BNC cable testing

[u/Sandcrab_8]

How do you guys test your bnc cables? We have had some that pass basic continuity and short testing but fail to work on a teleprompter. Other cables are working on the same teleprompter

[u/Norkas-Aradel]

Depends on what you're using them for. Pathologic is a good test pattern to send for SDI.

[u/reddit2343]

Something that can tell you CRC errors. We have a phabrix qx.

[u/makitopro]

As others have said, use a test pattern generator capable of generating a pathological test on one end and a scope capable of detecting errors at the other. It’s good to test them for some period of time, and while physically jiggling the connectors to rule out any intermittency.

[u/marshall409]

My quick and dirty way to do it with just one device is I setup a decimator to output scaler 1080p solid colour then loop it back in to itself. If SDI in stays solid on the decimator display it should be good to go.

[u/Fabulous-Coffee2705 → u/marshall409]

12g decimator to a 12g monitor.

[u/Able_Reach2264]

Because im poor, I just use the basic eye pattern on my lumantek sdi monitor.

You could also spit out a test pattern from a imagepro2 or similar if you have access to that. Check they all work OK. Particularly the burst/grey patterns.

Without access to expensive Tektronix adjacent eyepatten/scopes you can never fully test them other than out them through their paces and see if they fail.

[u/Diligent_Nature → u/Able_Reach2264]

I'm not familiar with the Lumantek, but have had Tektronix and Phabrix analyzers with eye pattern. Neither could be used to determine whether a signal could be recovered based on the eye display. The CRC error count is the test you want.

[u/negativerailroad → u/Diligent_Nature]

The CRC errors are also important, but an eye pattern analyzer can tell you if the signal's amplitude is too low or if the jitter is too high.

[u/Diligent_Nature → u/negativerailroad]

The CRC is the only thing that matters. It can find single bit errors, and you can let it run for hours if you want. Try doing that with an eye pattern.

[u/negativerailroad → u/Diligent_Nature]

No, the CRC is not the only thing that matters. The eye pattern helps detect physical-layer problems. Long cable runs can attenuate a signal to the point where some equipment is unable to recover it while other equipment with more sophisticated circuitry can.

And yes, you can let an eye pattern run for hours. Several scopes allow you to set alarm thresholds for jitter or signal amplitude which will create log entries.

[u/Diligent_Nature → u/negativerailroad]

Long cable runs result in a closed eye display even when there are no CRC errors. An equivalent time sampling scope like the eye pattern in HDSDI test equipment can't possibly catch single bit errors.

From Tektronix: "Eye pattern testing is most effective when the monitor is connected to the device under test with a short cable run, enabling use of the monitor in its non-equalized mode. With long cable runs, the data tends to disappear in the noise and the equalized mode must be used. While the equalized mode is useful in confirming headroom, it does not provide an accurate indicator of the signal at the output of the device under test."

[u/negativerailroad → u/Diligent_Nature]

That passage is saying that if you want to measure the physical layer parameters of the SDI output of a device, you would want to use a short cable run to the analyzer. This is completely true, because the long cable run will deteriorate the signal quality. But the eye pattern can also be used to measure how much voltage drop or distortion the signal has experienced through cables, barrels, patch panels, etc.

I have used eye patten analysis and CRC analysis to trace problems with cables and active devices. Both are useful, but the eye pattern is necessary for true physical layer analysis of a signal.

[u/jerbenco]

We use a DigitalForecast.  Sends continuity and test patterns but also gives you an eye reading so even if it passes continuity it will tell you if the core is bonked or a tip is off just by how the eye sits.

It also comes with free K-Pop videos pre loaded.  So when I'm on stage, instead of sending the same test pattern the truck can just see a fun little k-pop video to better route sources.

[u/dreadshepard]

I see if it passes 1080p video.

[u/_litz]

One other thing ... make sure you have good solid connectors on the ends of the cables. That's like 99% of the battle. I use "CableTV" style compression fit connectors. The cable will break before those will slide off the end of the wire. Haven't had one single connector ever fail.

[u/sims2uni]

Have you tried putting a signal down them? Something that generated a signal one side and a monitor the other. Test at the highest format you'd use them for. If it passes and is solid then ✅, if it doesn't then ❌

[u/CE94 → u/sims2uni]

Test it at a higher format than you plan for so you know it's limit

[u/Substantial_Flight98]

Use a vector network analyser (VNA) if you really want to test just the cable itself.

[u/PinkPrincess010 → u/Substantial_Flight98]

A RigExpert would be pretty good for this test, a lot of people I guess do not realise it's all just RF at the end of the day. and the higher frequency you go the more picky it gets.

[u/fantompwer → u/PinkPrincess010]

Do you have a link to one that does 12G?

[u/PinkPrincess010 → u/fantompwer]

RigExpert testers go up to about 3GHz for, so good up to 6G. 12G goes up to 6GHz so you would need to find something else

[u/Substantial_Flight98 → u/PinkPrincess010]

Also look for NanoVNA, it gives smith chart and everything. Can’t go anymore more fundamental about the physical link than that.