[TenTec] http://lists.contesting.com/_tentec/2014-07/msg00214.html

[Peter Bertini]

Hi Rick

No, this was broad band noise, generated in the IF stage and amplified by
subsequent amplifier stages.

IMD would require at least two signals, implying modulation being
present... this noise was evident when the TX was keyed, and with no audio
input.

Had Heathkit placed the SSB filter after the IF amplifier, the TX noise
level would have been reduced considerable.  This was typical of Heathkit
designs--which were often rushed to market before being fully debugged and
tested.  The most notable example was an early two meter synthesized rig
they produced--it had spurs and would key several repeaters at the same
time... they didn't have a spectrum analyzer in the lab at the time, and
were oblivious to the problem.

Pete