Hello Dave's aficionados!
A tough question for you... Once upon a time in the Mailbag section somebody sent in an homebrew device which only purpose was...
picking up EMI from electric/electronic appliances!
Sorry I'm unable to provide any more info... I just remember that this cute gadget could tune in on EMI by swiping it all over the device under test!
I'm into electronic music and from time to time - in my earphones - I can barely hear this noises that sometimes has excellent rhytmical features!
Unfortunately I can't amplify them enough to be usable in my "choons"!
Sounds weird, huh?
I'd love to buy the kit to build that!!
Have a nice day,
Francesco