[CW] 600 Hz Resonant Speaker for CW - Plans

[Patrick]

Jeffrey Herman wrote:
>  I seem to recall an article about a VERY narrow CW mechanical filter, 
> constructed as such: Take a pair of old headphone "cans", remove the 
> outer plastic ear cover, then remove the metal diaphram. Using a metal 
> cutter called a nipper (?), trim the diaphram in such a way that, for 
> the most part, just a reed appears in the center (the longer the reed, 
> the lower its resonant frequency, and vice versa). Replace the diaphram 
> and cover. Now that particular earpiece will only pass signals whose 
> audio freq'y exactly matches the reed's resonant freq'y.
>  
> One of those "ah-ha" type of simple but effective projects.
>  
> 73, Jeff  KH6O

This was from an article in the April 1976 QST. I think this was 
something for the April Fools issue as the author's name was "Tinh 
Ehres" (Tin Ears) with a call of WH0OP. I remember reading about it 
before I was a ham (an Elmer had given me a bunch of old QST's) back in 
the early 80's. I have the .pdf of it or if you are a member of the 
ARRL, you can do an article search. The title is "CW Super-Selectivity".

Patrick KA4ZNU