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

[David Woolley]

Paul Webb wrote:

> now when i select SSB and tune to a AM signal i can alter the
] bandwidth to anything up to 6KHz, when i switch to AM i can only adjust
] the bandwidth up to 3KHz , the audio sounds like it is a 3KHz filter
] too, what am i doing wrong since i cant set the 6KHz bandwidth in AM.
> any ideas???

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.

[ Note: excessively long lines re-wrapped. See RFC 1855. (Probably using 
yahoo.) ]


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David Woolley
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