fxbuilder wrote: > We purchased a uhf repeater from a local SoCal GMRS dealer and have > had problems with it's working correctly since we purchased it. The
I agree with Ed's recommendation that this might be simple desense. If the problem only happens on weak signals, your duplexer/antenna system isn't providing adequate TX/RX isolation. It's likely the repeater is fine. You might share what kind of antenna, feedline, duplexer, and interconnection cables you're using on the system. Folks here will share their experience regarding those items, which are often more important (and also often more expensive) than the repeater itself, in a properly engineered repeater system. To do a quick test for major desense problems, if you agree there's only a problem on weak signals (otherwise, the problem is likely to be something else entirely): Turn the receiver radio on only, leave the transmit radio off. Listen to the local speaker on the receiver. Have someone help you by transmitting a weak signal into the repeater's receiver radio, down into the noise quite a bit, where you can still understand them, but they're very noisy. Another thing that could be happening is desense of your receiver by nearby transmitters, and/or mixing products. You need to describe your site location a bit for anyone to have any thoughts on that. Those radios you're using don't have very good front-end filtering. Okay, so to characterize some of this to see where your problem really lies: Have them transmit and hold, and listen for a bit to the overall noise floor. Is it changing? The person on the other end should be using a fixed antenna and you should be listening to see if their signal strength is going up and down, or worse, they're getting "wiped out" regularly. If they are, you're fighting other nearby transmitters desensing your receiver, or similar. You will need at least a bandpass filter cavity on the receiver to save it from its own lack of selectivity or a more selective receiver. If their signal is pretty steady and no major changes are happening, have them continue to transmit as you simultaneously turn on the transmitter of the repeater. If the repeater's reciever loses their signal at this point in time, or starts to chatter on/off. You have a desense problem in your own repeater system. Perhaps you used cheap interconnect cable that's leaking badly, perhaps you used an antenna that doesn't duplex well, perhaps your duplexer isn't rated for the power level you're using, or ... well there's a lot of things. Do the test, send more info. Of course, you can also do this with proper test gear much easier than this, as well as it's a good opportunity to measure your usable receiver sensitivity (including site noise) at your site, if you can borrow someone who knows how to run it, as well as the test gear itself. If you don't feel like doing this level of troubleshooting, see if the shop you bought the repeater from has installation/troubleshooting services. Otherwise, let us know on the questions above... we'll try to keep guessing from afar. (It's far more effective to just hook up real test gear and find the problem, but sometimes you don't have that option, so the mailing list has to be "good enough"... and you'll end up making multiple trips to the site and wasting a lot of time. Time vs. money, just like everything else in life.) Nate WY0X
