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

[Dave Martin]

I've seen a number of old U.S. broadcast receivers with a 10 KHz notch
filter in the audio to get rid of the high pitched hetrodynes from the
adjacent channels.  But the wide IF sure brightens up the music when
listening to your local honky-tonk station, and nobody gave a rip how
wide their IF was if their music sounded good.  That's why I was
hoping for the option of going as wide as I see fit when conditions
allow.  But then who (other than yours truly) would be using a K3 to
listen to the local BC when he could be working CW while enjoying 100
Hz selectivity?

Dave  W5DHM
>
>
> 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.
>
...
> David Woolley