Tom says:
>That's right. A 500Hz 8 pole IF filter right after the second mixer
>works about right to protect the DSP filter on CW.
In which case, one might ask what the point of the DSP is! Desirably, it
could well be argued that the first IF should be low enough (1.4 - 10MHz)
that the first mixer is followed by the 500 (or 250Hz) filter.
>I'd want more than one bit toggling on noise. I don't know about
>you, but I (like most CW DX ops) can copy signals below noise
>level.
Good point. 1 bit is OK for digital cellular telephony, but we're talking
real radio, and presumably, real oeprators.
One could argue that you don't want any bits toggling at all!
Hans, SM5KI, mentioned phase distortion in filters. According to the
experts, the ear is not sensitive to phase distortion. There's been lots in
both the acoustics and the medical journals on that, but personally, I'm
still not totally convinced. Of course, for processed speech in
transmitters, where some flattening of the envelope takes place,
differential group delay will alter the wave shape, so perhaps that's a
special case.
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|