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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

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