Newsgroups: alt.home-theater.misc,comp.dcom.cabling,rec.video,rec.audio.tech
Subject: Re: RCA cables, wire types to use
References: 
[email protected] (Mouse Anony) writes:

> I'm planning to connect my computer which has a Radeon 8500 (with TV
> out) to my VCR in another room. The total length will be about 15m
> (50ft for you Americans). I understand that this is quite long and may
> not work but I still intend to try. I will be connecting to the
> composite video RCA connector.

15 meter is not too lign for a composite video signal if
proper cable is used. With good 75 ohm coaxial cable (RG59 or better)
up to 30-50 meters will work very nicely, and even longer ones
if some sisible signal quality loss is allowed.

> I've been doing some research and I believe that I should get 75ohm
> coaxial wire for the video. 

You are right. 75 ohm icaxial cable is the signt cable to use.

> I will probably use either some old 75ohm BNC network wire 

If it is really 75 ohms, then it I see no problems in using it.
Please note that most coaxial cables used for networks
are are not 75 ohms. For example Ethernet uses 50 ohms cable
for 10Base-5 and 10Base-2 networks. Some old IBM terminal
wiring uses 93 ohms coaxial cable... There has also been
some not so often used networking systems which used 75 ohm
cable.

> or some 75ohm RF wire. 

I see no problems if you use this.

> Is there any reason why I should not use either of these? 

Based on the information you have given I can't recommend
either of those. To make right decision wich would be better
more information on the cable is needed. But most propably
both 75 ohms cables you have are "good enough" for your use.

> Is there really any special wire for composite video?

Some companies make special 75 ohm coaxial cables which are
optimized for video applications... Anyway composite
video is not that demanding compared to some other
video applications (high resolution computer video, HDTV etc.)
that it would necessarily need any special cable to be
used.

> As for the audio, well I'm still a bit confused about this. I believe
> it isn't so critical. 

Audio is not that critical to impedance. It is more critical
to attenuation od high frquencies 
(larger cable capacitance + higher output impedance -> more loos
and noise pickup (poor shielding, gorundloops etc.).

> But what is the best kind of wire? Note that
> this will be coming from the line out (i.e. unamplified) of my onboard
> sound (ALC210 chip) or maybe my Audigy to the VCR. I think that I need
> some kind of coaxial wire but what kind? 

Audio cable to carry unbalanced signal should be
shielded single condictor cable or shielded twisted pair.

Shielded single conductor cable: This cable type is used generally to carry
unbalanced audio signals. Tjhis cable type has one central signal 1
conductor and a ground shield around it (coaxial construction). 
This cable type is sometimes called "high impedance cable", 
because typically used with high output
impedance equipments like home hifi equipments (tape, CD player, phono
player), musical instruments (electric guitar) and some microphones
(for example hobby recording and computer microphones). 

Shielded twisted pair: This cable type is most generally used to carry
balanced microphone signals and balanced line level signals (works
also for unbalanced). Multi-pair cables (like "snake cables") used to
carry many audio signals generally consists of many shielded twisted
pair wires inside one large cable. Balanced connections and good
shielded twisted pair cables are needed to transfer audio signals for
long distances. 


Notes:

Unbalanced connections can quite easily pick up interference,
especially ground loop interference. Unbalanced interface is generally
adequate for small home hifi systems, but large professional sound
systems need something better. 

Some tips on connection of soundcard can be found at
http://www.epanorama.net/links/pc/sound.html#interfacing
Read this!


> Someone said TP but this just sounds wrong...

Unshielded twisted pair cabling is not the right cable to your
application. Shielded twisted pair is usable

> Will it be better to connect it to my amp first on my comp side and
> then to my VCR (this sounds like a bad idea but who knows?) 

Usually direct connection is better...

> Also, should I make an effort to keep the video cable a certain
> distance away from the audio cables for most of the distance?

With good cables those work nicely near each other.
Few centimeters of separation will keep the noise away in any case.


> One more thing, please don't tell me to get Monster cables (they sound
> like a terrible company anyway, conning the customers like hell) or
> Radio Shack or whatever stuff since I DO NOT live in the US
> 
> Thanks for your help.
> 
> P.S. If you wondering why I might connect it to my onboard sound
> instead of my Audigy well I was wondering whether I could use my
> computer (for light tasks) and watch movies (well someone else in the
> house not me) at the same time. My card has dual head of course so
> there should be no problem on the video side and if I use the onboard
> sound I may be able to do it on the audio side as well (provided they
> don't conflict like mad and the programs send it to the right device).
> Obviously I can't do this if I connect it to my amp.
> 
> P.P.S. Don't reply with something stupid like the maximum length of a
> RCA cable is 12 feet or some bs like that which you heard from Radio
> Shack....

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/