[Repeater-Builder] Duplexers

[Cort Buffington]

Repeater Builders,

I pose to you all a question. I have two UHF duplexers, both 4 cavity  
pass-reject. One is a Wacom (the ubiquitous 3U rackmount guy) and the  
other is from a Motorola MSR2000. I have really poor equipment, and  
don't necessarily "trust" manufacturer specs. Anybody have an opinion  
on which one is better, or pros and cons to each?

The rest of the RF equipment are Hamtronics T304 and R305 and a Mirage  
D-1010-RN. The T304 is "throttled" back so that the Mirage is making  
about 55-60W. I'm currently running on the MSR2000 duplexer, not tuned  
as well as it could be. Some desense, and some is probably curable  
with better tuning of the duplexer, helical preselector on the front  
end, etc. But so far, I'm finding the additional receiver sensitivity  
(over say a Mitrek/MSR or Micor) is far out-weighing the desense

73 DE N0MJS

--
Cort Buffington
H: +1-785-838-3034
M: +1-785-865-7206

[Repeater-Builder] Duplexers

[w7hsg]

Looking for factory alignment for the following 

Telwave TPRD 1554

Wacom WP655-R2




Ralph, W7HSG

--- Begin Message ---
















Check out COMTELCO antennas, they 
are on the web at www.comtelcoantennas.com  I have 
many of them in service with 100% results. They are equal in gain and 
performance to other more expensive antennas. I recommend the ones with 1.5 inch 
tubes, not the smaller 1inch tube models.
Lance

  - Original Message - 
  From: 
  Tony 
  L. 
  To: Repeater-Builder@yahoogroups.com 
  
  Sent: Thursday, December 20, 2007 10:22 
  AM
  Subject: [Repeater-Builder] Re: antennas 
  for gmrs repeater
  
  
  My first recommendation would be a RF Systems PD1151, but since you 
  don't want to spend the money for a Station Master, how about a 
  Hustler Newtronics G6-450-3?You should be able to pick one of 
  these up for under $200. Reportedly, they stand up to the weather pretty 
  well. The first choice PD1151 would run you about $650.--- In Repeater-Builder@yahoogroups.com, 
  Jed Barton <[EMAIL PROTECTED]> wrote:>> Hey guys,> Any 
  opinions on an antenna for a gmrs repeater? It won't be going on > 
  a 300 foot tower, but it will be on the top of a hospital.> I would 
  rather not get a station master, but something that could > withstand a 
  little weather.> Any ideas on the biggest bang for the buck?> 
  > Thanks,> Jed>

  






--- End Message ---

[Repeater-Builder] duplexers

[ua3ahm]

I wish to take an interest at American HAM's how much actually now to 
sell new duplexers in the USA. My company makes antennas and duplexers 
for a professional radio communication. Your opinion interests, I was 
not late for 20 years?)
 Evgeny, IK-Telecom

[Repeater-Builder] Duplexers

[dallasreact112]

Anyone one know what to expect SWR wise with a duplexer?
I have a DB products 2 meter duplexer on an amateur repeater.
Measuring with a Bird wattmeter between the duplexer and antenna I
read 50W forward and a couple watts reverse. That is ok. But when I
check between the transmitter and the TX port on the duplexer I get a
about 60 W forward and 25W reverse power. Is there a rule fo thumb for
a known good SWR value thru a duplexer? Should a good duplexer introduce
any significant SWR?

Thanks

Bernie Parker

K5BP

[Repeater-Builder] Duplexers

[mung]

I am having some receive problems on my repeater and I am 
thinking that it might be desense.  I am on 2M running a 
MASRII repeater with a Decibal Products band reject 6 can 
duplexer.

While I can key the repeater from a pretty good distance 
the audio that makes it through the repeater drops off 
pretty quickly.  I just had the duplexers tuned and they 
are tuned very well.

So on to my question.  If I were to take and seperate the 
recv cans from the xmit cans and run to 2 seperate 
antennas would that mess up the duplexer tuning?  will 20' 
of vertical seperation plus the cans and the fact that I 
would be running through seperate cable, make a 
difference?

Thanks,
Vern
KI4ONW

[Repeater-Builder] Duplexers

[Mung Bungholio]

Is it OK to get some kind of storage container or something like that and
put my duplexer outside?  What would be the risks of doing so?  I am in
Florida so lots of rain and heat but no freezing months or anything like
that?

 

Thanks,

Vern

KI4ONW

[Repeater-Builder] duplexers

[David Schornak]

has anyone or does anyone know where tofind the math formulas to help you
design a set of cavities for a duplexer? I have been looking on the web and
in the arrl handbook and the big book of antennas, and todate I have found
plans for 2 meter duplexers.
I have yet to find any place where they show or have written out the
formulas for designing your own cavities.
I was thinking that there should be something out that that that for this
frequency range your cavity hieght is this and the diameter is this.
so is there a site or a book that gives you the theory and or the math so
that you could design your own set of duplexers/ cavities?





 
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[Repeater-Builder] Duplexers

[KB7RSI]

Title: Duplexers





Hey guys and gals.
First time poster here.

Just wondering if anyone has a set of duplexers with notch for 2M that they have hanging around and would like to get rid of?

Please let me know directly @ [EMAIL PROTECTED]
I really do appreciate it.

Thanks

Harold
kb7rsi
Las Vegas, NV.

IRLP Node 3240, Echolink Node 29232

 
 

















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[Repeater-Builder] Duplexers

[Richard D. Reese]

Dave;
 
Sorry about that.  The two meter one is a 28-37-02 and 
the specifications are:
 


  
  
Frequency Range 
:
144-174 MHz 
  

  

  
Minimum T-R Separation 
:
0.5 MHz 
  

  

  
Tx Insertion Loss 
:
1.5 dB 
  

  

  
Rx Insertion Loss 
:
1.5 dB 
  

  

  
Transmitter Noise Suppression 
:
85 dB 
  

  

  
Transmitter Carrier Suppression 
:
85 dB 
  

  

  
Between Channel Isolation 
:
50 dB 
  

  

  
Impedance 
:
50 Ohms 
  

  

  
VSWR 
:
1.3:1 
  

  

  
Power Rating 
:
400 W 
  

  
Mechanical 
  
Temperature Range 
:
-40°C to +80°C 
  

  

  
Connectors 
:
TX and RX Ports: N, Antenna Port: N 
  

  

  
Height 
:
33" 
  

  

  
Width 
:
19" 
  

  

  
Depth 
:
±7.5" 
  

  

  
Mechanical Mounting 
:
19" Rack Mount 
  

  

  
Weight 
:
50 lbs. 
 
Richard D. Reesehttp://www.wa8dbw.ifip.com

  - Original Message - 
  From: 
  Dave Baughn 
  
  To: [EMAIL PROTECTED] 
  Sent: Thursday, January 27, 2005 10:19 
  AM
  Subject: Fwd: Re: [Repeater-Builder] 
  Repeater Rx is Better than TX, Why
  
  But his is VHF with 600 kHz spacing. Must be some giant cans!
   
  Dave BaughnDirector of EngineeringThe University of 
  AlabamaCenter for Public Television and RadioBox 870150Tuscaloosa, 
  Alabama 35487205.348.8622 cell 205-310-8798NEW EMAIL [EMAIL PROTECTED]>>> [EMAIL PROTECTED] 01/26/05 08:41AM 
  >>>I have two TX-RX in service on UHF and they are 
  :28-70-02 (450-470 MHz)Type: 4 cavities 4" diameterFreq. 
  spacing  5 MHzInsertion 
  loss 
  <0.6 dBMax. continuous power  350 
  wattsChannel 
  isolation  100+ 
  dBThese spects have been verified on the bench as 
  well.73Richard D. Reesehttp://www.wa8dbw.ifip.com













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[Repeater-Builder] Duplexers

[Mackey]

Our club was recently given a 220 repeater. We have two seperate antennas.  We 
do not have a duplexer. My question is do we have to have a duplexer? How can 
we keep the transmitter from desensitizing the receiver? The antennas are apart 
but can be moved farther.
Thanks
Chris
Kg4bek

[Repeater-Builder] Duplexers Question

[Bob]

any way to tune duplexers without a scope or monitor ?

Bobby/N2BR





 

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RE: [Repeater-Builder] Duplexers

[Eric Lemmon]

Ralph,

Contact Telewave at www.telewave.com for both Telewave and Wacom duplexer
tuning information.

73, Eric Lemmon WB6FLY
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
Sent: Thursday, December 20, 2007 6:17 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Duplexers

Looking for factory alignment for the following 

Telwave TPRD 1554

Wacom WP655-R2

Ralph, W7HSG

Re: [Repeater-Builder] duplexers

[Jack Hayes]

Are you seeking U.S. distribution?
Please contact [EMAIL PROTECTED] directly.
Thanks


ua3ahm <[EMAIL PROTECTED]> wrote:   I wish to take 
an interest at American HAM's how much actually now to 
 sell new duplexers in the USA. My company makes antennas and duplexers 
 for a professional radio communication. Your opinion interests, I was 
 not late for 20 years?)
  Evgeny, IK-Telecom
 
 
 
   

   
-
Looking for last minute shopping deals?  Find them fast with Yahoo! Search.

[Repeater-Builder] Duplexers vhf

[gervais]

hi all

i have 3 little duplexers

sinclair sd-220

rx 152.660

tx 157.950

if someone is interested send me an email direct please

73/s

make me an offer will see,i dont need them as their GE radio connected
too.

gervais ve2ckn

Re: [Repeater-Builder] Duplexers

[Steve S. Bosshard (NU5D)]

Generally the duplexer only makes a slight contribution to the reflected
power.  How doe the reflected power between the transmitter and antenna,
without the duplexer in line look?  Steve NU5D


dallasreact112 wrote:
> Anyone one know what to expect SWR wise with a duplexer?
> I have a DB products 2 meter duplexer on an amateur repeater.
> Measuring with a Bird wattmeter between the duplexer and antenna I
> read 50W forward and a couple watts reverse. That is ok. But when I
> check between the transmitter and the TX port on the duplexer I get a
> about 60 W forward and 25W reverse power. Is there a rule fo thumb for
> a known good SWR value thru a duplexer? Should a good duplexer introduce
> any significant SWR?
>
> Thanks
>
> Bernie Parker
>
> K5BP
>
>
>
>
>
>  
> Yahoo! Groups Links
>
>
>
>
>   

Re: [Repeater-Builder] Duplexers

[Captainlance]

If the duplexer is correctly tuned, there will be NO measurable SWR into it. If 
you have 25/60 watts, it is way off frequency.

  - Original Message - 
  From: dallasreact112 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Friday, August 24, 2007 7:16 PM
  Subject: [Repeater-Builder] Duplexers


  Anyone one know what to expect SWR wise with a duplexer?
  I have a DB products 2 meter duplexer on an amateur repeater.
  Measuring with a Bird wattmeter between the duplexer and antenna I
  read 50W forward and a couple watts reverse. That is ok. But when I
  check between the transmitter and the TX port on the duplexer I get a
  about 60 W forward and 25W reverse power. Is there a rule fo thumb for
  a known good SWR value thru a duplexer? Should a good duplexer introduce
  any significant SWR?

  Thanks

  Bernie Parker

  K5BP



   

Re: [Repeater-Builder] Duplexers

[rfd rfd]

>From the Dup. to the Ant. is ok. But the Dup. is out of tune or no good. Might 
>even be a bad jumper on the Dup. 

dallasreact112 <[EMAIL PROTECTED]> wrote:  Anyone one know what to expect SWR 
wise with a duplexer?
I have a DB products 2 meter duplexer on an amateur repeater.
Measuring with a Bird wattmeter between the duplexer and antenna I
read 50W forward and a couple watts reverse. That is ok. But when I
check between the transmitter and the TX port on the duplexer I get a
about 60 W forward and 25W reverse power. Is there a rule fo thumb for
a known good SWR value thru a duplexer? Should a good duplexer introduce
any significant SWR?

Thanks

Bernie Parker

K5BP






Yahoo! Groups Links

Re: [Repeater-Builder] Duplexers

[Ron Wright]

Bernie,

A typical VSWR for a duplexer would be 1.5:1 or less, more like less.  Will not 
be 1:1 most times, but low.  A lot lower than your 65/25W which is more like a 
4.5:1 VSWR.

Really sounds as the duplexer is out of tune or has an internal problem.

Wonder if you tuned these from another band such as 150-160 down to 144-148.  
Did you keep the upper freq on the same side and the lower on the new lower???  
Often one should keep the same even if the upper/lower is say tx/rx and the new 
is upper/lower rx/tx.  Not always, but have seen a problem if one tries to 
reverse the cavity sides, make upper side the lower freq just because one says 
tx and the other rx and try to keep on same side, but reverse the upper/lower.  
This is getting confusing, hi.

73, ron, n9ee/r



>From: dallasreact112 <[EMAIL PROTECTED]>
>Date: 2007/08/24 Fri PM 07:16:22 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: [Repeater-Builder] Duplexers

>  
>Anyone one know what to expect SWR wise with a duplexer?
>I have a DB products 2 meter duplexer on an amateur repeater.
>Measuring with a Bird wattmeter between the duplexer and antenna I
>read 50W forward and a couple watts reverse. That is ok. But when I
>check between the transmitter and the TX port on the duplexer I get a
>about 60 W forward and 25W reverse power. Is there a rule fo thumb for
>a known good SWR value thru a duplexer? Should a good duplexer introduce
>any significant SWR?
>
>Thanks
>
>Bernie Parker
>
>K5BP
>
>


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

RE: [Repeater-Builder] Duplexers

[Eric Lemmon]

Bernie,

When you put the Bird between the TX and the duplexer, you have changed the
length of the jumper cable, which upset the tuning.  But, really, you need
not worry about what the SWR is, if the forward power to the antenna is
appropriate.

Let's say you have a 4-can duplexer, which might have about 1.5 dB insertion
loss.  If your power amp delivers exactly 100 watts into a dummy load when
connected directly at the TX output, you should expect about 70 watts going
to the antenna when the duplexer is in the circuit.  A 6-can duplexer might
have about 2.2 dB insertion loss, and you should see about 59 watts going to
the antenna.

73, Eric Lemmon WB6FLY


 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of dallasreact112
Sent: Friday, August 24, 2007 5:16 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Duplexers

Anyone one know what to expect SWR wise with a duplexer?
I have a DB products 2 meter duplexer on an amateur repeater.
Measuring with a Bird wattmeter between the duplexer and antenna I
read 50W forward and a couple watts reverse. That is ok. But when I
check between the transmitter and the TX port on the duplexer I get a
about 60 W forward and 25W reverse power. Is there a rule fo thumb for
a known good SWR value thru a duplexer? Should a good duplexer introduce
any significant SWR?

Thanks

Bernie Parker

K5BP

RE: [Repeater-Builder] Duplexers

[Ralph Mowery]

--- Eric Lemmon <[EMAIL PROTECTED]> wrote:

> Bernie,
> 
> When you put the Bird between the TX and the
> duplexer, you have changed the
> length of the jumper cable, which upset the tuning. 
> But, really, you need
> not worry about what the SWR is, if the forward
> power to the antenna is
> appropriate.
> 
> Let's say you have a 4-can duplexer, which might
> have about 1.5 dB insertion
> loss.  If your power amp delivers exactly 100 watts
> into a dummy load when
> connected directly at the TX output, you should
> expect about 70 watts going
> to the antenna when the duplexer is in the circuit. 
> A 6-can duplexer might
> have about 2.2 dB insertion loss, and you should see
> about 59 watts going to
> the antenna.
> 
> 73, Eric Lemmon WB6FLY
> 
> 

When the wattmeter is inserted it will not upset the
tuning of the duplexer enough to reflect that kind of
power. 

About all it could do is upset the tuning of the
transmitter so that it will not put out the same
ammount of forward power.  This should not have much
effect of the reflected power.

One thing that could be (but not likely) is the
transmitter is producing spurs and harmonices the
duplexer is not letting pass to the antenna and is
being reflected back.



   

Boardwalk for $500? In 2007? Ha! Play Monopoly Here and Now (it's updated for 
today's economy) at Yahoo! Games.
http://get.games.yahoo.com/proddesc?gamekey=monopolyherenow  

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning.  

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer.  It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself.  

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

-
Jeff DePolo - [EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030

RE: [Repeater-Builder] Duplexers

[Eric Lemmon]

My statement regarding "tuning" did not explicitly refer to the actual
tuning of the duplexer, but to the matching of the TX and duplexer in
combination.  This can be proven if two Birds are used, one between the TX
and the duplexer input and the other between the duplexer output and the
antenna.  In the majority of cases I have witnessed, adding a Bird between
the TX and the duplexer will cause the forward power shown on the other Bird
to change significantly.  To avoid the misunderstanding, perhaps I should
have used the term impedance match.

73, Eric Lemmon WB6FLY
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Friday, August 24, 2007 9:30 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning. 

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer. It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself. 

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

RE: [Repeater-Builder] Duplexers

[Ralph Mowery]

--- Jeff DePolo <[EMAIL PROTECTED]> wrote:

> > When you put the Bird between the TX and the
> duplexer, you 
> > have changed the
> > length of the jumper cable, which upset the
> tuning.  
> 
> Adding a wattmeter or any other length of cable
> between the transmitter and
> the duplexer Tx input port has no effect on the
> tuning of the duplexer.  It
> may change the load Z the transmitter sees, which
> may make the transmitter
> happier (or sadder) depending on the resulting Z,
> but in no way does it
> alter the tuning of the duplexer itself.  
> 
> 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
>
Jeff you have just made two statements that are the
exect opposit of each other.  If changing the length
of cable makes a differance, then the swr as seen by
the transmitter must change.

As some transmitters can not be tuned for impedance
mismatch, adding lengths of line may change the
impedance where the transmitter will produce the
maximan ammout of power out.  

If say the duplexer is setup for a 50 ohm load and the
transmitter wants to load into a 60 ohm load, then
changing the length of cable between the duplexer and
transmitter may let the transmitter see 60 ohms
instead of 50 ohms.  The swr will not really change on
the line as a whole, but at a given point it may match
the impedance of the transmitter for maximum power
transfer.



   

Moody friends. Drama queens. Your life? Nope! - their life, your story. Play 
Sims Stories at Yahoo! Games.
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Re: [Repeater-Builder] Duplexers

[Jesse Lloyd]

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.

Also with cans usually, if I have enough time on my hands, I tune them one
way (higher frequency = cans marked TX), then the other (lower frequency =
cans marked TX).  Almost every time you'll get a different outcome.  Which
way you tune them in the end depends on your situation, weather your putting
out lots of TX power and need the isolation, or if you care about receive
sensitivity.  I find that usually one side of the duplexer will have a
better insertion loss than the other, while the other will have better null
than the other.  The one with better insertion loss I usually put on the RX
side (I can simply bump the TX power by a dB to compensate for the extra
loss).  This of course only applies to cans where you can not set the
insertion loss.  For cans that you can change the insertion loss you can
spend hours on fiddleing.

If you take your transmitter and put it into a dummy load what's its TX
power?

Also no one mentioned this (I think), but check you cables and connectors, I
had one that was bad, produced a bunch of swr, cans were fine.

Jesse



On 8/25/07, Ralph Mowery <[EMAIL PROTECTED]> wrote:
>
>
> --- Jeff DePolo <[EMAIL PROTECTED] > wrote:
>
> > > When you put the Bird between the TX and the
> > duplexer, you
> > > have changed the
> > > length of the jumper cable, which upset the
> > tuning.
> >
> > Adding a wattmeter or any other length of cable
> > between the transmitter and
> > the duplexer Tx input port has no effect on the
> > tuning of the duplexer. It
> > may change the load Z the transmitter sees, which
> > may make the transmitter
> > happier (or sadder) depending on the resulting Z,
> > but in no way does it
> > alter the tuning of the duplexer itself.
> >
> > 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
> >
> Jeff you have just made two statements that are the
> exect opposit of each other. If changing the length
> of cable makes a differance, then the swr as seen by
> the transmitter must change.
>
> As some transmitters can not be tuned for impedance
> mismatch, adding lengths of line may change the
> impedance where the transmitter will produce the
> maximan ammout of power out.
>
> If say the duplexer is setup for a 50 ohm load and the
> transmitter wants to load into a 60 ohm load, then
> changing the length of cable between the duplexer and
> transmitter may let the transmitter see 60 ohms
> instead of 50 ohms. The swr will not really change on
> the line as a whole, but at a given point it may match
> the impedance of the transmitter for maximum power
> transfer.
>
> __
> Moody friends. Drama queens. Your life? Nope! - their life, your story.
> Play Sims Stories at Yahoo! Games.
> http://sims.yahoo.com/
>  
>

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> 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 on the line between the transmitter and the duplexer is anything
other than 1:1, THERE DOES NOT EXIST a point along that line where the
impedence is 50+j0.

Line losses go up with VSWR, but coax doesn't radiate unless there are
currents flowing on the shield, and those aren't a function of VSWR on the
line.

--- Jeff

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> Jeff you have just made two statements that are the
> exect opposit of each other.  If changing the length
> of cable makes a differance, then the swr as seen by
> the transmitter must change.

Re-read what I said.  Changing the cable length changes the *Z*, but it
doesn't change the *VSWR*.  As you vary the cable length, the Z changes in a
cyclical fashion, but always remains at a constant VSWR.  For any given
VSWR, there are an infinite number of complex Z's that will produce that
VSWR.

> As some transmitters can not be tuned for impedance
> mismatch, adding lengths of line may change the
> impedance where the transmitter will produce the
> maximan ammout of power out.  

Yes.  But it doesn't change the VSWR.

> If say the duplexer is setup for a 50 ohm load and the
> transmitter wants to load into a 60 ohm load, then
> changing the length of cable between the duplexer and
> transmitter may let the transmitter see 60 ohms
> instead of 50 ohms.  

Not if the cables your using are also 50 ohms.  If the duplexer presents a
50 ohms like you said, you can use whatever cable lengths you want and the
resulting Z as seen by the transmitter 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

RE: [Repeater-Builder] Duplexers

[R. K. Brumback]

I have heard this point argued for years. “Does trimming the coax affect the
SWR?”  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II’s. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.

Randy

W4CPT

 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Saturday, August 25, 2007 12:30 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers

 

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning. 

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer. It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself. 

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

-
Jeff DePolo - HYPERLINK "mailto:jd1%40broadsci.com"[EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030

 


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Checked by AVG Free Edition.
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Checked by AVG Free Edition. 
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Re: [Repeater-Builder] Duplexers

[Jesse Lloyd]

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
min voltage peaks.  Also current will go up and down too.  When you are
using a VSWR meter you are measuring voltage, if you move the meter to a
different spot on the cable, the voltage is different, therefor it gives you
a different reading.

Now if you put a voltage null at your transmitter, what would happen?
Normally with high SWR your transmitter will get hot because its dissipating
the reflected power into its heatsink.  If you put it at a voltage null, I
would suspect that the SWR would not get dissipated by the transmitter as
much as if you put it at a voltage peak.  The standing waves are still
there, there is still a mismatch, you will get the same power out, but its
just not going to hurt your transmitter as much because of the heat.

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that.

Jesse

On 8/27/07, R. K. Brumback <[EMAIL PROTECTED]> wrote:
>
>I have heard this point argued for years. "Does trimming the coax
> affect the SWR?"  If the length of coax has an affect on impedance, then how
> could it not affect power out? We strive to maintain 50 ohms at the tail of
> all devices to match the end load. GE puts matching networks in their Mastr
> II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
> started trimming the coax down and watched the impedance change
> significantly with each cut. Duplexers come with precise lengths of cabling.
>  I have heard that trimming coax only fools the meter. Not being an engineer
> with millions worth of equipment I can only make a SWAG (scientific wild ass
> guess) as to whether coax length makes a difference in power out.
>
> Randy
>
> W4CPT
>
>
>
> -Original Message-
> *From:* Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED]
> ups.com] *On Behalf Of *Jeff DePolo
> *Sent:* Saturday, August 25, 2007 12:30 AM
> *To:* Repeater-Builder@yahoogroups.com
> *Subject:* RE: [Repeater-Builder] Duplexers
>
>
>
> > When you put the Bird between the TX and the duplexer, you
> > have changed the
> > length of the jumper cable, which upset the tuning.
>
> Adding a wattmeter or any other length of cable between the transmitter
> and
> the duplexer Tx input port has no effect on the tuning of the duplexer. It
> may change the load Z the transmitter sees, which may make the transmitter
> happier (or sadder) depending on the resulting Z, but in no way does it
> alter the tuning of the duplexer itself.
>
> 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
>
> -
> Jeff DePolo - [EMAIL PROTECTED] 
> Broadcast Sciences LLC, Valley Forge PA
> v: 610.917.3000
> f: 610.917.3030
>
>
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007
> 12:00 AM
>
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007
> 12:00 AM
>
>  
>

RE: [Repeater-Builder] Duplexers

[n9wys]

One can also use 1/4- and 1/2- λ stubs of coaxial cable of the same
impedance as matching networks in conjunction with a "Tee" connector.
"Shorting" or "Opening" the end of the matching stub also makes a
difference, based upon the length being employed.

I believe that VSWR is *one* reason that cabling on a duplexer must be a
function of length, based upon a fraction of the characteristic frequency.
But not being a "duplexer person" I'm not all that familiar with the precise
engineering behind their interconnecting cabling.

Mark - N9WYS


From: Repeater-Builder@yahoogroups.com On Behalf Of Jesse Lloyd

--- snip ---

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that. 

Jesse

On 8/27/07, R. K. Brumback wrote:
I have heard this point argued for years. "Does trimming the coax affect the
SWR?"  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
 I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.
Randy
W4CPT
 





 
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RE: [Repeater-Builder] Duplexers

[R. K. Brumback]

Quote from Jesse: “When you are using a VSWR meter you are measuring
voltage, if you move the meter to a different spot on the cable, the voltage
is different, therefore it gives you a different reading.”

 

This now makes more sense to me as I once saw a feed line demonstration with
voltage and current sleds showing the difference at different points along
the line. At some places the voltage was null (as with any sine wave). I
don’t see how this could happen at the antenna port of a transmitter unless
it was microwave as the cabling from the tuner to the output connector is
not near ½ wave.  Also to Alan, I appreciate your sympathy for us “little
people” but I do find this very interesting. And as you can see, the experts
sometimes need a tune up.

Randy

W4CPT

 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd
Sent: Monday, August 27, 2007 12:48 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
min voltage peaks.  Also current will go up and down too.  When you are
using a VSWR meter you are measuring voltage, if you move the meter to a
different spot on the cable, the voltage is different, therefor it gives you
a different reading. 

Now if you put a voltage null at your transmitter, what would happen?
Normally with high SWR your transmitter will get hot because its dissipating
the reflected power into its heatsink.  If you put it at a voltage null, I
would suspect that the SWR would not get dissipated by the transmitter as
much as if you put it at a voltage peak.  The standing waves are still
there, there is still a mismatch, you will get the same power out, but its
just not going to hurt your transmitter as much because of the heat. 

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that. 

Jesse

On 8/27/07, R. K. Brumback mailto:[EMAIL PROTECTED]"[EMAIL PROTECTED]> wrote:

I have heard this point argued for years. "Does trimming the coax affect the
SWR?"  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.

Randy

W4CPT

 

-Original Message-
From: HYPERLINK
"mailto:Repeater-Builder@yahoogroups.com"[EMAIL PROTECTED]
[mailto:HYPERLINK "mailto:Repeater-"; [EMAIL PROTECTED] HYPERLINK
"http://ups.com"; \nups.com] On Behalf Of Jeff DePolo
Sent: Saturday, August 25, 2007 12:30 AM
To: HYPERLINK
"mailto:Repeater-Builder@yahoogroups.com"[EMAIL PROTECTED]
Subject: RE: [Repeater-Builder] Duplexers

 

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning. 

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer. It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself. 

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

-
Jeff DePolo - HYPERLINK "mailto:jd1%40broadsci.com"; [EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030

 

No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007 12:00
AM

 

No

RE: [Repeater-Builder] Duplexers

[n9wys]

Randy, the null repeats at - IIRC - odd ½-λ intervals. so if the cable was
cut to a length equal to an odd multiple of ½ of the wavelength (1/2, 3/2,
5/2, etc.) you would see the null at the transmitter end repetitively.
Regarding your reference to microwave, it doesn't matter what the frequency
range is - it could be HF, VHF, UHF of SHF. so you could make this occur as
long as your cable was cut to ½ wavelength.  This only becomes "difficult"
at HF frequencies, where ½ of a wavelength might be, for example, 40 meters
long for the 80m band.  But when you get to VHF your cable is now
considerably more "manageable", such as for 2m - only 1 meter long, or
approximately a bit over 3'.

 

I also think I remember that voltage and current are at opposites along the
cable - where voltage is lowest, current is highest. and vice versa.

 

I'm not in radio as a profession, so I don't work with this stuff on a
day-to-day basis - therefore my memory may be a bit foggy regarding this
phenomenon. 

 

Now putting on my flame-proof underwear.  ;-)

73 de Mark - N9WYS

 

  _  

From: Repeater-Builder@yahoogroups.com On Behalf Of R. K. Brumback



Quote from Jesse: "When you are using a VSWR meter you are measuring
voltage, if you move the meter to a different spot on the cable, the voltage
is different, therefore it gives you a different reading."

 

This now makes more sense to me as I once saw a feed line demonstration with
voltage and current sleds showing the difference at different points along
the line. At some places the voltage was null (as with any sine wave). I
don't see how this could happen at the antenna port of a transmitter unless
it was microwave as the cabling from the tuner to the output connector is
not near ½ wave.  Also to Alan, I appreciate your sympathy for us "little
people" but I do find this very interesting. And as you can see, the experts
sometimes need a tune up.

Randy

W4CPT

 

-Original Message-
From: Repeater-Builder@yahoogroups.com On Behalf Of Jesse Lloyd
Sent: Monday, August 27, 2007 12:48 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
min voltage peaks.  Also current will go up and down too.  When you are
using a VSWR meter you are measuring voltage, if you move the meter to a
different spot on the cable, the voltage is different, therefor it gives you
a different reading. 

Now if you put a voltage null at your transmitter, what would happen?
Normally with high SWR your transmitter will get hot because its dissipating
the reflected power into its heatsink.  If you put it at a voltage null, I
would suspect that the SWR would not get dissipated by the transmitter as
much as if you put it at a voltage peak.  The standing waves are still
there, there is still a mismatch, you will get the same power out, but its
just not going to hurt your transmitter as much because of the heat. 

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that. 

Jesse

On 8/27/07, R. K. Brumback <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
org> wrote:

I have heard this point argued for years. "Does trimming the coax affect the
SWR?"  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.

Randy

W4CPT


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Checked by AVG Free Edition.
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RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> 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 source end of the line (i.e. the transmitter
end) WILL vary depending on the length of the coax.

Don't confuse Z with VSWR.  The two are related, but you can't use them
interchangably.

> Now if you put a voltage null at your transmitter, what would 
> happen?  Normally with high SWR your transmitter will get hot 
> because its dissipating the reflected power into its 
> heatsink.  

No, that's not right.  Reflected power doesn't get dissipated into the
heatsink, unless the transmitter happens to have an isolator on its output,
in which case most of the reflected power ends up in the reject load which
sometimes is mounted to the same heatsink as the devices, but that's really
stretching...

A mismatch between the transmitter and the load can result in lots of
things.  It may cause the amplifier's efficiency to degrade as the devices
are no longer able to transfer power to the load efficiently, but that's
only one possibility.  In some cases, it might actually cause the
transmitter to make more power, sometimes at higher or lower efficiency,
depending on many factors related to the design of the amplifier itself.  If
the matching network (if one xists) was adjusted to properly match the PA to
the mis-matched load, all of the power (minus transmission line losses) will
ultimately get to the antenna.

> The only time coax length makes a difference to power out is 
> if your using it in a matching stub, or a matching section 
> ie. if you take 1/4 wave of 75 ohm cable put it on the end of 
> 50 ohm cable you will get a match with a 112.5 ohm load.

Coax itself doesn't affect the power output.  The LOAD IMPEDANCE that
terminates the transmitter, and how the transmitter is (or isn't) matched to
that load is what affects the power output in real-world transmitters.
Varying the length of the coax MAY result in a change in the transmitter's
power output when the VSWR is not 1:1 because the coax acts as a
transformer.  It transforms the antenna's mis-matched feedpoint Z to some
other Z at the far (transmitter) end.  

Since a perfect 50+j0 match is practically impossible to achieve, coax (or
any other form of transmission line) will virtually ALWAYS act as a
transformer except at exact half-wavelength multiples.

> You make an interesting point though, why does the cabling of 
> duplexer's need to be a certain length.  

If you're talking about the cables within the duplexer harness, the reason
is to properly repeat and transform impedances.  The simplest example I can
give you is to consider what happens at the antenna tee of a duplexer.  At
the transmit frequency, one side of the tee feeds the transmit side of the
duplexer which presents a good match.  Looking toward the opposite side of
the tee, the receive side of the duplexer typically presents a SHORT at the
transmit frequency (typical of a pass/reject cavity).  By offsetting that
SHORT by a 1/4 wavelength section of cable going to the tee, the SHORT gets
transformed to an OPEN, therefore no power can flow in that undesired
direction.

Maybe it's time for somebody to do a "Smith Chart 101" article.  No, I'm not
volunteering myself :-)

--- Jeff

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> 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 1:1).

Changling the length of the line DOES NOT change the VSWR on the line.

Both of these statements ignore feedline losses, which are negligible when
we're talking about adding or subtracting a few inches or a few feet of
cable at HF/VHF/UHF frequencies for the kinds of cable we normally deal
with.  The more cable loss, the lower the VSWR will be at the source end.
Likewise, the longer the cable, the closer the Z at the source end will be
to the cable's characteristic impedance.

> We strive 
> to maintain 50 ohms at the tail of all devices to match the 
> end load. GE puts matching networks in their Mastr II's. I 
> have taken a MFJ-259 and soldered a PL259 only at one end and 
> then started trimming the coax down and watched the impedance 
> change significantly with each cut. Duplexers come with 
> precise lengths of cabling.  I have heard that trimming coax 
> only fools the meter. Not being an engineer with millions 
> worth of equipment I can only make a SWAG (scientific wild 
> ass guess) as to whether coax length makes a difference in power out.

Everything you just said above is right.  I think what has you confused is
that you're thinking that Z and VSWR are interchangable.  They aren't.  Z
changes with coax length.  VSWR does not.

--- Jeff

Re: [Repeater-Builder] Duplexers

[Nate Duehr]

As a side note for this discussion, I think Jeff's doing a great job of 
explaining how transmission line theory works...

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 enough that a mathematical dolt like myself can still 
follow the concepts and not scratch my head at the math.

Too bad the book is something like $70 bucks... I won my copy as a door 
prize at a hamfest or I'd have never bought one... the book is 
definitely worth the "price of admission" and the CD along with it 
contains some useful tools that just add to the value...

Nate WY0X

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> 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 enough that a mathematical dolt like myself can still 
> follow the concepts and not scratch my head at the math.

Another good, readily-available book is "Reflections" by Walt Maxwell W2DU.
My copy is old; he put out an updated edition "Reflections II" later.  It's
a good read, but has one drawback (to me anyway).  A lot of what he
discusses relates to pi matching networks common in tube HF rigs.  You have
to keep in mind that a lot of the myths he dispels don't always translate
directly to the world of VHF/UHF solid state amplifiers, but theory behind
what he preaches is dead nuts on.

--- Jeff

RE: [Repeater-Builder] Duplexers

[Gary Schafer]

VSWR (voltage standing wave ratio) will be the same at any point on a
transmission  line. The imaginary standing wave does not move as the forward
and reflected power does. The voltage standing wave ratio is the ratio of
the forward voltage to the reflected voltage at a given point on the line.
As you move up or down the line the forward voltage will change and so will
the reflected voltage but the ratio or difference between the two will work
out to the same value. Thus the term "standing wave". The wave appears to
stand still on the line as it oscillates up and down in a sin wave manor. 

 

As Jeff has said the impedance shown to the transmitter will be different
with different lengths of transmission line only if the load is not a
perfect 50 ohms assuming a 50 ohm line. With a load that does not match the
line the line operates as an impedance transformer. Think about what a
quarter wave length line looks like with a short on one end. It transforms
that short to a high impedance or open at the other end. If one end is open
the other end will look like a short to the transmitter.

With a load impedance that is not 50 ohms what is seen at the transmitter is
something between an open and a short depending on how far from 50 ohms the
load is. In other words the load impedance gets "transformed" to something
else.

 

73

Gary  K4FMX

 

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd
Sent: Monday, August 27, 2007 11:48 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
min voltage peaks.  Also current will go up and down too.  When you are
using a VSWR meter you are measuring voltage, if you move the meter to a
different spot on the cable, the voltage is different, therefor it gives you
a different reading. 

Now if you put a voltage null at your transmitter, what would happen?
Normally with high SWR your transmitter will get hot because its dissipating
the reflected power into its heatsink.  If you put it at a voltage null, I
would suspect that the SWR would not get dissipated by the transmitter as
much as if you put it at a voltage peak.  The standing waves are still
there, there is still a mismatch, you will get the same power out, but its
just not going to hurt your transmitter as much because of the heat. 

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that. 

Jesse

On 8/27/07, R. K. Brumback <[EMAIL PROTECTED]> wrote:

I have heard this point argued for years. "Does trimming the coax affect the
SWR?"  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.

Randy

W4CPT

 

-Original Message-
From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED]
ups.com] On Behalf Of Jeff DePolo
Sent: Saturday, August 25, 2007 12:30 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers

 

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning. 

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer. It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself. 

Adding or removing cable lengths between the transmitter and duplexer also
does not change the VSWR as seen by the transmit

Re: [Repeater-Builder] Duplexers

[Jesse Lloyd]

If your coax is the same impedance as your transmitter, but different than
your load, can it still be a transformer though?  Is it possible to
transform a load that isn't 50 ohms to 50 ohms using 50 ohm coax?

Yes your right VSWR is the ratio between Vmax and Vmin, node and anodes, of
the interference pattern caused by standing waves.  Even still there is a
point where the voltage is at a minimum on the line.  What happens if that
point is at the transmitters output... does it help keep the heat down in
the transmitter due to high SWR?



On 8/27/07, Gary Schafer <[EMAIL PROTECTED]> wrote:
>
>VSWR (voltage standing wave ratio) will be the same at any point on a
> transmission  line. The imaginary standing wave does not move as the forward
> and reflected power does. The voltage standing wave ratio is the ratio of
> the forward voltage to the reflected voltage at a given point on the line.
> As you move up or down the line the forward voltage will change and so will
> the reflected voltage but the ratio or difference between the two will work
> out to the same value. Thus the term "standing wave". The wave appears to
> stand still on the line as it oscillates up and down in a sin wave manor.
>
>
>
> As Jeff has said the impedance shown to the transmitter will be different
> with different lengths of transmission line only if the load is not a
> perfect 50 ohms assuming a 50 ohm line. With a load that does not match the
> line the line operates as an impedance transformer. Think about what a
> quarter wave length line looks like with a short on one end. It transforms
> that short to a high impedance or open at the other end. If one end is open
> the other end will look like a short to the transmitter.
>
> With a load impedance that is not 50 ohms what is seen at the transmitter
> is something between an open and a short depending on how far from 50 ohms
> the load is. In other words the load impedance gets "transformed" to
> something else.
>
>
>
> 73
>
> Gary  K4FMX
>
>
>
>
>   --
>
> *From:* Repeater-Builder@yahoogroups.com [mailto:
> [EMAIL PROTECTED] *On Behalf Of *Jesse Lloyd
> *Sent:* Monday, August 27, 2007 11:48 AM
> *To:* Repeater-Builder@yahoogroups.com
> *Subject:* Re: [Repeater-Builder] Duplexers
>
>
>
> The length of coax doesn't effect impedance.  Trimming the coax effects
> what is read on the VSWR meter because what is actually happening is that
> there is an interference pattern created when you have a mismatch on the end
> of feedline.  This pattern is sinusoidal and changes in voltage and current
> along the line, in 1/2 wave periods.  You will find max voltage peaks and
> min voltage peaks.  Also current will go up and down too.  When you are
> using a VSWR meter you are measuring voltage, if you move the meter to a
> different spot on the cable, the voltage is different, therefor it gives you
> a different reading.
>
> Now if you put a voltage null at your transmitter, what would happen?
> Normally with high SWR your transmitter will get hot because its dissipating
> the reflected power into its heatsink.  If you put it at a voltage null, I
> would suspect that the SWR would not get dissipated by the transmitter as
> much as if you put it at a voltage peak.  The standing waves are still
> there, there is still a mismatch, you will get the same power out, but its
> just not going to hurt your transmitter as much because of the heat.
>
> The only time coax length makes a difference to power out is if your using
> it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
> ohm cable put it on the end of 50 ohm cable you will get a match with a
> 112.5 ohm load.
>
> You make an interesting point though, why does the cabling of duplexer's
> need to be a certain length.  I would suspect that its because they are
> looped and make an inductor. This then is part of the LC filtering, and
> changing the length effects L.  But I could be wrong on that.
>
> Jesse
>
> On 8/27/07, *R. K. Brumback* <[EMAIL PROTECTED]> wrote:
>
> I have heard this point argued for years. "Does trimming the coax affect
> the SWR?"  If the length of coax has an affect on impedance, then how could
> it not affect power out? We strive to maintain 50 ohms at the tail of all
> devices to match the end load. GE puts matching networks in their Mastr
> II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
> started trimming the coax down and watched the impedance change
> significantly with each cut. Duplexers come with precise lengths of cabling.
>  I have heard that trimming coax only fools the meter. Not being an engineer
> with millions worth

RE: [Repeater-Builder] Duplexers

[Gary Schafer]

 

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd
Sent: Monday, August 27, 2007 9:39 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

If your coax is the same impedance as your transmitter, but different than
your load, can it still be a transformer though?  Is it possible to
transform a load that isn't 50 ohms to 50 ohms using 50 ohm coax? 

 

Yes it always acts as a transformer when the load impedance is not the same
as the coax impedance.

You can not transform any impedance to 50 ohms with a 50 ohm cable. You can
transform to something above or below the 50 ohm cable impedance.

The reason changing the length of the coax to a transmitter helps sometimes,
even though the transformation of impedance is not to 50 ohms, is that the
transmitter may see an impedance that it is happier with than what the
original transformed impedance was.



Yes your right VSWR is the ratio between Vmax and Vmin, node and anodes, of
the interference pattern caused by standing waves.  Even still there is a
point where the voltage is at a minimum on the line.  What happens if that
point is at the transmitters output... does it help keep the heat down in
the transmitter due to high SWR?

 

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.

If you have a 100 watt transmitter with 10 watts reflected from the load
your wattmeter will read 110 watts forward and 10 watts reflected. The extra
10 watts forward power comes from the 10 watts that is reflected from the
load and re-reflected at the transmitter. The re-reflected power adds to the
original 100 watts forward power for a total of 110 watts forward power. All
of the 100 watts eventually gets radiated by the antenna. This is of course
disregarding any line loss which would lower the reflected power indication
by the amount of line loss. Line loss would also claim a portion of the
re-reflected power too.

If you have two watt meters and an antenna matching device you can put one
wattmeter between the transmitter and the matching device and tune it for
minimum reflected power on the first meter. Then with a second meter between
the tuner and the mismatched load you can see the second wattmeter that is
reading the reflected power. The second wattmeter will have a higher forward
power reading than the first due to the added re-reflected power.

 

With a mismatched load the transmitter may run hotter because it is under or
overloaded due to the non 50 ohm load that it is seeing but it is not
dissipating any of the reflected power. Many solid state transmitters are
sensitive to reactive loads  and may draw more current because of this.

 

73

Gary  K4FMX






On 8/27/07, Gary Schafer <[EMAIL PROTECTED]> wrote:

VSWR (voltage standing wave ratio) will be the same at any point on a
transmission  line. The imaginary standing wave does not move as the forward
and reflected power does. The voltage standing wave ratio is the ratio of
the forward voltage to the reflected voltage at a given point on the line.
As you move up or down the line the forward voltage will change and so will
the reflected voltage but the ratio or difference between the two will work
out to the same value. Thus the term "standing wave". The wave appears to
stand still on the line as it oscillates up and down in a sin wave manor. 

 

As Jeff has said the impedance shown to the transmitter will be different
with different lengths of transmission line only if the load is not a
perfect 50 ohms assuming a 50 ohm line. With a load that does not match the
line the line operates as an impedance transformer. Think about what a
quarter wave length line looks like with a short on one end. It transforms
that short to a high impedance or open at the other end. If one end is open
the other end will look like a short to the transmitter.

With a load impedance that is not 50 ohms what is seen at the transmitter is
something between an open and a short depending on how far from 50 ohms the
load is. In other words the load impedance gets "transformed" to something
else.

 

73

Gary   K4FMX

 

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd
Sent: Monday, August 27, 2007 11:48 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
mi

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> 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.  The Z at the source end of the line is a function of only
three things: the load Z (antenna, duplexer, whatever), the cable's
characteristic Z, and the cable's electrical length (in
degrees/wavelengths/radians/whatever).  

Cable loss also plays into it, as its effect is to always bring the load Z
closer to the cable's characteristic Z as cable loss goes up, but let's
leave that out for the sake of simplicity.

The source device's impedance does not factor into the equation at all when
it comes to determining what the resultant Z is at the source end of the
line.  Any mismatch that occurs at that end of the line (the
source/transmitter end) does NOT affect the VSWR on the line, nor does it
change the Z at the source end of the line.

It's very important to not put the cart before the horse here.  While it may
seem to be contrary to instinct, the device that is sourcing the power is
NOT what determinates what happens on the transmission line with respect Z
and VSWR, it's the LOAD mismatch that sets up the standing waves and the
resulting Z's along the length of the line.  It is for this reason that your
transmitter CANNOT "detune" your duplexer, and for the same reason, you
can't "tune" (change the Z) of your antenna from the far end of the cable.

> Is it possible to transform a load that isn't 50 ohms to 50 ohms using 50
ohm coax? 

NO.

> Yes your right VSWR is the ratio between Vmax and Vmin, node 
> and anodes, of the interference pattern caused by standing 
> waves.  Even still there is a point where the voltage is at a 
> minimum on the line.  What happens if that point is at the 
> transmitters output... does it help keep the heat down in the 
> transmitter due to high SWR?

NO.  VSWR on a transmission line doesn't directly manifest as "heat" in a
transmitter.  The whole notion of high VSWR creating heat in a transmitter
is likely based on a drop in efficiency in SOME transmitters when they are
not properly matched to the feedline.  You can have a very high VSWR on the
feedline, and provided the transmitter is matched to the Z at the source end
of the line, the efficiency will not suffer, and there will be nother ill
effects (including "heating") that occur within the transmitter.

A PROPER MATCH DOES NOT OCCUR WHEN THE TRANSMITTER'S SOURCE Z IS THE SAME AS
THE CABLE'S CHARACTERISTIC Z EXCEPT WHEN THE LOAD Z ALSO MATCHES THE CABLE'S
CHARACTERISTIC Z.  Or, rewritten, if the load Z (antenna) is not 50+j0, a 50
ohm transmitter delivering power into a 50 ohm transmission line will NEVER
be matched.  (Didn't mean to shout, but it's important to understand and
accept that fact.) 

Sidebar: VSWR is a conveniently-simplistic scalar value, but it doesn't tell
you anything about the specific impedance at a particular point along the
line, nor what the ratio and phase relationships are between voltage and
current.  You can calculate VSWR based on a specific Z, but you can't do the
reverse, except in the case of a true 1:1 VSWR.  All Corvettes are Chevys,
but not all Chevys are Corvettes.  You get the idea.  Many hams like to talk
in terms of VSWR as it's a nice easy number to deal with, and the lower the
number, the better.  But that oversimplification seems to also translate
into a relaxation in the attention paid to the theory behind what's really
going on along the transmission line, at the source-to-line interface, and
at the line-to-load interface.  When it really comes down to the nuts and
bolts of designing and building matching networks, you don't care about the
VSWR value, you need to know, think, and design based on complex impedances.

Back in the good ol' days when your rig running 6146's had a pi matching
network on its output, you could tune the transmitter into some not-so-good
loads, often in excess of 3:1 VSWR, without any problem.  Why?  The pi
network did its job, matching the high-Z (and somewhat reactive) output Z of
the tubes to the whatever-Z existed at the end of the antenna feedline.  You
could get efficiency just as good at a 3:1 VSWR as you could at 1:1 because
the output of the matching network provided a conjugate match.

--- Jeff

Re: [Repeater-Builder] Duplexers

[Nate Duehr]

Jeff DePolo wrote:

> NO.  VSWR on a transmission line doesn't directly manifest as "heat" in a
> transmitter.  The whole notion of high VSWR creating heat in a transmitter
> is likely based on a drop in efficiency in SOME transmitters when they are
> not properly matched to the feedline.  

Or worse, a transmitter that when feeding anything other than its design 
Z starts throwing spurs.  In that case, it's output filters (if it has 
any!) may be eating all that "spur" power... because folks set power 
AFTER the final low-pass filter.

I could see that being another possible way you'd get "transmitter 
heating" if things were mismatched.  It wouldn't be as significant as 
the whole PA getting inefficient, though.

Jeff also already mentioned (and set aside for purposes of this 
discussion) transmitters that have built-in directional couplers and 
loads that are mounted to a common heatsink with the PA transistors. 
Moto likes to do this on most of their continuous-duty PA's.

That can cause "heating" too, if reflected power is high, but it's not 
relevant to the discussion at hand, because it's not the transmitter 
heating up, it's the load hanging off of the directional coupler.

Nate WY0X

RE: [Repeater-Builder] Duplexers

[no6b]

At 8/27/2007 20:52, you wrote:

>Yes your right VSWR is the ratio between Vmax and Vmin, node and anodes, 
>of the interference pattern caused by standing waves.  Even still there is 
>a point where the voltage is at a minimum on the line.  What happens if 
>that point is at the transmitters output... does it help keep the heat 
>down in the transmitter due to high SWR?
>
>
>
>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 this.  In order for reflected power to not be absorbed by 
the TX, it would have to appear totally reactive.  Although I've never 
measured one, I don't believe that's the case.

>If you have two watt meters and an antenna matching device you can put one 
>wattmeter between the transmitter and the matching device and tune it for 
>minimum reflected power on the first meter. Then with a second meter 
>between the tuner and the mismatched load you can see the second wattmeter 
>that is reading the reflected power. The second wattmeter will have a 
>higher forward power reading than the first due to the added re-reflected 
>power.

This doesn't sound right either, as there should be no reflected power at 
the antenna if it's been matched further down the line.  The tuner would be 
adjusted so as to create a conjugate impedance of the antenna at the end of 
the feeding coax, thus eliminating the mismatch.

My guess is that the higher power reading on the wattmeter is due to the 
weird impedances it's seeing on both its input & output.

Bob NO6B

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> >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 this.  In order for reflected power to not 
> be absorbed by 
> the TX, it would have to appear totally reactive.

Not necessarily true.  If there exists a conjugate match at the transmitter,
the reflected power will be re-reflected back to the load.  The problem,
though, is most of our solid state repeater amps may exhibit other problems
due to the mis-matched load Z (efficiency drops, PA goes into oscillation,
whatever).

> This doesn't sound right either, as there should be no 
> reflected power at 
> the antenna if it's been matched further down the line.  

There won't be any reflected power if the matching is done *at the antenna*.
If the matching is done at the source end of the line (via a transmatch or
similiar device), which is what I believe the topic of discussion was, then
there will be reflected power (and likewise VSWR) on the feedline if the
load (antenna) Z does not match the cable's characteristic Z.

> My guess is that the higher power reading on the wattmeter is 
> due to the 
> weird impedances it's seeing on both its input & output.

If placed along a length of transmission line that has a VSWR other than
1:1, a directional wattmeter (Bird or similiar) will show the sum of
forward+reflected with the slug rotated to the forward direction due to the
reflected power being re-reflected at the source end.

--- Jeff

RE: [Repeater-Builder] Duplexers

[Gary Schafer]

> -Original Message-
> From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
> [EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
> Sent: Tuesday, August 28, 2007 10:54 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Duplexers
> 
> At 8/27/2007 20:52, you wrote:
> 
> >Yes your right VSWR is the ratio between Vmax and Vmin, node and anodes,
> >of the interference pattern caused by standing waves.  Even still there
> is
> >a point where the voltage is at a minimum on the line.  What happens if
> >that point is at the transmitters output... does it help keep the heat
> >down in the transmitter due to high SWR?
> >
> >
> >
> >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 this.  In order for reflected power to not be absorbed by
> the TX, it would have to appear totally reactive.  Although I've never
> measured one, I don't believe that's the case.
> 
> >If you have two watt meters and an antenna matching device you can put
> one
> >wattmeter between the transmitter and the matching device and tune it for
> >minimum reflected power on the first meter. Then with a second meter
> >between the tuner and the mismatched load you can see the second
> wattmeter
> >that is reading the reflected power. The second wattmeter will have a
> >higher forward power reading than the first due to the added re-reflected
> >power.
> 
> This doesn't sound right either, as there should be no reflected power at
> the antenna if it's been matched further down the line.  The tuner would
> be
> adjusted so as to create a conjugate impedance of the antenna at the end
> of
> the feeding coax, thus eliminating the mismatch.
> 
> My guess is that the higher power reading on the wattmeter is due to the
> weird impedances it's seeing on both its input & output.
> 
> Bob NO6B
> 

Hi Bob,

Please read again what I wrote. I am not sure that you are following how the
meters are in the circuit. Remember that whatever you do at the transmitter
end of a transmission line has no affect on what is going on in the line
itself. The only thing that will change the swr on the line is what you do
at the load.

73
Gary  K4FMX

RE: [Repeater-Builder] Duplexers

[Bob Dengler]

At 8/29/2007 06:40 PM, you wrote:

> > >If you have two watt meters and an antenna matching device you can put
> > one
> > >wattmeter between the transmitter and the matching device and tune it for
> > >minimum reflected power on the first meter. Then with a second meter
> > >between the tuner and the mismatched load you can see the second
> > wattmeter
> > >that is reading the reflected power. The second wattmeter will have a
> > >higher forward power reading than the first due to the added re-reflected
> > >power.
> >
> > This doesn't sound right either, as there should be no reflected power at
> > the antenna if it's been matched further down the line.  The tuner would
> > be
> > adjusted so as to create a conjugate impedance of the antenna at the end
> > of
> > the feeding coax, thus eliminating the mismatch.
> >
> > My guess is that the higher power reading on the wattmeter is due to the
> > weird impedances it's seeing on both its input & output.
> >
> > Bob NO6B
> >
>
>Hi Bob,
>
>Please read again what I wrote. I am not sure that you are following how the
>meters are in the circuit. Remember that whatever you do at the transmitter
>end of a transmission line has no affect on what is going on in the line
>itself. The only thing that will change the swr on the line is what you do
>at the load.
>
>73
>Gary  K4FMX

OK, after talking to a senior RF engineer at lunch here at work I think I 
understand what's going on.  The part that threw me was having the matching 
circuit in the middle of the feedline & the fact that any reflected power 
from the load MUST be totally re-reflected back by the matching circuit, 
otherwise there would be power reflected back to the TX, which by 
definition does not occur in this example.  Because of the multiple 
re-reflections between the matching circuit & load resulting in multiple 
waves back & forth within that coax section, typical single-wave thinking 
doesn't apply.

I guess it's a useful way to illustrate why coax gets lossier if you use a 
tuner far from the antenna.

Bob NO6B

RE: [Repeater-Builder] Duplexers

[Gary Schafer]

> -Original Message-
> From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
> [EMAIL PROTECTED] On Behalf Of Bob Dengler
> Sent: Thursday, August 30, 2007 12:53 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Duplexers
> 
> At 8/29/2007 06:40 PM, you wrote:
> 
> > > >If you have two watt meters and an antenna matching device you can
> put
> > > one
> > > >wattmeter between the transmitter and the matching device and tune it
> for
> > > >minimum reflected power on the first meter. Then with a second meter
> > > >between the tuner and the mismatched load you can see the second
> > > wattmeter
> > > >that is reading the reflected power. The second wattmeter will have a
> > > >higher forward power reading than the first due to the added re-
> reflected
> > > >power.
> > >
> > > This doesn't sound right either, as there should be no reflected power
> at
> > > the antenna if it's been matched further down the line.  The tuner
> would
> > > be
> > > adjusted so as to create a conjugate impedance of the antenna at the
> end
> > > of
> > > the feeding coax, thus eliminating the mismatch.
> > >
> > > My guess is that the higher power reading on the wattmeter is due to
> the
> > > weird impedances it's seeing on both its input & output.
> > >
> > > Bob NO6B
> > >
> >
> >Hi Bob,
> >
> >Please read again what I wrote. I am not sure that you are following how
> the
> >meters are in the circuit. Remember that whatever you do at the
> transmitter
> >end of a transmission line has no affect on what is going on in the line
> >itself. The only thing that will change the swr on the line is what you
> do
> >at the load.
> >
> >73
> >Gary  K4FMX
> 
> OK, after talking to a senior RF engineer at lunch here at work I think I
> understand what's going on.  The part that threw me was having the
> matching
> circuit in the middle of the feedline & the fact that any reflected power
> from the load MUST be totally re-reflected back by the matching circuit,
> otherwise there would be power reflected back to the TX, which by
> definition does not occur in this example.  Because of the multiple
> re-reflections between the matching circuit & load resulting in multiple
> waves back & forth within that coax section, typical single-wave thinking
> doesn't apply.
> 
> I guess it's a useful way to illustrate why coax gets lossier if you use a
> tuner far from the antenna.
> 
> Bob NO6B


Yes coax is lossier with reflected power on it. The part of the power that
gets reflected from the antenna back toward the transmitter gets attenuated
a second time by whatever lose the cable has to begin with. Then when that
portion of the power gets re-reflected at the transmitter end and is on its
way back to the antenna again it suffers attenuation a 3rd time by the coax
so all the re-reflected power does not make it back to the antenna. 
Then a portion of the re-reflected power gets reflected again back toward
the transmitter along with the new wave of power. This repeats itself again
and again adding to the loss but after a few round trips of bouncing up and
down the feed line most of it gets radiated and some has gotten attenuated
to a miniscule amount.
Of course this process is continuously repeated as power is constantly
applied from the transmitter.

But my reason for using the first wattmeter and the tuner was to have a
nearly perfect flat load on the transmitter so that one could see the true
power coming out of the transmitter. 
The second wattmeter after the tuner will then show the higher power which
would be the sum of the forward and re-reflected power so it could be seen
that reflected power does indeed get re-reflected at the transmitter (in
this case at the tuner)and makes its way back to the antenna.

In common applications with just a single wattmeter and no tuner involved
where there is reflected power on the line the wattmeter in the forward
position will show the forward power plus the re-reflected power. To find
power out of the transmitter you would subtract the reflected power shown in
the reverse position from the indicated forward power on the meter. This
works over a wide range of impedances with a bird wattmeter.

73
Gary  K4FMX
 

RE: [Repeater-Builder] Duplexers

[tsoliver]

>
>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 matched Z.

If duplexer in and tx output are not exactly the same then adding or 
subtracting cable lengths can change the vswr the tx sees. 

I have seen this in real life, I do not have a network anylizer so I can not be 
sure what was happening but to make the tx happy some cable was added until the 
reflected power was minimized and the desense went away like magic.

I think the manual that came with my Wacom duplexer talks about this phenomena.


tom

Re: [Repeater-Builder] Duplexers

[Milt]

IIRC the Bird manual had a chart in the back for making up 1/2 wavelength 
coax lines (Bird + coax = 1/2 wl).  If this combination is inserted on the 
input side of the duplexer then the measurement should be fairly correct. 
Other lengths "could" give other readings.

My guess would be a cable problem.

Milt
N3LTQ



- Original Message - 
From: "Eric Lemmon" <[EMAIL PROTECTED]>
To: 
Sent: Saturday, August 25, 2007 1:38 AM
Subject: RE: [Repeater-Builder] Duplexers


> My statement regarding "tuning" did not explicitly refer to the actual
> tuning of the duplexer, but to the matching of the TX and duplexer in
> combination.  This can be proven if two Birds are used, one between the TX
> and the duplexer input and the other between the duplexer output and the
> antenna.  In the majority of cases I have witnessed, adding a Bird between
> the TX and the duplexer will cause the forward power shown on the other 
> Bird
> to change significantly.  To avoid the misunderstanding, perhaps I should
> have used the term impedance match.
>
> 73, Eric Lemmon WB6FLY
>
>
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
> Sent: Friday, August 24, 2007 9:30 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Duplexers
>
>> When you put the Bird between the TX and the duplexer, you
>> have changed the
>> length of the jumper cable, which upset the tuning.
>
> Adding a wattmeter or any other length of cable between the transmitter 
> and
> the duplexer Tx input port has no effect on the tuning of the duplexer. It
> may change the load Z the transmitter sees, which may make the transmitter
> happier (or sadder) depending on the resulting Z, but in no way does it
> alter the tuning of the duplexer itself.
>
> 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
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>

RE: [Repeater-Builder] Duplexers

[Jeff DePolo]

> >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 matched Z.

No, NOT true.  The VSWR always remains the same, only the impedance at the
transmitter end of the interconnect cable going to the duplexer changes.
 
> If duplexer in and tx output are not exactly the same then 
> adding or subtracting cable lengths can change the vswr the tx sees. 

No, it will not.
 
> I have seen this in real life, I do not have a network 
> anylizer so I can not be sure what was happening but to make 
> the tx happy some cable was added until the reflected power 
> was minimized and the desense went away like magic.

Yes, you were changing the Z the transmitter sees.  You were NOT changing
the VSWR.  The two are not the same.  Re-read follow up posts from the last
week or so for further clarification.

--- Jeff

Re: [Repeater-Builder] Duplexers

[Steve S. Bosshard (NU5D)]

Time for an isolated TEE test with a dummy load.  Why did you have the 
duplexers tuned ?  Was there a problem prior?

You should be able to split the duplexer without any trouble - just mark 
things so you can go back as it was.

Best luck and 73, Steve NU5D

[EMAIL PROTECTED] wrote:
> I am having some receive problems on my repeater and I am 
> thinking that it might be desense.  I am on 2M running a 
> MASRII repeater with a Decibal Products band reject 6 can 
> duplexer.
>
> While I can key the repeater from a pretty good distance 
> the audio that makes it through the repeater drops off 
> pretty quickly.  I just had the duplexers tuned and they 
> are tuned very well.
>
> So on to my question.  If I were to take and seperate the 
> recv cans from the xmit cans and run to 2 seperate 
> antennas would that mess up the duplexer tuning?  will 20' 
> of vertical seperation plus the cans and the fact that I 
> would be running through seperate cable, make a 
> difference?
>
> Thanks,
> Vern
> KI4ONW
>
>   

Re: [Repeater-Builder] Duplexers

[Doug Bade]

I would be quite surprised if you are NOT having desense with a Mastr 
II and a 6 can notch only duplexer at 600 khz

Typically a 6 can reject only duplexer is not sufficient isolation at 
600khz for 2 meters with a solid state PA.. Vertical separation or a 
pass/reject duplexer will be needed. 6 can notch only's were designed 
in a time where they were sufficient on Mastr Pro or similar tube 
PA's as they were significantly quieter in band noise off freq...Not 
so with a Mastr II or eq. these days...

A 4 can Pass/reject is just barely enough and usually takes a dump if 
you try to run a Preamp.. on 100w or so repeaters...

A 6 can pass/reject is the ticket if you want to really get the 
receiver working to it's fullest, or separate antennas can help.. 
There are isolation curves for antenna spacing at the repeater 
builder website...

Typically the 6 can notch will make 65-80 db isolation.. from my 
experience you need at least 100db isolation on 2m probably more like 
110 -120...Our TX/RX 6 can pass/reject is in the neighborhood of -127 
db at 600khz on 2 meters

You are on the right track

Doug
KD8B

[EMAIL PROTECTED] wrote:
> > I am having some receive problems on my repeater and I am
> > thinking that it might be desense. I am on 2M running a
> > MASRII repeater with a Decibal Products band reject 6 can
> > duplexer.
> >
> > While I can key the repeater from a pretty good distance
> > the audio that makes it through the repeater drops off
> > pretty quickly. I just had the duplexers tuned and they
> > are tuned very well.
> >
> > So on to my question. If I were to take and seperate the
> > recv cans from the xmit cans and run to 2 seperate
> > antennas would that mess up the duplexer tuning? will 20'
> > of vertical seperation plus the cans and the fact that I
> > would be running through seperate cable, make a
> > difference?
> >
> > Thanks,
> > Vern
> > KI4ONW
> >
> >

Re: [Repeater-Builder] Duplexers

[mung]

I had them tuned because I had just bought them and didn't 
really trust that they were right.  They were very far out 
so it's good that I got them tuned.  I was having the same 
problem as now though very poor receive.  Right now I have 
a radio on there for receive that was getting about 30 
miles of coverage as an Echolink link node with home made 
antenna and now hooked up to the repeater using a big Tram 
Dualband antenna through the duplexer I am lucky if I am 
getting 3 miles.

So I don't think the repeater's built in receiver is the 
problem which leads me to either desense or a bad antenna 
cable.  Transmit is getting out very well and the swr is 
almost 1 to 1 so I think the cable is OK.  I am running 
LMR 400 up the tower 95% of the way.  I just have a short 
coax jumper that goes into the antenna.

I am going to try to split them and see what I get.

Thanks,
Vern
KI4ONW

On Mon, 24 Sep 2007 12:50:48 -0500
  "Steve S. Bosshard (NU5D)" <[EMAIL PROTECTED]> wrote:
> Time for an isolated TEE test with a dummy load.  Why 
>did you have the 
> duplexers tuned ?  Was there a problem prior?
> 
> You should be able to split the duplexer without any 
>trouble - just mark 
> things so you can go back as it was.
> 
> Best luck and 73, Steve NU5D
> 
> [EMAIL PROTECTED] wrote:
>> I am having some receive problems on my repeater and I 
>>am 
>> thinking that it might be desense.  I am on 2M running a 
>> MASRII repeater with a Decibal Products band reject 6 
>>can 
>> duplexer.
>>
>> While I can key the repeater from a pretty good distance 
>> the audio that makes it through the repeater drops off 
>> pretty quickly.  I just had the duplexers tuned and they 
>> are tuned very well.
>>
>> So on to my question.  If I were to take and seperate 
>>the 
>> recv cans from the xmit cans and run to 2 seperate 
>> antennas would that mess up the duplexer tuning?  will 
>>20' 
>> of vertical seperation plus the cans and the fact that I 
>> would be running through seperate cable, make a 
>> difference?
>>
>> Thanks,
>> Vern
>> KI4ONW
>>
>>   
> 

RE: [Repeater-Builder] Duplexers

[Eric Lemmon]

Vern,

Did this problem exist before you had the duplexer tuned?  Was anything at
all done to your repeater system just before the problem was noticed?

A band reject (notch) duplexer may be incapable of performing even
satisfactorily at 2m.  Please advise the model number of your duplexer, so
we can understand your situation.  Are all of your cables double-shielded?
It might be a good idea to perform a noise-floor test using an "iso-tee" and
a service monitor.

Some helpful information about investigating desense problems can be found
here:



73, Eric Lemmon WB6FLY
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
Sent: Monday, September 24, 2007 7:02 AM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Duplexers

I am having some receive problems on my repeater and I am 
thinking that it might be desense. I am on 2M running a 
MASTRII repeater with a Decibel Products band reject 6 can 
duplexer.

While I can key the repeater from a pretty good distance 
the audio that makes it through the repeater drops off 
pretty quickly. I just had the duplexers tuned and they 
are tuned very well.

So on to my question. If I were to take and separate the 
recv cans from the xmit cans and run to 2 separate 
antennas would that mess up the duplexer tuning?  will 20' 
of vertical seperation plus the cans and the fact that I 
would be running through separate cable, make a 
difference?

Thanks,
Vern
KI4ONW


 

Re: [Repeater-Builder] Duplexers

[Steve S. Bosshard (NU5D)]

Decibel did make a 6 cavity notch duplexer - 4" full sized cavities - 
that would work nicely on a 110 Watt  M2 station @ 600 kHz.  Isolated
TEE test into a dummy load - how bad is the receiver desense ?  If you
don't have some test equipment - signal gen, dummy load, and a TEE
fitting with the side pin cut away (makes 60 dB lossy coupling, there
abouts) you probably will need to find someone who does locally that can
help.  73,  Steve NU5D

Eric Lemmon wrote:
> Vern,
>
> Did this problem exist before you had the duplexer tuned?  Was anything at
> all done to your repeater system just before the problem was noticed?
>
> A band reject (notch) duplexer may be incapable of performing even
> satisfactorily at 2m.  Please advise the model number of your duplexer, so
> we can understand your situation.  Are all of your cables double-shielded?
> It might be a good idea to perform a noise-floor test using an "iso-tee" and
> a service monitor.
>
> Some helpful information about investigating desense problems can be found
> here:
>
> 
>
> 73, Eric Lemmon WB6FLY
>  
>
>   

Re: [Repeater-Builder] Duplexers

[Jim Brown]

Our local club recently installed a 2 meter repeater on a water tank adjacent 
to a cell site.  Two cell towers are serviced by four buildings housing 
equipement, and we are having some desense due to noise pickup on the antenna.  
Running an iso-tee we found that our GE Mastr II receiver with GE preamp shows 
.6 uV for 12 dB SINAD using a dummy load in place of the antenna (.2 uV direct 
to the receiver bypassing the duplexer).  With the antenna connected we see a 2 
uV sensitivity for 12 dB SINAD.
   
  These readings are the same, with the repeater transmitter (40 watts) keyed 
or unkeyed.  
   
  The noise floor is really decreasing the utility of the new repeater.  The 
noise source seems to come and go as a quiet signal on the repeater input can 
become suddenly noisey, and vice versa - a noisey signal can become suddenly 
quiet.
   
  I hear the air conditioning units in the cell site buildings cycling and 
wonder if they might be the cause of the noise?  Our antenna is only about 40 
feet above the ground (at 7400 ft) while the cell antennas are at about 100 ft. 
 So we are much closer to the cell site equipment buildings than the cell 
antennas.
   
  Two uV for the receiver sensitivity sure does limit the usefulness of the new 
repeater -
   
  Anyone have any thoughts?
   
  73 - Jim  W5ZIT

[EMAIL PROTECTED] wrote:
  I am having some receive problems on my repeater and I am 
thinking that it might be desense. I am on 2M running a 
MASRII repeater with a Decibal Products band reject 6 can 
duplexer.

While I can key the repeater from a pretty good distance 
the audio that makes it through the repeater drops off 
pretty quickly. I just had the duplexers tuned and they 
are tuned very well.

So on to my question. If I were to take and seperate the 
recv cans from the xmit cans and run to 2 seperate 
antennas would that mess up the duplexer tuning? will 20' 
of vertical seperation plus the cans and the fact that I 
would be running through seperate cable, make a 
difference?

Thanks,
Vern
KI4ONW


 

   
-
Yahoo! oneSearch: Finally,  mobile search that gives answers, not web links. 

Re: [Repeater-Builder] Duplexers

[mung]

The duplexer is a DB-4048.

I have had this repeater for a couple of months and it has 
always had problems.  I don't have access to a service 
monitor or anything like that right now but I have a 
friend that has one however someone is borrowing it right 
now.

 From what I can tell the desense is pretty bad.  I can 
key up the repeater a lot further than I can send audio 
through it.

all of my cables are double shielded or better.

Thanks,
Vern

On Mon, 24 Sep 2007 19:54:33 -0500
  "Steve S. Bosshard (NU5D)" <[EMAIL PROTECTED]> wrote:
> Decibel did make a 6 cavity notch duplexer - 4" full 
>sized cavities - 
> that would work nicely on a 110 Watt  M2 station @ 600 
>kHz.  Isolated
> TEE test into a dummy load - how bad is the receiver 
>desense ?  If you
> don't have some test equipment - signal gen, dummy load, 
>and a TEE
> fitting with the side pin cut away (makes 60 dB lossy 
>coupling, there
> abouts) you probably will need to find someone who does 
>locally that can
> help.  73,  Steve NU5D
> 
> Eric Lemmon wrote:
>> Vern,
>>
>> Did this problem exist before you had the duplexer 
>>tuned?  Was anything at
>> all done to your repeater system just before the problem 
>>was noticed?
>>
>> A band reject (notch) duplexer may be incapable of 
>>performing even
>> satisfactorily at 2m.  Please advise the model number of 
>>your duplexer, so
>> we can understand your situation.  Are all of your 
>>cables double-shielded?
>> It might be a good idea to perform a noise-floor test 
>>using an "iso-tee" and
>> a service monitor.
>>
>> Some helpful information about investigating desense 
>>problems can be found
>> here:
>>
>> 
>>
>> 73, Eric Lemmon WB6FLY
>>  
>>
>>   

RE: [Repeater-Builder] Duplexers

[Glenn Shaw]

Hey Jim

I have a few thoughts that come to mind.  Based on my experience with VHF
and UHF repeaters colocated in cell sites I would say that you may want to
consider the following.  First the AC unit motors etc will not be a problem
to the excellent FM rec you have there with the GE M2 even with the preamp.
Plain electrical noise is not going to be your problem.  It is an RF issue.
And Multi RCC sites are very often a big mess as far as RF goes.  Its too
bad you have to go through all this but it is a fact of life in crowded
sites that are also the best ones to be on. 

The fact that your tests indicated the same actual values with the xmt on or
off tells us that your duplexers are fine.  And your rec tests direct
connected are fine.  Many cell sites are *real* bad with regard to rf on
numerous freqs due to harmonics and mixing products/intermod.  Some times
you will only see your rf problem when 2 or more things occur at the same
time aming it time consuming to pin it down. Sometimes the RF signal is
slightly off your rcv freq but very strong and the skirts of the sweep are
slightly coming into your channel.  So you have to sweep the area with a
good service monitor or Spectrum Analyzer to see what is going on. I use the
IFR or R2200 plus the HP for this and it will show right up. 

It sounds like from the description you are in a very dirty site.  You will
have to consider 1.  Moving to a new site even just a few hundred yards away
on a new tower, or 2. Sweep with a spectrum analyzer to actually see if you
can find the culprit(s) causing your problem and see if you can work with
the equipment owner to clean it up.  I doubt you will have much luck with
this since if the techs at Verizon or Cell 1 ATT think their stuff is
working fine they cant be bothered with your ham radio problems.  They will
tell you to take the site or leave it most of the time.  3. What I have had
to do when the RF product was sitting just off our rcv freq and was fairly
strong is install another cavity to clean it up.  You may find it easier to
use a pass type on your rcv channel unless you can definitely pin down the
offending signal and reject it.  Be aware that the preamp on your repeater
can be a problem.  GE and Moto reccomend those only for a base station and
not a repeater unless you have a really clean site.  They are notorious for
intermod issues and most times are not worth the extra rvc gain in multi
user sites. 

These suggestions are a start and may or may not do it for you but I would
start with these basics.  Keep an open mind to the fact that something at
the site which is radiating some RF into your install may not be able to get
fixed in practical terms and you may have to move either the frequency of
your repeater or your site location, since I doubt you can get the cell
guys/Paging RCCs to go away:)

Let us know how this progresses

73
Glenn  N1GBY

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jim Brown
Sent: Tuesday, September 25, 2007 8:20 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

Our local club recently installed a 2 meter repeater on a water tank
adjacent to a cell site.  Two cell towers are serviced by four buildings
housing equipement, and we are having some desense due to noise pickup on
the antenna.  Running an iso-tee we found that our GE Mastr II receiver with
GE preamp shows .6 uV for 12 dB SINAD using a dummy load in place of the
antenna (.2 uV direct to the receiver bypassing the duplexer).  With the
antenna connected we see a 2 uV sensitivity for 12 dB SINAD.
 
These readings are the same, with the repeater transmitter (40 watts) keyed
or unkeyed.  
 
The noise floor is really decreasing the utility of the new repeater.  The
noise source seems to come and go as a quiet signal on the repeater input
can become suddenly noisey, and vice versa - a noisey signal can become
suddenly quiet.
 
I hear the air conditioning units in the cell site buildings cycling and
wonder if they might be the cause of the noise?  Our antenna is only about
40 feet above the ground (at 7400 ft) while the cell antennas are at about
100 ft.  So we are much closer to the cell site equipment buildings than the
cell antennas.
 
Two uV for the receiver sensitivity sure does limit the usefulness of the
new repeater -
 
Anyone have any thoughts?
 
73 - Jim  W5ZIT

[EMAIL PROTECTED] wrote:

I am having some receive problems on my repeater and I am 
thinking that it might be desense. I am on 2M running a 
MASRII repeater with a Decibal Products band reject 6 can 
duplexer.

While I can key the repeater from a pretty good distance 
the audio that makes it through the repeater drops off 
pretty quickly. I just had the duplexers tuned and they 
are tuned very well.

So on to my question. If I were to take and seperate the 
recv cans from the

Re: [Repeater-Builder] Duplexers

[no6b]

At 9/25/2007 05:20, you wrote:

>Our local club recently installed a 2 meter repeater on a water tank 
>adjacent to a cell site.  Two cell towers are serviced by four buildings 
>housing equipement, and we are having some desense due to noise pickup on 
>the antenna.  Running an iso-tee we found that our GE Mastr II receiver 
>with GE preamp shows .6 uV for 12 dB SINAD using a dummy load in place of 
>the antenna (.2 uV direct to the receiver bypassing the duplexer).  With 
>the antenna connected we see a 2 uV sensitivity for 12 dB SINAD.
>
>These readings are the same, with the repeater transmitter (40 watts) 
>keyed or unkeyed.
>
>The noise floor is really decreasing the utility of the new repeater.  The 
>noise source seems to come and go as a quiet signal on the repeater input 
>can become suddenly noisey, and vice versa - a noisey signal can become 
>suddenly quiet.
>
>I hear the air conditioning units in the cell site buildings cycling and 
>wonder if they might be the cause of the noise?  Our antenna is only about 
>40 feet above the ground (at 7400 ft) while the cell antennas are at about 
>100 ft.  So we are much closer to the cell site equipment buildings than 
>the cell antennas.
>
>Two uV for the receiver sensitivity sure does limit the usefulness of the 
>new repeater -
>
>Anyone have any thoughts?

Anything with a CPU in it could be the culprit @ 2 meters.  Anytime I drive 
within ~200 ft. of a local "Foothill Transit" bus the squelch on my mobile 
radio blows open; within 50 ft., normally full quieting signals are 
completely captured by the noise.  I suspect it's the electronic scroll 
sign on the back of the bus.

Fortunately I haven't seen this on 440 MHz, but with faster CPUs finding 
their way into everything it may only be a matter of time.

Bob NO6B

Re: [Repeater-Builder] Duplexers

[Mark Miller]

>The noise floor is really decreasing the utility of the new 
>repeater.  The noise source seems to come and go as a quiet signal 
>on the repeater input can become suddenly noisey, and vice versa - a 
>noisey signal can become suddenly quiet.

It looks like you have a 10dB degradation.  Many times this is from 
phase noise from other transmitters, but intermod can give you the 
same problems.  I would look for a VHF paging transmitter if phase 
noise is suspected. This type of troubleshooting requires a good 
spectrum analyzer in most cases.  I typically use the RX part of a 
duplexer on the front end of an ANRITSU 2721B to keep the first mixer 
in the spectrum analyzer happy.  I hook up a 10dBd Yagi to the 
duplexer and start looking for the noise floor to rise.  Once I have 
found the site that is causing the increase in noise floor, then the 
hard part comes, getting the other site to cooperate in further 
testing.  What we ultimately want is for the other site to completely 
shut down for the time it takes to test the sensitivity of the 
receiver that is experiencing the degradation.

Since you mention that the degradation is intermittent, you may be 
able to monitor other signals and see a correlation between when the 
suspect transmitter keys, and an increase in the noise floor in your 
bandpass.  If the problem is because of intermod, then it becomes a 
little more difficult as you have multiple culprits.

The spectrum analyzer you use should have a noise floor of around 
-120 dBm @10 KHz bandwidth.

73,
Mark N5RFX

Re: [Repeater-Builder] Duplexers

[Mark Miller]

The 10dBd Yagi I mentioned is for 900MHz, something smaller would 
have to be used for VHF :)

73,
Mark N5RFX

Re: [Repeater-Builder] Duplexers

[no6b]

At 9/25/2007 07:59, you wrote:


> >The noise floor is really decreasing the utility of the new
> >repeater. The noise source seems to come and go as a quiet signal
> >on the repeater input can become suddenly noisey, and vice versa - a
> >noisey signal can become suddenly quiet.
>
>It looks like you have a 10dB degradation. Many times this is from
>phase noise from other transmitters, but intermod can give you the
>same problems. I would look for a VHF paging transmitter if phase
>noise is suspected. This type of troubleshooting requires a good
>spectrum analyzer in most cases. I typically use the RX part of a
>duplexer on the front end of an ANRITSU 2721B to keep the first mixer
>in the spectrum analyzer happy. I hook up a 10dBd Yagi to the
>duplexer and start looking for the noise floor to rise. Once I have
>found the site that is causing the increase in noise floor, then the
>hard part comes, getting the other site to cooperate in further
>testing. What we ultimately want is for the other site to completely
>shut down for the time it takes to test the sensitivity of the
>receiver that is experiencing the degradation.
>
>Since you mention that the degradation is intermittent, you may be
>able to monitor other signals and see a correlation between when the
>suspect transmitter keys, and an increase in the noise floor in your
>bandpass. If the problem is because of intermod, then it becomes a
>little more difficult as you have multiple culprits.
>
>The spectrum analyzer you use should have a noise floor of around
>-120 dBm @10 KHz bandwidth.

The spectrum analyzer method is of course an excellent way to look for 
interference sources.  However, a noise floor of -120 dBm @ 10 kHz RBW is a 
bit on the deaf side when you consider that your repeater RX will be almost 
10 dB better than that.  You might consider adding a preamp & an additional 
pass cavity in front of the analyzer to maximize sensitivity if at first 
you don't find anything.

Bob NO6B

Re: [Repeater-Builder] Duplexers

[Nate Duehr]

[EMAIL PROTECTED] wrote:
> I had them tuned because I had just bought them and didn't 
> really trust that they were right.  They were very far out 
> so it's good that I got them tuned.  I was having the same 
> problem as now though very poor receive.  Right now I have 
> a radio on there for receive that was getting about 30 
> miles of coverage as an Echolink link node with home made 
> antenna and now hooked up to the repeater using a big Tram 
> Dualband antenna through the duplexer I am lucky if I am 
> getting 3 miles.
> 
> So I don't think the repeater's built in receiver is the 
> problem which leads me to either desense or a bad antenna 
> cable.  Transmit is getting out very well and the swr is 
> almost 1 to 1 so I think the cable is OK.  I am running 
> LMR 400 up the tower 95% of the way.  I just have a short 
> coax jumper that goes into the antenna.
> 
> I am going to try to split them and see what I get.
> 
> Thanks,
> Vern
> KI4ONW

Before you do that.  Have someone transmit a weak signal (or use an 
iso-T and transmit it in yourself, as someone else mentioned) into the 
repeater while you're at the site, listening to the receiver while the 
transmitter is on.

Turn the transmitter off.  If their signal gets better, you're fighting 
desense.  It's that simple to find out.

To find out exactly how bad it is, feeding a weak signal into the 
receiver with an iso-T and measuring the audio coming from the repeater 
receiver with a SINAD meter is the "next level" of knowing what's going 
on.  (I've seen people do this by ear with practice and get close, but 
you need to see it on a meter first or have someone demonstrate to even 
try it.  Hey... sometimes when you're starting out you don't have the 
gear, we understand...)

Feed a weak signal (usually 12 dB SINAD for these tests, as a standard 
starting point) and then turn the transmitter on.  The weak signal will 
disappear or be noisier if you have a desense problem, as mentione above.

Increase the signal generator to the point where the weak signal is the 
same as before (usually 12 dB SINAD is used when you have a meter).

The difference between where the signal generator was level-wise when 
you started, and where you end up, is how MUCH desense you're fighting, 
and how much more isolation you need in the overall system to make it 
work.  Plus if gather numbers like this, folks here can tell you 
"ballpark" numbers to expect from your particular radio and setup.

Also be forewarned, some antennas simply don't "duplex" well... it's 
difficult to explain, but you'll find antennas that throw all sorts of 
crap around when used in duplex operation, that are fine for simplex.  I 
know nothing about the Tram antennas, but "dual-band" antennas for 
repeater operation, sets off warning bells for me.

Use the best cables for interconnect you can possibly buy!  Having nice 
double-shielded stuff built onto the duplexer by the manufacturer, only 
to run lossy/leaky crud from the repeater to the duplexer, is just 
asking for trouble.  If you used your LMR 400 for that, good... it'll 
work in most cases, just fine.  Many people do have problems with LMR 
400 in duplexed service, other's don't.  There's a long thread about it 
around here somewhere in the archives...

If you can afford/get hardline - always do it. 1/2" will work fine at 
VHF unless you have an enormous run, and you might want 7/8" for UHF, 
depending on the length of your run.  Keep an ear to the ground and 
scrounge hardline any which way you can.  Hardline connectors too. 
They're not cheap.

You can test your "inside" setup by replacing the antenna with a GOOD 
dummy load rated for the power you're pushing, and that is a solid 50 
ohm load.  (Don't use a cheap one for this.  Find something big and 
stable.  I found a 500W Bird load at a hamfest once for $12, best 
purchase that year.)  See if the system desenses itself when not hooked 
to the outside antenna.  If it does, you have something wrong right 
there in the repeater itself.  Stop and figure that out.

I could go on and on, but will stop and give the admonishment my elmers 
gave me... "MEASURE IT"... don't guess.  Beg, borrow or steal test gear 
and get someone to show you how to use it.  You can "stumble" into 
correct setups without it, but you can KNOW how well your repeater 
performs if you measure.

- Receiver sensitivity -- put a very weak calibrated signal directly 
into the receiver and measure the 12 dB SINAD point.

- Useable receiver sensitivity -- do the same test, but with an iso-T or 
directional coupler of known loss (measure that too!) and see how much 
more signal you need to have the same receiver performance through the 
duplexer, and final cabling.

[If you have a pre-amp this becomes more important to see if the gain 
has driven the receiver into the noise floor at the site, and/or if 
you're overdriving the receiver with too much RF.]

Those are good starting points, both with the transmitter on and 

Re: [Repeater-Builder] Duplexers

[mung]

Thanks for the great info as soon as we get the service 
monitor back we are going to try these things.

I have already seperated the 2 sides and have seen much 
improvement so I think that this is really my problem.

I do have a question about duplexers in general.  I am 
sure that this is a dumb question but
What is the purpose of notching out the receive frequency 
on the transmit side?  Since I have 6 cans couldn't I move 
one of the cans from the transmit side to the receive side 
to give me 4 on the receive and 2 on the transmit?

Thanks,
Vern

On Tue, 25 Sep 2007 23:46:12 -0600
  Nate Duehr <[EMAIL PROTECTED]> wrote:
> [EMAIL PROTECTED] wrote:
>> I had them tuned because I had just bought them and 
>>didn't 
>> really trust that they were right.  They were very far 
>>out 
>> so it's good that I got them tuned.  I was having the 
>>same 
>> problem as now though very poor receive.  Right now I 
>>have 
>> a radio on there for receive that was getting about 30 
>> miles of coverage as an Echolink link node with home 
>>made 
>> antenna and now hooked up to the repeater using a big 
>>Tram 
>> Dualband antenna through the duplexer I am lucky if I am 
>> getting 3 miles.
>> 
>> So I don't think the repeater's built in receiver is the 
>> problem which leads me to either desense or a bad 
>>antenna 
>> cable.  Transmit is getting out very well and the swr is 
>> almost 1 to 1 so I think the cable is OK.  I am running 
>> LMR 400 up the tower 95% of the way.  I just have a 
>>short 
>> coax jumper that goes into the antenna.
>> 
>> I am going to try to split them and see what I get.
>> 
>> Thanks,
>> Vern
>> KI4ONW
> 
> Before you do that.  Have someone transmit a weak signal 
>(or use an 
> iso-T and transmit it in yourself, as someone else 
>mentioned) into the 
> repeater while you're at the site, listening to the 
>receiver while the 
> transmitter is on.
> 
> Turn the transmitter off.  If their signal gets better, 
>you're fighting 
> desense.  It's that simple to find out.
> 
> To find out exactly how bad it is, feeding a weak signal 
>into the 
> receiver with an iso-T and measuring the audio coming 
>from the repeater 
> receiver with a SINAD meter is the "next level" of 
>knowing what's going 
> on.  (I've seen people do this by ear with practice and 
>get close, but 
> you need to see it on a meter first or have someone 
>demonstrate to even 
> try it.  Hey... sometimes when you're starting out you 
>don't have the 
> gear, we understand...)
> 
>Feed a weak signal (usually 12 dB SINAD for these tests, 
>as a standard 
> starting point) and then turn the transmitter on.  The 
>weak signal will 
> disappear or be noisier if you have a desense problem, 
>as mentione above.
> 
> Increase the signal generator to the point where the 
>weak signal is the 
> same as before (usually 12 dB SINAD is used when you 
>have a meter).
> 
> The difference between where the signal generator was 
>level-wise when 
> you started, and where you end up, is how MUCH desense 
>you're fighting, 
> and how much more isolation you need in the overall 
>system to make it 
> work.  Plus if gather numbers like this, folks here can 
>tell you 
> "ballpark" numbers to expect from your particular radio 
>and setup.
> 
> Also be forewarned, some antennas simply don't "duplex" 
>well... it's 
> difficult to explain, but you'll find antennas that 
>throw all sorts of 
> crap around when used in duplex operation, that are fine 
>for simplex.  I 
> know nothing about the Tram antennas, but "dual-band" 
>antennas for 
> repeater operation, sets off warning bells for me.
> 
> Use the best cables for interconnect you can possibly 
>buy!  Having nice 
> double-shielded stuff built onto the duplexer by the 
>manufacturer, only 
> to run lossy/leaky crud from the repeater to the 
>duplexer, is just 
> asking for trouble.  If you used your LMR 400 for that, 
>good... it'll 
> work in most cases, just fine.  Many people do have 
>problems with LMR 
> 400 in duplexed service, other's don't.  There's a long 
>thread about it 
> around here somewhere in the archives...
> 
> If you can afford/get hardline - always do it. 1/2" will 
>work fine at 
> VHF unless you have an enormous run, and you might want 
>7/8" for UHF, 
> depending on the length of your run.  Keep an ear to the 
>ground and 
> scrounge hardline any which way you can.  Hardline 
>connectors too. 
> They're not cheap.
> 
> You can test your "inside" setup by replacing the 
>antenna with a GOOD 
> dummy load rated for the power you're pushing, and that 
>is a solid 50 
> ohm load.  (Don't use a cheap one for this.  Find 
>something big and 
> stable.  I found a 500W Bird load at a hamfest once for 
>$12, best 
> purchase that year.)  See if the system desenses itself 
>when not hooked 
> to the outside antenna.  If it does, you have something 
>wrong right 
> there in the repeater itself.  Stop and figure that out.
> 
> I could go on and on, but will stop and give the 
>admon

Re: [Repeater-Builder] Duplexers

[Steve S. Bosshard (NU5D)]

A transmitter may have broadband noise with considerable noise content 
at the receive frequency.  The notch in the transmit side removes 
transmitter noise that may impair your receiver's capability.  In an 
earlier post there was mention of a solid state transmitter.  
Traditionally tube transmitters have higher Q output circuits as opposed 
to wideband circuits in solid state transmitters, so a solid state 
transmitter may need more filtering.

There are also combination band pass / band reject duplexers and also 
band pass only.  Each has a characteristic suited for a particular job.  
Beware, a duplexer may pass an intended frequency PLUS unintended 
frequencies outside the normal band pass.  I found that 158.100 radio 
paging was being received by a dual band antenna, and passed right thru 
a 440 duplexer to cause overload in the receiver front end.  In this 
particular instance the best solution was to go to a monoband antenna.

Wishing you best success, Steve NU5D


[EMAIL PROTECTED] wrote:
> Thanks for the great info as soon as we get the service 
> monitor back we are going to try these things.
>
> I have already seperated the 2 sides and have seen much 
> improvement so I think that this is really my problem.
>
> I do have a question about duplexers in general.  I am 
> sure that this is a dumb question but
> What is the purpose of notching out the receive frequency 
> on the transmit side?  Since I have 6 cans couldn't I move 
> one of the cans from the transmit side to the receive side 
> to give me 4 on the receive and 2 on the transmit?
>
> Thanks,
> Vern
>
>   

Re: [Repeater-Builder] Duplexers

[Mark Miller]

At 11:12 AM 9/26/2007, Steve wrote:
>A transmitter may have broadband noise with considerable noise content
>at the receive frequency. The notch in the transmit side removes
>transmitter noise that may impair your receiver's capability.


In my day job 99% of the problems I have with noise floor is related 
to transmitter noise that is in band on my RX freq.  Usually it is 
another transmitter at the site and we ask them to install a 
bandpass/notch filter to lower the noise floor on our receiver.  The 
notch is tuned to our receiver frequency.  That happened two weeks 
ago in Hawaii.

73,
Mark N5RFX

Re: [Repeater-Builder] Duplexers

[mung]

This makes sense.

I guess what might help is to find a single VHF bandpass 
can to put in front of the receive side of the duplexer.

How much does the power output effect the required filter 
attinuation?  Right now I am running about 70w out would 
turning it down make much of a difference?  From the 
charts I have seen it doesn't seem to be more than 3 or so 
db difference between 10w and 70w.  Am I reading it wrong?

Thanks,
Vern

On Wed, 26 Sep 2007 11:12:29 -0500
  "Steve S. Bosshard (NU5D)" <[EMAIL PROTECTED]> wrote:
> A transmitter may have broadband noise with considerable 
>noise content 
> at the receive frequency.  The notch in the transmit 
>side removes 
> transmitter noise that may impair your receiver's 
>capability.  In an 
> earlier post there was mention of a solid state 
>transmitter.  
> Traditionally tube transmitters have higher Q output 
>circuits as opposed 
> to wideband circuits in solid state transmitters, so a 
>solid state 
> transmitter may need more filtering.
> 
> There are also combination band pass / band reject 
>duplexers and also 
> band pass only.  Each has a characteristic suited for a 
>particular job.  
> Beware, a duplexer may pass an intended frequency PLUS 
>unintended 
> frequencies outside the normal band pass.  I found that 
>158.100 radio 
> paging was being received by a dual band antenna, and 
>passed right thru 
> a 440 duplexer to cause overload in the receiver front 
>end.  In this 
> particular instance the best solution was to go to a 
>monoband antenna.
> 
> Wishing you best success, Steve NU5D
> 
> 
> [EMAIL PROTECTED] wrote:
>> Thanks for the great info as soon as we get the service 
>> monitor back we are going to try these things.
>>
>> I have already seperated the 2 sides and have seen much 
>> improvement so I think that this is really my problem.
>>
>> I do have a question about duplexers in general.  I am 
>> sure that this is a dumb question but
>> What is the purpose of notching out the receive 
>>frequency 
>> on the transmit side?  Since I have 6 cans couldn't I 
>>move 
>> one of the cans from the transmit side to the receive 
>>side 
>> to give me 4 on the receive and 2 on the transmit?
>>
>> Thanks,
>> Vern
>>
>>   
> 

Re: [Repeater-Builder] Duplexers

[David Piche]

I would think that at the least you would want to build a small building, even 
something close to a large dog house, 3'D X 4'W x 4'H.  Leaves at least a 
little room to breath and work around, heat may be a factor depending on the 
cans you use and may send them a bit out of tune from the hot/humid summer 
months to the cooler less humid winter ones. Maybe a hinged lid for ease of 
access and a padlock.  Worked a several sites I have seen but just a small box, 
that may be too easy to blow around, steal, no room to work, but depends on 
where you are putting it as it is all relative.

--- On Mon, 10/27/08, Mung Bungholio <[EMAIL PROTECTED]> wrote:

From: Mung Bungholio <[EMAIL PROTECTED]>
Subject: [Repeater-Builder] Duplexers
To: Repeater-Builder@yahoogroups.com
Date: Monday, October 27, 2008, 9:14 AM








Is it OK to get some kind of storage container or something like that and put 
my duplexer outside?  What would be the risks of doing so?  I am in Florida so 
lots of rain and heat but no freezing months or anything like that?
 
Thanks,
Vern
KI4ONW 














  

RE: [Repeater-Builder] Duplexers

[Mung Bungholio]

The repeater is at my house so it's fairly safe as far as theft goes.  It's
a DB 2m 6 can duplexer in a metal case.

 

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of David Piche
Sent: Monday, October 27, 2008 9:24 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 


I would think that at the least you would want to build a small building,
even something close to a large dog house, 3'D X 4'W x 4'H.  Leaves at least
a little room to breath and work around, heat may be a factor depending on
the cans you use and may send them a bit out of tune from the hot/humid
summer months to the cooler less humid winter ones. Maybe a hinged lid for
ease of access and a padlock.  Worked a several sites I have seen but just a
small box, that may be too easy to blow around, steal, no room to work, but
depends on where you are putting it as it is all relative.

--- On Mon, 10/27/08, Mung Bungholio <[EMAIL PROTECTED]> wrote:

From: Mung Bungholio <[EMAIL PROTECTED]>
Subject: [Repeater-Builder] Duplexers
To: Repeater-Builder@yahoogroups.com
Date: Monday, October 27, 2008, 9:14 AM

Is it OK to get some kind of storage container or something like that and
put my duplexer outside?  What would be the risks of doing so?  I am in
Florida so lots of rain and heat but no freezing months or anything like
that?

 

Thanks,

Vern

KI4ONW

 

 

Re: [Repeater-Builder] Duplexers

[Scott Zimmerman]

I often thought about using a Rubbermaid product.

Here is a deck box:
Rubbermaid item #3743

or a vertical storage cabinet:
Rubbermaid item #3749

I'm not saying these would be 100% waterproof, but I think they would work well 
enough.

I think the last price I saw on the storage cabinet at wally-world was around 
$100 or so.

Scott

Scott Zimmerman
Amateur Radio Call N3XCC
474 Barnett Rd
Boswell, PA 15531

  - Original Message - 
  From: Mung Bungholio 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Monday, October 27, 2008 10:40 AM
  Subject: RE: [Repeater-Builder] Duplexers


  The repeater is at my house so it's fairly safe as far as theft goes.  It's a 
DB 2m 6 can duplexer in a metal case.

   

  From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of 
David Piche
  Sent: Monday, October 27, 2008 9:24 AM
  To: Repeater-Builder@yahoogroups.com
  Subject: Re: [Repeater-Builder] Duplexers

   

I would think that at the least you would want to build a small 
building, even something close to a large dog house, 3'D X 4'W x 4'H.  Leaves 
at least a little room to breath and work around, heat may be a factor 
depending on the cans you use and may send them a bit out of tune from the 
hot/humid summer months to the cooler less humid winter ones. Maybe a hinged 
lid for ease of access and a padlock.  Worked a several sites I have seen but 
just a small box, that may be too easy to blow around, steal, no room to work, 
but depends on where you are putting it as it is all relative.

--- On Mon, 10/27/08, Mung Bungholio <[EMAIL PROTECTED]> wrote:

From: Mung Bungholio <[EMAIL PROTECTED]>
    Subject: [Repeater-Builder] Duplexers
To: Repeater-Builder@yahoogroups.com
Date: Monday, October 27, 2008, 9:14 AM

Is it OK to get some kind of storage container or something like that 
and put my duplexer outside?  What would be the risks of doing so?  I am in 
Florida so lots of rain and heat but no freezing months or anything like that?

 

Thanks,

Vern

KI4ONW
   

   


   


--



  No virus found in this incoming message.
  Checked by AVG - http://www.avg.com 
  Version: 8.0.175 / Virus Database: 270.8.4/1749 - Release Date: 10/27/2008 
7:57 AM

Re: [Repeater-Builder] Duplexers

[David Piche]

Yes I agree, something designed to be out in the elements a bit more.





From: Scott Zimmerman <[EMAIL PROTECTED]>
To: Repeater-Builder@yahoogroups.com
Sent: Monday, October 27, 2008 10:59:24 AM
Subject: Re: [Repeater-Builder] Duplexers


I often thought about using a Rubbermaid product.
 
Here is a deck box:
Rubbermaid item #3743
 
or a vertical storage cabinet:
Rubbermaid item #3749
 
I'm not saying these would be 100% waterproof, but I think they would work well 
enough.
 
I think the last price I saw on the storage cabinet at wally-world was around 
$100 or so.
 
Scott
 
Scott Zimmerman
Amateur Radio Call N3XCC
474 Barnett Rd
Boswell, PA 15531

- Original Message - 
From: Mung Bungholio 
To: Repeater-Builder@ yahoogroups. com 
Sent: Monday, October 27, 2008 10:40 AM
Subject: RE: [Repeater-Builder] Duplexers

The repeater is at my house so it’s fairly safe as far as theft goes.  It’s a 
DB 2m 6 can duplexer in a metal case.
 
From:Repeater-Builder@ yahoogroups. com [mailto:Repeater- [EMAIL PROTECTED] 
ups.com] On Behalf Of David Piche
Sent: Monday, October 27, 2008 9:24 AM
To: Repeater-Builder@ yahoogroups. com
Subject: Re: [Repeater-Builder] Duplexers
 
I would think that at the least you would want to build a small building, even 
something close to a large dog house, 3'D X 4'W x 4'H.  Leaves at least a 
little room to breath and work around, heat may be a factor depending on the 
cans you use and may send them a bit out of tune from the hot/humid summer 
months to the cooler less humid winter ones. Maybe a hinged lid for ease of 
access and a padlock.  Worked a several sites I have seen but just a small box, 
that may be too easy to blow around, steal, no room to work, but depends on 
where you are putting it as it is all relative.

--- On Mon, 10/27/08, Mung Bungholio <[EMAIL PROTECTED] com> wrote:
From: Mung Bungholio <[EMAIL PROTECTED] com>
Subject: [Repeater-Builder] Duplexers
To: Repeater-Builder@ yahoogroups. com
Date: Monday, October 27, 2008, 9:14 AM
Is it OK to get some kind of storage container or something like that and put 
my duplexer outside?  What would be the risks of doing so?  I am in Florida so 
lots of rain and heat but no freezing months or anything like that?
 
Thanks,
Vern
KI4ONW 
 


No virus found in this incoming message.
Checked by AVG - http://www.avg. com 
Version: 8.0.175 / Virus Database: 270.8.4/1749 - Release Date: 10/27/2008 7:57 
AM
 


  

RE: [Repeater-Builder] Duplexers

[Mung Bungholio]

That is what I was thinking of too.

 

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Scott Zimmerman
Sent: Monday, October 27, 2008 10:59 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

I often thought about using a Rubbermaid product.

 

Here is a deck box:

Rubbermaid item #3743

 

or a vertical storage cabinet:

Rubbermaid item #3749

 

I'm not saying these would be 100% waterproof, but I think they would work
well enough.

 

I think the last price I saw on the storage cabinet at wally-world was
around $100 or so.

 

Scott

 

Scott Zimmerman
Amateur Radio Call N3XCC
474 Barnett Rd
Boswell, PA 15531

- Original Message - 

From: Mung Bungholio <mailto:[EMAIL PROTECTED]>  

To: Repeater-Builder@yahoogroups.com 

Sent: Monday, October 27, 2008 10:40 AM

Subject: RE: [Repeater-Builder] Duplexers

 

The repeater is at my house so it's fairly safe as far as theft goes.  It's
a DB 2m 6 can duplexer in a metal case.

 

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of David Piche
Sent: Monday, October 27, 2008 9:24 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 


I would think that at the least you would want to build a small building,
even something close to a large dog house, 3'D X 4'W x 4'H.  Leaves at least
a little room to breath and work around, heat may be a factor depending on
the cans you use and may send them a bit out of tune from the hot/humid
summer months to the cooler less humid winter ones. Maybe a hinged lid for
ease of access and a padlock.  Worked a several sites I have seen but just a
small box, that may be too easy to blow around, steal, no room to work, but
depends on where you are putting it as it is all relative.

--- On Mon, 10/27/08, Mung Bungholio <[EMAIL PROTECTED]> wrote:

From: Mung Bungholio <[EMAIL PROTECTED]>
Subject: [Repeater-Builder] Duplexers
To: Repeater-Builder@yahoogroups.com
Date: Monday, October 27, 2008, 9:14 AM

Is it OK to get some kind of storage container or something like that and
put my duplexer outside?  What would be the risks of doing so?  I am in
Florida so lots of rain and heat but no freezing months or anything like
that?

 

Thanks,

Vern

KI4ONW

 

  _  


No virus found in this incoming message.
Checked by AVG - http://www.avg.com 
Version: 8.0.175 / Virus Database: 270.8.4/1749 - Release Date: 10/27/2008
7:57 AM

 

RE: [Repeater-Builder] Duplexers

[Mung Bungholio]

That deck box would work.  If I laid it down.  I actually have a nice
storage cabinet in my shed that if I put the stuff in it onto shelves I
could have room for the duplexer and some other storage above it.  Shelves
are probably cheaper than the cabinet.

 

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Scott Zimmerman
Sent: Monday, October 27, 2008 10:59 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

I often thought about using a Rubbermaid product.

 

Here is a deck box:

Rubbermaid item #3743

 

or a vertical storage cabinet:

Rubbermaid item #3749

 

I'm not saying these would be 100% waterproof, but I think they would work
well enough.

 

I think the last price I saw on the storage cabinet at wally-world was
around $100 or so.

 

Scott

 

Scott Zimmerman
Amateur Radio Call N3XCC
474 Barnett Rd
Boswell, PA 15531

- Original Message - 

From: Mung Bungholio <mailto:[EMAIL PROTECTED]>  

To: Repeater-Builder@yahoogroups.com 

Sent: Monday, October 27, 2008 10:40 AM

Subject: RE: [Repeater-Builder] Duplexers

 

The repeater is at my house so it's fairly safe as far as theft goes.  It's
a DB 2m 6 can duplexer in a metal case.

 

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of David Piche
Sent: Monday, October 27, 2008 9:24 AM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 


I would think that at the least you would want to build a small building,
even something close to a large dog house, 3'D X 4'W x 4'H.  Leaves at least
a little room to breath and work around, heat may be a factor depending on
the cans you use and may send them a bit out of tune from the hot/humid
summer months to the cooler less humid winter ones. Maybe a hinged lid for
ease of access and a padlock.  Worked a several sites I have seen but just a
small box, that may be too easy to blow around, steal, no room to work, but
depends on where you are putting it as it is all relative.

--- On Mon, 10/27/08, Mung Bungholio <[EMAIL PROTECTED]> wrote:

From: Mung Bungholio <[EMAIL PROTECTED]>
Subject: [Repeater-Builder] Duplexers
To: Repeater-Builder@yahoogroups.com
Date: Monday, October 27, 2008, 9:14 AM

Is it OK to get some kind of storage container or something like that and
put my duplexer outside?  What would be the risks of doing so?  I am in
Florida so lots of rain and heat but no freezing months or anything like
that?

 

Thanks,

Vern

KI4ONW

 

  _  


No virus found in this incoming message.
Checked by AVG - http://www.avg.com 
Version: 8.0.175 / Virus Database: 270.8.4/1749 - Release Date: 10/27/2008
7:57 AM

 

Re: [Repeater-Builder] Duplexers

[Paul Plack]

Vern,

This will probably raise some eyebrows, but I put up a ham repeater on the top 
of an 18-story office building in Orlando, and will tell you what i did.

I used a very stout, steel rack box, cast off from the computer industry, 
sealed the few holes in it, weatherstripped the door and gasketed the latch, 
painted it with a light almond-colored Rust-O-Leum (similar to that beige used 
on zillions of computers) and put it out there with no ventilation whatsoever. 
It held an Astron supply, a UHF Mastr II mobile converted for dull duplex and 
running about 25 watts, an S-Com 7K controller, and a TX-RX duplexer. The only 
path for heat dissipation was whatever conduction transfer happened through the 
surface area of the metal cabinet.

I used an attic fan thermal switch tied to a controler logic input to fire a 
macro and change the courtesy tone whenever the switch's 119-degree F 
threshhold was hit. Even on the hottest summer day and with heavy repeater use, 
it never tripped. I later mounted a digital thermometer which recorded highest 
and lowest observed temps on a rack panel, put it in the cabinet, and watched 
it through part of a summer. The hottest the inside of the cabinet ever got was 
about 4 degrees above ambient. If I recall, the highest ambient temp recorded 
by the NOAA for Orlando during those weeks was 94, and the highest recorded 
temp in the cabinet was 98.

I did find a little condensation pooled on the floor of the cabinet once when 
made a visit. I bought a "Damp Rid" cup, a dessicant product designed for use 
in residential closets, from Ace Hardware, and never had that problem again.

After I left town, the guys who took over the repeater added a 100W HF remote, 
IRLP node in the cabinet, and even provided some rack space to a Part 15 
wireless internet provider in barter for their wireless connection for IRLP. 
Apparently the extra heat was not an issue. The repeater was installed in 1995. 
It's still there.

By the way, when the repeater was still in its early stages, using solar power 
and 2-watt Repco transmitter strip, I did enclose the whole thing in a 
Rubbermaid "Action Packer" storage box. It didn't work out so well. In the 
Florida sun, the lid and the box will expand unevenly during warm-up, and spend 
part of each day misaligned, letting small insects find their way in, sometimes 
in large numbers. After a few weeks, it will get so beat up by UV that it will 
start to crack and warp.

My feeling in taking the approach I did was that in that climate, bugs and 
condensation would be bigger problems than heat, especially for a moble rig 
designed to work properly in a car trunk. If you limit the ingress/egress of 
ambient air, and have equipment which holds the inside of the cabinet even a 
degree or two above outside temp, you will avoid condensation in the equipment 
itself.

If you put just a duplexer in a box by itself, there will be very little heat 
generated inside the box, especially when the repeater is idle, so condensation 
may be a bigger issue for you. I'm guessing a duplexer that gets wet inside is 
no fun.

I learned alot with that repeater. It started out with a cheapo hamfest 
duplexer, Belden 9913 jumpers and feedline to a Cushcraft Ringo Ranger, and a 
Repco UHF data receiver board with a homemade squelch circuit and a Motrac 
helical front end grafted on. Needless to say, there were newbie mistakes I 
wouldn't make again. But I was very happy with the way the cabinet worked out.

Your mileage may vary. There has to be a reason they sell high-dollar NEMA 
cabinets with their own air conditioners, but they probably won't sell one to 
me!

73,
Paul, AE4KR


  - Original Message - 
  From: Mung Bungholio 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Monday, October 27, 2008 7:14 AM
  Subject: [Repeater-Builder] Duplexers



  Is it OK to get some kind of storage container or something like that and put 
my duplexer outside?  What would be the risks of doing so?  I am in Florida so 
lots of rain and heat but no freezing months or anything like that?



  Thanks,

  Vern

  KI4ONW


   

RE: [Repeater-Builder] duplexers

[Steve Bosshard]

I have it on good advice from Lloyd Alcorn at Wacom Products (RIP Wacom)
that Black Magic is involved.

Steve

In a nutshell, the cavities are either 1/4 or 3/4 wavelength with
coupling loops oriented for a particular degree of coupling, and also
the length affects coupling.  Some cavities use 2 loops in band pass
configuration, and some use one loop for band pass / band reject
configuration.  Cable lengths plus coupling loop length are set for 1/4
wavelength taking into account velocity factor of the cables and
connector length.  Interstage cable length has large impact on loss.

Get everything just right and it might work.

73,

Steve
NU5D









 
Yahoo! Groups Links

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Re: [Repeater-Builder] duplexers

[N6KYD]

Do 3/4 wavelength cavities use 1/4 wave interstage coupling cables? I
recently bought some used DB-4023 bandpass duplexers and the coupling cables
are aprox. 1/2 wavelength ??
~Mike N6KYD~
- Original Message - 
From: "Steve Bosshard" <[EMAIL PROTECTED]>
To: 
Sent: Monday, March 15, 2004 2:42 PM
Subject: RE: [Repeater-Builder] duplexers


> I have it on good advice from Lloyd Alcorn at Wacom Products (RIP Wacom)
> that Black Magic is involved.
>
> Steve
>
> In a nutshell, the cavities are either 1/4 or 3/4 wavelength with
> coupling loops oriented for a particular degree of coupling, and also
> the length affects coupling.  Some cavities use 2 loops in band pass
> configuration, and some use one loop for band pass / band reject
> configuration.  Cable lengths plus coupling loop length are set for 1/4
> wavelength taking into account velocity factor of the cables and
> connector length.  Interstage cable length has large impact on loss.
>
> Get everything just right and it might work.
>
> 73,
>
> Steve
> NU5D
>
>
>
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>







 
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 http://groups.yahoo.com/group/Repeater-Builder/

<*> To unsubscribe from this group, send an email to:
 [EMAIL PROTECTED]

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Re: [Repeater-Builder] duplexers

[Chuck Kelsey]

Best bet is to pick up a used can and duplicate it times the number you
need. After you've done that and poured tons of hours into your project, you
decide whether you want to document in detail and share the info with the
rest of the world.

Chuck
WB2EDV



- Original Message - 
From: "David Schornak" <[EMAIL PROTECTED]>
To: 
Sent: Monday, March 15, 2004 5:25 PM
Subject: [Repeater-Builder] duplexers


> has anyone or does anyone know where tofind the math formulas to help you
> design a set of cavities for a duplexer? I have been looking on the web
and
> in the arrl handbook and the big book of antennas, and todate I have found
> plans for 2 meter duplexers.
> I have yet to find any place where they show or have written out the
> formulas for designing your own cavities.
> I was thinking that there should be something out that that that for this
> frequency range your cavity hieght is this and the diameter is this.
> so is there a site or a book that gives you the theory and or the math so
> that you could design your own set of duplexers/ cavities?
>
>






 
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Re: [Repeater-Builder] duplexers

[[EMAIL PROTECTED]]

This site explains some of the basics:

http://www.xs4all.nl/~pa0nhc/repeater/duplexfilter/English/duplexfilter.htm


Here are some plans:

http://www.vacsew.com/435/dup.htm

http://www.dalek.org/srg/cavity.html

http://www.repeater-builder.com/rbtip/2mduplexer.html

http://www.btinternet.com/~g4kqu/gb3dx_photos.htm







- Original Message - 
From: "David Schornak" <[EMAIL PROTECTED]>
To: 
Sent: Monday, March 15, 2004 4:25 PM
Subject: [Repeater-Builder] duplexers


has anyone or does anyone know where tofind the math formulas to help you
design a set of cavities for a duplexer? I have been looking on the web and
in the arrl handbook and the big book of antennas, and todate I have found
plans for 2 meter duplexers.
I have yet to find any place where they show or have written out the
formulas for designing your own cavities.
I was thinking that there should be something out that that that for this
frequency range your cavity hieght is this and the diameter is this.
so is there a site or a book that gives you the theory and or the math so
that you could design your own set of duplexers/ cavities?





 
Yahoo! Groups Links



 






 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
 http://groups.yahoo.com/group/Repeater-Builder/

<*> To unsubscribe from this group, send an email to:
 [EMAIL PROTECTED]

<*> Your use of Yahoo! Groups is subject to:
 http://docs.yahoo.com/info/terms/
 

Re: [Repeater-Builder] duplexers

[[EMAIL PROTECTED]]

Found this site too:

http://www.amalgamate2000.com/radio-hobbies/radio/coaxial_resonators.htm


- Original Message - 
From: "David Schornak" <[EMAIL PROTECTED]>
To: 
Sent: Monday, March 15, 2004 4:25 PM
Subject: [Repeater-Builder] duplexers


has anyone or does anyone know where tofind the math formulas to help you
design a set of cavities for a duplexer? I have been looking on the web and
in the arrl handbook and the big book of antennas, and todate I have found
plans for 2 meter duplexers.
I have yet to find any place where they show or have written out the
formulas for designing your own cavities.
I was thinking that there should be something out that that that for this
frequency range your cavity hieght is this and the diameter is this.
so is there a site or a book that gives you the theory and or the math so
that you could design your own set of duplexers/ cavities?








 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
 http://groups.yahoo.com/group/Repeater-Builder/

<*> To unsubscribe from this group, send an email to:
 [EMAIL PROTECTED]

<*> Your use of Yahoo! Groups is subject to:
 http://docs.yahoo.com/info/terms/
 

RE: [Repeater-Builder] duplexers

[Steve S. Bosshard \(NU5D\)]

I suspect when you add the coupling loop length that the interstage cables
will be on the order of 3/4 wave length, or around 10" or so.

I ran into the 3/4 wavelength business taking some 10" Sinclair VHF
cavities, and building a 5 channel UHF combiner with cavities and dual
junction isolators.

Steve







 
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Re: [Repeater-Builder] duplexers

[David Schornak]

Steve I am beginning to believe that with as much info as I have found.

> I have it on good advice from Lloyd Alcorn at Wacom Products (RIP Wacom)
> that Black Magic is involved.
> 
> Steve
> 
> In a nutshell, the cavities are either 1/4 or 3/4 wavelength with
> coupling loops oriented for a particular degree of coupling, and also
> the length affects coupling.  Some cavities use 2 loops in band pass
> configuration, and some use one loop for band pass / band reject
> configuration.  Cable lengths plus coupling loop length are set for 1/4
> wavelength taking into account velocity factor of the cables and
> connector length.  Interstage cable length has large impact on loss.
> 
> Get everything just right and it might work.
> 
> 73,
> 
> Steve
> NU5D
> 
see ya

73's
N1IB
David Schornak

K2 03027

arf
don't forget me
Mis Ginger





 
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RE: [Repeater-Builder] Duplexers

[Eric Lemmon]

Chris,

You do not have to use a duplexer, but it makes building a repeater SO much
easier!  Keep in mind that "antenna separation" usually means vertical
separation, not horizontal separation.  Moreover, the same isolation
provided by 1000 feet of horizontal separation might be provided by 10 feet
of vertical separation.  The amount of isolation you need is based generally
on the transmit power, frequency separation between TX and RX, and the
sensitivity of the receiver.  The receiver bandwidth and antenna types also
play a factor.

73, Eric Lemmon WB6FLY
 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Mackey
Sent: Monday, August 30, 2010 4:44 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Duplexers

  

Our club was recently given a 220 repeater. We have two seperate antennas.
We do not have a duplexer. My question is do we have to have a duplexer? How
can we keep the transmitter from desensitizing the receiver? The antennas
are apart but can be moved farther.
Thanks
Chris
Kg4bek

Re: [Repeater-Builder] Duplexers

[CMcClellan]

Thank you for your response.
The problem is that the repeater is located on top of a building and  the 
tower on that building is only about 20 feet tall. We can move the two  
antennas apart horizontally, but only 20 feet vertically.  Duplexers are  way 
too 
expensive and hard to find for the 200 Mhz band.  We are running  about 20 
watts and the frequency separation is 1.6 mhz.  Sometimes a week  signal 
comes in and sometimes the transceiver is desensitizing the receiver and  
covers it up.  Any suggestions?
Thanks
Chris
 
 
In a message dated 8/30/2010 8:36:53 P.M. Eastern Daylight Time,  
wb6...@verizon.net writes:

 
 
 
Chris,

You do not have to use a duplexer, but it makes building a  repeater SO much
easier! Keep in mind that "antenna separation" usually  means vertical
separation, not horizontal separation. Moreover, the same  isolation
provided by 1000 feet of horizontal separation might be provided  by 10 feet
of vertical separation. The amount of isolation you need is  based generally
on the transmit power, frequency separation between TX and  RX, and the
sensitivity of the receiver. The receiver bandwidth and antenna  types also
play a factor.

73, Eric Lemmon  WB6FLY


-Original Message-
From: _repeater-buil...@yahoogroups.com_ 
(mailto:Repeater-Builder@yahoogroups.com) 
[mailto:_repeater-buil...@yahoogroups.com_ 
(mailto:Repeater-Builder@yahoogroups.com) ]  On Behalf Of Mackey
Sent: Monday, August 30, 2010 4:44 PM
To: _repeater-buil...@yahoogroups.com_ 
(mailto:Repeater-Builder@yahoogroups.com) 
Subject:  [Repeater-Builder] Duplexers

Our club was recently given a 220  repeater. We have two seperate antennas.
We do not have a duplexer. My  question is do we have to have a duplexer? 
How
can we keep the transmitter  from desensitizing the receiver? The antennas
are apart but can be moved  farther.
Thanks
Chris
Kg4bek

Re: [Repeater-Builder] Duplexers

[Rick Szajkowski]

if you keep your eyes open you can find 220 duplexers at a good price ..
Email Bob Morton and I am sure he can find you one at a good price .. I had
2 from him and love his work

and the shipping cost of a 220 duplexer is not that bad either



On Mon, Aug 30, 2010 at 8:44 PM,  wrote:

>
>
>  Thank you for your response.
> The problem is that the repeater is located on top of a building and the
> tower on that building is only about 20 feet tall. We can move the two
> antennas apart horizontally, but only 20 feet vertically.  Duplexers are way
> too expensive and hard to find for the 200 Mhz band.  We are running about
> 20 watts and the frequency separation is 1.6 mhz.  Sometimes a week signal
> comes in and sometimes the transceiver is desensitizing the receiver and
> covers it up.  Any suggestions?
> Thanks
> Chris
>
>  In a message dated 8/30/2010 8:36:53 P.M. Eastern Daylight Time,
> wb6...@verizon.net writes:
>
>
>
> Chris,
>
> You do not have to use a duplexer, but it makes building a repeater SO much
> easier! Keep in mind that "antenna separation" usually means vertical
> separation, not horizontal separation. Moreover, the same isolation
> provided by 1000 feet of horizontal separation might be provided by 10 feet
> of vertical separation. The amount of isolation you need is based generally
> on the transmit power, frequency separation between TX and RX, and the
> sensitivity of the receiver. The receiver bandwidth and antenna types also
> play a factor.
>
> 73, Eric Lemmon WB6FLY
>
>
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:Repeater-Builder@yahoogroups.com]
> On Behalf Of Mackey
> Sent: Monday, August 30, 2010 4:44 PM
> To: Repeater-Builder@yahoogroups.com 
> Subject: [Repeater-Builder] Duplexers
>
> Our club was recently given a 220 repeater. We have two seperate antennas.
> We do not have a duplexer. My question is do we have to have a duplexer?
> How
> can we keep the transmitter from desensitizing the receiver? The antennas
> are apart but can be moved farther.
> Thanks
> Chris
> Kg4bek
>
>   
>

Re: [Repeater-Builder] Duplexers

[Paul Plack]

Chris,

There aren't many ways around the laws of physics. If you can't get adequate 
physical separation, and can't afford a duplexer...perhaps you just can't 
afford to operate a repeater.

Can you gather enough interested users, and get everyone to chip in for a 
duplexer? If not, maybe your local user community isn't large enough to need a 
220 MHz repeater!

You might be able to gather a group adequate to fund and support a 220 repeater 
if you got closer to the Charleston area, linked into a hub in Charleston, etc. 
Your elevation might have some definite linking possibilities if folks in 
Charleston wanted a 220 MHz hub that could get them coverage farther west on US 
26, for example.

Generally, if you need to raise money to get a project done, you need to be 
able to cover a population center large enough to include a bunch of potential 
users. Given your area's population growth, if you have the connections, 
getting the town or county to help fund a sanctioned emergency repeater system 
might be an avenue, but you'd better have enough users on 220 to make it work 
if it's ever called up. The economy will be against you in this pursuit; your 
population growth will be an advantage.

Remember, finding the money to get it built and installed is only the start of 
the financial fun. You'll need an ongoing budget for maintenance and repair, or 
the machine will spend too much time down, and the users will wander off to 
other pursuits.

Good luck!

73,
Paul, AE4KR

  - Original Message - 
  From: cmcclel...@aol.com 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Monday, August 30, 2010 6:44 PM
  Subject: Re: [Repeater-Builder] Duplexers




  Thank you for your response.
  The problem is that the repeater is located on top of a building and the 
tower on that building is only about 20 feet tall. We can move the two antennas 
apart horizontally, but only 20 feet vertically.  Duplexers are way too 
expensive and hard to find for the 200 Mhz band.  We are running about 20 watts 
and the frequency separation is 1.6 mhz.  Sometimes a week signal comes in and 
sometimes the transceiver is desensitizing the receiver and covers it up.  Any 
suggestions?
  Thanks
  Chris

  In a message dated 8/30/2010 8:36:53 P.M. Eastern Daylight Time, 
wb6...@verizon.net writes:
  
Chris,

You do not have to use a duplexer, but it makes building a repeater SO much
easier! Keep in mind that "antenna separation" usually means vertical
separation, not horizontal separation. Moreover, the same isolation
provided by 1000 feet of horizontal separation might be provided by 10 feet
of vertical separation. The amount of isolation you need is based generally
on the transmit power, frequency separation between TX and RX, and the
sensitivity of the receiver. The receiver bandwidth and antenna types also
play a factor.

73, Eric Lemmon WB6FLY


-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Mackey
Sent: Monday, August 30, 2010 4:44 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Duplexers

Our club was recently given a 220 repeater. We have two seperate antennas.
We do not have a duplexer. My question is do we have to have a duplexer? How
can we keep the transmitter from desensitizing the receiver? The antennas
are apart but can be moved farther.
Thanks
Chris
Kg4bek





  

RE: [Repeater-Builder] Duplexers

[Eric Lemmon]

Chris,

I plugged your frequency separation and power level into CommShop, and
assumed a receiver sensitivity of 0.3 microvolts.  The program responded
that at least 77 dB of isolation is needed for zero desense- which is the
obvious goal of any repeater builder.  CommShop calculated that 77 dB of
isolation can be achieved by 112 feet of vertical separation or 5,681 feet
of horizontal separation.  I will readily admit that CommShop is not
perfect, since it makes many assumptions that may or may not be valid in
your particular case.  That said, it has been remarkably close in its
projections- in my personal experience, anyway.

The reality of your situation is that you do not have sufficient real estate
or tower height to construct a workable repeater with separate TX and RX
antennas.  I strongly suggest that you give up on the two antenna idea and
start looking for a good used 220 MHz duplexer.  My own 220 MHz repeater
uses a Telewave TPRD-2254 duplexer, and has been desense-free.  Although
this duplexer is available new for about $1,120 with a Ham discount, I have
seen this exact duplexer on the used market for less than $500.  More info
about the TPRD-2254 duplexer is here:


73, Eric Lemmon WB6FLY


-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of cmcclel...@aol.com
Sent: Monday, August 30, 2010 5:45 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

  

Thank you for your response.
The problem is that the repeater is located on top of a building and the
tower on that building is only about 20 feet tall. We can move the two
antennas apart horizontally, but only 20 feet vertically.  Duplexers are way
too expensive and hard to find for the 200 Mhz band.  We are running about
20 watts and the frequency separation is 1.6 mhz.  Sometimes a week signal
comes in and sometimes the transceiver is desensitizing the receiver and
covers it up.  Any suggestions?
Thanks
Chris
 
In a message dated 8/30/2010 8:36:53 P.M. Eastern Daylight Time,
wb6...@verizon.net writes:

  

Chris,

You do not have to use a duplexer, but it makes building a repeater
SO much
easier! Keep in mind that "antenna separation" usually means
vertical
separation, not horizontal separation. Moreover, the same isolation
provided by 1000 feet of horizontal separation might be provided by
10 feet
of vertical separation. The amount of isolation you need is based
generally
on the transmit power, frequency separation between TX and RX, and
the
sensitivity of the receiver. The receiver bandwidth and antenna
types also
play a factor.

73, Eric Lemmon WB6FLY


-Original Message-
From: Repeater-Builder@yahoogroups.com
<mailto:Repeater-Builder%40yahoogroups.com> 
[mailto:Repeater-Builder@yahoogroups.com
<mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Mackey
Sent: Monday, August 30, 2010 4:44 PM
To: Repeater-Builder@yahoogroups.com
<mailto:Repeater-Builder%40yahoogroups.com> 
    Subject: [Repeater-Builder] Duplexers

Our club was recently given a 220 repeater. We have two seperate
antennas.
We do not have a duplexer. My question is do we have to have a
duplexer? How
can we keep the transmitter from desensitizing the receiver? The
antennas
are apart but can be moved farther.
Thanks
Chris
Kg4bek

RE: [Repeater-Builder] Duplexers

[ka9qjg]

Since We are on the Topic of Duplexers,  And some claim there is no such
thing as a Dumb Question but  at the Risk of  Asking one  I will take a
chance ,   I have the Wacom 4 can on My 220 System, 

 

The Question I have in a non controlled environment such as No Heat or Air 

 

  Will the Duplexer have any problems inside with Condensation from Heating
up in use and Cooling down 

 

Thanks Don 

 

KA9QJG 

 

 

 

RE: [Repeater-Builder] Duplexers

[Mike Morris]

Theory: <http://www.repeater-builder.com/antenna/thoughts-on-isolation.html>

Applications: <http://www.repeater-builder.com/antenna/separation.html>

Mike WA6ILQ


At 05:36 PM 08/30/10, you wrote:
>Chris,
>
>You do not have to use a duplexer, but it makes building a repeater SO much
>easier!  Keep in mind that "antenna separation" usually means vertical
>separation, not horizontal separation.  Moreover, the same isolation
>provided by 1000 feet of horizontal separation might be provided by 10 feet
>of vertical separation.  The amount of isolation you need is based generally
>on the transmit power, frequency separation between TX and RX, and the
>sensitivity of the receiver.  The receiver bandwidth and antenna types also
>play a factor.
>
>73, Eric Lemmon WB6FLY
>
>
>-Original Message-
>From: Repeater-Builder@yahoogroups.com
>[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Mackey
>Sent: Monday, August 30, 2010 4:44 PM
>To: Repeater-Builder@yahoogroups.com
>Subject: [Repeater-Builder] Duplexers
>
>
>
>Our club was recently given a 220 repeater. We have two seperate antennas.
>We do not have a duplexer. My question is do we have to have a duplexer? How
>can we keep the transmitter from desensitizing the receiver? The antennas
>are apart but can be moved farther.
>Thanks
>Chris
>Kg4bek
>
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
>No virus found in this incoming message.
>Checked by AVG - www.avg.com
>Version: 9.0.851 / Virus Database: 271.1.1/3103 - Release Date: 
>08/30/10 11:34:00

RE: [Repeater-Builder] Duplexers

[ka9qjg]

Wow this must of Really been a Dumb question  , No one  answered it

 

Don KA9QJG 

 

From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of ka9qjg
Sent: Monday, August 30, 2010 9:07 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers

 

  

Since We are on the Topic of Duplexers,  And some claim there is no such
thing as a Dumb Question but  at the Risk of  Asking one  I will take a
chance ,   I have the Wacom 4 can on My 220 System, 

 

The Question I have in a non controlled environment such as No Heat or Air 

 

  Will the Duplexer have any problems inside with Condensation from Heating
up in use and Cooling down 

 

Thanks Don 

 

KA9QJG 

 

 

 



 

Re: [Repeater-Builder] Duplexers

[Chuck Kelsey]

No problem. Most are in non-climate controlled environments.

Chuck
WB2EDV


  - Original Message - 
  From: ka9qjg 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Tuesday, August 31, 2010 1:42 PM
  Subject: RE: [Repeater-Builder] Duplexers





  Wow this must of Really been a Dumb question  , No one  answered it

   

  Don KA9QJG 

   

  From: Repeater-Builder@yahoogroups.com 
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of ka9qjg
  Sent: Monday, August 30, 2010 9:07 PM
  To: Repeater-Builder@yahoogroups.com
  Subject: RE: [Repeater-Builder] Duplexers

   



  Since We are on the Topic of Duplexers,  And some claim there is no such 
thing as a Dumb Question but  at the Risk of  Asking one  I will take a chance 
,   I have the Wacom 4 can on My 220 System, 

   

  The Question I have in a non controlled environment such as No Heat or Air 

   

Will the Duplexer have any problems inside with Condensation from Heating 
up in use and Cooling down 

   

  Thanks Don 

   

  KA9QJG 

   

Re: [Repeater-Builder] Duplexers

[DCFluX]

I haven't seen problems from condensation.

Now salt water corrosion from installations on a coast, that's a pretty big
problem. I've got a set of cans where the invar has actually rusted, and the
connectors were all shot.

On Tue, Aug 31, 2010 at 10:42 AM, ka9qjg  wrote:

>
>
>  Wow this must of Really been a Dumb question  , No one  answered it
>
>
>
> Don KA9QJG
>
>
>
> *From:* Repeater-Builder@yahoogroups.com [mailto:
> repeater-buil...@yahoogroups.com] *On Behalf Of *ka9qjg
> *Sent:* Monday, August 30, 2010 9:07 PM
> *To:* Repeater-Builder@yahoogroups.com
> *Subject:* RE: [Repeater-Builder] Duplexers
>
>
>
>
>
> Since We are on the Topic of Duplexers,  And some claim there is no such
> thing as a Dumb Question but  at the Risk of  Asking one  I will take a
> chance ,   I have the Wacom 4 can on My 220 System,
>
>
>
> The Question I have in a non controlled environment such as No Heat or Air
>
>
>
>   Will the Duplexer have any problems inside with Condensation from Heating
> up in use and Cooling down
>
>
>
> Thanks Don
>
>
>
> KA9QJG
>
>
>
>
>
>
>
>
>
>
> 

RE: [Repeater-Builder] Duplexers

[mwbesemer]

I have a set of Wacoms on 2-meters in a totally uncompensated shack, 
running from the teens in the winter to probably 150 in the summer. 
I've never had an issued.  I have another set in a similar shack, but it 
it air conditioned in the summer.  They've been out there for 10 years 
and are pristine.  Last time I checked them for alignment, they were 
still perfect.


73,

Mike
WM4B

On Tue, Aug 31, 2010 at 1:42 PM, ka9qjg wrote:


Wow this must of Really been a Dumb question  , No one  answered it

Don KA9QJG

From: Repeater-Builder@yahoogroups.com 
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of ka9qjg

Sent: Monday, August 30, 2010 9:07 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers


Since We are on the Topic of Duplexers,  And some claim there is no such 
thing as a Dumb Question but  at the Risk of  Asking one  I will take a 
chance ,   I have the Wacom 4 can on My 220 System,


The Question I have in a non controlled environment such as No Heat or 
Air


  Will the Duplexer have any problems inside with Condensation from 
Heating up in use and Cooling down


Thanks Don

KA9QJG





 <http://docs.yahoo.com/info/terms/>

RE: [Repeater-Builder] Duplexers

[ka9qjg]

OK Great , Thanks to Everyone who answered ,  I will sleep better now  one less 
thing to worry about 

 

Don KA9QJG 

 

From: Repeater-Builder@yahoogroups.com 
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of mwbese...@cox.net
Sent: Tuesday, August 31, 2010 12:51 PM
To: repeater-builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers

 

  

I have a set of Wacoms on 2-meters in a totally uncompensated shack, running 
from the teens in the winter to probably 150 in the summer.  I've never had an 
issued.  I have another set in a similar shack, but it it air conditioned in 
the summer.  They've been out there for 10 years and are pristine.  Last time I 
checked them for alignment, they were still perfect.

 

73,

 

Mike

WM4B 





On Tue, Aug 31, 2010 at 1:42 PM, ka9qjg wrote:

 

   

Wow this must of Really been a Dumb question  , No one  answered it 

  

Don KA9QJG 

  

From: Repeater-Builder@yahoogroups.com 
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of ka9qjg 

Sent: Monday, August 30, 2010 9:07 PM 

To: Repeater-Builder@yahoogroups.com 

Subject: RE: [Repeater-Builder] Duplexers 

  

  

Since We are on the Topic of Duplexers,  And some claim there is no such thing 
as a Dumb Question but  at the Risk of  Asking one  I will take a chance ,   I 
have the Wacom 4 can on My 220 System, 

  

The Question I have in a non controlled environment such as No Heat or Air 

  

  Will the Duplexer have any problems inside with Condensation from Heating up 
in use and Cooling down 

  

Thanks Don 

  

KA9QJG 

  

  

  

 

  



 

RE: [Repeater-Builder] Duplexers

[Chris Fowler]

For there to be condensation there must be humidity in the air. The more
humidity, the more condensation.

Duplexers are in harsh environments now and I don't think it has been a
problem.  Condensation on the outside of the cans should not cause any
issue for what is going inside.


On Tue, 2010-08-31 at 12:42 -0500, ka9qjg wrote:
> 
> 
> Wow this must of Really been a Dumb question  , No one  answered it
> 
>  
> 
> Don KA9QJG 
> 
>  
> 
> From:Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of ka9qjg
> Sent: Monday, August 30, 2010 9:07 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Duplexers
> 
> 
>  
> 
>   
> 
> Since We are on the Topic of Duplexers,  And some claim there is no
> such thing as a Dumb Question but  at the Risk of  Asking one  I will
> take a chance ,   I have the Wacom 4 can on My 220 System, 
> 
>  
> 
> The Question I have in a non controlled environment such as No Heat or
> Air 
> 
>  
> 
>   Will the Duplexer have any problems inside with Condensation from
> Heating up in use and Cooling down 
> 
>  
> 
> Thanks Don 
> 
>  
> 
> KA9QJG 
> 
>  
> 
>  
> 
>  
> 
> 
> 
>  
> 
> 
> 
> 
> 

RE: [Repeater-Builder] Duplexers

[mwbesemer]

Typically, you'll get condensation when you have high humidity (with 
HIGH being a relative term) and rapid changes in temperature.  Working 
in an air-conditioned building and walking outside into a hot, Georgia 
afternoon, my glasses and I are quite familiar with the scenario.


73,

Mike
WM4B

On Tue, Aug 31, 2010 at 2:08 PM, Chris Fowler wrote:

   For there to be condensation there must be humidity in the air. The 
more

humidity, the more condensation.

Duplexers are in harsh environments now and I don't think it has been a
problem.  Condensation on the outside of the cans should not cause any
issue for what is going inside.

On Tue, 2010-08-31 at 12:42 -0500, ka9qjg wrote:



Wow this must of Really been a Dumb question  , No one  answered it


Don KA9QJG


From: Repeater-Builder@yahoogroups.com 
 
[mailto: Repeater-Builder@yahoogroups.com 
 
] On Behalf Of ka9qjg Sent: Monday, August 30, 2010 9:07 PM To: 
Repeater-Builder@yahoogroups.com 
 
Subject: RE: [Repeater-Builder] Duplexers






Since We are on the Topic of Duplexers,  And some claim there is no 
such thing as a Dumb Question but  at the Risk of  Asking one  I will 
take a chance ,   I have the Wacom 4 can on My 220 System,



The Question I have in a non controlled environment such as No Heat or 
Air



  Will the Duplexer have any problems inside with Condensation from 
Heating up in use and Cooling down



Thanks Don


KA9QJG


















 <http://docs.yahoo.com/info/terms/>

Re: [Repeater-Builder] Duplexers

[mwbesemer]

Wow... that's UGLY!

I wonder if a small heat-tape would prevent that from happening?

73,

Mike
WM4B

On Tue, Aug 31, 2010 at 2:17 PM, Roger Stacey wrote:

   On Vancouver Island B.C we do have humidity. The site is at 4400 ft.

Roger
VA7RS

- Original Message -
From: "Chris Fowler" < k...@k4fh.com 
 >
To: < Repeater-Builder@yahoogroups.com 
 


Cc: "ka9qjg" < ka9...@wowway.com 
 >

Sent: Tuesday, August 31, 2010 11:08 AM
Subject: RE: [Repeater-Builder] Duplexers

For there to be condensation there must be humidity in the air. The 
more humidity, the more condensation.
Duplexers are in harsh environments now and I don't think it has been 
a problem.  Condensation on the outside of the cans should not cause 
any issue for what is going inside.


On Tue, 2010-08-31 at 12:42 -0500, ka9qjg wrote:



Wow this must of Really been a Dumb question  , No one  answered it


Don KA9QJG


From: Repeater-Builder@yahoogroups.com 
 
[mailto: Repeater-Builder@yahoogroups.com 
 
] On Behalf Of ka9qjg Sent: Monday, August 30, 2010 9:07 PM To: 
Repeater-Builder@yahoogroups.com 
 
Subject: RE: [Repeater-Builder] Duplexers






Since We are on the Topic of Duplexers,  And some claim there is no 
such thing as a Dumb Question but  at the Risk of  Asking one  I will 
take a chance ,   I have the Wacom 4 can on My 220 System,



The Question I have in a non controlled environment such as No Heat 
or Air



  Will the Duplexer have any problems inside with Condensation from 
Heating up in use and Cooling down



Thanks Don


KA9QJG






















Yahoo! Groups Links




--

No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.851 / Virus Database: 271.1.1/3104 - Release Date: 08/30/10
23:34:00


 <http://docs.yahoo.com/info/terms/>

Re: [Repeater-Builder] Duplexers

[Ralph Mowery]

Guess that I should answer it then.  I have had a 4 can Wacom 220 mhz duplexer 
in a 6 foot by 6 foot building for around 20 years and it still works.  Also in 
the same building is a Phelps Dodge 6 can 146 mhz duplexer that has been there 
for about 35 years.

This is in the middle of North Carolina where it gets up to around 100 in the 
summer and around 15 deg in the winter.  The building only has a couple of 
repeaters in it and is not heated or cooled.  Made out of cinder blocks.

 




From: ka9qjg 
To: Repeater-Builder@yahoogroups.com
Sent: Tue, August 31, 2010 1:42:32 PM
Subject: RE: [Repeater-Builder] Duplexers




Wow this must of Really been a Dumb question  , No one  answered it
 
Don KA9QJG 
 
From:Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] 
On Behalf Of ka9qjg
Sent: Monday, August 30, 2010 9:07 PM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers
 
  
Since We are on the Topic of Duplexers,  And some claim there is no such thing 
as a Dumb Question but  at the Risk of  Asking one  I will take a chance ,   I 
have the Wacom 4 can on My 220 System, 

 
The Question I have in a non controlled environment such as No Heat or Air 
 
  Will the Duplexer have any problems inside with Condensation from Heating up 
in use and Cooling down 

 
Thanks Don 
 
KA9QJG 



  

Re: [Repeater-Builder] Duplexers

[Joe]

 I've never had a problem.  I would say that if the duplexers are out 
of tune on the transmit side there is a possibility that they might get 
hot, then cool off.  This may cause them to take in moist air and cause 
condensation.  I've never seen it happen, but I can see how it could.


73, Jow, K1ike

On 8/31/2010 2:05 PM, ka9qjg wrote:
OK Great , Thanks to Everyone who answered ,  I will sleep better now  
one less thing to worry about 

RE: [Repeater-Builder] Duplexers

[Ross Johnson]

Has anyone mentioned band-pass cavities? One on the RX side could be
enough and one more on the TX would do it for sure. There're some for
220 for less then a $100 on ebay right now. This might sound off the
wall but I once saw a DB4021 UHF band-pass cavity tune up quite well on
2 meters!!! Only about .6db insertion loss on 2 meters. So if you have a
VHF or UHF band-pass I would try sweeping it with the resonator in a few
different spots and see if you find any harmonics near your target
frequency. And I would only do this on the RX side. That UHF cavity
tuned to 2 meters did get warmer then the other db4001's, probably an
impedance issue. Forgot to mention the swr on that cavity was about 1.3
. So is this the worst practice ever, or what happened? 
 
~Ross
-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Mackey
Sent: Monday, August 30, 2010 4:44 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Duplexers
 
  
Our club was recently given a 220 repeater. We have two seperate
antennas. We do not have a duplexer. My question is do we have to have a
duplexer? How can we keep the transmitter from desensitizing the
receiver? The antennas are apart but can be moved farther.
Thanks
Chris
Kg4bek

Re: [Repeater-Builder] Duplexers

[Rick Szajkowski]

My 2 duplexers are in a space with no heat and no air .. and no problems

Keep them off a COLD floor and you should be fine as they can move with the
temp in the room they are in

On Tue, Aug 31, 2010 at 1:42 PM, ka9qjg  wrote:

>
>
>  Wow this must of Really been a Dumb question  , No one  answered it
>
>
>
> Don KA9QJG
>
>
>
> *From:* Repeater-Builder@yahoogroups.com [mailto:
> repeater-buil...@yahoogroups.com] *On Behalf Of *ka9qjg
> *Sent:* Monday, August 30, 2010 9:07 PM
>
> *To:* Repeater-Builder@yahoogroups.com
> *Subject:* RE: [Repeater-Builder] Duplexers
>
>
>
>
>
> Since We are on the Topic of Duplexers,  And some claim there is no such
> thing as a Dumb Question but  at the Risk of  Asking one  I will take a
> chance ,   I have the Wacom 4 can on My 220 System,
>
>
>
> The Question I have in a non controlled environment such as No Heat or Air
>
>
>
>   Will the Duplexer have any problems inside with Condensation from Heating
> up in use and Cooling down
>
>
>
> Thanks Don
>
>
>
> KA9QJG
>
>
>
>
>
>
>
>
>   
>

Re: [Repeater-Builder] Duplexers

[Rick Szajkowski]

Thats the same duplexer I had .. built my Bob Mortorn when he was at
sinclair .. never had that problem here though

Rick va3rzs

On Tue, Aug 31, 2010 at 2:17 PM, Roger Stacey  wrote:

>
>
> On Vancouver Island B.C we do have humidity. The site is at 4400 ft.
>
> Roger
> VA7RS
>
>
> - Original Message -
> From: "Chris Fowler" >
> To: 
> >
> Cc: "ka9qjg" >
> Sent: Tuesday, August 31, 2010 11:08 AM
> Subject: RE: [Repeater-Builder] Duplexers
>
> > For there to be condensation there must be humidity in the air. The more
> > humidity, the more condensation.
> >
> > Duplexers are in harsh environments now and I don't think it has been a
> > problem. Condensation on the outside of the cans should not cause any
> > issue for what is going inside.
> >
> >
> > On Tue, 2010-08-31 at 12:42 -0500, ka9qjg wrote:
> >>
> >>
> >> Wow this must of Really been a Dumb question , No one answered it
> >>
> >>
> >>
> >> Don KA9QJG
> >>
> >>
> >>
> >> From:Repeater-Builder@yahoogroups.com
> >> [mailto:Repeater-Builder@yahoogroups.com]
> On Behalf Of ka9qjg
> >> Sent: Monday, August 30, 2010 9:07 PM
> >> To: Repeater-Builder@yahoogroups.com
> >> Subject: RE: [Repeater-Builder] Duplexers
> >>
> >>
> >>
> >>
> >>
> >>
> >> Since We are on the Topic of Duplexers, And some claim there is no
> >> such thing as a Dumb Question but at the Risk of Asking one I will
> >> take a chance , I have the Wacom 4 can on My 220 System,
> >>
> >>
> >>
> >> The Question I have in a non controlled environment such as No Heat or
> >> Air
> >>
> >>
> >>
> >> Will the Duplexer have any problems inside with Condensation from
> >> Heating up in use and Cooling down
> >>
> >>
> >>
> >> Thanks Don
> >>
> >>
> >>
> >> KA9QJG
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> > 
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
>
> --
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.851 / Virus Database: 271.1.1/3104 - Release Date: 08/30/10
> 23:34:00
>  
>

Re: [Repeater-Builder] Duplexers

[Paul Plack]

Don, this is a natural response, or lack thereof. If you ask, "will I have this 
problem," and nobody else has had it, that doesn't mean they can guarantee YOU 
won't have it, so they refrain from commenting.

I learned a lot from my experience with one outdoor, rooftop repeater I built. 
I was expecting condensation in places where I could find no evidence of it 
actually occurring. It finally dawned on me that even if the ambient humidity 
is 100%, and condensation is collecting on the outside of the cabinet, the 
equipment inside is safe as long as the temp there remains even slightly above 
the outside.

If you have to mount the duplexers away from the transmitter and power supply, 
condensation may be more difficult to control. Whenever possible, I will always 
try to keep the cans (and all the equipment) slightly warmer than outside 
ambient. I believe that in most installations, even in non-climate-controlled 
buildings, this is likely to happen by default, especially if you are co-sited 
with lots of other people's stuff.

On my rooftop repeater, I ended up using a completely sealed, gasketed steel 
cabinet, painted a light color, with no vents to the outside whatsoever, and 
relied on plain old heat loss through the cabinet walls for dissipation. When I 
changed out my 2-watt, solar-powered, Repco UHF repeater for a 35-watt, 
converted GE Mastr II powered from the AC mains, I expected problems, so I put 
a 119ºF attic fan switch on the transmitter's heatsink, wired to a logic input 
on the controller. It never triggered, even in the summer, and this was in 
orlando, FL.

The commercial stuff is based on components which were designed to stay happy 
for years locked in a car trunk. It may be possible to overdo ventilation. I 
think I'd rather err on the side of staying a little warm in a repeater shack, 
within reason.

73,
Paul, AE4KR
  - Original Message - 
  From: ka9qjg 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Tuesday, August 31, 2010 11:42 AM
  Subject: RE: [Repeater-Builder] Duplexers




  Wow this must of Really been a Dumb question  , No one  answered it

  >>  Will the Duplexer have any problems inside with Condensation from Heating 
up in use and Cooling down