Single Mode Fiber Issues

[Tom Matthies]

We have single mode fiber camera cables that will carry 4 channels of audio, HD video, and tally/CCU data down a single fiber. Not sure if more than one fiber is necessary. Maybe it depends on your installation and encoder/decoder combination.

E=MC2+/-2db

[Mark Walleman]

I’m slightly confused by your explanation of your usage. When you say “channels” are you talking about actual strands of glass (fiber) or embedded channels over 1 strand of glass?

Typically, if you’re just pushing SDI video with two channels of audio, the audio is embedded in the SDI stream, therefore only requiring one strand of glass.

If that’s what you’re doing, then what make/model fiber optic converter are you using? That’s important to know being that some converters are better than others (some more problematic than others).

However, that being said, your symptoms can be attributed to a bend or kink in your fiber line between rooms. When explaining this problem I like to ask people to think of their garden hose at home. What happens when you kink your hose or bend it sharply? It reduces the flow of water through the hose of course. Fiber optic cable is very similar, where as the light traveling through the optical cable is like the water. Asking your installation company to come in and test it with an OTDR will immediately resolve that possibility.

Dirty connectors are also a possible cause. Like the garden hose, if your nozzle/valve is somewhat closed, it will also restrict flow causing reduced signal.

Additionally, check your SDI signal input going into your converter. Make sure the your feed is not dirty going in. Saying goes: put crap in, get crap out.

Mark D. Walleman
Relay House Inc.

[Dan Carter]

Hi,
Having spoken in depth to the IT dept at the college where we’re based. I have a few more answers, and a few more questions…..

We’re pushing a combined audio/video SDI signal down one channel. The single mode fiber that was installed has 4 channels (4x glass fiber lines). 3 of these channels work, however 1 does not (I’m still waiting on a reason as to what happened).

The original installation company will come back and check the lines at some point. However, I’m not being given a timescale as to when (Very frustrating!).

I’ve checked the signal going into the fiber, and that is fine, everything seems ok. However, I’ve now noticed that the audio levels are lower at the output end than they are at the input.

We’re using Kramer 613T/R units as these were recommended to me at the time of our move into these facilities.

The thing is…. I’m certain it’s the fiber. I’ve checked everything else. I’d be surprised if it is the converters, as they’re brand new.

I’m open to suggestions if you guys can recommend an alternative converter, but I’m restricted by power issues, so it would have to be an “all in one unit” if you catch my drift. Plus I’d have to try and source it in the UK.

[Dan Carter]

Hi Mark,
I’ve had several meetings with the college’s IT dept (where we’re now based), and it appears to have answered some questions, however I have a few more now….

You are right in that the baseband video we’re sending goes down 1 fiber channel, as a video signal with embedded audio. However the single mode fiber that was installed has 4 channels (4 lines if you like). 1 of these channels is faulty – and the company that installed the fiber 12 months ago is dragging their heals to come and assess this.

We’re using Kramer 613R/T units for the SDI/Fiber converter as these were recommeded to us at the time of moving.

Now, I’ve checked the signal going into the fiber – and I can confirm that the signal is clean – and everything is fine. It’s just at the other end that there’s this intermittent problem.

I’ll be honest and say that i’d find it hard to believe that the converters are faulty as they’re brand new – but if there’s something else we should be doing i’m open t suggestions as long as it won’t cost much – as the company I work for run on a shoestring at best….

Any advice you can give i’d happily listen to and work on, as this fault is driving me up the wall!

[Mark Walleman]

Gotcha. Alright,(you may have already done this), have you attempted using your exact setup – but on a different fiber strand? That will seal the deal to confirm what you already suspect. If your setup works on the other 3 strands then it’s one of two problems: A dirty connector or a bad connector.

You can try to clean both fiber ends with some lint-free/lens disposable wipes with some isopropyl alcohol wipes. Or just dampen some of the lint-free wipes with the alcohol (99% isopropyl – not the 70% pharmacy grade rubbing alcohol). Do not use any type of cloth or regular paper towel. Either take the pre-saturated wipe or the dampened dry wipe and fold it up in a small-padded square. Take the ST connector and lightly press the end of the ferrule (the tip of the white part) to the wipe. Move the tip across the wipe in a circular – “Figure 8” pattern about 10-15 times. Dry it with a clean-dry lint-free wipe. Test your signal after cleaning the first connector before cleaning the second.

I’d also recommend that you acquire some ST/SC fiber cleaning pens. Every house big or small should have the ability to clean their own fiber.

Good luck!

Mark D. Walleman
Relay House Inc.

[Dan Carter]

Apologies for the double post….din’t think the first one worked, so typed it again to make sure, Doh!

Anyway, as you suggested, I tried the TX through another fiber strand, and the same fault came back after a few hours. So, I was called out to the studios at 05:30 this morning to see that the video glitch was occuring again. I shut the converters down, and changed the TX to another fiber strand, the rebooted the converters, and the signal seems ok for now – but, I’m going to monitor it throughout the day.

I’m going to try and change the fiber converters for a new set, and hopefully if the glitch comes back then that’s proof that the converters aren’t at fault. I’m also going to get a cleaning kit and see if that improves things…..

Just out of interest, is there another model/manufacturer that you’d recommend? I’ve always used Kramer as their kit normally seems rock solid, and I’ve had so little problems in the past.

[Mark Walleman]

We don’t use Kramer too much in the field, but I’ve never been burned by them. That said however, I’m a huge fan of Telecast and AJA. I have a pile of blackmagic optical converters that I don’t trust anymore (I’ve had 3 out of 8 go bad = never again).

If the problem followed when you changed strands then that throws the converters back in to mix as a possible culprit. The problem though may very well be dust inside the optical I/O. Try shooting a little duster in the fiber ports to try to clean them out. The slightest little speck of dust can cause what you’re experiencing.

If that still doesn’t work then swap them out. If you have to purchase a set, I’d recommend the AJA Fido R/T-ST optical converters or Telecast Rattlers. Although, most optical converters “should” be fine for your purpose. Get a short fiber jumper (3ft, etc) and bench test your Kramer converters.

One more thing: How did you test your SDI feeding your optical transmitter?

Mark D. Walleman
Relay House Inc.

[Dan Carter]

Funny that – I’ve just put the order through for a set of AJA FiDO R/T-ST converters, so hopefully they should be with me soon.

Once they’re on – I’m going to bench test the Kramers and see how we get on….

I’ve also ordered a few cleaning pens for the fibre tips.

As for the SDI signal, I’ve routed the feed into a WFM then taken the loop out into the converter – that way I can check the signal, and audio, I’ve also put one at the other end of the building where the fibre terminates.

Once i’ve got all the bits, I’ll update you…..

[Terrencee Lew]

Hi

Single Mode cable is a single stand of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fiber with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550nm.

Single-mode optical fiber is an optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest typically 1300 to 1320nm. You must clean both the fibre ends with the disposable wipes like alcohol wipes. Avoid using any type of cloth or the regular paper towel. You can get more information on the single mode fibre from https://www.andcorp.com.au/

[Mike Thomson]

The equipment used for communications over multi-mode optical fiber is less expensive than that for single-mode optical fiber. Typical transmission speed and distance limits are 100 Mbit/s for distances up to 2 km (100BASE-FX), 1 Gbit/s up to 1000 m, and 10 Gbit/s up to 550 m.
Also I found this company they have full scope SDI OVER FIBER products single mode