[CQ-Contest] SO2R and broadband noise

[Pete Smith]

I have been doing some tests with my new single-tower SO2R setup, transmitting on a TS-930S and listening on a Mark 5.
Results so far are very gratifying.  I have noticed, though, that regardless of band, when I have the TS-930 in transmit, but not key-down, I can hear a slight increase in the noise floor on the Mark 5.  The amount of increase is subjectively the same, whatever band I'm listening on, and does *not* change between key up and key down.

I'd characterize this as a nuisance, and probably not an operational problem under extreme weak-signal conditions, but I'm curious what could be causing it.  Any thoughts?  

73, Pete N4ZR
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