[Ian Thompson-Bell]

Jeff Liebermann wrote:
On Sat, 13 Sep 2008 08:42:53 +0100, Ian Thompson-Bell
wrote:

Green Xenon [Radium] wrote:
Hi:

What would be heard on a 40 Hz AM DX receiver that uses the most
sensitive type of magnetic loop antenna? I doubt there would be any
hissing since that artifact would involve high-frequency sounds and a
40 Hz carrier cannot transport modulation-signals higher than 40 Hz
[violation of Nyquist theorem].
Not strictly true I think - depends on the modulation scheme - how else
do you think we manage to get 56K bps down a 3KHz phone line.

Ummm... Mr Radium clearly specified that he's using AM as in amplitude
modulation. If there were a different method of modulation employed,
methinks he would have specified it. You can get more bits per baud
out of relatively narrow bandwidths. The various HDRadio schemes:
http://en.wikipedia.org/wiki/HD_Radio
are good examples with about 40Kbits/sec in a 9KHz bandwidth. However,
they don't use AM.




Depends on your definition of AM. There are many types of amplitude
modulation, ask any radio amateur - and then of course there's VPAM.

Cheers

Ian