Topband: New supper narrow APF 3S

[Mike Waters]

That is fascinating! Thanks for sharing.

Many years ago (late 1960s? 70s?), I built a resonant speaker from plans in
an older ham magazine. It was tuned by moving a plunger up and down in a
cylinder facing a 4" speaker, with a small opening around the circumference
just above the speaker. It was *nothing* like this design! :-)

73 Mike
W0BTU
https://web.archive.org/web/20190827040547/http://w0btu.com

On Fri, Mar 14, 2025, 11:29 AM JC(Jose Carlos) via Topband <
topband at contesting.com> wrote:

>
> I am sharing the results of a project I started back in 2017; I am calling
> it 3S, super selective speaker. 5Hz to 10 Hz BW APF. ...
>