[Kenwood] TS950SDX RFI Issues

[Brad Johnson]

Hello all.

I've posted this in a few places hoping that someone might be familiar with 
the phenomenon, have an explanation, or know of a fix....

I am having some odd issues with my TS950SDX. The  first oddity occurred 
when I connected a W2IHY equalizer. There was a "proximity issue"...the only 
solution to which was to move the eq several feet from the radio. It was a 
very low level hum that seemed to have its origins in the radio, rather than 
the mic, cable, or eq. All of the usual "fixes" didn't improve it. I was 
able to reduce it enough that I forgot about it. I did make one interesting 
discovery though....with the rig in TX, and a mic connected, if you tap on 
the mic connector with your finger or pencil, you can hear it through the 
audio chain...almost as if you were tapping on a live mic. I have called 
this phenomenon "microphonics" in the past...not sure if that is the correct 
term.

Having run mostly non-resonant antennas and parallel feed lines into the 
shack, I am no stranger to RFI, particularly when I started running a small 
amplifier. In the course of experimenting with different mic, tuner, 
antenna, grounding scenarios with the 950, I discovered that it appears to 
be unusually susceptible to RFI. When I switch to the TS2000, connect the 
same mic, the same amplifier, use the same tuner settings, and the same 
antenna...my audio is clean, even with the processor on (which I never use). 
The same operating conditions produces noticeable RFI in the 950's 
audio...and turning on the processor results in.... well...you can imagine.

I made another interesting discovery.... with NO microphone attached to the 
950, RFI can be introduced into the audio chain by turning on the processor 
and turning it up. Perhaps this is not as unusual as I think it is...?

I was able to reduce, but not completely eliminate RFI by disconnecting the 
950 from the station ground buss and inserting an MFJ artificial ground 
connected to a 135 foot counterpoise. Of course operating the 950 into a 
dummy load or resonant antenna eliminates the RFI issue. Ideally all 
antennas used would be resonant ones, but that isn't always achievable. I 
have been looking around and have not found any mention of unusual 
sensitivity to RFI being a well known quirk of the 950.

I have heard that there may be something "unusual" about the mic amp circuit 
in the 950...that it might not be at the same ground potential as the 
chassis? Given the odd behavior I have observed, I am wondering if this 
might not be the case...or perhaps there has been a component failure or 
poor connection in that section?

Thanks,

Brad Johnson  AA5CH
http://aa5ch.smugmug.com/