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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 junction...you 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.
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.