Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Kevin Custer]

Mathew, et al,

Without very expensive test equipment, there is no way to calculate 
the correct length needed to match a transmitter to a duplexer.   The 
correct length will seldom be some an exact wavelength or simple 
fraction of it.  The terminal impedance of a transmitter can change with 
the change of output power level, so the correct length at one power 
*could* be different from another outputted power.  For most of us, this 
length must be determined experimentally, and is another reason why a T 
Matcher is nice, because it's simpler to tune it, then cut cables.

In the case of Charles' repeater, I believe he was simply lucky when he 
cut the cable to length, and all was well.

Kevin

Mathew Quaife wrote:

 Seems like I might be learning something here.  I took for assumption 
 that the shortest cable length to from the transmitter to the amp, and 
 from the amp to the duplexer was the way to go.  Am I to understand 
 that a certain length should be used, ie a full wave length perhaps?  
 I have some cables lying there, I could try them and see if I notice 
 any changes.  I know 20 watts will not make the difference, but am 
 rather more concerned with spurs that might make it's way out of the 
 repeater.
  
 Mathew


 */Charles Miller [EMAIL PROTECTED]/* wrote:

 Mathew,

 I would think that you have a little more insertion loss on the TX
 side than
 you think, or the cavity may need a little tuning. You may also
 need to try
 different lengths of coax between the transmitter and duplexer.

 I have had to change the coax length on one of my UHF repeater
 because the
 coax was to short. After calculating the correct length for the
 coax I was
 using for a full wavelength I was getting the proper RF out.

 I believe someone else suggested doing this, and it is a very good
 idea. If
 all else fails, and this is NOT recommended with 200 watts RF
 input, you can
 make very small adjustments on the tuning rods. DO NOT tune the
 rods with
 the transmitter on as you can ARC the cavity tuning slug and
 damage it. Try
 1/8th turns at first and see if the output power goes up or down.

 I have done this in the past, however it is NOT recommended. Great
 care must
 be taken when tuning a cavity in this manor as the cavity can be
 damaged
 easily at this power level. If you have 25 watts available you
 should be
 able to tune it easier but still be careful.

 Charles Miller





 
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Mathew Quaife]

Well just for the sake of trying, I'm going to change the one length of cable going from the pa to the duplexer and see if that helps. I am beginning to believe it is the first can in the TX side that is giving me all the fits, as this is the second time I have had to retune it. I don't knowif 600 Kc's is going to really make a big difference, but I'm going to switch it with one from the RX side and see if I can get past that notch in the rod, where tunning is extrememly difficult. It has been that way since I got it, I believe it was overtighten at one point. My goal next year is to remove the duplexers and use remote receive sites with the first one being about three miles from the transmitter.Will try it this evening and see what happens and let everyone know if I seen any change. Thanks for the input.Now I see why they say it is such mass confusion when two people talk at once..Hi
 Hi. DUPLEX, not a "SINGLE" thing easy about itlol...Mathew  Chuck Kelsey [EMAIL PROTECTED] wrote:  According to duplexer manufacturers, there is not a "right" length but there can be a "wrong" length. Some call it an "adverse" length. They suggest trying a different length if there is a problem. It's impossible to get a specific length like 1/4 or 1/2. Where do you measure from and to? From the PA transistors? From the connector? No way to tell, so you can't.ChuckWB2EDVMathew Quaife wrote: Seems like I might be learning something here. I took for assumption  that the shortest cable length to from the transmitter to the amp, and  from the amp to the duplexer was the way to go. Am I to understand that  a certain
 length should be used, ie a full wave length perhaps? I have  some cables lying there, I could try them and see if I notice any  changes. I know 20 watts will not make the difference, but am rather  more concerned with spurs that might make it's way out of the repeater.  Mathew  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/  
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Mathew Quaife]

Well I did some testing this evening with some cables, several different lengths. The original is a 4' length of Superflex FSJ1, power out of the duplexer is 115 Watts, now tested on a Bird, and a smalltweak on the duplexers, so I am very close. I changed to a 5' cable, 90 watts, 6' gave 90 watts, a 4.5' and got 100 watts, 3.5' gave me 110 watts, so I guess my magical number was 4'. I guess they say, if it ain't broke, don't fix it. "And no, I did not tune the duplexers while transmitting". Thanks to all whom replied, I think I am as close as I am going to get, and the system seems to be working like it should, other than the normal receiver problems that I have, and they will live that way until the receiver is changed out.Mathew  Kevin Custer [EMAIL PROTECTED] wrote:  Mathew, et al,Without very expensive test equipment, there is no way to "calculate" the correct length needed to match a transmitter to a duplexer. The correct length will seldom be some an exact wavelength or simple fraction of it. The terminal impedance of a transmitter can change with the change of output power level, so the correct length at one power *could* be different from another outputted power. For most of us, this length must be determined experimentally, and is another reason why a T Matcher is nice, because it's simpler to tune it, then cut cables.In the case of Charles' repeater, I believe he was simply lucky when he cut the cable to length, and all was well.KevinMathew Quaife wrote: Seems like I might be learning something here. I took for assumption  that the shortest cable length to from the transmitter to the amp, and  from the amp to
 the duplexer was the way to go. Am I to understand  that a certain length should be used, ie a full wave length perhaps?  I have some cables lying there, I could try them and see if I notice  any changes. I know 20 watts will not make the difference, but am  rather more concerned with spurs that might make it's way out of the  repeater.  Mathew */Charles Miller <[EMAIL PROTECTED]>/* wrote: Mathew, I would think that you have a little more insertion loss on the TX side than you think, or the cavity may need a little tuning. You may also need to try different lengths of coax between the transmitter and duplexer. I have had to change the coax length on one of my UHF repeater because the coax was to short. After calculating the correct length for the coax I was using for a full wavelength I
 was getting the proper RF out. I believe someone else suggested doing this, and it is a very good idea. If all else fails, and this is NOT recommended with 200 watts RF input, you can make very small adjustments on the tuning rods. DO NOT tune the rods with the transmitter on as you can ARC the cavity tuning slug and damage it. Try 1/8th turns at first and see if the output power goes up or down. I have done this in the past, however it is NOT recommended. Great care must be taken when tuning a cavity in this manor as the cavity can be damaged easily at this power level. If you have 25 watts available you should be able to tune it easier but still be careful. Charles MillerYahoo! Groups Links* To visit your group on the web, go
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Charles Miller]

- Original Message - 
From: Kevin Custer [EMAIL PROTECTED]

 In the case of Charles' repeater, I believe he was simply lucky when he
 cut the cable to length, and all was well.


Could not have said it better Kevin. I was lucky. I did have one thing going
for me though. I had an isolator on the output of the transmitter that
helped a lot.

Charles Miller






 
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Kevin Custer]

See additional information below Eric's well written dissertation,

Actually, if the duplexer insertion loss is really 2.2 dB, you should get
120.5 watts out for 200 watts in.  Once you consider the small additional
loss in jumpers, connectors, adapters, etc., you're not too far off the
mark.  The tolerance and linearity of your power measuring instrument may
contribute a small error.

The major difference between your two conditions is that in one, the PA is
feeding a resistive load, and in the other, it is feeding a highly
reactive load- the duplexer.  If you experiment with the length of the
jumper connecting the PA to the duplexer, you will probably see a
significant change in output power- which may be better or worse.  You can
also try an impedance matcher (Z-Matcher) at the output of the PA, to
see if you can optimize the match between the PA and the duplexer.

Bear in mind that when a duplexer leaves the factory with precisely-set
tuning and insertion loss, it may suffer considerable vibration during
shipment.  That's why I always check duplexers and bandpass cavities on a
network analyzer before installing them.  It's rare that such devices
arrive in perfect adjustment.


Very much agreed, and in addition, the Duplexer Factorys uses equipment 
that presents a perfect 50 ohm source/load impedance to the duplexer.  
Many of us hams use converted commercial equipment for our repeaters.  
This equipment, when operated outside its intended tuning frequency, may 
not present a perfect 50 ohm impedance anymore, and the use of custom 
cable lengths and Z Matchers become more common to match the duplexer to 
the radio set.

The other thing   All of the RF power being produced at the 200 watt 
level may not be on the operating frequency.  Remember that a watt meter 
reads total power, not just the power on the repeater frequency.  If the 
transmitter or PA or both are spurious or dirty to some degree, you may 
actually have less power (on your transmitter frequency) than you think, 
even though the power 'reads' higher.  Since the duplexer provides 
filtering, the power leaving the duplexer may show less due to the 
removal of the spurious energy.

Kevin Custer




 
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RE: [Repeater-Builder] Duplexer loss different with more power, Why?

[Jeff DePolo WN3A]

 The other thing   All of the RF power being produced at 
 the 200 watt 
 level may not be on the operating frequency.  Remember that a 
 watt meter 
 reads total power, not just the power on the repeater 
 frequency.  If the 
 transmitter or PA or both are spurious or dirty to some 
 degree, you may 
 actually have less power (on your transmitter frequency) than 
 you think, 
 even though the power 'reads' higher.  Since the duplexer provides 
 filtering, the power leaving the duplexer may show less due to the 
 removal of the spurious energy.
 
 Kevin Custer

And to add to that, bear in mind that if you only have one wattmeter and you
use it to first measure the input power to the duplexer, and then disconnect
it and move it to the output of the duplexer that you've changed the
electrical length of the cabling between the devices.  Unless everything is
tuned and operating at exactly 50+j0, changing the effective length of any
of the cables is going to change the Z that the transmitter sees.  To get
around this problem you have two options:

1.  Make up a short patch cable with the same connectors as your wattmeter,
and substitute it in place of the wattmeter to maintain a constant
electrical length when moving the wattmeter between devices in the system.
The cable must be the same electrical length as the wattmeter's effective
electrical length.  For something like a Bird 43, the length is known (and
published by Bird) making this easy.  For other wattmeters, particularly
non-thruline types, this becomes more difficult.  

2.  Use two wattmeters, calibrating the differences in readings by first
connecting the two back-to-back (preferably without an jumper cable).
Transmit through the wattmeters into a dummy load and record the forward
power readings of both wattmeters.  Determine the error between the two in
dB.  Then put the wattmeters into the system at their appropirate locations,
determine the measured loss based on their readings, and then correct that
value by the difference you originally recorded.

--- Jeff

Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant 






 
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Paul Kelley]

OK, let's think about several things here...

 All three of them looked identical, 
 with rejection on the rx side of -80 dBm on each single cavity.

Do you mean -80 dB? I have never seen a single cavity that could 
offer 80 dB notch depth. If you really meant -80 dBm (80 dB below 1 
milliwatt) then we need to know what the power input was...

 I tied them all together, the rx rejection was better then -10 dBm, 

I assume you meant -100 dB... OK, sounds good.

 I input 4 watts into them all tied together, 
 connected to a dummy load, and got three watts out.  Then I tied the 
 duplexers back into the repeater, with 200 watts input, I am getting 
 100 watts output, into the same dummy load.  Refelcted power was less 
 than 1/10 of a watt.  What am I missing here.  

1/10 of a watt *where*? Is this on a meter inserted between the 
duplexer and dummy load? Or on a meter inserted between the 
transmitter and duplexer?

You may not have a good SWR looking into the duplexer, which could:
1) cause your transmitter to make more or less than rated power
2) affect accuracy of any power readings you try to make at that 
point in the system
3) cause the tramsitter to go spurious and not all the power is on 
the frequency you think it is

Try this for a rough look at things... put the meter between the 
transmitter and duplexer. What is the SWR there? Now, add one 
quarter wavelength (electrical) of additional coax between the meter 
and duplexer... do you now get a different SWR reading? If yes then 
you don't really know what impedance the transmitter is really 
seeing, because  SWR is varying with line length. In that case even 
if you put the meter right at the transmitter output socket, you 
still don't know what the real story is. Most all transmitters / PAs 
have a length of 50 ohm cable inside, and perhaps a relay, filter, 
etc. between the impedance matching circuit of the output stage and 
the coax connector going out of the unit. If SWR is varying along 
the transmission line it will also vary along this internal path, 
ending up being who-knows-what at the actual output stage.

The above isn't the best or most recommended method, but is the best 
I can do with one meter... at least I can determine if SWR is 
varying considerably along the line, and if so then I know that my 
trasmitter may not be liking what it sees and my power readings in 
that part of the system may not be accurate.

And none of this takes into account if the transmitter isn't happy 
with the load it may be producing significant power on frequencies 
other than you intend, which totally screws up your power and SWR 
measurements.

 If I am thinking right, 
 I should be getting about 137 watts back out of the duplexer, or close 
 to there. 

As someone else mentioned (sorry, forgot who already!), 200 watts 
-2.2 dB loss is approximately 120 watts, not 137.


 Could there be a mismatch bewteen the duplexers 
 and the amp?

Very likely. See above.

BTW, 3 watts out with 4 watts in would be 1.25 dB loss, so there's 
something fishy about those readings too

Paul




 
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[DCFluX]

If you can't make something work, mess with the test equipment until it does. 

What watt meter were you using? If a Bird, what are the ranges on the
slugs you tested with? I would assume you have one 400-1000MHz 10W, and
one 400-1000MHz 250W. Also you might want to compare the slugs to a
known good slug/meter as occasionally the slugs go out of calibration.














  




  
  
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Charles Miller]

Mathew,

I would think that you have a little more insertion loss on the TX side than
you think, or the cavity may need a little tuning. You may also need to try
different lengths of coax between the transmitter and duplexer.

I have had to change the coax length on one of my UHF repeater because the
coax was to short. After calculating the correct length for the coax I was
using for a full wavelength I was getting the proper RF out.

I believe someone else suggested doing this, and it is a very good idea. If
all else fails, and this is NOT recommended with 200 watts RF input, you can
make very small adjustments on the tuning rods. DO NOT tune the rods with
the transmitter on as you can ARC the cavity tuning slug and damage it. Try
1/8th turns at first and see if the output power goes up or down.

I have done this in the past, however it is NOT recommended. Great care must
be taken when tuning a cavity in this manor as the cavity can be damaged
easily at this power level. If you have 25 watts available you should be
able to tune it easier but still be careful.

Charles Miller

***


 I agree, but at this point, I am only getting 100 watts out of the
duplexers instead of the 137 watts I would like to see.  Now you mention
something that I might now be aware of, and that is the interaction between
the rx side and the tx side, could that have an effect on the power out,
however the rx side of them seems to be great, as I can hear much farther
than I can transmit.  I'm up about 130' in the air with a DB224, the
repeater can be heard for about 30 to 35 miles, but can hear users in about
the 40 to 50 mile range.

   Mathew

***

   Mathew,

 I think you will find that the RF at high power is probable correct. The
 difference you see between low power and high is about 17dB. Unless you
are
 measuring the low power down to 0.01 watts it will be difficult to find
the
 real loss. Provided all is working correctly the RF power levels you list
is
 about right. I would think a little minor tuning could get a little more
 out, but not much.

 The 2.2dB insertion loss is only one calculation. You have the connectors,
 coax, loops (very little here) and some going through to the other side
 (again, very little) has to be calculated.

 Taking this into account you probable have close to 2.5dB loss through the
 whole thing. If this is correct then 200 in and 137 out is about right.

 Just my thoughts.

 Charles Miller


 - Original Message - 
 From: n9lv
 To:
 Sent: Wednesday, November 30, 2005 8:29 PM
 Subject: [Repeater-Builder] Duplexer loss different with more power, Why?


  Ok, running the TX-RX duplexer, with a 2.2 dB insertion loss, I tuned
  the duplexers on the monitor. All three of them looked identical,
  with rejection on the rx side of -80 dBm on each single cavity. Once
  I tied them all together, the rx rejection was better then -10 dBm,
  all went well there. I input 4 watts into them all tied together,
  connected to a dummy load, and got three watts out. Then I tied the
  duplexers back into the repeater, with 200 watts input, I am getting
  100 watts output, into the same dummy load. Refelcted power was less
  than 1/10 of a watt. What am I missing here. If I am thinking right,
  I should be getting about 137 watts back out of the duplexer, or close
  to there. Any ideas? Could there be a mismatch bewteen the duplexers
  and the amp? Cables are all ingood shape.
 
  Mathew
 





 
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Mathew Quaife]

Seems like I might be learning something here. I took for assumption that the shortest cable length to from the transmitter to the amp, and from the amp to the duplexer was the way to go. Am I to understand that a certain length should be used, ie a full wave length perhaps? I have some cables lying there, I could try them and see if I notice any changes. I know 20 watts will not make the difference, but am rather more concerned with spurs that might make it's way out of the repeater.Mathew  Charles Miller [EMAIL PROTECTED] wrote:  Mathew,I would think that you have a little more insertion loss on the TX side thanyou think, or the cavity may need a little tuning. You may also need to trydifferent lengths of coax between the transmitter and duplexer.I
 have had to change the coax length on one of my UHF repeater because thecoax was to short. After calculating the correct length for the coax I wasusing for a full wavelength I was getting the proper RF out.I believe someone else suggested doing this, and it is a very good idea. Ifall else fails, and this is NOT recommended with 200 watts RF input, you canmake very small adjustments on the tuning rods. DO NOT tune the rods withthe transmitter on as you can ARC the cavity tuning slug and damage it. Try1/8th turns at first and see if the output power goes up or down.I have done this in the past, however it is NOT recommended. Great care mustbe taken when tuning a cavity in this manor as the cavity can be damagedeasily at this power level. If you have 25 watts available you should beable to tune it easier but still be careful.Charles Miller*** I agree, but at this
 point, I am only getting 100 watts out of theduplexers instead of the 137 watts I would like to see. Now you mentionsomething that I might now be aware of, and that is the interaction betweenthe rx side and the tx side, could that have an effect on the power out,however the rx side of them seems to be great, as I can hear much fartherthan I can transmit. I'm up about 130' in the air with a DB224, therepeater can be heard for about 30 to 35 miles, but can hear users in aboutthe 40 to 50 mile range. Mathew*** Mathew, I think you will find that the RF at high power is probable correct. The difference you see between low power and high is about 17dB. Unless youare measuring the low power down to 0.01 watts it will be difficult to findthe real loss. Provided all is working correctly the RF power levels you listis about
 right. I would think a little minor tuning could get a little more out, but not much. The 2.2dB insertion loss is only one calculation. You have the connectors, coax, loops (very little here) and some going through to the other side (again, very little) has to be calculated. Taking this into account you probable have close to 2.5dB loss through the whole thing. If this is correct then 200 in and 137 out is about right. Just my thoughts. Charles Miller - Original Message -  From: "n9lv" To: Sent: Wednesday, November 30, 2005 8:29 PM Subject: [Repeater-Builder] Duplexer loss different with more power, Why?  Ok, running the TX-RX duplexer, with a 2.2 dB insertion loss, I tuned  the duplexers on the monitor. All three of them looked identical,  with rejection on the rx side of
 -80 dBm on each single cavity. Once  I tied them all together, the rx rejection was better then -10 dBm,  all went well there. I input 4 watts into them all tied together,  connected to a dummy load, and got three watts out. Then I tied the  duplexers back into the repeater, with 200 watts input, I am getting  100 watts output, into the same dummy load. Refelcted power was less  than 1/10 of a watt. What am I missing here. If I am thinking right,  I should be getting about 137 watts back out of the duplexer, or close  to there. Any ideas? Could there be a mismatch bewteen the duplexers  and the amp? Cables are all ingood shape.   Mathew 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
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Chuck Kelsey]

According to duplexer manufacturers, there is not a right length but 
there can be a wrong length. Some call it an adverse length. They 
suggest trying a different length if there is a problem. It's impossible 
to get a specific length like 1/4 or 1/2. Where do you measure from and 
to? From the PA transistors? From the connector? No way to tell, so you 
can't.

Chuck
WB2EDV





Mathew Quaife wrote:
 Seems like I might be learning something here.  I took for assumption 
 that the shortest cable length to from the transmitter to the amp, and 
 from the amp to the duplexer was the way to go.  Am I to understand that 
 a certain length should be used, ie a full wave length perhaps?  I have 
 some cables lying there, I could try them and see if I notice any 
 changes.  I know 20 watts will not make the difference, but am rather 
 more concerned with spurs that might make it's way out of the repeater.
  
 Mathew
 
 





 
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Charles Miller]

Mathew,

I think you will find that the RF at high power is probable correct. The
difference you see between low power and high is about 17dB. Unless you are
measuring the low power down to 0.01 watts it will be difficult to find the
real loss. Provided all is working correctly the RF power levels you list is
about right. I would think a little minor tuning could get a little more
out, but not much.

The 2.2dB insertion loss is only one calculation. You have the connectors,
coax, loops (very little here) and some going through to the other side
(again, very little) has to be calculated.

Taking this into account you probable have close to 2.5dB loss through the
whole thing. If this is correct then 200 in and 137 out is about right.

Just my thoughts.

Charles Miller


- Original Message - 
From: n9lv [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Wednesday, November 30, 2005 8:29 PM
Subject: [Repeater-Builder] Duplexer loss different with more power, Why?


 Ok, running the TX-RX duplexer, with a 2.2 dB insertion loss, I tuned
 the duplexers on the monitor.  All three of them looked identical,
 with rejection on the rx side of -80 dBm on each single cavity.  Once
 I tied them all together, the rx rejection was better then -10 dBm,
 all went well there.  I input 4 watts into them all tied together,
 connected to a dummy load, and got three watts out.  Then I tied the
 duplexers back into the repeater, with 200 watts input, I am getting
 100 watts output, into the same dummy load.  Refelcted power was less
 than 1/10 of a watt.  What am I missing here.  If I am thinking right,
 I should be getting about 137 watts back out of the duplexer, or close
 to there.  Any ideas?  Could there be a mismatch bewteen the duplexers
 and the amp?  Cables are all ingood shape.

 Mathew









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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Mathew Quaife]

I agree, but at this point, I am only getting 100 watts out of the duplexers instead of the 137 watts I would like to see. Now you mention something that I might now be aware of, and that is the interaction between the rx side and the tx side, could that have an effect on the power out, however the rx side of them seems to be great, as I can hear much farther than I can transmit. I'm up about 130' in the air with a DB224, the repeater can be heard for about 30 to 35 miles, but can hear users in about the 40 to 50 mile range.Mathew  Charles Miller [EMAIL PROTECTED] wrote:  Mathew,I think you will find that the RF at high power is probable correct. Thedifference you see between low power and high is about 17dB. Unless you aremeasuring the low power down to 0.01 watts it
 will be difficult to find thereal loss. Provided all is working correctly the RF power levels you list isabout right. I would think a little minor tuning could get a little moreout, but not much.The 2.2dB insertion loss is only one calculation. You have the connectors,coax, loops (very little here) and some going through to the other side(again, very little) has to be calculated.Taking this into account you probable have close to 2.5dB loss through thewhole thing. If this is correct then 200 in and 137 out is about right.Just my thoughts.Charles Miller- Original Message - From: "n9lv" <[EMAIL PROTECTED]>To: Sent: Wednesday, November 30, 2005 8:29 PMSubject: [Repeater-Builder] Duplexer loss different with more power, Why? Ok, running the TX-RX duplexer, with a 2.2 dB insertion loss, I tuned the duplexers on the monitor. All three of them
 looked identical, with rejection on the rx side of -80 dBm on each single cavity. Once I tied them all together, the rx rejection was better then -10 dBm, all went well there. I input 4 watts into them all tied together, connected to a dummy load, and got three watts out. Then I tied the duplexers back into the repeater, with 200 watts input, I am getting 100 watts output, into the same dummy load. Refelcted power was less than 1/10 of a watt. What am I missing here. If I am thinking right, I should be getting about 137 watts back out of the duplexer, or close to there. Any ideas? Could there be a mismatch bewteen the duplexers and the amp? Cables are all ingood shape. Mathew Yahoo! Groups LinksYahoo! Groups
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Re: [Repeater-Builder] Duplexer loss different with more power, Why?

[Eric Lemmon]

Mathew,

Actually, if the duplexer insertion loss is really 2.2 dB, you should get
120.5 watts out for 200 watts in.  Once you consider the small additional
loss in jumpers, connectors, adapters, etc., you're not too far off the
mark.  The tolerance and linearity of your power measuring instrument may
contribute a small error.

The major difference between your two conditions is that in one, the PA is
feeding a resistive load, and in the other, it is feeding a highly
reactive load- the duplexer.  If you experiment with the length of the
jumper connecting the PA to the duplexer, you will probably see a
significant change in output power- which may be better or worse.  You can
also try an impedance matcher (Z-Matcher) at the output of the PA, to
see if you can optimize the match between the PA and the duplexer.

Bear in mind that when a duplexer leaves the factory with precisely-set
tuning and insertion loss, it may suffer considerable vibration during
shipment.  That's why I always check duplexers and bandpass cavities on a
network analyzer before installing them.  It's rare that such devices
arrive in perfect adjustment.

73, Eric Lemmon WB6FLY

n9lv wrote:

 Ok, running the TX-RX duplexer, with a 2.2 dB insertion loss, I tuned
 the duplexers on the monitor.  All three of them looked identical,
 with rejection on the rx side of -80 dBm on each single cavity.  Once
 I tied them all together, the rx rejection was better then -10 dBm,
 all went well there.  I input 4 watts into them all tied together,
 connected to a dummy load, and got three watts out.  Then I tied the
 duplexers back into the repeater, with 200 watts input, I am getting
 100 watts output, into the same dummy load.  Refelcted power was less
 than 1/10 of a watt.  What am I missing here.  If I am thinking right,
 I should be getting about 137 watts back out of the duplexer, or close
 to there.  Any ideas?  Could there be a mismatch bewteen the duplexers
 and the amp?  Cables are all ingood shape.

 Mathew


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