[Elecraft] SSB Filter Bandwidth Control

[Ron D'Eau Claire]

Hi, Bill!=20

The SSB filter is fixed. It can't be tuned to change it's bandpass. =
That's
the OPT-1 filter in your setup, and you'll notice that you cannot choose =
a
bandwidth for it. The only adjustment you can make in OPT1 filter =
position
is in the frequency of the BFO oscillator in the product detector.  You =
have
that exactly right!  Changing the BFO frequency has the effect of moving =
the
OPT1 bandpass in relation to a signal, but it does not change the =
bandpass
or  "width" of the filter passband. =20

The CW filters have voltage-variable capacitors (varicaps) between the
crystals. Changing the capacitance of those "varicaps" by adjusting the
voltage changes the bandwidth. That voltage is controlled by firmware. =
You
choose it running CAL FIL, and it's stored in memory. So, on the CW =
filters
(those are the ones on the RF board itself, of course) you have two
adjustments: bandpass and BFO setting. Both of those settings are =
recalled
when you select that filter in operation.=20

Ron AC7AC
K2 # 1289

-----Original Message-----
...How is bandwidth control for the SSB filters accomplished.  I see NO
hardware that can alter the frequency of the filter string on the SSB =
board.
I may have missed something.  In OP1, the CW crystal filter is bypassed, =
as
I understand it.  So, what is done in software to adjust bandwidth?  Is =
it a
stored look-up table to change shift the BFO and adjust the VFO to
compensate for center frequency?????????  Or does the Control Board do
things at audio to change the bandwidth of the signal content you hear?

The roof won't fall in if I don't get an answer, but it will haunt me =
past
the grave if I don't.... ;-)

Thanks for any insight.

Bill
NA7Y