1. BITX20@groups.io

Re: cw filters

Jerry Gaffke
 

The MAX7400 is a low pass filter, however if the uBitx crystal filter is doing 
its job there should already be a sharp lower cutoff frequency of around 300 Hz.
So the total system is effectively a good sharp bandpass filter.
That lower cutoff frequency can be adjusted by moving the BFO.

Jerry, KE7ER


On Fri, Oct 18, 2019 at 03:58 PM, Jerry Gaffke 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
 
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