JE> Should be simple enough to build something, with a 555 IC,
JE> and R/C component to obtain the frequency.
JE> However you decide to come up with the actual tone, remember
JE> to inject it at the CARRIER level, and not in the audio
JE> section.  Remember to keep the ouput low enough to not be
JE> heard by human ears, yet detectable by the repeater
JE> reciever.  They're -supposed- to be sub-audible ;-)
        That's why I wondered why our association would pick an AUDIBLE 
sub-audible tone frequency. Some places I have heard of use the lower ones 
40.x hz or the like. I do have one commercial kit that generates a single 
tone, but it uses the no-longer-common 567 chip that Radio Shack -USED- to 
sell. Also, it generates more of a square-ish wave than a sine. It sounds 
'funny' to those who hear me on the air with it, and friends who hear me 
talking on a non-PL repeater say "hey, turn your tone off!" to remind me.. 
:-) But at least it works.
        Good point about carrier-level injection, since as someone else 
pointed out that injection at the audio-processor level would result in 
clipping during voice peaks - and our local repeater will drop you like a hot 
stone the second that PL disappears! The fellow who installed the kit in my 
radio for me did it at mic input cicuit level, so I have to be careful not to 
speak overly loud into it or I can cause a drop out. But it DOES work, within 
those limits, and  he did the best he knew how to for me.
Mark KC7RUB

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