[Elecraft] Watkins-Johnson

[Geoffrey Mackenzie-Kennedy]

 Alex NS6Y wrote:

 And #2, how well do audio filters, or even audio DSP like SGC sells,  for
 narrowing things down for listening to CW?

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 IF, and that can be a big IF sometimes, all the signals getting through the
 2.5kHz IF filter do not overload anything between the IF filter and an 
added
 audio filter, and the circuits between the two do not generate detectable
 intermodulation products i.e.crud, the audio filter will help in two ways.
 (1) Prevent you hearing the signals blocked by the filter. (2) Improve the
 'sensitivity' of the receiver because its noise floor is reduced. How much
 the noise floor is reduced depends in this case on the ratio IF Bandwidth /
 Audio Filter bandwidth, so a 250Hz Audio filter should reduce the noise
 floor by a factor of 10, or by 10dbm. This is an approximate but very close
 figure, the actual amount depends on the 'shape' of the response of both
 filters.

 73,
Geoff
GM4ESD