>(A useful circuit would be nice, also, but I'd still like to know=20
>what to call it. :-)

i'd call it ...Fred!, but seriously, look up the=20
signetics NE565 Phase-locked loop I.C.
it will lock on to an incoming frequency and give
a squarewave output of around 4.5v (5v max.)
you would need some form of amplifier/limiting circuit
ahead of it (automatic gain control plus diode 'clipping'?)
theres nothing like the smell=20
of freshly blown transistors in the morning ;-)
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