After changing out the RF deck and spectrum sweeping the repeater site and not finding anything last weekend, Mike, WQZF427, took his analyzer out this morning while it was cold and the repeater was acting up and found a lot of noise! His analysis pointed to very old power distribution equipment throwing off broad-spectrum noise.
Noisy power systems are more common than you may think-especially systems that are poorly maintained like this one. In the cold, splices and taps that are old, corroded, or loose will contract, causing almost undetectable arcing to the human eye or ear. However, on the electromagnetic spectrum, this can be quite loud. The noise coming off this suspect pole and transformer was a popping noise, heard as static on the repeater, and a hum, which we also hear. Since this noise is being fed directly into our receiver though the duplexer, there is no way to notch it out.
Mike has very graciously offered to go back out there early tomorrow morning to see if he can pinpoint the noise more precisely, as you may have noticed the noise goes away as the weather warms. Our sweep of the site last weekend did not find anything, but the weather was warmer and we did not look outside the radio room and surrounding area. If this is a power company issue, there is little we can do. We can turn in our noise profile, but it will be up to them to make any repairs.
One thing is for sure: After going through this site piece by piece, it is not any of our equipment. We have basically changed out or tested every possible combination of equipment, thinking "this will fix it," only to be foiled again and again. Spectrum analyzers will be high on my list of troubleshooting items from now on!
Please remember, if this repeater is swamped with noise, we do also have the 700 paired repeater system available for use.