Greetings all, My club has an Advanced Communication Systems (ACS) KRP-5000 repeater (this is the same MR-4 receiver used in the Kendecom Mark 4) with a strange intermittent problem. Several times a day, we get a signal that sounds like a scratching noise or a thumping sound (It's hard to describe. I need to make a recording of it. if I can ever catch it). It starts off as a slow scratching (or thumping or clicking) and gradually gets faster and faster and then it fades back down to nothing and the signal drops.
For the past year or so, we've just put up with it because it was intermittent and I assumed it was external interference coming from another transmitter. (Although we are the only one on the water tower, there is a Water Department telemetry transmitter on-site.) My thought process changed on Saturday when I was doing some extended maintenance at the site and had the repeater pretty much disconnected from the outside world (transmitter on a dummy load, transmitter switch off, receive antenna disconnected at the repeater) and the dang thing started doing its 'thing'. I turned the transmitter switch back on and that had no impact on the noise, and the squelch control had no impact either. So, now I'm convinced that the issue is in the receiver (or power supply feeding it). Most of the processing in the MR4 takes place in U1. including the development of the COS signal. Since this problem can start on its own (without the transmitter already being on) and it captures the COS, I assume that the problem is in the general vicinity of (or before) U1. This is also the area of the circuit where the fast squelch/slow squelch is developed. Has anyone seen issues like this in repeaters that use the MR4 receiver (KRP-5000/Mark 4, etc.)? Any ideas? One thing that was mentioned to me today by a fellow who does repeater-type stuff professionally is that he's seem odd squelch problems caused by power sags. I did notice Saturday that when one of the pumps kicked on at the tower, the lights dimmed noticeably for 2 or 3 seconds. Because I wasn't paying attention to it at the time, I can't confirm or deny that the problem correlates with the voltage dip, but it seems like a good place to start. We're not running any power conditioning on the line now, and I don't really want to go to a full-blown UPS because we've got a good, reliable battery backup system already installed. Any thoughts on power conditioning without going to a UPS? Admittedly, on my 'to-do' list, this is priority 23, but it'd sure be good to have a starting place if this issue ever gets to be more of a problem, or if it happens to show up again when I'm at the site. Thanks to all es 73, Mike WM4B 146.85 - Warner Robins, GA 145.11 - Cochran, GA
