[CW] 600 Hz Resonant Speaker for CW - Plans

[Frank Kamp]

On Aug 31, 2009, at 11:27 AM, wealsowalk at aol.com wrote:

> Ken, modern receivers with "narrow filters" on the IF usually means  
> 300 or 250 hz wide.  A mechanical device like the one you are  
> talking about here is very much sharper than that and can be a very  
> large help.  You can also use an electronic audio filter to get  
> down to 1 or 2 hz wide band now, but it is not usual to see those  
> and the ringing sometimes gets on your nerves a bit.  Either way  
> can be very helpful though.  Another way to get at a signal is to  
> feed the audio to a computer audio card and scan it, like what is  
> done for psk31, and then you are really spreading out the noise you  
> would ordinarily hear so that you can ignore that part.  Also you  
> can make multiple scans and average out the noise so that signal  
> detection by computer far outperforms either the narrow filters or  
> the mechanical method.  Still, the mechanical resonant speaker is  
> very intriguing, though expensive by comparison with electronic  
> audio filters.
> Bill


More expensive?  I guess that all depends on who you have to hire to  
build the box.  Or if you have to buy a table saw and particle board  
to build the box.  Luckily I have both, a good table saw and plenty  
of usable wood.  It is going to cost me as much to do the mechanical  
filter as it will the electronic filter, mainly nothing.  Got a fat  
junkbox too.

Even so, I think I will try for the speaker enclosure.  I have used  
both passive and active electronic filters before and don't care for  
the way they ring at times.  Besides, you can't have an informed  
opinion on something you have never tried.  I have never tried the  
mechanical approach.  It is still an active item on my bucket list.

Regards,
Frank Kamp