("orange book") here for the Micor, but
one other thing to check is the PL encoder on the transmitter (if it has
one). If the keying transistor or other logic on that board got hosed, it
could "latch on", keeping the transmitter keyed.
I'd be happy to trade you (or anyone else) a nice UHF duplexer for your
highband duplexer. Have many to choose from...
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of n3dab
> Sent: Thursday, June 07, 2007 5:29 PM
> To: Repeater-Buil
--- Jeff
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of skipp025
> Sent: Thursday, June 07, 2007 3:13 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Re: Which coax cables to use
Call Joel at the RF Connection (www.therfc.com) and ask him for the "good"
RF-type RCA's. His have the short center pin, teflon dielectric, and are
silver-plated. About the best you'll find. And they're inexpensive.
--- Jeff
> -Original Message-
> From: Repea
> Someone decided to pull the hardline out of the shack - I
> think the idea was to remove the bottom 35 feet, which had
> been spliced on using a hardline splice) to test the two
> sections individually. As we uncoiled it from where it
> passed behind the shack, next to the chainlink fence, t
nsidering. What are
> your thoughts?
>
>
>
>
>
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
> Sent: Thursday, June 21, 2007 10:03 AM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] RE: VSWR Issues - Repa
peater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Nate Duehr
> Sent: Thursday, June 21, 2007 1:18 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: Re: [Repeater-Builder] RE: VSWR Issues - Repairs Complete
>
>
> On Jun 21, 2007, at 8:56 AM, Jeff DePolo wr
> You forgot to blame him for birds flying into towers and being
> killed
In a given year, somewhere around a dozen birds die by crashing into the big
windows on the front of my house. In contrast, I might see one or two dead
birds per year in total at all of the 50 or more tower sites I go
> 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 a
> 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
> 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 oh
>
> While the receive-side jumper may work well at any random
> jumper length, the
> transmit-side jumper is a different matter.
My experience has been just the opposite. Unless you sweep-tune a receiver
front end that uses helical resonators, the chance of having a Z even
remotely close to 5
> I don't think I ever suggested otherwise. I never said that
> using a half wave cable would improve
> anything. What I did say was that a half wave cable would
> repeat the prevailing condition neither
> making it better or worse and I further said that using any
> variation from a half wave c
> Jeff
>
> You make some excellent points. Thanks!
>
> Bruce K7IJ
Yer welcome, and thank you for bringing up some issues for discussion that
frequently get confused by even many seasoned techs.
--- Jeff
> Can't argue with your analysis. My only point is that if you
> are intent on dealing with a
> TX to duplexer mismatch, a half wave cable replicates what
> ever mismatch exists. A
> random length cable can mask the real world condition by
> making the apparent mismatch
> better or worse than i
> > > 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 im
> 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
> 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
> 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 no
> 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.
> 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 t
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 you
> 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 thro
> 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 mi
> ...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 tow
> > 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 transmi
> 50 ohms is ONLY at the pass frequency. The concern here is
> that the wrong
> cable length between the pass cavity & duplexer can cause
> undesired effects
> at reject frequencies.
'zactly.
Although a bandpass cavity (or multiple cavities) is always a good idea in
front of any receiver
> 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 c
> 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
cab
> 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.
> 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. I
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 measur
> 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 silve
> 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
en by the transmitter (minimal cable loss
effects notwithstanding).
--- Jeff
-----
Jeff DePolo - [EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030
> 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 V
ransmitter will always be 50 ohms. Transmission
lines only act 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 th
> 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 p
gt;>Subject: Re: RE: [Repeater-Builder] Re: Duplexers
> >
> >
> >>
> >>I^2R losses do change with frequency because of the skineffect.
> >>
> >>
> >>
> >>On 8/26/07, Ron Wright <[EMAIL PROTECTED]>wrote:
> >>Jeff,
> 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
> 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
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