Amateur Radio Tower
W3NQN's High Performance CW Audio Filter

The filter kit is temporarily unavailable.

The kit is being redesigned.

A note from Ed: Thanks to all the hams who have purchased and enjoyed my passive audio filter.

Unfortunately, my filter kit is no longer available because I have exhausted my stock of the 5-inductor stacks that are a major part of the kit. After 30+ years of gathering and distributing these surplus inductors, my stock has finally run out. So, for now, I no longer can provide the kit of parts that are described on this web site.

However, I still have a small stock of individually potted surplus 88-mH inductors that I am planning to use in a new design that I expect will provide an attenuation response that will be similar to my original design that used a 5-inductor stack with two external inductors that were modified by removing turns to get a number of different center frequencies.

This new design using potted inductors will be set for only a center frequency of 600 Hz, and the design will have a similar 200-Hz passband as the original design, but the stopband will be only about 30 dB instead of the steadily increasing stopband attenuation of the old design. I believe it is not necessary to have the stopband continually increasing if a 30 dB stopband will still provide the stopband response adequate to attenuate the QRM and QRN outside the filter passband.

I plan to assemble several of these new CW filters and have hams try them out to see if they are acceptable. If my new designs are favorably received, I will give details on this web site in which the filter will be described as was done with my original CW filter design. So, check back in about two months and see if my new design is available.
Ed Wetherhold W3NQN

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