[Elecraft] K2 KIO2 Serial Data causes RX Interference

[Vic K2VCO]

Stephen Arnold wrote:

> I now have RX audio interference. It sounds like a low volume puffing
> steam train or a chuff-chuff type noise. It is pretty obvious what is
> causing it. The constant serial data stream being sent by the fldigi
> program.
> 
> The interference is all bands and all frequencies so far as I can tell. It
> is very low level but quite audible and would drive you mad if you tried
> to use the radio for any length without turning the volume down. Needless
> to say it will no doubt play havoc with weak digital signals.
> 
> Questions is: Am I looking at a fault in my particular K2 set-up or just a
> design limitation? (you would never notice the issue except for the
> constant polling by fldigi). And how does one go about trying to fix the
> problem?

This is present with a non-split K2, although at a low-enough level that 
it is masked by band noise. It is generated by the RS232 chip in the K2. 
Apparently your setup is such that the noise is being radiated by the 
control cables and somehow is getting into the antenna.

What might help is to wrap the control cable between the K2 and the 
KPA/KAT in the EC2 around a chunk of ferrite. I am not sure what the 
best location would be; try near the radio and near the EC2. You might 
also do this to the cable that goes to the computer.

Clamp-on ferrite beads will probably not help unless you have one with a 
hole big enough to wrap several turns of the cable through.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco