[mythtv-users] coax vs. composite

[Cory Papenfuss]

>> 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.
>
> Could you clarify this a bit? I always thought that "composite" video
> was carried on a cable with RCA plugs at both ends, i.e. the same type
> of cable that non-digital audio typically travels on. As far as I know,
> this is NOT the same thing as coax. Which one of us is confused?
>
> --Greg
>
 	Coax is short for co-axial.  All it means is that two wires are 
put together on the same center, rather than side-by-side, or 
side-by-side-twisted.  Coaxial cable has a center conductor and a round 
shield around insulation placed around the center conductor... thus the 
co-axial part of the name.

 	Whatever connector you put on this type of wire doesn't (much) 
matter.  BNC, RCA, SMA, TNC, Type-R, Type-N, Type-GR, etc, etc... they are 
all forms of coaxial cable ends that can be placed on coaxial cable. 
Many people colloquially call RF-modulated TV signals coming in on 75 Ohm 
coaxial cable with Type-F ends "coax" for short.  It's equally correct to 
call RCA patch cords for composite video "coax," but video patch cords 
with RCA ends typically carry composite video (i.e. non-RF modulated 
baseband video as described very well by a previous poster).  Thus they 
are often colloquially called "composite" cables.  Heck... it's generally 
even correct to call s-video "dual-coax" because all but the crappiest of 
s-video cables carry the chrominance and luminance signals separately on 
their own coaxial cables inside the main cable.

 	Saying, "I connected my PVR-xxx to my STB via the coax connection" 
is a content-free statement regarding the *type* of connection between the 
STB and the capture card unless taken within this vernacular context.

 	Hopefully thus endeth the confusion.

-Cory

-- 

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* Cory Papenfuss, Ph.D., PPSEL-IA                                       *
* Electrical Engineering                                                *
* Virginia Polytechnic Institute and State University                   *
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