From: cantrell@seqp4.sequoia.com (Paul Cantrell)
Newsgroups: rec.video
Subject: Re: LD vs Broadcast TV
Date: 17 Aug 92 21:40:42 GMT
Distribution: usa
Organization: Sequoia Computer Systems

In article <1992Aug14.204811.3960@shearson.com>, kaplanr@knish.shearson.com (Roger Kaplan) writes:
[he didn't attribute this to me, but it was from my posting]
> >>When watching cable through the cable box (for encoded channels such as
> >>HBO) there is a severe decrease in quality associated with using the cable
> >>box. However, watching some unencoded channels directly off the cable
> >>(local Boston stations such as WCVB, as well as remote stations such as
> >>TBS, TWC, WPIX) usually are excellent quality in both resolution and S/N.
> 
> This is not true in New York.  Running the cable directly into the TV
> creates terrible interference on broadcast channels.  Reason?  The 
> TV is receiving two signals: one thru the cable and one over the air.
> Since the cable signal has travelled a longer path than the line-of-sight
> broadcast signal, the two are out of phase.

What you are describing is multi-path error. It would only occur the way
you describe if you combined the antenna and cable RF with a combiner (a
reverse splitter) or just tied the two electrically together. Neither
sounds like a good idea to me. If you read my posting carefully, my
monitor has two separate RF inputs (along with several a/v line inputs and
outputs and an RF output). Thus multi-path would not be a problem since at
any given time, the receiver is only connected to one RF input. Given your
description, I would suggest that an inexpensive RF switchbox would solve
the problem of selecting Cable versus Cable Box.

Previously, I used a switch box to select RF inputs for my old 13"
Hitachi, but this is not normally necessary with my current set. I don't
currently use an antenna at all because the cable reception is so good.
However, I still use the switchbox occasionally when I want to do
something unusual such as watch the RF output of a VCR which is being used
to record from the Denon AV switcher outputs. (the Denon can only route
one a/v signal at a time, so it can't, for instance, route LD->VCR and
simultaneously route a separate VCR->TV a/v signal).

> Also, the cable box acts as an amp, so unless you compensate with another
> amp, the signal is noticeably weaker if it is run directly into the sets.
> The cable co. is expecting the amp in the box, and weakens the signal
>  accordingly.

I don't understand this from several aspects. Are you saying that the
cable signal is substantially lower than you would see coming from an
antenna? I would have expected just the opposite. Does anyone know typical
signal strength of cable versus antenna leads? Also, I fail to see how
running a signal through an amplifier/tuner -> RF modulator, and then into
another amplifier/Tuner would produce a better signal than simply going
into a single stage amplifier/Tuner in the TV set, unless the Cable Box
Tuner is substantially better than that found in the average TV set. Given
the need to keep the Cable Box relatively inexpensive, I find this very
unlikely.

					Paul

[in case nobody noticed, the second and subsequent non-attributed paragraphs
 are from someone else, not me]
> >I have noticed that recently some of my more recent video disks, while
> >very low in noise level, appear to have lower resolution.   Can't tell
> >for sure without a test pattern, but detail seems to be missing.
> >Things look too smooth - as if they were bandwidth limited more than
> >some of my older disks.
-- 
cantrell@sequoia.com
Newsgroups: rec.video