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Logan Shaw at wrote on 7/3/04 11:09 PM:

The point being, I don't see how there can be a distinction between
hum caused by changing magnetic fields and hum caused by radio.
If the two wires are really close together and the frequency is,
say, 100 Hz, then wavelength is really, really long, and in fact
the distance between the transmitting and receiving antenna is
waaay less than one wavelength. But does that mean it's not
the same thing as radio?

while they are essentially the same in what they ARE, they are HUGELY
different in how they ACT. I general the higher the frequency, the more
intrusive and seemingly creative it is in showing up as newer
harder-to-diagnose problems. I think this is due to both extremely (well
above audio) Hf material's ability to travel across all sorts of electrical
'barriers' to audio as well as the fact that we can;t hear it unless/until
it gets rectified/demodulated into audible range, and that happens in MANY
'intereting')annoying and varied and unpredictable) ways in all sorts of
different circuit topologies... Scott can undoubtedly shed a a better light
on the WHY's of this but simple practical fact is, RF is DAMNED good at
creating all SORTS of seemingly IMPOSSIBLE symptoms.. I've been chasing one
gremlin in this flavor for YEARS here, while PRACTICALLY it's been solved by
simply NOT USING THAT SET OF LINES for anythign other than headphone returns
and other line-level feeds, it's turned into a personal thing as to wanting
to know just WHY this one in-house snake is PLAGUED with RFI, differently on
different lines, while other single lines and snakes running along the same
route are CLEAN... and according to my electrical and shop inspections and
tests There's (apparently) Nothing Wrong with any of the lines, the box or
the connectors...

By the way, from what I can dig up, it seems that the US Navy
uses radio at 76 Hz to communicate with submarines. Apparently
the antennas are fairly long, like way over 10 miles long.

and getting information across a SLOOWWWWWWW system like that is like
pouring marbles through molasses.

--
John I-22
(that's 'I' for Initial...)
Recognising what's NOT worth your time, THAT'S the key.
--