Noise identify on repeater

[paulrrulon]

Hello

I hope I am in the right forum for this question. If not I apologize as I did not see any forums closer to the issue. I belong to an Amateur radio club in the town I live in and lately we have been experiencing what sounds like a pipe dragging down the highway at 40 mph. Poor descriptions I know but it is the best I can do. Does anyone know of a database of sounds I can go to so as to help try & ID the obnoxious sound we hear on our repeater.
I think if we can ID this sound it would put us one step closer to locating the issue. It does not make the sound all the time & is not audible while someone is talking. It seems to act up worse after you release the ptt button. I thought about recording the sound but not sure who could help us ID the noise. The frequency is on 447.275. Any help would be much appreciated.

Respectfully
Paul

[fineshot1]

It would be best if you could post a link to a recording of it or attach a recorded file of it otherwise we will all be just guessing.

[jim202]

My first guess is that your having an intermod / desense problem. Best way to start to locate the
issue is to put a weak signal into the repeater receiver with the transmitter shut off. While maintaining
the signal, turn the transmitter on. If the input signal goes away, at least you have one part of the
equation. The rest may take weeks or months to resolve.

A good question to ask, is there any relation to time of day when this happens.

Does the noise problem change with wet or dry weather?

Has anything changed at the site to cause the problem like a new transmitter being installed?

Has any work been done on the tower, like add a new antenna?

Are there any loose metal parts on the tower that can move around?

Does the problem get worse with wind?


As you can see, there are a number of areas that can cause this problem. The list above is
not inclusive. There are a good deal of other causes, but these will get you looking.

Another place to look is right inside your own repeater. Are all the shield in place? Are all the
grounds tight? Are you using double shielded coax for all cables? Are all the connectors tight?
Is there an antenna surge protector in line with the antenna feed line coax? If so, try taking it
out for a test.

You could write a book on the steps to try and resolve noise on a repeater system. Keep track
of what you do and what you find. It may be more than one item causing your repeater noise.

Jim

Originally Posted by paulrrulon

Hello

I hope I am in the right forum for this question. If not I apologize as I did not see any forums closer to the issue. I belong to an Amateur radio club in the town I live in and lately we have been experiencing what sounds like a pipe dragging down the highway at 40 mph. Poor descriptions I know but it is the best I can do. Does anyone know of a database of sounds I can go to so as to help try & ID the obnoxious sound we hear on our repeater.
I think if we can ID this sound it would put us one step closer to locating the issue. It does not make the sound all the time & is not audible while someone is talking. It seems to act up worse after you release the ptt button. I thought about recording the sound but not sure who could help us ID the noise. The frequency is on 447.275. Any help would be much appreciated.

Respectfully
Paul

[nd5y]

Does it do it all the time or only during band openings?
Does it sound like audio feedback or some type of digital sound?
If it sounds sort of like a squealing audio feedback it might be from another repeater.
I assume you mean 447.275 output and 442.275 input, right?
Does the repeater have CTCSS or other tone access?

For some reason CO has a lot of "backwards" (low in, high out) 70cm repeaters. Sometimes during band openings you can get interference from other far away repeaters that have the same tone but opposite tx/rx frequencies.
The repeaters will lock eachother up and make all kinds of feedback type noises. If that is the case then you can't really do anything but change PL tones and hope you don't get interference from some other repeater.

You could also have a duplexing problem where intermod or something is causing the repeater to hear its own transmitter, again causing all kinds of squealing noises from audio feedback.

[paulrrulon]

Thanks to all of you for some great ideas. It looks like I will need to spend some time digging into this issue. I did not realize their are so many things to look at. I will start with a log or diary to try and come up with more data IE what time of day , What the weather is doing , if the wind is blowing etc. I really appreciate all your help & if we ever do figure out what it was I will post the repair. Thanks again.

Respectfully