[Lowfer] 67.5 kHz noise question

[Michael Sapp]

HI All: Anyone familar with this noise signature ??

http://i1296.photobucket.com/albums/ag19/wa3tts/67d5khz_zps1ef2aa76.jpg


It's likely from nearby power line coupling on my NE EWE antenna. It comes and goes.
 When I disconnect the antenna  the noise goes away.  It's 30 dB or more weaker on the
 SW EWE antenna, which leads me to believe some inductive coupling to the power line
(100ft away point to point) is going on with the NE EWE antenna.

Problem is it is potentially strong enough  to create IMD products in the MC1496 mixer
 that would be second harmonic near 136~138 kHz range.  Quick Google search suggests
 possible cause are florescent  lamp ballasts---plenty of those in use these days....

I'm thinking shunt trap at the NE antenna transformer......any thoughts appreciated.

73  Mike wa3tts