On Feb 26, 9:10*pm, Michael Black wrote:
On Fri, 26 Feb 2010, Kevin Alfred Strom wrote:
If you don't mind it looking strange, it would probably work just as well to
wrap a few turns (experiment with the number and orientation) of wire around
the outside of the radio and then attach the ends of the wire to your
external antenna.

Better yet, open the radio and wind a few turns around the existing rod, then
bring the ends out to a terminal strip or connector.

And that's all that's necessary.

The winding of wire around the radio, the external coupling loop, those
are all constructs to deal with people not wanting to open the radio.

Well, that's the whole point! I did not want to open the radio up and
mess with the ferrite already wrapped with the most fragile-looking
wire imaginable.

Winding some turns on the actual loopstick is what would be happening if
that radio had an external antenna connection.

And it would be the same if a radio didn't have a loopstick but just a
tuning coil, there'd be a few turns of wire as a primary to couple the
antenna to the tuned circuit.

Understood.

* * Michael

I actually tried wrapping a wire around the radio per Kevin's
suggestion. What I found was that a single loose wrap of wire, with
about 10 feet going across the room and the other end attached to a
ground, was enough to dramatically increase the coupled signal. 4.8 -
6.2 MHz became significantly louder. 1/2 additional wrap was enough
to begin to overload the band with intermod products from 3 or 4
nearby 50 kW MW blowtorches. Two full wraps obliviated any resonant
signals. My wires on the roof are clearly severe overkill, possibly
in the literal sense. I did not try my PAR high-pass MW attenuation
filter inline; it might have had some effect.

My guess is that this inexpensive old single-conversion portable is
probably too sensitive and too loose on its front end to worry about
it much more. If I did the external ferrite rod, it would likely
perform best positioned linearly with the internal ferrite rod rather
than broadside, although the radio is so sensitive that broadside
might work OK. I think it might have to be tuned with a slug or a VC,
just to allow some selectivity to remain.

Bruce