[mythtv-users] coax vs. composite

Brian Wood beww at beww.org
Mon May 15 18:56:46 EDT 2006


On May 15, 2006, at 1:04 PM, 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.
>
> "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?

If it hasn't been made clear (I just had 63 messages in my inbox and  
may have missed a few):

In home consumer systems:

RCA connectors are used for composite video, and are also used (in  
groups of three) for component video.

When used for composite video they are sometimes color-coded yellow,  
and when used for component video they are sometimes color coded red,  
blue and green.

They are also used for unbalanced audio, and when in this service  
they are sometimes color-coded red and white.

RCA connectors are also sometimes (not very often these days) used  
for RF signals in radio receiver systems.

An RCA connector is probably the worst connector ever designed (IMHO)  
for either video or audio. They have no real "nominal" impedance, are  
difficult to solder properly, make the "hot" connection before the  
ground (thus rendering audio systems susceptible to loud hums and  
pops). The provision for strain-relieving the cable is poor to non- 
existent and they tend to get noisy easily. They depend on friction  
to "lock" the connector in the socket. Whwn used in audio systems  
they make no provision for keeping left and right oriented properly  
(except for color, if that's used correctly,which is rare).

In short, they suck. Why are they used? You can guess that, they are  
cheap.

>
> Even this summary is extremely brief, and leaves out most of the
> subject matter. You probably don't really want to know all the
> details, just use whatever looks good to you :-)
>
> *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! Otherwise, thanks for all the info. :)
>
> Jack.
>
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