[Elecraft] SSB Filter Bandwidth Control

[Don Brown]

Hi

Bill may be talking about the bandwidth change on the SSB board talked =
about on the reflector recently. That requires changing out about a =
dozen capacitors on the SSB board and possibly the crystals. The =
bandwidth is still fixed but by selecting the correct values you can =
have 1.9 KHz, 2.0 KHz, 2.2 KHz or 2.5 KHz your choice. I have made this =
change on about half a dozen K2 SSB boards and it sounds quite nice at =
2.5 KHz. See =
http://home.pacbell.net/johngreb/modifications_to_the_ksb2.pdf for the =
instructions=20

Don Brown
KD5NDB=20
  ----- Original Message -----=20
  From: Ron D'Eau Claire=20
  To: 'Elecraft Reflector'=20
  Sent: Friday, July 25, 2003 11:26 AM
  Subject: RE: [Elecraft] SSB Filter Bandwidth Control


  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

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