On Thu, 09 Jul 2009 13:54:10 -0400, Michael Coslo
wrote:

There was an article in QST (or was it CQ?) about building a ultrasonic
"downconverter" to listen for noise sources. Yup, sound.. Many (most?)
Power pole RFI sources are mechanical in nature, and have an ultrasonic
component.

It would seem easier to build a multipole high pass filter (above 200
Hz, say) and feed a many turned loop into it, measure the AC out of
the filter.

73's
Richard Clark, KB7QHC