[mythtv-users] coax vs. composite

[Steve Hodge]

On 5/16/06, John Brooks <iresprite at gmail.com> wrote:
>  I  see- I may have confused terms, then, because like Greg I conceive of
> composite as using RCA cable. My STB- a Motorola DCT2200- offers outputs in
> both coaxial form and RCA form.

You mean your STB offers RF and composite outputs.

It's important to realise that the type of cable and connectors is not
directly tied to the format of the signal, instead they're usually
determined only by convention. People should talk about the format of
the signal but they tend to talk about the type of the cable because
that is what they are familiar with. This is analogous to the
confusion between media file container formats (e.g. avi, nuv, etc)
and the codecs used to encode the contents (h264 video, vorbis audio,
etc).

> > "Composite" refers to a "baseband" or "video" signal of 1 volt peak-
> > to-peak (nominally) running on a coax cable. With NTSC the color is
>
>  So what is it that runs over RCA cables?

It could be anything. Usually it's a composite signal or part of a
component signal. Or a channel of audio.

> Part of the reason I asked
> was because beyond using just what looks good, I wanted to be able to change
> my recording profile to use a recording quality that would allow the most to
> come through without unnecessarily inflating the size of the transcoding.

Your question is really about the limitations of NTSC video, and not
the type of cable. For NTSC video the vertical resolution is fixed at
480 lines. But horizontal resolution will depend primarily on the
video source. This page
(http://lyberty.com/encyc/articles/tech/vid_horizontal_resolution.html)
claims broadcast signals have about 330 pixels horizontally. This page
(http://members.aol.com/ajaynejr/vidres.htm) has some more info, and
states that signals provide about 80 pixels of width for each MHz of
bandwidth. As Brian said TV stations provide about 4.2MHz bandwidth
which also gives about 330 pixels.

The type of cable you use is not likely to affect the horizontal
resolution much, but it might introduce other artifacts - color
bleeding, blurring, etc. Your best bet is to try the outputs you have
available and see what looks the best.

Steve