Re: cw filters

Jerry Gaffke
 

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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