[CW] 600 Hz Resonant Speaker for CW - Plans

[Jeffrey Herman]

 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
 
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