dmmartindale@watcgl.UUCP (Dave Martindale) (02/02/85)
Background info:
The NTSC television standards require colour information to be
transmitted as two colour-difference signals (I and Q) which have
different bandwidths. The I and Q axes are rotated 33 degrees
from the axes of the colour difference signals R-Y and B-Y,
necessitating the use of a precision resistor matrix to
perform the basis transformation.
If a television receiver wishes to be cheap, it can decode
the colour signals using the R-Y and B-Y axes directly, limiting
both colour signals to about 0.7MHz bandwidth. But to do the job
"properly" (according to the spec.), it must decode the signals
along the I and Q axes, filter the signals to 1.5MHz and 0.5MHz
respectively, use a delay line in the I channel to compensate
for the greater delay of the Q filter, and use a resistor matrix
to regenerate R-Y and B-Y from I and Q. Also, more delay in
the luminance channel is needed. All this adds cost.
The question:
Some things I've read seem to imply that many, if not almost all,
commercial TV receivers do the simpler "narrow-band" demodulation
of the colour signal, thus throwing away half of the bandwidth
of the I signal that was transmitted. Does anyone know for sure?
The specs for professional cameras, I know, tell you which sort
of modulation they use, but I've never seen this matter discussed
by ads or data sheets for home equipment.
Dave Martindale
{decvax,ihnp4,utcsrgv,allegra}!watmath!dmmartindaledoug@terak.UUCP (Doug Pardee) (02/06/85)
> Some things I've read seem to imply that many, if not almost all, > commercial TV receivers do the simpler "narrow-band" demodulation > of the colour signal, thus throwing away half of the bandwidth > of the I signal that was transmitted. Does anyone know for sure? This isn't necessarily definitive, but last year RCA introduced a new color TV chassis (CTC31?) which they claimed was the first to have the full 1.5MHz I bandwidth. -- Doug Pardee -- Terak Corp. -- !{hao,ihnp4,decvax}!noao!terak!doug