In the telephone world, equipment allows out to 4Kc.
That was considered optimal for intelligibility vs bandwidth.
The telephone network bandwidth is 3.1kHz (300 to 3400Hz). 4kHz was the
analogue bearer channel separation, and allows for realistic shape
factors on the channel filters. On digital signals, the 8kHz sampling
rate allows the use of realistic anti-aliasing filters when the audio
bandwidth is 3.1kHz.
For swl use, 16Kc is not unreasonable for people with good ears, that gives
8Kc
The channel spacing for SW broadcast stations is 5kHz, although I
suspect they are are allowed to overlap each other. I'm sure there are
standards for this, but I suspect a well maintained transmitter is
limited to a similar audio bandwidth as the telephone system, or less. I
would think that one would normally expect to be received with a filter
that was well down the skirt at 10kHz, so as to suppress the adjacent
carriers. Propaganda stations and commercial ones in a poorly regulated
environment might well transmit more bandwidth. (Medium and long wave
transmissions use 9kHz channel spacing.)
--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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