[RFI] Is My Radio Possessed?

[N4ZR]

73, Pete N4ZR
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Looking for an explanation for a weird experience I recently had, which 
*may* fall in the category of RFI.

I was tuning my K3 across 40M CW during theWAE CW contest, while at the 
same time watching the band using HDSDR with my QS1R, which was also 
running CWSL_Tee and both CW and RTTY Skimservs.  The QS1R's antenna was 
being split off the K3's external antenna loop.

I noticed on the HDSDR waterfall what looked like SSB signals, way down 
in 40 CW (one even below the band edge). Curious, I tuned several of 
them in on HDSDR. All were obviously hams, and I inferred from what they 
said that they were on 40 phone.  Even weirder, the signals were on 
upper sideband!

After a few minutes of this, I shut down both Skimservs and turned my 
attention back to the contest.  When I returned a few minutes later, 
HDSDR showed NO SSB signals at all down in the CW band, even with the 
two Skimservs restarted. It has not recurred.