In article ,
Clark Magnuson wrote:

Could a spy modify an AM radio by adding a few capacitors?

Possibly, but I doubt that it would work well if you started from a
standard US-type AM broadcast-band receiver. The frequencies that
this article speaks of are up in the HF band, roughly 10 times higher
than the AM broadcast-band frequencies, and these radios' built-in
loopstick antennas are not well suited to receive these sorts of
signals.

A spy in most Western countries could simply buy an off-the-shelf
AM/FM/shortwave receiver (very widely available).

Simple but very effective direct-conversion or superheterodyne
receivers (capable of receiving CW, SSB, and AM) can be built out of
"junk box" parts by anyone with a modest amount of training and
experience. Many of the popular QRP receiver designs could be tweaked
to receive on these sorts of frequencies with very little difficulty.

Now, if somebody had an old "7-transistor" AM radio (circa 1960
or so), it would likely be possible to salvage enough parts from it
to build a simple direct-conversion shortwave receiver.

I doubt that this would be possible (or at least not easy) for today's
highly-integrated IC-based radios.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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