Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!bellcore!uunet!pilchuck!ssc!markz
From: markz@ssc.UUCP (Mark Zenier)
Newsgroups: sci.electronics
Subject: Re: video chroma circuit
Message-ID: <791@ssc.UUCP>
Date: 19 Jan 91 04:43:56 GMT
References: <767@ssc.UUCP> <14501@milton.u.washington.edu> <38104@cup.portal.com> <1991Jan17.192816.23881@batcomputer.tn.cornell.edu>
Distribution: usa
Organization: SSC, Inc., Seattle, WA
Lines: 15

In article <1991Jan17.192816.23881@batcomputer.tn.cornell.edu>, gaarder@batcomputer.tn.cornell.edu (Steve Gaarder) writes:
> >In article <767@ssc.UUCP> markz@ssc.UUCP (Mark Zenier) writes:
> >>Does anyone know the reason they picked 3.579545... Mhz for the
> Actually, it was done to make deriving those frequencies from the 3.579545
> master easier.  A the time, frequency division was done by syncronizing 
> an oscillator, which was fine for small divisors but impractical for large
> ones.  Thus a division ratio was chosen that could be factored completely
> into small numbers. (Divide the burst by 13, 5, and 7, then double it, to
> get the horizontal frequency)

Ok, and 5 Mhz divided by 8 and 11 then multplied by 7 then 9 is
3.579545...  Has anyone seen any design rationale published by the 
NTSC.  Ancient history, electronic style.

markz@ssc.uucp