Allison KB1GMX has come up with an improved pop fix based on the one in the v4 board design, originally submitted to the BITX20 list by Joe VE1BWV.
Allison finally got annoyed enough by the pop to fix it.
Parts count 5:
- 2x 1n4148/914 diodes
- 10K resistor (any value from 10 to 100K really)
- 2n7000 MOSFET
- 0.1 µF capacitor
Allison has added a second diode. Why? The TX line is relay switched and relays take milliseconds to physically move contacts. So the second diode to the T/R line from the Raduino is the fast acting “audio kill”. The second diode and parallel resistor is the hold until the relay returns to RX position.
Allison assures us that this fully mutes the rig with no pop, no thump in either transition (from RX to TX or TX to RX).
Michael VE3WMB points out that connecting to VOL-H will kill the sidetone output. He notes that Ashhar Farhan VU2ESE has his V4 pop circuit connected at M2(R70) with the value of R70 increased to 1K ohms in order to hear the CW sidetone.