John et al :
The RF burst on PTT closure, on the BITX40, has been addressed by Allard (PE1NWL) in his Raduino Code.
His approach is to shut down the CLK output on the SI5351 for 50 mS on PTT closure and wait for things to settle before re-enabling it to allow TX.
There is also a simple hardware mod that can be used to reduce this burst from 50 mS to less than 20 mS so that the delay time can be reduced in the code.
The mod is to change C124 from 47uF to 4.7 uF. C124 is near Q12 (mic input). See message #29101 in this group for the original discussion on this.