In article , Don Foreman says...

...Some tube-type AM radios had loops comprised of
several turns of Litz wire spiral-wound on a fiberboard form the size
of the back of the radio. Sometimes it *was* the back of the radio.
They worked quite well if the radio was "pointed" at the radio
station.

That's how old loop antennas (the kind built on large crosses or
turnstyles) worked. IIRC they're sensitive off the edge of the
loop (it's been a while since I've had mine out and running).

They make great antennas for crystal radios where there's a
strong local station (WLNA in my case) so the strong local
signal can be nulled out. Basically just a germanium diode
and a set of phones makes a pretty good radio with that.

Jim


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