[UK-CONTEST] Polling noise on transmit

[G3SJJ]

Having sorted out the reason why my DVK wouldn't work, it was an open 
circuit feature in a cable between mHam Keyer and PC sound card, I would 
like to pursue another problem.

mHam Keyer, ie with DVK switching between radio and PC. There are 
several connections from the large D connector which go into the radio - 
Serial interface, +12v, Key, radio mic and PTT. There are also 3 single 
screened cables to the sound card - Line In, Line Out and Mic (the 
problem one above, now fixed.) Finally the USB cable to the PC.

When I transmit. ie hold footswitch down, I can hear a background 
ticking noise, it is also audible on recorded messages. I never really 
found what it was until Don G3BJ suggested it could be noise generated 
by the radio polling. Sure enough the ticking frequency correlates 
exactly with the FT1kMP polling indicator flashing. It was lso audible 
on Don's setup using the EZMaster SO2R unit with integral soundcard. 
Removing the USB connector and thereby turning the mHam keyer unit off 
removes the noise completely.

We came to the conclusion it is some kind of cross-talk between audio 
and polling but not sure where to go from there. Has anyone got any 
thoughts?

Chris G3SJJ