Audio filter for CW

[Michael Waldrop]

Hello everyone,

I work alot of CW using either an SB-300 or SB-303 receiver. Although the Heath CW filter does a good job, the audio output to either a speaker or headphones is a bit high in frequency for my taste. 

The idea of using an outboard filter came about while looking for an alternative to the Heath filters. The cost for a replacement IF CW filter was $100 or more. 

The filter is built around the popular LM-741 op amp in a high Q bandpass configuration  Using the High Q bandpass configuration, the filter is capable of providing an adjustable resonate frequency between 50Hz to 1KHz with an overall bandwidth of 500Hz, perfect for CW work. The filter runs on a single supply, a 9 volt battery, and draws no more than 3.5ma. I tested the filter using a dual supply but I could not see any difference in performance between single versus dual supplies. The battery supply eliminates the need for a seperate power supply.

A great cost savings that provides great filtering for CW work.

73's,

Mike
W5RKL


 		
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