Re: cw filters

Martin Potter

On Thu, Oct 17, 2019 at 11:39 AM, <@biker> wrote:

I have my basic ubitx working nicely, i just wish the cw filtering was a bit
(lot) better.  What is the best way to improve the cw filtering and narrow it
down.   Dave c
Here is a simple circuit that I have been using and find that it works quite well for both CW and SSB. It is a variable bandwidth filter, based entirely on the circuit developed by Andy, RW9RN (thanks, Andy!!). It uses the MAX7400 switched-capacitor filter (SCAF) chip, common (I am told) in the telecomms industry. Component values are ones I had on hand and are all close to values suggested by RW9RN. It runs on 5VDC but needs a 12V reference as well, as you can see in the schematic. The pot controls the bandwidth. Connect the circuit input to the audio output of your uBITX and plug your phones or speaker into its output. Mount it either internally (as I did) or add it externally.
Have fun.
... Martin VE3OAT

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