Blake Bowers writes in a message to Scott Christensen
  
 SC> Today, there are 2 kinds of "PL tones" - the old fashioned low
 SC> frequency audio tones from about 55 Hz to about 250 Hz (yes there are
 SC> specified frequencies - you can't pick a frequency "between" two of
 SC> the specified frequencies) - and since the early '70s a "digital" form
 BB>  
 BB> Beg pardon? Sure you can. non-standard PL's are used in a number 
 BB> of applications, such as a local SO we have, that has had a 
 BB> problem with a person discovering their input and tone, and 
 BB> disrupting their communications. 
 BB> Non-standard tones, and presto, the problem disappeared. 
  
Blake, if you can do that with the FSSAs (GE) and permacode filters 
(Motorola) you should be able to market it and sell it.  I said it couldn't 
be done, which is wrong.  What I should of said is that it is very 
impractical with the equipment made by the big boys.
 
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