Topband: New supper narrow APF 3S

[Jim Brown]

These are solid concepts -- IF you like copying CW through a speaker. 
I've always preferred cans (headphones).

73, Jim K9YC

On 3/14/2025 8:51 AM, JC(Jose Carlos) via Topband wrote:
> Hi guys
> 
>   
> 
> 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.
> 
> The idea of chasing an acoustic filter was motivated my early situations
> reported by N4II Ed, and NX4D, Doug, when it was possible to copy a weak
> signal far from the radio room, the walls was working like a filter removing
> the QRM. The first project I should call beginners luck, worked straight
> away. With two speakers behind my monitors, I was able to copy that weak
> signal you can see on the SDR waterfall but not pull it out.  Since I start
> using the system, I and other friends here at my station were able to copy
> any signal that we can see at the waterfall, I like to use HPSDR audio water
> fall to identify the weak signals. Most of the time it was not possible to
> copy the same signal with my IC7851using headphones.
> 
> In the last few months, I was recovering from an eye surgery, and I decided
> to work on a new pair of speakers, for my surprise it was very complicated.
> After a lot of try and building, now I can share the results with a huge
> improvement from the original project.
> 
> This project was based on the work of Ed Loranger (WE6W), and N5FC Resonant
> Speaker (N5ESE Prototype) found here >
> 
> https://www.n5ese.com/res_spkr.htm
> 
> Several deep diving on organ pipe builders, psychoacoustic, the human ear,
> CW pitch and NASA 3-D initial work that today moved to multimedia, all that
> results on the paper attached. The new 3S, or super selective speaker can
> provide narrow bandwidth between 5 and 10 Hz with no ringing or
> intermodulation.
> 
>   
> 
> There is enough information to build the system on the pdf attached. I used
> PVC 2" sch40 because it provides the best Q, for lower CW pitch, like 200Hz
> I used aluminum tube 3"x1/8 wall.
> 
>   
> 
> Enjoy it,
> 
>   
> 
> 73
> 
> N4IS
> 
>   
> 
> 
> _________________
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