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-   -   B n C and SVideo cables (http://www.dvinfo.net/forum/open-dv-discussion/10430-b-n-c-svideo-cables.html)

Josh Bass June 3rd, 2003 12:47 AM

B n C and SVideo cables
Which of these are better? Why? I want to buy a really long cable to use with my monitor, and would like some opinions.

Zac Stein June 3rd, 2003 01:18 AM

You are mixing your thoughts a bit here, s-video is a cable type that carries a super vhs type signal.

BNC is a plug socket type.

BNC became a pro standard because it twists and locks in, so it is difficult near impossible for it to drop out or become loose, especially when used over and over again. But as far as i know, BNC can only carry a composite signal, and s-video will provide u a better image than that.

But watch out, s-video plugs/cables like to wear out quick, and the little tiny pins inside the plug like to bend if not attached in correctly, or worse break off into the female socket, that is a total bitch when that happens. So you have to be careful how you plug it in each time.

One advantage is, if you step on a svideo cable it usually just rips it out and may damage the cable. With BNC it will bring whatever it is attached too down with it.


PS. Gaffa tape is your friend.

Bryan Beasleigh June 3rd, 2003 07:23 AM

BNC is simply composite video. Go for Svideo

Josh Bass June 3rd, 2003 02:09 PM

I appreciate the advice. I went to Radio Shack seeking a very long S video cable, and was told they don't make 'em longer than 12 feet! Is this true? He told me any longer and you'd have signal loss. What if I have an instance where I need the monitor but also need to be physically far from the camera, i.e., more than 12 feet?

Edward Troxel June 3rd, 2003 02:19 PM

No it is not true. We are using some 100 foot S-Video runs. Here's a 100' cable: http://www.bhphotovideo.com/bh3.sph/...ID=F5C77831F60

James Emory June 3rd, 2003 05:27 PM

Y/C to BNC 'Y' cable
B&H also carries Y/C to 2 BNC Comprehensive cables. You can order these at customized lengths. I use these from my XLs splitting the Y and C carriers down two 200 ft 75 ohm broadcast BNC video returns made in a snake and rejoining them the same way at the truck. This way you get the benefit of a Y/C signal and the durability of tough BNC jackets if not made into a PVC snake.

Robert Knecht Schmidt June 3rd, 2003 06:51 PM

If you can afford it, Monster cable makes some very nice 50' and 100' S-Video cable runs.

Josh Bass June 3rd, 2003 11:27 PM

but we all agree that the best signal quality will come from Svideo, right?

Robert Knecht Schmidt June 3rd, 2003 11:37 PM

Yes. Coaxial is to be used only when necessary. (I.e., when budget dictates.)

Josh Bass June 3rd, 2003 11:39 PM

Coaxial being what James Emory described above? How do I know when it's necessary--remember, I'm still new and have almost no idea what the hell I'm doing.

Robert Knecht Schmidt June 3rd, 2003 11:59 PM

BNC (British Naval Connectors) are one type of end plug for coaxial cable.

Remember, to transmit any type of signal, you need two conductors: one conductor to carry the signal, and the other to carry whatever baseline you're comparing the signal to. (Usually we call this baseline "ground," but it doesn't necessarily need to be earth ground.)

If your two conductors are two wires, and you just lay them parallel to one another, like so


well, you end up having problems. Current travelling down one wire creates a magnetic field that curls around the wire, and that magnetic field in turn generates a current in the other wire. This is called crosstalk, and it has the effect of weakening the signal, sometimes corrupting it beyond the point of recognition.

So, usually to combat this, you'd twist the wires together every so often:

------ ----- ------ ------- ------ ------- (ignore the dots in the
. . . . X. . . X . . . .X . . . .X . . . .X . . . . . middle, they're just there
------ ----- ------ ------- ------ -------- to keep the spacing.)

This is called Unshielded Twisted Pair (UTP). Most ethernet cables are Category 5 UTP.

Another thing you could do is ensheath the signal cable INSIDE of the ground cable, giving you coaxial cable. Most cable TV cable is coaxial. This is an ingenous layout. Not only does the physics of it work out so that the magnetic field generated by the signal wire has no effect on the grounding sheath, but the grounding sheath shields the signal wire from any outside magnetic fields that may be nastily trying to distort the signal. (Why isn't all cable coaxial? It's more expensive to manufacture than twisted pair!)

So now let's say you have your vanilla analog video signal, and it has several components. Break them up however you want to: Red, Green, Blue (3 signals), Luminance, Red Chrominance, Blue Chrominance (3 signals), however you wish. (When the signals are separated, you've got what you call component video, because each of the components are transmitted distinctly.) Through the magic of modulation, you can combine signals together to carry more than one signal on a single wire. Hence Y/C (Luminance, Chrominance) in which the chrominance signals have been modulated together. Or go one better, and modulate it all together for maximum transmission economy. We're going to send it all down just one signal/ground wire pair (coaxial cable, if you so desire). And now you've got so-called composite video, because all of the components are composited together on one signal carrier.

The RCA jack cables--the kind with the little yellow, red, and white jacks--those are composite video. The red and white are for the stereo audio channels and the yellow is what all of the video travels down.

The only problem with modulating down all these component signals into composite signals is that you cut into the bandwidth of each signal when you do so. It's a lossy process.

Cable TV modulates the stereo audio in with the video on one coaxial cable. Yuck. (But the compression codecs used by the digital dish guys aren't much better!)

So back to our story. When you use BNC (maybe what you were really thinking of was RCA, since the XL1s offers S-Video and RCA jacks), you're using composite video. S-Video keeps luminance and chrominance separate within the cable, plus includes separate ground wires for each, hence the four pins you see inside the connector. S-Video is not quite component, but it's less composite than your RCA jack (which you could convert to a BNC connector with a simple little adapter).

You should have no problem running S-Video cables for up to 1000 feet.

Josh Bass June 4th, 2003 12:19 AM

Ah. Thanks. And I actually got most of that! No, I was thinking of BNC. That's the one where the end of the cable has a little twisty lock to ensure that your stuff stays hooked up, right? I have that and Svideo in on my monitor, no RCA except for audio. I guess the only pro of BNC is the sturdiness of the material, then?

Robert Knecht Schmidt June 4th, 2003 12:28 AM

Well a coaxial cable with a BNC connector on the end won't pull out with a yank, if that's what you mean. On the other hand, it could mean that it'll pull your monitor off of its table if a clutz trips on the wire!

Bryan Beasleigh June 4th, 2003 11:40 AM

You can buy an RCA to BNC adapter.

Hosatech make an S Video from 5 ft to 100 ft. The 50 ft cable is $15 at B&H and the Monster cable is 450 for 25 ft. For field monitoring do you really need to be that picky? Don't waste your money on the premium stuff for the field.

You can buy a 50' RCA to BNC for $20


Josh Bass June 4th, 2003 12:01 PM

I wanted an all around cable. Technically, anything I do is field work.

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