Testing optical fibre

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SirHumphreyAppleby

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#305781 3-Jun-2023 06:58

We have arranged for a fibre to be installed in conduit between a house and sleepout as part of a much larger project.

I supplied 50m of pre-terminated 3mm armoured cable (LC, simplex) for this purpose. The electrician doing the work decided the fibre needed protection down the walls (because of the other work being done), so placed it in conduit. The problem is, he left the rest of the fibre rolled up on the outside of the house, ahead of installing the conduit to the other building, where of course it has been trampled into the mud by other contractors.

We're only installing 1Gb networking gear on site for now, but I expect this to work reliably in the future, regardless of what equipment is installed.

What's the right way for me to test this isn't damaged in any way? There are OTDRs, which seem more suited to multi-km runs, and cheap attenuation testers which don't inspire much confidence.

Depending on the cost and complexity, I may buy the equipment myself, since I'm moving to 10Gb at home, but initially at least I need to make sure it is tested using the right equipment for the job. I'm also unsure of the timing, and it would be best if I could find someone to test this before it is installed in the conduit with other cables.

The property is in Hobsonville, if anyone can recommend someone who can test this, assuming the electrician doesn't have the right equipment for the job.

cyril7

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#3084311 3-Jun-2023 10:05

Hi, is this single mode or multi, I think its reasonable to assume its either fine, or may have suffered a break in the fan out pigtail, if its armoured it will be pretty tuff so the main fibre length would be unlikely damaged by foot traffic. Other issue is if the connector covers have been breached they will need a clean, an IPA cleaning wipe is sufficient.

So I guess what I am saying is it will be an all or nothing, rather than a degraded state, so a simple light source to confirm there is no break is probably all that is required, 50m is not much in fibre speak. If its multimode then your phone LED light will suffice, if its SM then same but a bit harder to see.

Cyril

SirHumphreyAppleby

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#3084318 3-Jun-2023 10:19

cyril7:

So I guess what I am saying is it will be an all or nothing, rather than a degraded state, so a simple light source to confirm there is no break is probably all that is required

Thanks for your feedback. It's good to get some reassurance around it.

The cap has been lost at the network enclosure end, but is fortunately still intact on the end where the fibre was left outside. Single mode and multi-mode are now pretty much even in terms of cost, so I'm using single mode.

cyril7

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#3084320 3-Jun-2023 10:34

So just to say, spent a good part of last week chasing fibre break's due to rodents, we have many 100km of armoured mm and blown sm on site, all non chorus.

Cyril

Jase2985

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#3084335 3-Jun-2023 12:06

do you know if anyone has an OTDR? i was under the impression that most just pull it out and replace it.

bit different in your situation though.

SirHumphreyAppleby

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#3084336 3-Jun-2023 12:10

Jase2985:

do you know if anyone has an OTDR? i was under the impression that most just pull it out and replace it.

I do not. The electricians may have one, but I wanted to see what the experts here recommended before I insisted on testing using specific hardware.

everettpsycho

615 posts

Ultimate Geek

#3084343 3-Jun-2023 12:47

Attenuation would be fine I'd think. I only heard of order being done on full point to point dark fibre runs. A normal residential connection it was always attenuation that was monitored and most of the time high loss was down to fimma dirty termination point. Ultimately attenuation will tell you how much of the signal is reaching the other end and more importantly if it's reaching the other end at all. I'd imagine that would be all you need to know to make sure the cable works.

cyril7

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#3084390 3-Jun-2023 12:54

Another cheaper way, as I guess you are eventually going to purchase and put an SFP on each end, if you have a manged switch or router the Rx signal at each end is usually reported, you can reference it with a short 2m fly lead SFP-SFP then put the 50m length in, I would be surprised if you had more than a dB diff if working ok.

Cyril

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Wellingtondave

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#3084427 3-Jun-2023 15:48

Get to know the local Chorus guy or ask when they're working at the local cabinet. Perk job.

SirHumphreyAppleby

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#3084453 3-Jun-2023 17:13

Thanks for your feedback.

I live 40km away, so there is little chance of getting to know the local Chorus guy, although Chorus will be installing fibre to the location towards the end of the project, so I may ask if he'll give it a test.

Just dumb switches for this install. I don't have any other SFP gear that isn't 'in production' in my own house.

BarTender

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#3085531 6-Jun-2023 15:08

I have various SFPs picked up along with switches I have purchased off Trademe over the years. A managed Cisco switch including a 1g SFP are fairly cheap and work well. Ideally if it has the SFP already in there then you know it is supported in-device and you can get optics diagnostics easily from the command line.

https://www.trademe.co.nz/a/marketplace/computers/networking-modems/hubs-switches/listing/4165282870

https://www.trademe.co.nz/a/marketplace/computers/networking-modems/hubs-switches/listing/4159181371

The second one already has two SFPs included, so you could move one into the first one and you know you are sorted.

show interfaces transceiver detail

Then run some iPerf tests through the connections and you should be done.

raytaylor

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#3091221 17-Jun-2023 19:24

Personally, I'd just chuck a 10mw VFL on it and see if there is visible light at the other end, or use a couple of mikrotiks and BiDi SFP modules to check the rx signal on each fiber.

If there is red light coming through, and its not a super powerful 20mw/30mw one then its most likely the fiber is okay. Sometimes a 20mw or larger can jump a gap. Even a 5mw one would be better if you can find one.

You can get a VFL on aliexpress for about $20 (they almost all take an SC ferrule) and then a SC to LC adapter for a few dollars also.

Ray Taylor

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SirHumphreyAppleby

2851 posts

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#3091223 17-Jun-2023 19:29

raytaylor:

Personally, I'd just chuck a 10mw VFL on it and see if there is visible light at the other end

I will be doing exactly this tomorrow. Unfortunately, I don't have any managed switch gear to test with, but I do have an optical light meter on its way. I'm planning on installing more fibre, so both will get some use.