> From: "Dave VanHorn" [EMAIL PROTECTED] > Date: Mon Apr 24, 2006 8:56pm(PDT) >Subject: Re: telco and ctcss tones
>>--- In [email protected], DCFluX <[EMAIL PROTECTED]> wrote: > >> Here is an age old question that has yet to be answered satisfactorly. >> >> What are the CTCSS frequencies derived from? Meaning why are they what >> they are? Like 123.0, 127.3, Why not 120, 125, 130 ETC? >I just asked about that a few days ago. >I haven't found any simple relationships between the tones. More trivia, Actually, adjacent CTCSS tones are approximately 103.5 % apart, so that they have no harmonic or simple integer relationship. Any closer in frequency would increase the likelihood of falsing by adjacent tones and any further would waste spectrum. The tones were picked back when the encoders and decoders used mechanically vibrating devices similar to tuning forks to select the proper tone frequency. The "Q" of the mechanical devices then and the manufacturing tolerances dictated this spacing. This was state of the art in the late 1950's and the tones were probably picked by Mother Motorola although GE, RCA and the others soon followed. Multiply a tone by 1.035 to get the next higher tone and divide by 1.035 to get the next lower tone. This usually comes close. They are rounded off to a tenth of a cycle. The use of CTCSS signaling was touted to allow up to ten times the number of users on a channel as compared to using simple carrier squelch. 73, Al, K9SI Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
