[Elecraft] New K3 SN#207 built but question on AM Filter

[Alan Bloom]

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