-=> On 08-04-97  16:22, Mark Magill said to Jeff Edmonson, <=-
-=> About Monitoring,..." <=-
 
Hi, Mark;
 
 JE> ...  They're -supposed- to be sub-audible ;-)
 MM> 
 MM> That's why I wondered why our association would pick an
 MM> AUDIBLE  sub-audible tone frequency. Some places I have heard of use
 MM> the lower ones 40.x hz or the like. I do have one commercial kit that
 MM> generates a single tone, but  it uses the no-longer-common 567 chip
 MM> that Radio Shack -USED- to sell. Also, it generates more of a
 MM> square-ish wave than a sine. It sounds 'funny' to those who hear me on
 MM> the air with it, and friends who hear me talking on a non-PL  repeater
 MM> say "hey, turn your tone off!" to remind me.. :-) But at least it 
 MM> works. 
 
Historical note:
 
The origional Motorola PL systems used a vibrating reed to generate and
detect the PL tones rather than an electronic circuit.  The generated
tone was a "sloppy" square wave, which was then run through an R-C circuit
which converted it to a triangular wave which was then transmitted.  A
triangular wave, (like /\/\/\/\) was more efficent at making the reed
in the receiving system vibrate properly.  Now, with PL generation and
detection done electronically, a sine wave is commonly used, which has the
advantage of being the least noticable because of the lack of harmonics in
other waveforms.
 
Catch you later es 73 de KB9QPM
   Ivy
 
 
 
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