Blackmagic Forum

I have a pile of unmarked 75 ohm, BNC tipped, SDI cables I would like to put into rotation.

Is there such thing as an "SDI cable rated for 12G"? (Or are all SDI cables rated for __G)

If so how, how can one tell from cables that are not labled?

Can they be visually identified, tested with a multimeter, or other special tool?

Does the gauge matter, or the length (I know this answer is yes, but what are the specifics?) 18AWG, 12AWG, 300ft max etc.

75ohm is standard, but is it required?

If you have good cable but "bad" connectors, will that not work? (is that even a real scenario?)

Referencing a few sources and getting conflicting results
I would like to know the science based WHY behind these questions if possible.

Basically if there is no text or indication on it.. You can expect 1.5G or less

6G / 12G cabling WILL have text on it what brand, what cable etc.

Also you need a higher grade connectors for 12G. Neutrik does indicate them with a sort metalic gray for UHD.. some other manufactures use Black and Gold combo..

But basically any Silver connector wont be anything higher then HD.

Does not say you can not run 12G on it. But the signal will degrade rapidly and if the cable is short enough it might work up to maybe 5 meters max..

But we use Belden 4855 and Neutrik UHD for all our 4K cabling in the racks.. And Procab PCX-165 for all our in the field cables.. As it riggid and sturdy enough to handle a bit of stress.

Thank you for all the info, a few more questions if possible.

Is there ANY way to test cables (even with a high end piece of gear) for throughput?
Would a larger gauge cable always putout more than a smaller one?

I am skeptical of cables bought from anywhere (except places like direct from belden or the like?). Even with UHD 12 G markings on it, I can't REALLY be sure can I?

Thank you again.

Tektronix make equipment that can test 12G but you're talking nonsense dollars. Like $30K. Lynx and Digital Forecast make 3G cable testers that are still expensive but a lot more accessible.

I do what I call 'last mile' testing. So for 3G, I know some of my cable stock is good for about 130m. If I make a 5m cable, I test it by putting 125m of cable in front of it, so I know the cable or its terminations aren't the weakest link in a longer cable run. As Xtreemtec says, almost any cable will carry HD or 3G over 5-10m.

Obviously you'll need to scale this for 12G. You might find the ceiling to be more like 20-30m.. And as I understand it, reflections are the primary issue at that frequency, so the number of cable joins will likely impact the max length.

When you test this, watch it for more than 30 seconds. If the signal to noise ratio is poor it can sometimes take 30 seconds before it'll actually glitch; as the receiving device confuses noise for the carrier signal and it drifts out of sync.

I actually think BMD would do well to make a 12G tester. It serves their interests as there's a hole in the market and they make a lot of 12G stuff! It doesn't need all the fancy features of the Tektronix or even the Digital Forecast units. Just a noise measurement and a Good / No good indication would be really useful.

Awesome solution. Not a for sure, but at least gives you something.
I do have access to a known good 200ft 12G SDI

We have analog lines in the building from 2004, I know the length of all patches and that the lines are 3G.

That gives me a starting point, thank you so much.

OvertureCenter wrote:We have analog lines in the building from 2004, I know the length of all patches and that the lines are 3G.

I wouldn’t be too sure. 3G was science fiction in 2004. Composite (analog) video had a bandwidth of about 6.5 mhz. Something here doesn’t compute. I still run into issues today with 1.5G versus 3G cabling.

Good Luck

The 3G SDI standard requires a maximum attenuation of 20 dB @ 1500 MHz, while 12G SDI requires 40 dB @ 6000 MHz. That's why many (not all) 3G SDI cables work relatively well with 12G over roughly the same distances. You may have to swap the connectors to types made for UHD, because return loss is more of a problem with 12G.

We use a Phabriq QX 12G with Eye measurement add on.

This gives a very good indication of the cable and connectors.. But still wont tell you how good the cable will perform with BMD hardware..

We once did a test for a cable manufacturer where we cut off 5m at a time from a 100M reel. ( Starting from 70 meters )
Crimp a new connector and start measuring.
In the end it came down to that the Phabrix with optimised path of SDI did MUCH better then the BMD Atem and Camera.. Basically Ursa to Atem would top out at 25m.. While the phabrix did up to 40m.. So the real test for your production enviroment is still testing it with the BMD hardware..