Xref: utzoo rec.video:6917 sci.electronics:6774
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!gatech!dscatl!wa4mei!kd4nc!ke4zv
From: ke4zv@kd4nc.UUCP (Gary Coffman)
Newsgroups: rec.video,sci.electronics
Subject: Re: VTR colour recording (and how does SECAM do it?)
Message-ID: <2599@kd4nc.UUCP>
Date: 27 Jun 89 16:17:11 GMT
References: <124@nisca.ircc.ohio-state.edu> <566@axis.fr> <367@ctycal.UUCP> <1533@unccvax.UUCP>
Reply-To: ke4zv@kd4nc.UUCP (Gary Coffman)
Followup-To: rec.video
Organization: /etc/MYORG
Lines: 23

In article <1533@unccvax.UUCP> dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) writes:
>	I'm not sure what consumer decks do; in fact, I'm not 
>sure what even our type "C" machine does!!!  In either case, the
>party of the first part (the "heterodyned" signal) and a replica
>of the party of the second part (the "heterodyning" signal) are
>both laid down for a total of three video signals on the tape.

Your description of color under or heterodyne color recording is basically
correct. However, type C machines DO NOT use color under. The reason for
color under is the lack of bandwidth NOT PHASE JITTER. On consumer and
industrial equipment such as VHS, Beta, and U-matic; there simply is not
a high enough writing speed to record a full bandwidth NTSC composite signal.
With type C one inch machines (as with the old two inch quads) there is
plenty of writing speed and COLOR UNDER IS NOT USED. In all cases a time
base corrector is required for broadcast use. In the old quad machines it
was a tapped glass delay line, in modern machines it is digital memory. A
analog to digital converter is clocked at four times recovered off tape
subcarrier and the resultant 8 bit words are written to memory. A DAC
clocked by reference subcarrier from the house master sync generator or
an internal crystal  reads the video back out of memory with
all jitter gone.

Gary Coffman Videotape Engineer WXIA-TV