Thanks, Rai!
What is about adding this note to the wiki? There are some very helpfully posts on this list. It would be nice if we would find the tips and tricks on the wiki, too.
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/g/BITX20/wiki)
Am 05.03.2017 um 07:33 schrieb Raj vu2zap:
Folks,
After much poking and probing with instruments I found the reason for the power pop when you press the PTT.
When PTT is pressed the TX voltage floods the mic preamp. Capacitor C122 charges up and the charging current flows into t4 and then
D15 - thereby for a fraction of a second the carrier leaks through and if you are listing with another RX you will hear a "tong" kind of sound.
Solution is to stop this flow through the diode then R106 - R220 to ground.
In my analog VFO version I desoldered the R106's center pin and put in a 0.1 capacitor in series. This stops the capacitor charge current from routing though the mixer diode.
For better measure add a 1K resistor across C107. I found a constant 30mV there which was unbalancing my diodes and the carrier balance pot R106 was more to clockwise than needed!
For the digital VFO board or boards without R106 trimmer, cut the track between D20 and R38 and solder a smd 0.1 cap there.
Result is a significantly reduced pop which is not bothersome anymore.
Farhan please incorporate this hack.
Cheers for a pop free Sunday!
--
Stephan, dc8lz
