Peculiar Behavior: EFJ 5100ES Rx Audio Feedback

[synegy3488]

I have a rather, peculiar issue with a EFJ 5100ES radio I own, and I wanted to see if anyone else has encountered this type of problem (or even something similar).

The radio seems to develop/get audio feedback when Rx long transmissions. It almost seems as if the mic is live during a Rx (and no, I am absolutely certain, the radio is NOT Tx during these events. I had it occur on one occasion while attached to a service monitor and there was no observable RF being emitted). It seems to occur most frequently when the volume is set quite loud.

As a side note in the programming, the Rx Gains, are slightly high at 5dB (I believe the maximum is 6dB). I haven't as of yet been able to reprogram the unit with lower gains to see if perhaps thats the problem.

Has anyone else observed the same or similar issue with the EFJ 5100ES (v6 radios)?

[Gtaman]

I have before. Sometimes static can get into the front end causing the issue you describe. If you do take it apart be very careful. You can trash the PCB flex connector if you put the housing on wrong. I almost lost one to the pins shredding.

[com501]

Sounds like a microphonics issue. Attach a speaker mike, get it far away from the radio and see if the problem goes away. As gtaman asserts, the fix is cleaning up the non-linear portions of the front end causing it.

[fczheng88]

Also, if you have noise reduction/cancellation turned on/off, you can try toggling that. Or, try a different mic sensitivity. Sometimes those things are the culprits, sometimes not, as others have suggested.

[Notarola]

I have seen the type of noise described from poor internal grounds as well. Step 1 would be to clean and secure all the grounds and board connections first.

[Gtaman]

I have seen the type of noise described from poor internal grounds as well. Step 1 would be to clean and secure all the grounds and board connections first.

I have an Ex U.S. Army fob 5100 that has that issue. No many how much I’ve cleaned it I can’t get the hum to go away.

[Notarola]

If its not a ground problem. then you have to do as suggested look for RFI related causes.