"Richard Clark" wrote in message
...
On Thu, 29 Jan 2009 06:41:17 GMT, "Spin"
wrote:

Is it feasable to remove the ferrite antenna from an am radio & replace
it
with an external multi-turn box loop with the same primary/secondary
inductance?

Those with more than one coil (almost all) are not primary to
secondary relationships. One coil is the RF/Mixer stage, and the
other is the Oscillator stage and the ferrite provides the mixing path
as well as the signal pickup path. If you closely examine the
variable capacitor, you should see that it is also two independent
sections on the same frame (or inside the same enclosure). There
should also be a trimmer for each, one for peaking the RF, the other
for tracking the Oscillator. If there is a TRF stage, it will
probably have another coil/cap combo and probably with that coil as a
separate item.

It would help if you identify the "am radio."

73's
Richard Clark, KB7QHC

This is why you would do just as well to add some turns to the ferrite
loopstick for an external antenna and simply shield the radio. That method
of coupling is very efficient.