I have two big time dxers/contesters near me - on 160 , one is -8 to -9 dBm
and the other is -10 to -11dBm . Folks , thats in the 50 to 100 mv area at
the poor K3 .(S9+60 to 70 area) Just for fun of it , I can easily see both
on my scope hung on my antenna.
With the 250 hz 8 pole - I could copy an HS0 at my noise level split 2.2
khz away from the -9 dBm station and not even know he was there except
seeing him on the P3. (He is using a K3 exciter and an ALPHA amp. )
Cannot say that for some of the other locals who have phase noise from
various and sundry other rigs.
73 Hank K7HP
(SNIP)
If the operator never encounters signal levels in excess of S-9+30,
there is no need for the roofing filter, but signals stronger than that
are encountered commonly in contests and tuning through a DX pileup.
If it were not for the Hardware AGC, they would overload the A-D
converter causing the entire output to become garbage.
With the Hardware AGC present, that is not going to happen, but strong
signals within the 1st IF bandpass will cause "pumping" of the Hardware
AGC as those signals come and go. In the K3, *that* condition is what
the roofing filters will prevent.
Bottom line, if you hear that "pumping" (and subsequent desensing of the
receiver), you would benefit from a more narrow filter.
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