On Thu, Oct 26, 2017 at 04:38 pm, Bruce Bjerke, K7BHB wrote:
I previously had to change from a speaker-mic to a separate speaker and microphone to avoid a big feedback howl for a half a second or so upon transmit. That worked, resulting in only a short "pop" sound. But now with sketch 1.26 the howl is back even with the separate speaker a good distance away from the Mike.
Bruce, I believe the howl is not related to the issue of the carrier burst.
The howl is probably caused by oscillations of the LM386. Not by audio feedback from the speaker to the mic.
The pop from the speaker is caused by the LM386 wich remains powered for at least half a second. In this short period the LM386 may even start to oscillate and produce a howl. Someone (can't remember who, sorry) recommended to add a 1K series resistor to the slider of the volume pot to prevent this.
Is there a hardware mod that has to be implemented to avoid the carrier burst, or lines of code that need to be uncommented?
No additional hardware mod required. No need to uncomment anything in the code.
The code adds only 75ms delay before the VFO signal is generated after PTT is keyed. Definitely much shorter than the length of the howl (half second) you are hearing.
73 Allard PE1NWL
Allard PE1NWL