"Jim" wrote in message
...
i see two different designs on the net for receiving loops. one is
to
wind the pickup loop with the main loop, and another is to use a 1/5
size loop off center at the bottom. what are the pros and cons for
each
setup? what benefit is there to a pickup winding as opposed to just
inductive coupling to the internal loopstick by proximity?

==================================

The coupling and main loops behave as the primary and secondary
windings on an impedance matching transformer.

The number of turns is fixed at 1 to 1. So the impedance matching is
done by using different loop diameters.

The 1/5 diameter coupling loop matches the antenna to a 50 ohm
receiver or transmitter.

The large diameter coupling loop matches the antenna to a high
impedance receiver such as 1000 ohms.

Theoretically, the impedance matching ratio is equal to the square of
the loop diameter ratio. The receiver input impedance is usually
known. The trouble is to find the impedance of the loop antenna. But
it is not a critical matter.
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Reg, G4FGQ