[mythtv-users] coax vs. composite

Jay R. Ashworth jra at baylink.com
Mon May 15 14:43:50 EDT 2006

On Mon, May 15, 2006 at 03:04:08PM -0400, John Brooks wrote:
>      When you say "coax" I assume you are referring to an RF signal with a
>      TV signal modulated onto it. I mention this because "composite" video
>      is normally carried on a co-axial cable.
>    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.

Well, as Cory says, yes and no.

In both RCA and F connectors, the *connector* is coaxial, as is the
cable (usually).  S-Video cables use non-coaxial connectors, but usualy
coaxial cable.

>      "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?

NTSC Composite, or 1/3 of a component (YPrPb) signal.  Cory was using
"coax cable" in it's strictly technical sense, not in the home-theater
colloquialism which means "RG-59/U cable with an F connector at each
end".  I commonly call those "RF cables" as do many others, though even
*that* can be misinterpreted as well, by a sufficiently determined
geek.  :-)

>    *grins* Like laws and sausage, eh? Fair enough. 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. If you could clarify that
>    one pont above, that would be really helpful!

The number one thing to do to reduce encoded space requirements is
*reduce video noise*.  You do the math.  RF amps, better shielded

-- jra
Jay R. Ashworth                                                jra at baylink.com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

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