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oh6eog_ · 25th Jan 2019, 12:19 pm

The problem I had with my PTR-1851 using the Clansman handpiece was feedback from the earpiece part to the microphone. The clansmans (as most military rigs) have a monitoring audio going to the earpiece also during TX. The microphone was able to pick this up. Especially if the sound levels around the microphone otherwise were low. This meant that if I was silent and didn't speak into the microphone, then it picked up it's own sound from the earpiece. Since it picked it up as a sound with low volume the automatic gain control of the mic line stepped in and increased the gain. This raised the output level on the earpiece which then again was picked up better... The feedback loop was born and the TX modulation was a squeal.

I'm not 100% sure of what the real cause for the problems were in my case. Either the AGC had become "hot" raising the gain a bit too much. But I also found that the rubber gasket around the earpiece speaker probably helped the feedback. It had become stiff making the sound transfer much easier to the plastic body of the handpiece. Loosening the speaker a little from it's fitting made the problem disappear.

What I ended up doing was putting a small electrolyte over the speaker line. Can't remember exactly but it was probably something like a 15uF. What this does is that the speaker reacts a bit slower, not "popping" so loudly when sound is applied. It was enough for the feedback not to appear any more.

25th Jan 2019, 12:19 pm	#11
oh6eog_ Retired Dormant Member Join Date: Dec 2018 Location: Vaasa, Ostrobothnia, Finland Posts: 10	Re: Clansman PRC320 problems The problem I had with my PTR-1851 using the Clansman handpiece was feedback from the earpiece part to the microphone. The clansmans (as most military rigs) have a monitoring audio going to the earpiece also during TX. The microphone was able to pick this up. Especially if the sound levels around the microphone otherwise were low. This meant that if I was silent and didn't speak into the microphone, then it picked up it's own sound from the earpiece. Since it picked it up as a sound with low volume the automatic gain control of the mic line stepped in and increased the gain. This raised the output level on the earpiece which then again was picked up better... The feedback loop was born and the TX modulation was a squeal. I'm not 100% sure of what the real cause for the problems were in my case. Either the AGC had become "hot" raising the gain a bit too much. But I also found that the rubber gasket around the earpiece speaker probably helped the feedback. It had become stiff making the sound transfer much easier to the plastic body of the handpiece. Loosening the speaker a little from it's fitting made the problem disappear. What I ended up doing was putting a small electrolyte over the speaker line. Can't remember exactly but it was probably something like a 15uF. What this does is that the speaker reacts a bit slower, not "popping" so loudly when sound is applied. It was enough for the feedback not to appear any more.