The circuit of the filter has little to do with the time and amplitude
response. It takes fewer crystals to get a square edged frequency
response if the time response is neglected. If the time response is
considered (and apparently time response is not considered for audio
communications filters even today) the skirts won't be as steep, nor the
shape factor as good. I notice that the 2.4 and 500 Hz filters in my
Corsair II (same parts as in the Omni VI) handle line noise and
thunderstorm static better than my Collins mechanical filter or the
crystal filter in my TS-130S. That is they pass static as clicks, not
half second crashes and the line noise has a distinct buzz, not
continuos nearly smooth noise that fills in the gaps between the pulses
that happen 120 or 360 times a second.
It doesn't matter if lattice or ladder filter, it depends on the design.
I've made a very nice ladder filter for fast sweeps, could sweep it as
the IF of a panadapter 8 or ten times faster than the typical better
shape factor filter for the same amount of ringing.
Listening to W1AW on 20m, I notice no difference between sidebands, only
that if I use the widest filter I have in the Corsair II and center the
signal that the leading edge click is most pronounced and if I use the
CW filter and slide it off to one side narrowing the bandpass even more
and throw in a passive speaker low pass filter that most of the thud
goes away. Yet I hear no CHIRP ever.
If there's a leading edge spike on CW from ALC action, then the drive
level is too high and the drive should be backed down until there's
barely ALC action, then the leading edge can have a slower rise without
creating a spike and the hard leading edge would no longer click. The
ALC should PEOTECT from accidental overdrive, not be the only controller
of the drive. When you work the ALC hard its just like driving a class C
amplifier, both will remove the leading edge shaping built into the
keying.
73, Jerry, K0CQ
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