[Elecraft] K3 FM filter required for full AM receive width

[David Woolley (E.L)]

Jerry Flanders wrote:
> for SWL. Only downside (a minor one, IMO) is that you might get response 
> from images 30 KHz away. How much weaker is a signal when you tune to 
> its image 30 KHz up/down?

Less than 30kHz.  The whole point of the exercise is to use wide 
filters, so, assuming that the interference is from a carrier and 
appears in the demodulated audio, the image can be 25 (5kHz audio) to 
20kHz (10kHz audio) away from the carrier (20 and 10kHz from the 
passband edge).  If the interference is from an audio component at the 
extreme of the bandwidth and the transmit is the same as the receive 
bandwidth, the carrier can be 20 to 10kHz away (although in the latter 
case would have other problems).  In practice, I would expect the 
carrier to get past a weak filter better than an extreme sideband frequency.

Note this means that if the signals are trying to reproduce audio up to 
10kHz, the adjacent channel will be an issue.




-- 
David Woolley
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