Batboard

I'm converting a uhf mitrek to a repeater. The receiver is giving me trouble. With the radio squelched, I am getting a lot of noise, a frying sound, when the receiver is idle, no signal present. If I send a signat from a transmitter on the receive frequency, the signal is dead quiet is no audio is transmitted, just carrier. I swapped the detector/limiter IC from another mitrek that had a dead RF power amp. noise is still present.

IDEAS?

Check the two audio output IC's for the correct voltages.
The squelch circuit controls the DC voltage at the first audio IC, muting the audio. The second, "bridge" audio IC just follows it 180 degrees out of phase.

Could have a bad cap in the squelch circuit or a bad bypass cap in the audio stages.

tennesseestargazer wrote:With the radio squelched, I am getting a lot of noise, a frying sound, when the receiver is idle, no signal present.

Start at the squelch, and move backwards to the RF input. Short one stage at a time and listen to the audio. (Be careful NOT to short an RX B+ line in the process)

In addition to the 30 year old capacitors Will mentioned, sometimes the cavity filters in the front end develop tendrills of oxide groth shorthing them out and result n some pretty weird noises as well.

Knowing which stage is actually causing the noise helps a lot. You'll know when shorting one stage makes a difference, and shorthing the next stage doesn't.

Jeff