On Sun, 2008-01-13 at 02:49, David Woolley wrote: > Paul Webb wrote: > ... > The basic reason has already been explained, however, there are very few > cases were exceeding 3kHz audio bandwidth is useful. HF broadcast > stations use 5kHz channelling, which would only allow them 2.5kHz with > brick wall filtering at both transmit and receive ends, although they > probably do expect to suffer significant adjacent channel interference. > > MF broadcast stations use 9kHz channelling in Europe and 10kHz in the > USA, but I suspect that adjacent channel interference is less > acceptable. As they were designed to be received with LC IF filters, > with poor shape factors, I suspect they don't even make use of the full > channel, and if they did, they would probably be required to have > filters which put the adjacent channel into the filter stop band.
Even with the 10 kHz channel spacing used in the USA, AM broadcast stations do not have 5 kHz audio bandwidth. The FCC requires a guard band between stations. As I recall, rgulations require that the audio start to drop off at about 4 kHz so that it can be down 20 dB or so by 6 kHz (the passband edge of the adjacent station). So there's not much point in the receiver audio being wider than 4 kHz. Al N1AL _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
