Re: CW Filter


Interesting note here... if you use series varactor diodes to ground on the inner caps (that go to ground) and put variable voltage on the instantly have a variable pass-band control.  I believe that was done in the Elecraft K2 as well.  Check the circuit. 



On Mar 14, 2020, at 11:58 PM, Scott McDonald via Groups.Io <ka9p@...> wrote:


Bob, that will give you an idea of what I got with a quick and dirty 4 pole, not to die for but a big improvement over the ssb filter.

73 Scott

On Mar 14, 2020, at 10:38 PM, Scott McDonald via Groups.Io <ka9p@...> wrote:

Bob, I built a quick simple 4 pole cw filter using matched crystals (Only 1.50 each) from W8DIZ for a UBITX Receiver based on v3, and I think he is stocking 12 MHz matched crystals now.

Only issue was getting the cw BFO where I needed it but using KD8CEC software made that easy enough.

73 Scott ka9p

Make something good happen!

On Mar 14, 2020, at 9:41 PM, Bob Clarke <bclarke@...> wrote:

Has anyone looked at designing a crystal filter for CW, any number of poles? I like the notion of using adjustable digital filters but believe based on my industry experience that any ADC should preceded by decent analog filtering to prevent overload by IMD. 


Bob, N1RC


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