In article ,
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.

Because it's not the *line* that limits the rate; it's gear at the
central office. Even so, 56k modems need to cleverly bypass some of the
CO stuff.

By using clever modulation techniques and error correction, a nominal
3600 Hz analog telco channel can manage about 32 kbps, but in that case,
the symbol rate (baud rate) is 2400 baud per second, well within the
passband of the channel.

Isaac