[Elecraft] K3 and spectrogram: dual passband

[Lyle Johnson]

> The outer PB is tipped, that is, the high frequency side of
> the inner filter is five to ten DB stronger than the low side.
>  Seems like it ought to be in balance.

I think if you plot the response at whatever width you have set, you'll 
see the low frequency rolloff before you engage Dual PB.  This is likely 
due to the relationship of the filter skirts and BFO.  If you then turn 
on Dual PB, you'll see the former passband suppressed about 25 dB and 
the 150 Hz wide peak rising above it.

Alternately, set the pitch higher to get away from the wide filter's 
passband edge and you'll see the suppression is in fact symmetrical 
about the peak.

73,

Lyle KK7P