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audio anomaly at the start of digital transmissions

Posted: Mon Jul 20, 2020 11:54 am
by ke4dyi
Every GD77 running the OpenGD77 firmware that I've heard on the air, or that I've used myself does this.

At the start of digital transmissions, there is a very audible "woosh" sound. If a transmission is particularly short, or if there is a loud enough constant sound going on in the transmitter's acoustic environment just before keying up, the resulting sound is a mess of digital hash. You can force this state by making a constant sound, "AH" works well, into the microphone, starting the sound just before keying the transmitter. If I had to guess about why this is happening, I'd say that the vocoder isn't fully initialized before the radio actually starts transmitting, and bad frames, or something, are being sent out before any useful audio. The sound I mention at the start of transmissions sounds an awful lot like autogain compensated DMR motorboating. It starts off loud, then goes down to normal levels quickly, about 200 to 300 MS or so. Depending on several factors, this sound can range from barely noticeable to extremely jarring. None of my other radios do this, just the GD77 running OpenGD77 firmware. IT doesn't happen with the stock GD77 firmware installed.

If desired, I can upload audio recordings of these findings, compared to other radios that don't exhibit this behavior.

On the blind hams DMR talkgroup, where many of us now have GD77's, it's very obvious any time anyone keys up with one of these radios, even if they never say anything.

Re: audio anomaly at the start of digital transmissions

Posted: Fri Aug 07, 2020 10:42 pm
This problem seems isolated to your radio. None of the thousand of other users have reported this problem

I suspect its a hardware fault, which has been exposed by the various enhanced features in the OpenGD77 firmware.