Re: cw filters

Jim Willis







From: <> On Behalf Of jim via Groups.Io
Sent: Friday, October 18, 2019 7:14 PM
Subject: Re: [BITX20] cw filters


As an "analog" alternative, I use this on my uBitx


On Friday, October 18, 2019, 3:59:02 PM PDT, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:



The MAX7400 switched capacitor audio low pass filter is an interesting part.
Simple to use, and only draws a couple ma.
Has an internal oscillator that Andy is tuning with the 1n4148 used as a varicap diode,
but could drive the clock pin from a Nano counter-timer at 100 times the desired corner frequency.
That way you could tune it in firmware.

However, this is a low pass filter, not a band pass filter like some of the alternatives are.
So it will not attenuate frequencies that are below the desired signal.

Jerry, KE7ER

On Fri, Oct 18, 2019 at 10:58 AM, Martin Potter wrote:

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

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