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I was asked to go out the site in the attached picture yesterday to help troubleshoot.? Before I go on, let me describe the site.? Although there are numerous antennas on the tower, we are the only 2-way user there.? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? There are licenses for Sprint, Verizon, and T-Mobile at this site, but we don’t know what’s active.? There is only one shelter besides our own.?
The panels around the perimeter of the catwalk have been there for quite some time.? The panels on top of the tower were installed a couple years ago, but the issue with this machine existed before they were installed.? This repeater used to have extremely good coverage, but now it’s limited to maybe 10 miles with a strong mobile.?
Users are complaining about not being able to hit the repeater and it sounded to me like it was desense.? Sure enough, I put an isotee inline at the output of the duplexer and there was so much desense I didn’t even try to measure it.? I cranked down the power on the TX and the desense was still there all the way down to nothing.? I cranked the power back up and replaced the feedline with a dummy load and there was zero desense in the repeater/duplexer combo.? As an aside, the duplexer is a WP642 (tuned by me) and the repeater is an MSR-2000 (built by me).?
All I had with me to test the feedline was a Bird 43, and reflected power was nil.? I have been told that the feedline has been swept with a NanoVNA, but they were unable to provide me with pictures of the sweeps, so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? I’ll have to go back another time and sweep it myself.
The feedline is LDF5-50A and the end of the heliax connects directly to the duplexer tee through a polyphaser.? (Yes… I tried testing it with and without the polyphaser inline.)? I can see where the feedline has been spliced where the ice-bridge meets the leg of the water tower just after the feedline goes vertical.? We didn’t have a ladder with us to go up and have a look at it, but we do plan to do that.? We tried to discern what kind of splice was installed… whether it was a heliax splice or two N-Connectors, but with the tape ball, it was impossible to tell.? If it’s N-connectors, we’ll replace the lower leg of feedline with a RG-214 jumper and retest, but my gut tells me that the feedline is spliced with a heliax splice; having an N-Connector there would be too easy.
The antenna is a G7-144 and was replaced at the same time the antennas were put up along the top perimeter of the water tower.? Against my advice, the antenna was hooked directly to the feedline without a jumper.? I ‘think’ the upper connector was replaced when the antenna was installed, but I need to check back on that.? I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? If I’m mistaken, I’m sure I’ll here about it here.? I offered to give them a DB-224, but that offer fell on deaf ears.?
Needless to say, we’re suspect of the feedline.? Nobody knows how long it’s been up there, but I do know it’s been up there for a long time.? I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good; it would not surprise me if the same thing had happened to the LDF5 cable at some point.? Clearly, there have been climbers all over that tower more than once.
The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.?
Standing by for advice; flameproof underwear has been donned.
Mike
WM4B
?
|
The G7 is a good performer but hates lightning...lost several in the 80s to Zap the lightning god...installed properly it can out do a DB224...opinions vary but I'm basing mine on 40 years of dealing with them...
I'd definitely sweep the line yourself...if you could get someone to climb and put a dummy load on the antenna end and check defense would be best..
The 5G could be an issue...might need to get a spectrum analyzer and look at the noise on 2m
Chris WB5ITT
On Sun, May 11, 2025, 4:57?PM Mike Besemer - WM4B via <mwbesemer= [email protected]> wrote:
I was asked to go out the site in the attached picture yesterday to help troubleshoot.? Before I go on, let me describe the site.? Although there are numerous antennas on the tower, we are the only 2-way user there.? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? There are licenses for Sprint, Verizon, and T-Mobile at this site, but we don’t know what’s active.? There is only one shelter besides our own.?
The panels around the perimeter of the catwalk have been there for quite some time.? The panels on top of the tower were installed a couple years ago, but the issue with this machine existed before they were installed.? This repeater used to have extremely good coverage, but now it’s limited to maybe 10 miles with a strong mobile.?
Users are complaining about not being able to hit the repeater and it sounded to me like it was desense.? Sure enough, I put an isotee inline at the output of the duplexer and there was so much desense I didn’t even try to measure it.? I cranked down the power on the TX and the desense was still there all the way down to nothing.? I cranked the power back up and replaced the feedline with a dummy load and there was zero desense in the repeater/duplexer combo.? As an aside, the duplexer is a WP642 (tuned by me) and the repeater is an MSR-2000 (built by me).?
All I had with me to test the feedline was a Bird 43, and reflected power was nil.? I have been told that the feedline has been swept with a NanoVNA, but they were unable to provide me with pictures of the sweeps, so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? I’ll have to go back another time and sweep it myself.
The feedline is LDF5-50A and the end of the heliax connects directly to the duplexer tee through a polyphaser.? (Yes… I tried testing it with and without the polyphaser inline.)? I can see where the feedline has been spliced where the ice-bridge meets the leg of the water tower just after the feedline goes vertical.? We didn’t have a ladder with us to go up and have a look at it, but we do plan to do that.? We tried to discern what kind of splice was installed… whether it was a heliax splice or two N-Connectors, but with the tape ball, it was impossible to tell.? If it’s N-connectors, we’ll replace the lower leg of feedline with a RG-214 jumper and retest, but my gut tells me that the feedline is spliced with a heliax splice; having an N-Connector there would be too easy.
The antenna is a G7-144 and was replaced at the same time the antennas were put up along the top perimeter of the water tower.? Against my advice, the antenna was hooked directly to the feedline without a jumper.? I ‘think’ the upper connector was replaced when the antenna was installed, but I need to check back on that.? I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? If I’m mistaken, I’m sure I’ll here about it here.? I offered to give them a DB-224, but that offer fell on deaf ears.?
Needless to say, we’re suspect of the feedline.? Nobody knows how long it’s been up there, but I do know it’s been up there for a long time.? I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good; it would not surprise me if the same thing had happened to the LDF5 cable at some point.? Clearly, there have been climbers all over that tower more than once.
The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.?
Standing by for advice; flameproof underwear has been donned.
Mike
WM4B
?
|
I am the kind of person who likes to test things myself so I know exactly what it says and what it's doing. And if someone would offer me a free DB 224 I would jump on it in a second! Chad Nelson WI9HF/WRPL979 Janesville Wisconsin 608-754-8671 Send from my spectrum iPhone 16.
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Show quoted text
On May 11, 2025, at 5:19?PM, Chris Boone WB5ITT via groups.io <setxtelecom@...> wrote:
? The G7 is a good performer but hates lightning...lost several in the 80s to Zap the lightning god...installed properly it can out do a DB224...opinions vary but I'm basing mine on 40 years of dealing with them...
I'd definitely sweep the line yourself...if you could get someone to climb and put a dummy load on the antenna end and check defense would be best..
The 5G could be an issue...might need to get a spectrum analyzer and look at the noise on 2m
Chris WB5ITT
On Sun, May 11, 2025, 4:57?PM Mike Besemer - WM4B via <mwbesemer= [email protected]> wrote:
I was asked to go out the site in the attached picture yesterday to help troubleshoot.? Before I go on, let me describe the site.? Although there are numerous antennas on the tower, we are the only 2-way user there.? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? There are licenses for Sprint, Verizon, and T-Mobile at this site, but we don’t know what’s active.? There is only one shelter besides our own.?
The panels around the perimeter of the catwalk have been there for quite some time.? The panels on top of the tower were installed a couple years ago, but the issue with this machine existed before they were installed.? This repeater used to have extremely good coverage, but now it’s limited to maybe 10 miles with a strong mobile.?
Users are complaining about not being able to hit the repeater and it sounded to me like it was desense.? Sure enough, I put an isotee inline at the output of the duplexer and there was so much desense I didn’t even try to measure it.? I cranked down the power on the TX and the desense was still there all the way down to nothing.? I cranked the power back up and replaced the feedline with a dummy load and there was zero desense in the repeater/duplexer combo.? As an aside, the duplexer is a WP642 (tuned by me) and the repeater is an MSR-2000 (built by me).?
All I had with me to test the feedline was a Bird 43, and reflected power was nil.? I have been told that the feedline has been swept with a NanoVNA, but they were unable to provide me with pictures of the sweeps, so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? I’ll have to go back another time and sweep it myself.
The feedline is LDF5-50A and the end of the heliax connects directly to the duplexer tee through a polyphaser.? (Yes… I tried testing it with and without the polyphaser inline.)? I can see where the feedline has been spliced where the ice-bridge meets the leg of the water tower just after the feedline goes vertical.? We didn’t have a ladder with us to go up and have a look at it, but we do plan to do that.? We tried to discern what kind of splice was installed… whether it was a heliax splice or two N-Connectors, but with the tape ball, it was impossible to tell.? If it’s N-connectors, we’ll replace the lower leg of feedline with a RG-214 jumper and retest, but my gut tells me that the feedline is spliced with a heliax splice; having an N-Connector there would be too easy.
The antenna is a G7-144 and was replaced at the same time the antennas were put up along the top perimeter of the water tower.? Against my advice, the antenna was hooked directly to the feedline without a jumper.? I ‘think’ the upper connector was replaced when the antenna was installed, but I need to check back on that.? I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? If I’m mistaken, I’m sure I’ll here about it here.? I offered to give them a DB-224, but that offer fell on deaf ears.?
Needless to say, we’re suspect of the feedline.? Nobody knows how long it’s been up there, but I do know it’s been up there for a long time.? I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good; it would not surprise me if the same thing had happened to the LDF5 cable at some point.? Clearly, there have been climbers all over that tower more than once.
The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.?
Standing by for advice; flameproof underwear has been donned.
Mike
WM4B
?
|
I had asked them to put a dummy load on the top and sweep the line when they replaced the antenna (or at very least recheck the VSWR), but that didn’t happen.? ? I’ll have to drag the spectrum analyzer out there next time I go to look for grunge. ? ? ?
toggle quoted message
Show quoted text
From: Christopher Boone <setxtelecom@...>
Sent: Sunday, May 11, 2025 6:20 PM
To: [email protected]
Cc: mwbesemer@...
Subject: Re: [repeater-builder] Major Desense? The G7 is a good performer but hates lightning...lost several in the 80s to Zap the lightning god...installed properly it can out do a DB224...opinions vary but I'm basing mine on 40 years of dealing with them...
I'd definitely sweep the line yourself...if you could get someone to climb and put a dummy load on the antenna end and check defense would be best. The 5G could be an issue...might need to get a spectrum analyzer and look at the noise on 2m Chris WB5ITT ? On Sun, May 11, 2025, 4:57?PM Mike Besemer - WM4B via <mwbesemer=[email protected]> wrote: I was asked to go out the site in the attached picture yesterday to help troubleshoot.? Before I go on, let me describe the site.? Although there are numerous antennas on the tower, we are the only 2-way user there.? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? There are licenses for Sprint, Verizon, and T-Mobile at this site, but we don’t know what’s active.? There is only one shelter besides our own.? The panels around the perimeter of the catwalk have been there for quite some time.? The panels on top of the tower were installed a couple years ago, but the issue with this machine existed before they were installed.? This repeater used to have extremely good coverage, but now it’s limited to maybe 10 miles with a strong mobile.? Users are complaining about not being able to hit the repeater and it sounded to me like it was desense.? Sure enough, I put an isotee inline at the output of the duplexer and there was so much desense I didn’t even try to measure it.? I cranked down the power on the TX and the desense was still there all the way down to nothing? I cranked the power back up and replaced the feedline with a dummy load and there was zero desense in the repeater/duplexer combo.? As an aside, the duplexer is a WP642 (tuned by me) and the repeater is an MSR-2000 (built by me).? All I had with me to test the feedline was a Bird 43, and reflected power was nil.? I have been told that the feedline has been swept with a NanoVNA, but they were unable to provide me with pictures of the sweeps, so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? I’ll have to go back another time and sweep it myself. The feedline is LDF5-50A and the end of the heliax connects directly to the duplexer tee through a polyphaser.? (Yes… I tried testing it with and without the polyphaser inline.)? I can see where the feedline has been spliced where the ice-bridge meets the leg of the water tower just after the feedline goes vertical.? We didn’t have a ladder with us to go up and have a look at it, but we do plan to do that.? We tried to discern what kind of splice was installed… whether it was a heliax splice or two N-Connectors, but with the tape ball, it was impossible to tell.? If it’s N-connectors, we’ll replace the lower leg of feedline with a RG-214 jumper and retest, but my gut tells me that the feedline is spliced with a heliax splice; having an N-Connector there would be too easy. The antenna is a G7-144 and was replaced at the same time the antennas were put up along the top perimeter of the water tower.? Against my advice, the antenna was hooked directly to the feedline without a jumper.? I ‘think’ the upper connector was replaced when the antenna was installed, but I need to check back on that.? I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? If I’m mistaken, I’m sure I’ll here about it here.? I offered to give them a DB-224, but that offer fell on deaf ears.? Needless to say, we’re suspect of the feedline.? Nobody knows how long it’s been up there, but I do know it’s been up there for a long time.? I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good; it would not surprise me if the same thing had happened to the LDF5 cable at some point.? Clearly, there have been climbers all over that tower more than once. The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.? Standing by for advice; flameproof underwear has been donned. Mike WM4B ? ?
|
Agreed.? I worked in avionics in the Air Force and if we were working a problem across several shifts, I rarely trusted the turnover I was given by the previous shift; I always validated what they’d told me before moving on.? I got bit in the ass by that once and learned my lesson! ? ? ?
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Show quoted text
From: Chad Nelson <chad.nelson71@...>
Sent: Sunday, May 11, 2025 6:24 PM
To: [email protected]
Cc: mwbesemer@...; [email protected]
Subject: Re: [repeater-builder] Major Desense? I am the kind of person who likes to test things myself so I know exactly what it says and what it's doing. And if someone would offer me a free DB 224 I would jump on it in a second! Chad Nelson WI9HF/WRPL979 Send from my spectrum iPhone 16.
On May 11, 2025, at 5:19?PM, Chris Boone WB5ITT via groups.io <setxtelecom@...> wrote:
? The G7 is a good performer but hates lightning...lost several in the 80s to Zap the lightning god..installed properly it can out do a DB224...opinions vary but I'm basing mine on 40 years of dealing with them...
I'd definitely sweep the line yourself...if you could get someone to climb and put a dummy load on the antenna end and check defense would be best.. The 5G could be an issue...might need to get a spectrum analyzer and look at the noise on 2m Chris WB5ITT ? On Sun, May 11, 2025, 4:57?PM Mike Besemer - WM4B via <mwbesemer=[email protected]> wrote: I was asked to go out the site in the attached picture yesterday to help troubleshoot.? Before I go on, let me describe the site.? Although there are numerous antennas on the tower, we are the only 2-way user there.? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? There are licenses for Sprint, Verizon, and T-Mobile at this site, but we don’t know what’s active.? There is only one shelter besides our own.? The panels around the perimeter of the catwalk have been there for quite some time.? The panels on top of the tower were installed a couple years ago, but the issue with this machine existed before they were installed.? This repeater used to have extremely good coverage, but now it’s limited to maybe 10 miles with a strong mobile.? Users are complaining about not being able to hit the repeater and it sounded to me like it was desense.? Sure enough, I put an isotee inline at the output of the duplexer and there was so much desense I didn’t even try to measure it.? I cranked down the power on the TX and the desense was still there all the way down to nothing.? I cranked the power back up and replaced the feedline with a dummy load and there was zero desense in the repeater/duplexer combo.? As an aside, the duplexer is a WP642 (tuned by me) and the repeater is an MSR-2000 (built by me).? All I had with me to test the feedline was a Bird 43, and reflected power was nil.? I have been told that the feedline has been swept with a NanoVNA, but they were unable to provide me with pictures of the sweeps, so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? I’ll have to go back another time and sweep it myself. The feedline is LDF5-50A and the end of the heliax connects directly to the duplexer tee through a polyphaser.? (Yes… I tried testing it with and without the polyphaser inline.)? I can see where the feedline has been spliced where the ice-bridge meets the leg of the water tower just after the feedline goes vertical.? We didn’t have a ladder with us to go up and have a look at it, but we do plan to do that.? We tried to discern what kind of splice was installed… whether it was a heliax splice or two N-Connectors, but with the tape ball, it was impossible to tell.? If it’s N-connectors, we’ll replace the lower leg of feedline with a RG-214 jumper and retest, but my gut tells me that the feedline is spliced with a heliax splice; having an N-Connector there would be too easy. The antenna is a G7-144 and was replaced at the same time the antennas were put up along the top perimeter of the water tower.? Against my advice, the antenna was hooked directly to the feedline without a jumper.? I ‘think’ the upper connector was replaced when the antenna was installed, but I need to check back on that.? I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? If I’m mistaken, I’m sure I’ll here about it here.? I offered to give them a DB-224, but that offer fell on deaf ears.? Needless to say, we’re suspect of the feedline.? Nobody knows how long it’s been up there, but I do know it’s been up there for a long time.? I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good; it would not surprise me if the same thing had happened to the LDF5 cable at some point.? Clearly, there have been climbers all over that tower more than once. The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.? Standing by for advice; flameproof underwear has been donned. Mike WM4B ? ?
|
At 5/11/2025 03:29 PM, you wrote:
I had asked them to put a dummy
load on the top and sweep the line when they replaced the antenna (or at
very least recheck the VSWR), but that didn?�?t happen.??
?
I?�?ll have to drag the spectrum analyzer out there next time I go to
look for grunge.
Another good test if you can get that 50 ohm load at the end of the
feedline is to check for desense with it in place.
Bob NO6B
|
Mike, I have a
site where the 224 on the VHF repeater is now about 3 feet from a
T mobile antenna. Today, the cell electronics, including RF is up
on the tower. The boxes are fed with 48 vdc and fiber. If I run 40
watts of RF on the MTR-2000 I have over 40 dB of desensing. I am
running 1 watt right now which brings me down to about 10 dB of
desensing. In a month of two I will have a tower climber look
around for me. I am planning on installing a huster G6 as a
transmit anteena, on the other side to the water tower ( the
antenna will be clear of the water tower "dome". There will be no
cell antennas close to it.
I have a telewave 6 cavity duplexer, that into a dummy load has
no desense. None. I am convinced that my 147 MHz RF is into the
broad band amps, and they are doing a wonderful job of spitting it
back. I cann't yell at them ,they pay rent!
I'll let you know what I find out in a few months.
Tom K8TB
The only thing
that worries me are the 5G panels at the
top of the water tower.? I’m concerned that broadband noise
from them is causing the desense,
but frankly I don’t know how to test for that.? Everything I
learned about repeaters I learned here and I’m a lot
stronger in the shop then I am on-site.? Clearly
the club doesn’t want to spend a bunch of money on feedline
and climbers only to find out that it didn’t
cure the problem.?
Standing by
for advice; flameproof underwear has been donned.
Mike
WM4B
?
|
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of K8TB
Sent: Sunday, May 11, 2025 8:23 PM
To: [email protected]
Subject: Re: [repeater-builder] Major Desense? Mike, I have a site where the 224 on the VHF repeater is now about 3 feet from a T mobile antenna. Today, the cell electronics, including RF is up on the tower. The boxes are fed with 48 vdc and fiber. If I run 40 watts of RF on the MTR-2000 I have over 40 dB of desensing. I am running 1 watt right now which brings me down to about 10 dB of desensing. In a month of two I will have a tower climber look around for me. I am planning on installing a huster G6 as a transmit anteena, on the other side to the water tower ( the antenna will be clear of the water tower "dome". There will be no cell antennas close to it.
I have a telewave 6 cavity duplexer, that into a dummy load has no desense. None. I am convinced that my 147 MHz RF is into the broad band amps, and they are doing a wonderful job of spitting it back. I cann't yell at them ,they pay rent! I'll let you know what I find out in a few months. Tom K8TB ? ? The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.? Standing by for advice; flameproof underwear has been donned. Mike WM4B ? ?
?
|
Hi Mike,
?
This may not apply to this site because no mention of AT&T, but perhaps our experience with very high noise floor? to our 6M repeater that was located 600 ft away from a guyed cell tower might be of help.
?
It turned out that AT&T took over this multi user cell/ 2 way site from a cell company that went out of business (can't remember the name) This company used an unfiltered either 24VDC or 48VDC switching supply to power their backup battery pack- AT&T kept the same equipment in service after taking over. AT&T and called it a "rectifier". The switcher was so noisy that it radiated RF not only backward on the AC supply outside the building, but also on the outside of the Heliax runs to the panels on the top of the tower, which re-radiated RF over to our 6M tower top antenna 600 ft away! From our spectrum analyzer attached to the 6M antenna feedline, the noise floor averaged -50 dBM (as compared to an expected about -110dBM), which was actually worse when more current drawn during peak cell service demand. Another AT&T take over site site in Mass had the identical scenario to 6M receive on a water tower with all antennas at the same level on top.
?
To sniff out the noise source, a 6M HT (Azden) with the squelch open to enable the LED signal strength dots showed? the strength of the interference, because the interference did not quiet the receiver and just sounded like clean white squelch noise. First used a beam antenna, then the rubber duck antenna , then exposed 50 ohm resistor loop on the HT BNC antenna connector to get down to the individual Heliax runs, etc.
?
John
On 05/11/2025 6:29 PM EDT Mike Besemer - WM4B via groups.io <mwbesemer@...> wrote:
?
?
I had asked them to put a dummy load on the top and sweep the line when they replaced the antenna (or at very least recheck the VSWR), but that didn’t happen.?
?
I’ll have to drag the spectrum analyzer out there next time I go to look for grunge.
?
?
?
From: Christopher Boone <setxtelecom@...>
Sent: Sunday, May 11, 2025 6:20 PM
To: [email protected]
Cc: mwbesemer@...
Subject: Re: [repeater-builder] Major Desense
?
The G7 is a good performer but hates lightning...lost several in the 80s to Zap the lightning god...installed properly it can out do a DB224...opinions vary but I'm basing mine on 40 years of dealing with them...
I'd definitely sweep the line yourself...if you could get someone to climb and put a dummy load on the antenna end and check defense would be best.
The 5G could be an issue...might need to get a spectrum analyzer and look at the noise on 2m
Chris WB5ITT
?
On Sun, May 11, 2025, 4:57?PM Mike Besemer - WM4B via <mwbesemer=[email protected]> wrote:
I was asked to go out the site in the attached picture yesterday to help troubleshoot.? Before I go on, let me describe the site.? Although there are numerous antennas on the tower, we are the only 2-way user there.? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? There are licenses for Sprint, Verizon, and T-Mobile at this site, but we don’t know what’s active.? There is only one shelter besides our own.?
The panels around the perimeter of the catwalk have been there for quite some time.? The panels on top of the tower were installed a couple years ago, but the issue with this machine existed before they were installed.? This repeater used to have extremely good coverage, but now it’s limited to maybe 10 miles with a strong mobile.?
Users are complaining about not being able to hit the repeater and it sounded to me like it was desense.? Sure enough, I put an isotee inline at the output of the duplexer and there was so much desense I didn’t even try to measure it.? I cranked down the power on the TX and the desense was still there all the way down to nothing? I cranked the power back up and replaced the feedline with a dummy load and there was zero desense in the repeater/duplexer combo.? As an aside, the duplexer is a WP642 (tuned by me) and the repeater is an MSR-2000 (built by me).?
All I had with me to test the feedline was a Bird 43, and reflected power was nil.? I have been told that the feedline has been swept with a NanoVNA, but they were unable to provide me with pictures of the sweeps, so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? I’ll have to go back another time and sweep it myself.
The feedline is LDF5-50A and the end of the heliax connects directly to the duplexer tee through a polyphaser.? (Yes… I tried testing it with and without the polyphaser inline.)? I can see where the feedline has been spliced where the ice-bridge meets the leg of the water tower just after the feedline goes vertical.? We didn’t have a ladder with us to go up and have a look at it, but we do plan to do that.? We tried to discern what kind of splice was installed… whether it was a heliax splice or two N-Connectors, but with the tape ball, it was impossible to tell.? If it’s N-connectors, we’ll replace the lower leg of feedline with a RG-214 jumper and retest, but my gut tells me that the feedline is spliced with a heliax splice; having an N-Connector there would be too easy.
The antenna is a G7-144 and was replaced at the same time the antennas were put up along the top perimeter of the water tower.? Against my advice, the antenna was hooked directly to the feedline without a jumper.? I ‘think’ the upper connector was replaced when the antenna was installed, but I need to check back on that.? I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? If I’m mistaken, I’m sure I’ll here about it here.? I offered to give them a DB-224, but that offer fell on deaf ears.?
Needless to say, we’re suspect of the feedline.? Nobody knows how long it’s been up there, but I do know it’s been up there for a long time.? I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good; it would not surprise me if the same thing had happened to the LDF5 cable at some point.? Clearly, there have been climbers all over that tower more than once.
The only thing that worries me are the 5G panels at the top of the water tower.? I’m concerned that broadband noise from them is causing the desense, but frankly I don’t know how to test for that.? Everything I learned about repeaters I learned here and I’m a lot stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a bunch of money on feedline and climbers only to find out that it didn’t cure the problem.?
Standing by for advice; flameproof underwear has been donned.
Mike
WM4B
?
?
|
At 5/11/2025 05:22 PM, you wrote:
Mike, I have a site where the
224 on the VHF repeater is now about 3 feet from a T mobile antenna.
Today, the cell electronics, including RF is up on the tower. The boxes
are fed with 48 vdc and fiber. If I run 40 watts of RF on the MTR-2000 I
have over 40 dB of desensing. I am running 1 watt right now which brings
me down to about 10 dB of desensing. In a month of two I will have a
tower climber look around for me. I am planning on installing a huster G6
as a transmit anteena, on the other side to the water tower ( the antenna
will be clear of the water tower "dome". There will be no cell
antennas close to it.
I have a telewave 6 cavity duplexer, that into a dummy load has no
desense. None. I am convinced that my 147 MHz RF is into the broad band
amps, and they are doing a wonderful job of spitting it back. I cann't
yell at them ,they pay rent!
When I first moved into my home in the late '90s I could not operate a 2
meter repeater from here: switched mode power supplies in cable TV set
top boxes in the neighbors' homes would mix my output to my input.?
Then streaming happened & everyone got rid of their STBs, & now I
can duplex on 2 meters but now the noise floor from LED street lighting
makes the repeater deaf at night.
Bob NO6B
|
Replace the electrolytic capacitors on the PA of your MSR-2000.
At 5/11/2025 05:22 PM, you wrote:
Mike, I have a site where the
224 on the VHF repeater is now about 3 feet from a T mobile antenna.
Today, the cell electronics, including RF is up on the tower. The boxes
are fed with 48 vdc and fiber. If I run 40 watts of RF on the MTR-2000 I
have over 40 dB of desensing. I am running 1 watt right now which brings
me down to about 10 dB of desensing. In a month of two I will have a
tower climber look around for me. I am planning on installing a huster G6
as a transmit anteena, on the other side to the water tower ( the antenna
will be clear of the water tower "dome". There will be no cell
antennas close to it.
I have a telewave 6 cavity duplexer, that into a dummy load has no
desense. None. I am convinced that my 147 MHz RF is into the broad band
amps, and they are doing a wonderful job of spitting it back. I cann't
yell at them ,they pay rent!
When I first moved into my home in the late '90s I could not operate a 2
meter repeater from here: switched mode power supplies in cable TV set
top boxes in the neighbors' homes would mix my output to my input.?
Then streaming happened & everyone got rid of their STBs, & now I
can duplex on 2 meters but now the noise floor from LED street lighting
makes the repeater deaf at night.
Bob NO6B
|
That has nothing to do with the desense. ? ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of DCFluX via groups.io
Sent: Sunday, May 11, 2025 10:25 PM
To: [email protected]
Subject: Re: [repeater-builder] Major Desense? Replace the electrolytic capacitors on the PA of your MSR-2000. ? At 5/11/2025 05:22 PM, you wrote:
Mike, I have a site where the 224 on the VHF repeater is now about 3 feet from a T mobile antenna. Today, the cell electronics, including RF is up on the tower. The boxes are fed with 48 vdc and fiber. If I run 40 watts of RF on the MTR-2000 I have over 40 dB of desensing. I am running 1 watt right now which brings me down to about 10 dB of desensing. In a month of two I will have a tower climber look around for me. I am planning on installing a huster G6 as a transmit anteena, on the other side to the water tower ( the antenna will be clear of the water tower "dome". There will be no cell antennas close to it.
I have a telewave 6 cavity duplexer, that into a dummy load has no desense. None. I am convinced that my 147 MHz RF is into the broad band amps, and they are doing a wonderful job of spitting it back. I cann't yell at them ,they pay rent!
When I first moved into my home in the late '90s I could not operate a 2 meter repeater from here: switched mode power supplies in cable TV set top boxes in the neighbors' homes would mix my output to my input.? Then streaming happened & everyone got rid of their STBs, & now I can duplex on 2 meters but now the noise floor from LED street lighting makes the repeater deaf at night.
Bob NO6B
|
You said there was desense with the tx power all the way to nothing. Was it the same level of desense using the iso-T and if so, then the problem is site noise floor. ?You have to track down the source first before you can start to fix it.?
|
I fought a problem similar to yours but slightly different.
The final diagnosis could help you but the solution will be
different.
After several weeks of constant pulsing interference I finally took
the spectrum analyzer to the site,
disconnected the repeater, and put the spectrum analyzer on the
repeater antenna.
The pulse was directly on the input frequency of the repeater.
We watched the tx light on the scada system and it corresponded to
the pulse we were receiving.
With the permission of the water system we turned it off for 5
minutes and the interference was gone.
The temporary solution was a cavity on the water system scada
system.
Our tower climber later found a break in their hard line and they
moved their antenna and reduced
their power to the level they were licensed for and got better
signal than they have had in years.
Everyone was very happy.
Your solution will probably be different but the diagnosis is the
best way to find de-sense.
Roger
On 5/11/2025 7:22 PM, K8TB wrote:
toggle quoted message
Show quoted text
Mike, I have
a site where the 224 on the VHF repeater is now about 3 feet
from a T mobile antenna. Today, the cell electronics, including
RF is up on the tower. The boxes are fed with 48 vdc and fiber.
If I run 40 watts of RF on the MTR-2000 I have over 40 dB of
desensing. I am running 1 watt right now which brings me down to
about 10 dB of desensing. In a month of two I will have a tower
climber look around for me. I am planning on installing a huster
G6 as a transmit anteena, on the other side to the water tower (
the antenna will be clear of the water tower "dome". There will
be no cell antennas close to it.
I have a telewave 6 cavity duplexer, that into a dummy load has
no desense. None. I am convinced that my 147 MHz RF is into the
broad band amps, and they are doing a wonderful job of spitting
it back. I cann't yell at them ,they pay rent!
I'll let you know what I find out in a few months.
Tom K8TB
The only
thing
that worries me are the 5G panels at the top of the water tower.? I’m concerned
that broadband noise from them is causing the desense,
but frankly I don’t know how to test for that.? Everything
I learned about repeaters I learned here and I’m a lot
stronger in the shop then I am on-site.? Clearly the club doesn’t want to spend a
bunch of money on feedline and climbers only
to find out that it didn’t cure the problem.?
Standing by
for advice; flameproof underwear has been donned.
Mike
WM4B
?
|
? The rest of the antennas are not connected to anything and the feedlines have (unfortunately) been hacked off just below the catwalk.? Unlike fine wine, abandoned antennas don’t get better with age. And, with their cables cut off, that doesn’t help matters either. Any of them could be creating noise when excited by your transmitter RF; it’s the same as the proverbial “rusty guy wire” problem. I cranked down the power on the TX and the desense was still there all the way down to nothing.? It would be helpful to know the amount of desense at a few different power output levels, like 100 watts yields X dB of desense, 10 watts yields Y dB of desense, and 1 watt yields Z dB. I have been told that the feedline has been swept with a NanoVNA Swept as in sweeping the line via time-domain, or swept for return loss as if sweeping the antenna? so I’m taking the word that ‘it looked fine’ with a huge grain of salt.? "Trust but verify". Or depending on the source, don't even trust. whether it was a heliax splice or two N-Connectors I hate Heliax splices. I'm glad they quit making them. Against my advice, the antenna was hooked directly to the feedline without a jumper. 7/8" is a hell of a moment arm?on a fixed N connector... I don’t know much about the G7-144, but from what I’ve seen here in the archives it appears to be ok for repeater service with the exception of not being particularly good in the weather.? That pretty much sums it up. For whatever reason, G7's seem to be lightning magnets. I don't know why. But, assuming lightning wasn't involved, the other common failure is water getting into the base coil assembly and corroding the works. Related to that is another common problem which is installer-induced - blocking the weep hole at the N connector, thus trapping water inside. Since you mention someone attached a 7/8" connector directly to the antenna, it seems quite possible, if not likely, that when they sealed the connection they blocked the weep hole. I did see one place at the end of the ice-bridge where someone had stepped on a piece of 5/8” heliax and crimped it good Unless it's crimped to the point of the center and shield coming in contact (which is damn near impossible), a dent isn't going to cause desense. The only thing that worries me are the 5G panels at the top of the water tower.? I wouldn’t put the cell carriers as being high on my list of suspects. I'd put your antenna at the top of the list, your feedline/connectors/splices second, and other potential noisemakers in your antenna's near field third (and that includes any/all abandoned antennas). ---- Jeff WN3A
|
At 5/12/2025 08:35 AM, you wrote:
I fought a problem similar to
yours but slightly different.
The final diagnosis could help you but the solution will be
different.
After several weeks of constant pulsing interference I finally took the
spectrum analyzer to the site,
disconnected the repeater, and put the spectrum analyzer on the repeater
antenna.
The pulse was directly on the input frequency of the repeater.
We watched the tx light on the scada system and it corresponded to the
pulse we were receiving.
We had the same thing happen at a site in LA.? I don't remember the
manufacturer of the SCADA system but wouldn't be surprised if it was the
same.
FWIW this is not "desense" but simply a noise signal being
transmitted directly on your input frequency.
Bob NO6B
|
Sir,
I have seen several MSR-2000 Power Amplifiers go spurious when the electrolytic capacitors dry out.
Unless you looked at the output of the PA with a spectrum analyzer, I wouldn't rule it out.
However I did see here that you said you get no desense with a dummy load connected instead of the PA so I will concede my initial suggestion may be wrong.
One of the best things you can do in this case is lock your transmitter on and turn the power level down to the lowest you can and still have a good amount of desense.? Then use a handheld tuned to your input frequency and a step attenuatior if you have one, and walk around the site to see where you get maximum noise. In the past I've had problems with CFL lights, boat and motorcycle battery chargers and FM radio stations that were spaced 600 kHz apart on the FM dial. Modern cellular radios are bolted behind the antennas and run fiber to the building, but the 48 volt power is usually supplied to the radio with unshielded 6 or 8 gauge wire. Could be the rectifier charging the batteries is creating your noise problem. Another thing to check is the Telewave TPRD-1556 duplexer can be prone to dissimilar metal corrosion between the coupling loop plates and the top of the can.
>? The rest of the antennas are not connected to anything and the feedlines
have (unfortunately) been hacked off just below the catwalk.?
Unlike fine wine, abandoned antennas don’t get better with age.? And, with
their cables cut off, that doesn’t help matters either.? Any of them could
be creating noise when excited by your transmitter RF; it’s the same as the
proverbial “rusty guy wire” problem.
> I cranked down the power on the TX and the desense was still there all the
way down to nothing.?
It would be helpful to know the amount of desense at a few different power
output levels, like 100 watts yields X dB of desense, 10 watts yields Y dB
of desense, and 1 watt yields Z dB.
> I have been told that the feedline has been swept with a NanoVNA
Swept as in sweeping the line via time-domain, or swept for return loss as
if sweeping the antenna?
> so I’m taking the word that ‘it looked fine’ with a huge grain of salt.?
"Trust but verify".? Or depending on the source, don't even trust.
> whether it was a heliax splice or two N-Connectors
I hate Heliax splices.? I'm glad they quit making them.
> Against my advice, the antenna was hooked directly to the feedline without
a jumper.
7/8" is a hell of a moment arm?on a fixed N connector...
> I don’t know much about the G7-144, but from what I’ve seen here in the
archives it appears
> to be ok for repeater service with the exception of not being particularly
good in the weather.?
That pretty much sums it up.? For whatever reason, G7's seem to be lightning
magnets.? I don't know why.? But, assuming lightning wasn't involved, the
other common failure is water getting into the base coil assembly and
corroding the works.? Related to that is another common problem which is
installer-induced - blocking the weep hole at the N connector, thus trapping
water inside.? Since you mention someone attached a 7/8" connector directly
to the antenna, it seems quite possible, if not likely, that when they
sealed the connection they blocked the weep hole.?
> I did see one place at the end of the ice-bridge where someone had stepped
on a piece of 5/8” heliax and crimped it good
Unless it's crimped to the point of the center and shield coming in contact
(which is damn near impossible), a dent isn't going to cause desense.
> The only thing that worries me are the 5G panels at the top of the water
tower.?
I wouldn’t put the cell carriers as being high on my list of suspects.? I'd
put your antenna at the top of the list, your feedline/connectors/splices
second, and other potential noisemakers in your antenna's near field third
(and that includes any/all abandoned antennas).
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ---- Jeff WN3A
|
Correct.? That’s not what we’re seeing.? In our case, it happens ONLY when our transmitter is active. ? ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Bob Dengler
Sent: Monday, May 12, 2025 12:49 PM
To: [email protected]
Subject: Re: [repeater-builder] Major Desense? At 5/12/2025 08:35 AM, you wrote:
I fought a problem similar to yours but slightly different.
The final diagnosis could help you but the solution will be different.
After several weeks of constant pulsing interference I finally took the spectrum analyzer to the site,
disconnected the repeater, and put the spectrum analyzer on the repeater antenna.
The pulse was directly on the input frequency of the repeater.
We watched the tx light on the scada system and it corresponded to the pulse we were receiving.
We had the same thing happen at a site in LA.? I don't remember the manufacturer of the SCADA system but wouldn't be surprised if it was the same.
FWIW this is not "desense" but simply a noise signal being transmitted directly on your input frequency.
Bob NO6B
|
Correct… no desense into a dummy load, so in my mind that rules out the PA unless something really wonky is happening.? Same goes for any potential issues with the duplexer. ? Unfortunately, in all likelihood, if we have a case of ‘rusty bolt syndrome’ it’s *PROBABLY* going to be on the water tank itself; e.g. one of the many abandoned antennas/truncated feedlines.? But, the 48 VDC power is certainly worth looking in to. ? Mike WM4B ? ?
toggle quoted message
Show quoted text
From: Matt Krick <dcflux@...>
Sent: Monday, May 12, 2025 1:15 PM
To: [email protected]
Cc: mwbesemer@...
Subject: Re: [repeater-builder] Major Desense? Sir, I have seen several MSR-2000 Power Amplifiers go spurious when the electrolytic capacitors dry out. Unless you looked at the output of the PA with a spectrum analyzer, I wouldn't rule it out. However I did see here that you said you get no desense with a dummy load connected instead of the PA so I will concede my initial suggestion may be wrong. One of the best things you can do in this case is lock your transmitter on and turn the power level down to the lowest you can and still have a good amount of desense.? Then use a handheld tuned to your input frequency and a step attenuatior if you have one, and walk around the site to see where you get maximum noise. In the past I've had problems with CFL lights, boat and motorcycle battery chargers and FM radio stations that were spaced 600 kHz apart on the FM dial. Modern cellular radios are bolted behind the antennas and run fiber to the building, but the 48 volt power is usually supplied to the radio with unshielded 6 or 8 gauge wire. Could be the rectifier charging the batteries is creating your noise problem. Another thing to check is the Telewave TPRD-1556 duplexer can be prone to dissimilar metal corrosion between the coupling loop plates and the top of the can. ? ? >? The rest of the antennas are not connected to anything and the feedlines
have (unfortunately) been hacked off just below the catwalk.?
Unlike fine wine, abandoned antennas don’t get better with age.? And, with
their cables cut off, that doesn’t help matters either.? Any of them could
be creating noise when excited by your transmitter RF; it’s the same as the
proverbial “rusty guy wire” problem.
> I cranked down the power on the TX and the desense was still there all the
way down to nothing.?
It would be helpful to know the amount of desense at a few different power
output levels, like 100 watts yields X dB of desense, 10 watts yields Y dB
of desense, and 1 watt yields Z dB.
> I have been told that the feedline has been swept with a NanoVNA
Swept as in sweeping the line via time-domain, or swept for return loss as
if sweeping the antenna?
> so I’m taking the word that ‘it looked fine’ with a huge grain of salt.?
"Trust but verify".? Or depending on the source, don't even trust.
> whether it was a heliax splice or two N-Connectors
I hate Heliax splices.? I'm glad they quit making them.
> Against my advice, the antenna was hooked directly to the feedline without
a jumper.
7/8" is a hell of a moment arm?on a fixed N connector...
> I don’t know much about the G7-144, but from what I’ve seen here in the
archives it appears
> to be ok for repeater service with the exception of not being particularly
good in the weather.?
That pretty much sums it up.? For whatever reason, G7's seem to be lightning
magnets.? I don't know why.? But, assuming lightning wasn't involved, the
other common failure is water getting into the base coil assembly and
corroding the works.? Related to that is another common problem which is
installer-induced - blocking the weep hole at the N connector, thus trapping
water inside.? Since you mention someone attached a 7/8" connector directly
to the antenna, it seems quite possible, if not likely, that when they
sealed the connection they blocked the weep hole.?
> I did see one place at the end of the ice-bridge where someone had stepped
on a piece of 5/8” heliax and crimped it good
Unless it's crimped to the point of the center and shield coming in contact
(which is damn near impossible), a dent isn't going to cause desense.
> The only thing that worries me are the 5G panels at the top of the water
tower.?
I wouldn’t put the cell carriers as being high on my list of suspects.? I'd
put your antenna at the top of the list, your feedline/connectors/splices
second, and other potential noisemakers in your antenna's near field third
(and that includes any/all abandoned antennas).
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ---- Jeff WN3A
|
At 5/12/2025 10:15 AM, you wrote:
Sir,
I have seen several MSR-2000 Power Amplifiers go spurious when the
electrolytic capacitors dry out.
Unless you looked at the output of the PA with a spectrum analyzer, I
wouldn't rule it out.
However I did see here that you said you get no desense with a dummy load
connected instead of the PA so I will concede my initial suggestion may
be wrong.
One of the best things you can do in this case is lock your transmitter
on and turn the power level down to the lowest you can and still have a
good amount of desense.?
Then use a handheld tuned to your input frequency and a step attenuatior
if you have one, and walk around the site to see where you get maximum
noise.
In the past I've had problems with CFL lights, boat and motorcycle
battery chargers and FM radio stations that were spaced 600 kHz apart on
the FM dial.
A few months ago I suddenly had a severe (over 10 dB) desense problem
with my 2 meter repeater at the house.? I used a method similar to
the above to locate the source: a 20+ year old document scanner.?
Funny thing is this scanner has always been plugged in & never caused
a problem until now, so yeah an electrolytic probably dried out.
Bob NO6B
|
Mike Besemer - WM4B
Chris Boone WB5ITT