in my hands even simper elegant circuit borrowed from QCX transceiver
takes care of the pop completely, see attached.
with 300K R and 440nf C timing is just right to keep BS170 open long
enough when switched back to RX.
AF CW self control tone gets weaker with this, however in my uBITX
board 10K R253 was geniusly replaced by 1K, so this
makes CW tone loud enough with this mod.
On Mon, Jan 15, 2018 at 8:32 AM, ve7hcw via Groups.Io
It's the current charging and discharging of C50 and c63 cause the modulator
diodes to conduct whereas after initial stabilization of the capacitor
charges by keeping the mic preamp and receiver preamp powered up by
connecting directly to the power supply. Then the AC audio is switched in
by the MOSFETs which has not change in DC will not create pulse pop. Last
year I had a similar problem with a commercial product I build for PA
system with mike pops on/off because of charging and discharging
capacitors. I did the same and leave the mike circuit active but use a
MOSFET to isolate the AC sound when OFF and switch ON by powering the
MOSFET. No DC was switched by the MOSFET only AC result in no clicks and
The 100k resistors in the drain side of the MOSFET is to bleed the
charge and stablilize the steady charge on the capacitors. The other 100k on
the MOSFET source side is to make sure the gate has a charge reference to
make the MOSFET work doing switching.