DIYbanter - build a video cable

On 26 Dec 2005 09:58:31 -0800, "werwer" wrote:

Depending on the price I may want to build my own coax video
cable to connect a "standard" tv to dvd player (and other things).

The video jack is an RCA. It's marked with a yellow band
(impedance spec?) What coax cable type is best for
building this type of cable?

Thanks

An ordinary twisted pair of wires may be just fine.

With video, if you mismatch the cable and connectors you can see the
result. You see a "ghost," (outlines are most noticeable as being
offset from the original . . . horizontally)

The "type F" connector is made for 75 ohm video. The RCA connector
isn't, it is made for audio. It does not match 75 ohms. The
connector and cable impedance is determined by the diameter of the
inside conductor and the shield. Type "F" was developed for video
(actually, is was around for a lot longer)- the RCA was only intended
for audio where impedance of the connector isn't important.

But . . . I have a few surveillance cameras with 75 ohm outputs
feeding a receiver about 100 feet away (with RCA's) , and am using
cat3 UTP. Category Three Unshielded Twisted Pair . . . It has a
nominal impedance of 100 ohms and makes no (visible) difference to my
75 ohm input and output. My cable is buried in 8+ inches of wet soil
with no outside coating or conduit, just the vinyl jacket.

From my experiments - don't sweat the impedance. Try it, you may like
it. If you want to buy a cable with RCA connectors and that works for
you, do it. Try it first. Try it with a simple twisted pair of
wires, or buy a cable with connectors that mate with your equipment,
or just buy the cable you need.

Nine times out of a ka zillion the signal source has a low impedance
(lower than 75 ohms) feeding an input that has a much higher
impedance, like in the millions. Match the impedance when you are
concerned about absolute fidelity. Botch it completely and you'd
still have better resolution than the ATC or "Convenience Mart"
camera's you see on TV.

If you need to send lots of bandwidth over lots of cable for lots of
subscribers . . . then signal strength and impedance matter much more.
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