HD SDI Cable Requirements?

[deweylikedonuts]

Let me first apologize if this is the wrong place to post this or if it has already been answered. I've searched and wasn't able to find it anywhere else.

My church has in place Quad Shield RG-6 for composite video runs. We're looking to upgrade to HD cameras and use HD SDI runs. My question is, can we use the cables that are already in place to accomplish this? The runs are about 200'. Here are the specs straight off the cable:

West Penn Wire Plant #6 #6300 RG-6/U Quad Shield 18 AWG (UL) CATV

Also, if the existing cables will work, can we just terminate the ends with standard BNC connectors or are there certain connectors required for HD SDI use?

Thanks in advance!

[chris2pher]

I emailed our Engineer. I will get back to you

[Esoteric]

We do HD SDI with BNC connectors.

Do you have enough conductors? 6/U is only 2 conductor right?

Mike

[deweylikedonuts]

Thanks for the replies. Not sure on the conductors. I don't quite understand all of this stuff yet. I'm hoping you guys can help with this. Sorry.

[zactommo]

Yes, SDI uses BNC connectors. RG-6 is 2 conductor.

RG-6 meets the specifications for SDI, and definatly should to the trick.
SDI, being digital, means that signal degredation shouldn't be a problem. Either the signal gets through, or it doesn't. The best way to check is to get some gear in and try it out.

Generally, people tend to use RG-59, mainly because its a lot easier to work with, and I think there may be marginal quality differences.

[Esoteric]

Yeah, it would work, but you would need more than 2 conductors for HD SDI.

Mike

[SamG]

HD-SDI travels on a coaxial (center conductor & shield) cable. It will generally be connected using BNC ends. HD *CAN* travel on component cable, but that's generally used for interconnects between devices (DVD player & TV for example). I guess that's what people are talking about HD needing more conductors.

Your main issue is distance & how much loss the cable has at the higher frequencies needed for HD-SDI.

Cable specced for HD-SDI (Beldon 1694A is one) will only go ~250-300 feet MAX before running into problems. I don't think your cable will work. But as mentioned earlier, you can give it a try. Keep in mind though, don't just hook it up, see a picture and call it good. Make sure you get some movement in the video (can even be moving the camera) and see what happens.

[Esoteric]

What Sam said. Our multiple conductors come from multiple input sources, not multiple cables from the same source.

Mike

[tdangelo]

Dewey,

Yes, that cable will work at 200' however understand that you are at the outside edge of the envelope already and you will likely not be able to barrel on any more length.

- Tom D'Angelo
NYC

[deweylikedonuts]

Thanks for the help on this issue. It looks like there are some mixed beliefs. You've given me something to work with though. Thanks!

[DTV-Engineer]

Originally Posted by deweylikedonuts

It looks like there are some mixed beliefs.

That's a rather diplomatic observation! Sam, indeed, comes closest, but doesn't quite address all of the OP's issues.

Here's the scoop about HD-SDI (per the SMPTE 292M specification): you're running a data rate of 1.485 gigabits per second, and selecting the correct cable and connectors is absolutely critical. As a general statement, cable that isn't designed for serial digital video isn't going to work acceptably over any significant distance. Belden 1694A is the most commonly used cable in broadcast facilities, and is good to about 364 feet. Belden has a chart that shows maximum transmission distance as a function of cable type and data rates.

These distances are based on the unstated assumption that you are connecting directly from the originating equipment to the destination, with nothing intervening (e.g., distribution amplifiers, routing switchers, etc.). Digital transmission distance limitations come mainly from two factor: first (and most intuitively), the signal drops in amplitude over distance. Second, extremely high frequency data that starts out as a nice square wave becomes increasingly distorted as the cable length increases. In particular, the once vertical transitions between logic high and low become rather sloppy and gradual rises and falls. This poor risetime makes it hard for the receiving equipment to discern precisely when each transition occurs, and the result is jitter in the recovered data. Given sufficient jitter, the receive equipment will stop recovering the data reliably, and the link will fail. (This jitter is in the data itself... we're not talking about motion in the picture here.)

An amplifier by itself can correct for the loss of level; with equalization (which most all HD-SDI input stages incorporate), some of the high frequency rolloff can be corrected. But a plain amplifier won't fix the jitter problem: to do that takes reclocking.

Reclocking means decoding the incoming data and putting it into a data butter -- actually, a shift register, if you want to be precise about it -- where the register is clocked by a stable oscillator that is loosely locked to the incoming data rate. The result is that you recover the original data, but remove the instability that came from the incoming jitter. You can then feed this reclocked data to an HD-SDI output driver, and feed another long run of cable.

So if you are talking about very short cable runs -- a total of 50 feet, say -- jitter and reclocking shouldn't be an issue. On the other hand, if you're trying to send an HD-SDI signal 500 feet, you will need to go about half the distance, hit a reclocking amplifier, and drive the other half of the line. Or, use a fiberoptic link to do it.

Finally, about connectors: HD-SDI wiring uses BNC connectors... but it's even more specific than that. What most people think of as a BNC connector is probably a 50-ohm style, and has plastic dielectric between the outer fingerstock and the center pin. Using a 50-ohm connector on a 75-ohm cable creates a mismatch that is unacceptable for digital video -- especially at higher HD data rates. You need to use a true 75-ohm connector, such as a Kings (now Winchester) 2065-10-9 for Belden 1694A cable.

For what it's worth, Belden 1855A is also a very nice cable for shorter HD-SDI runs -- for instance, within racks -- and it's quite small (about an eighth of an inch... similar in size to Belden 9451 audio cable). This would be paired with Kings 2065-11-9 connectors.

Happily, you can crimp Kings connectors for both 1694A and 1855A with the same tool: the Paladin 1612. Both types have the same center pin diameter, and the crimper's die has both .275" and .178" ferrule crimps.

Finally, a warning: both 1694A and 1855A will also work quite acceptably for analog video (including black burst for genlock applications) over fairly long distances. But 1505A, which is the size of RG-59 and used to be a fairly common SDI cable, does not perform well for analog -- in particular, it seriously attenuates color subcarrier. For longer distances, 1694A is a much better choice; for shorter distances, 1855A is cheaper and easier to handle. I would steer clear of 1505A.

-- Jeff

[capricornJZ]

thanks for this great thread