[Elecraft] SSB Filter Bandwidth Control

[Bob Nielsen]

The KSB2 filter does not have a variable bandwidth.  It is selected (as
OP1) when FL1 is used, and it always used in SSB transmit.

FL2-4 use the variable filter in the K2 itself.  These filters'
tuneablity is accomplished by a voltage applied to the varicaps in the
crystal filter circuitry (these can be considered as variable
capacitors, the capacity of which varies with the applied voltage,
tuning the filter).  As the filter is tuned, the lower edge stays fixed
and the upper edge moves (at the i.f.).  The BFO is shifted
appropriately to achieve the desired upper and lower audio frequencies.

73,
Bob, N7XY

On Thu, Jul 24, 2003 at 11:43:44PM -0700, William M. Spaulding, Sr. wrote:
> Folks,
> 
> I have a "how does that work" question.  After all, I think there is huge
> benefit to building a K2 just from the education you are forced to get to be
> a successful builder and alignment tech.
> 
> 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