[Elecraft] Variable bandwidth crystal filter

[Julian, G4ILO]

Joe Subich, W4TV-4 wrote:
> 
> 
> Where the capability becomes noticeable is on SSB due to the 
> wide steps between 2.8 KHz and 1.5 KHz and in digital modes 
> with the step between 2.8 KHz and 400 Hz.
> 
In digital modes it shouldn't be an issue because you don't, in theory, need
narrow filtering. In theory you can run with the AGC off because you don't
have to listen to the signals and the digimode software ignores all but the
bit of the passband you're interested in.

In practise you can't, because the audio side doesn't seem to have the same
dynamic range as the RF side of the K3. If a strong PSK31 signal comes on
the air I see "ghost" images of it on the waterfall, often quite strong
ones. If I back off the RF gain they disappear, but often I have to back it
off far enough that I also lose the weakest signals.

Yes, I have done the mod to the KIO board. And I don't think it's the sound
card, because I installed an SB Live 24 for radio use and the ghosts are
still present.

-----
Julian, G4ILO. K2 #392  K3 #222.
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

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