Testing 12G-SDI cable

[misquamacus]

I work in video production, and have purchased a spool of Belden 4855r coax cable to make my own custom cable runs. Right now I am testing them by simply connecting two components together to see if a signal goes through, but I'd like to test them more comprehensively. How does one check for things like the actual strength of the signal from one end to the other.

https://www.iewc.com/assets/specsheets/spec_4855r_belden_4k%20uhd%20coax.pdf

Any advice would be greatly appreciated. Thank you

[BrianHG]

It's been awhile, but, when I was testing development of 3G SDI hardware for distance on 3G cable, 1 thing was a must, do not test the cable on the spool.  It will almost always work.  You must have the cable off the spool, running huge straight lengths even if you need to make a few loops around the outer perimeter of the office.  The signal in the cable degrades that way as stray interference begins to penetrate the coax shielding which does not happen in a compact spool as only the outer edges of that spool have to deal with the bulk of such external emi.

[dmills]

A Tek Prism or similar with the 12G physical layer option ($$$) or a VNA capable of S parameters to at least 25GHz (Would be my preferred option, slightly cheaper and more generally applicable, but you want the 75 ohm option).

The elephant in the room is usually cable termination, closely followed by things like installation bend radius and not crushing the cable by over tightening the cable ties (Some installers can be a little heavy handed).

I will admit to being a little surprised to see 12G single link being used, it tends to be a Japan and Korea thing at the moment in my experience, the US seems to be doing the quadlink 3G thing (Pain in the arse that is), and EU is going hard for the 2022-6 and 2110 IP approach for all that both are still more then a little immature on the control and system timing fronts (There is sometimes even a little TECO in there but the football types seem to have decided that any compression is a no go, so...).

Regards, Dan

[misquamacus]

Thanks very much Dan and Brian! It sounds like proper testing myself will be too expensive, so I'll try to hire someone with the proper equipment. @dmills, I'm with you on the single link 12G, but a lot of this is being pushed through by companies like Blackmagic Design. They started selling 12G equipment to people before the SMPTE standards were even ratified.   

[dmills]

BMD the Bheringer of broadcast!
Nobody shopping BMD has any actual need for 12G

I mean the glass you need to actually manage to capture 4K, never mind the sensors means that even if you are shopping GV or the like you probably don't bother with the 4K option for most things.

Yes, I know BMD advertise a "4K" camera but there is not much point in outputting 4K if the sensor and glass are not up to the job.

The Japs are going 12G on fibre, the Koreans on coax, Europe is mostly ignoring 12G as an SDI thing and going IP (Now they have finally ratified 2110, shame the control layer is still a bit of a puzzler), and the yanks seem to be mostly doing quadlink..... 

Regards, Dan.

[Dubbie]

We use 4K BMD gear because we shoot 6 or 8K and resample to 4K.
The glass resolves 4K just fine. (Cooke)

This is for feature film work or for specialised advertising projects.

Dunno about TV.

[basinstreetdesign]

...They started selling 12G equipment to people before the SMPTE standards were even ratified.    ...

Was a member of SMPTE for years.  They tend to finalize a standard for something just in time for it to go obsolete. 

[dmills]

We use 4K BMD gear because we shoot 6 or 8K and resample to 4K.

Odd production workflow, but whatever works I guess.

When I last looked the BMD 4K camera sensor could not actually resolve 4K, and a lens capable of actually producing a true 4k image at reasonable aperture was enough money that you may as well add the pocket change for the GVG back....

But TV always did care about being able to shoot ambient light more then film did, so maybe we just need faster glass.
The two industries are much less similar then one would expect.

Regards, Dan.

[DVX]

dmills you have a good handle on 12G vs, quad link vs IP. The broadcast industry is at a crossroads, OB has mostly gone 4K with larger trucks using IP (here in Europe), but most broadcasters are sat on the fence, most have upgraded from SD to HD and the capex repay in many cases has a few more years to run. Some early adopters have built 2022 systems but the advantages over SDI are not clear unless 4K is part of the picture. So now many are waiting for 2110 and some real interoperability testing between manufacturers, which as you you have pointed out still leaves a few holes to plug for the control layer and associated protocols. For 12G some manufacturers have taken this route but as broadcasters become more confident in their IP knowledge the advantages vs. IP is likely to decline. For BM they are giving the traditional broadcast market a good shake, time will tell what the real fall out from this will be.

[dmills]

I think the real SDI Vs IP question (Which is actually orthogonal to the 4K question) comes down to facility size.

A small facility will be cheaper (at the moment) done SDI, if you are talking say a 64 square router or so, by the time you are looking at maybe 256 square or up, leaf and spine on IP is looking very good, and for a playout as opposed to a production facility, 2022-6 gets you everything you need (In fact for playout it is arguably a better choice then 2110 because you avoid a whole mess of audio timing pain), of course playout is largely compressed domain which is a whole other can of worms.   

Lots of interop still to do, and the NMOS guys need to get the finger out or someone is going to hack a control protocol for video routing control on top of something like Ember+ (Probably the VSM guys).

I am betting that most IP facilities, even most 4K capable ones will spend their time @1080p60 except when there is big sporting events on.

I am not seeing much BMD in broadcast facilities (At least not in chain), churches, theatres, schools, wedding video types and conference centres seem to be where that stuff mostly lives in my experience.

Regards, Dan.

[rx8pilot]

I have been in this industry for decades, and now design 12G gear.

The short answer is that it is very expensive to test anything. A Leader or Phabrix with eye pattern option and payload analysis is by far the easiest. They can show the signal integrity, errors, and a description of the payload. You can see impedance issues, although you will not know where they are. You will see the amplitude, eye width, hight, rise and fall times.

The only problem is that for 12G, I think they are around $15-20k or so with eye options. You can also get a VNA for twice that if you really want to look close.

[shoulderkey]

Just had to reply to a few things:

"BMD the Bheringer of broadcast!"

Most broadcast cameras in use aren't Arri Alexas. They're old Sony HD (at best) cams.

"Nobody shopping BMD has any actual need for 12G "

BMD Ursa cameras (since 2014) push out 12G-SDI for 4K RAW or ProRes consistently and reliably. The quality is up there with the Sony FS7 or Red's. Sure it ain't no Arri or Red Helium, but look at the price tag.

"I mean the glass you need to actually manage to capture 4K, never mind the sensors means that even if you are shopping GV or the like you probably don't bother with the 4K option for most things."

The Sensors capture 4K quite effectively. BMD uses Fairchild Imaging LTN4625A sCMOS sensors for the Ursa. They can do 12MP at 120FPS with Global shutter at very low noise. I'd wager that this sensor is better than the Arri Alexa SXT sensor (ON Semiconductor designed ALEV III sensor). The difference is Arri has in camera Fixed Pattern Noise control and far better native ISO. What they do with a less capable sensor beats the competition hands down. On BMD you have to remove your FPN in post.

They fill up a 512GB SSD under 45 mins with 4K RAW.
BMD Ursa's uses EF/PL/MFT glass. Even the cheapest glass can resolve 8MP quite effectively (albeit with distortion and aberration)

"Yes, I know BMD advertise a "4K" camera but there is not much point in outputting 4K if the sensor and glass are not up to the job."

Who says it's not up to the job?



"I am not seeing much BMD in broadcast facilities (At least not in chain), churches, theatres, schools, wedding video types and conference centres seem to be where that stuff mostly lives in my experience."

Most traditional broadcast facilities are closing down. The few that are left of them are still using old Sony HDCAMs.
YouTube and streaming will replace all of them in the end.

Sorry for the necro.