[Elecraft] RF in the K2 on RTTY

[Stewart Baker]

> This really smells like RF getting in somewhere, but I can't figure what
> it's doing to the radio to begin to try and choke it off.  All the audio
> cables have chokes/shielding/beads/bypasses.  Looking at the KPA-100
> schematic, it would seem that the only devices capable of that kind of a
> current spike are the finals or the TR switch diodes, and I can't figure
> how they would be turning on on the return-to-receive cycle.  It seems
> like some sort of stored energy being dissipated as the transmitter is
> shut off.  I'm leaning toward the SSB module since there is no problem
> in CW mode ( I know, just stay on CW!!), but I can't make the connection
> between the SSB module and the PA..
> Any ideas you folks can toss my way I'd appreciate.  Since I didn't have
> any problems in the initial construction, I didn't get to dig into the
> schematics the way some of you have.  I'm hoping someone can take all
> these pieces and complete the puzzle.
> tnx,
> Ken K6MR
 Hi Ken,

You are certainly digging into this one !
Don't know if it may help, but as you are heading towards RF feedback thru the 
SSB module you might like to try a mod that I put in my K2.
I was getting RF into the KSB2 on 40m despite good external decoupling.
I added a 1mH RF choke in series with the input to U3 (pin 4) and a 0.001uF 
between pin 4 and ground. It got rid of the problem. Worth a try, and will do no 
harm. Let us know how you get on.

73
Stewart G3RXQ