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Fiber optic cable

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Speedy Builder512/06/2022 17:49:47
2653 forum posts
219 photos

just had fiber optic cable installed. Its incredible how it works. The fibre is 0.16mm diameter (near enough 0.006". Light as we know travels in straight lines, so how many times must it bounce off the walls of the fibre before it reaches its destination?

Bob

Frances IoM12/06/2022 17:55:39
1283 forum posts
28 photos
it doesn't so much as bounce as being refracted such that there is only one mode of transmission down the cable - bends or other disturbances do cause losses as light is partially deviated from its path
Mark Rand12/06/2022 20:21:54
1314 forum posts
38 photos

Actually, .The outside diameter of the cladding will be 0.125mm. The fibre itself will be 0.05mm for multimode fibre (good for a few hundred metres) or 0.009mm for single mode fibre (good for kilometres).

Nick Clarke 312/06/2022 21:31:23
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1475 forum posts
64 photos
Posted by Frances IoM on 12/06/2022 17:55:39:
it doesn't so much as bounce as being refracted such that there is only one mode of transmission down the cable - bends or other disturbances do cause losses as light is partially deviated from its path

Agreed - but as a physics teacher I had to teach the 'bouncing off the sides' as that was what exam syllabuses required.

I always enjoyed big physics so for a small evening class I laid out a load of 2x4 glass blocks in a snake and shone a laser through them so the group could see the internal reflection of the beam along the line of blocks representing a fibre optic but big!

Unfortunately the end of my giant fibre optic was facing one of the lab's windows and I saw a red spot near the top floor of a block of flats up the road about a quarter of a mile away .............

Jon Lawes13/06/2022 07:40:07
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993 forum posts

Total internal reflection I think its called. Something to do with making sure a limiting angle isn't exceeded.

Dave Halford13/06/2022 11:17:29
2093 forum posts
23 photos
Posted by Jon Lawes on 13/06/2022 07:40:07:

Total internal reflection I think its called. Something to do with making sure a limiting angle isn't exceeded.

It's easier to think of that as a 50mm radius.

Chris Mate13/06/2022 16:23:55
151 forum posts
32 photos

I worked with double loop fibre systems with terminal boxes at sites in series(addresses) and back to the originating equipment. If one fibre fail(Wind, Accident, Joints, Fibre itself-age), it loops and isolate the failed part, then the fibre guys has the opertunity to repair that. The last one=Fibre itself-Age was the interesting one, the one that give headaches to all.

Now my experience was that the fibre works excellent for some years, then it gets older and older and start giving Age--intermittant problems....At this stage in the beginning, the scopes don't illustrate the problem clearly enough to make a new fibre replacement(Costly), so fibre faults are thrown back to techs on inside maintaining the equipment, where modules are replaced or tuned a bit, it may or may not help, its very confusing for all in the beginning of experiene with it. It escalates where problems start to cause total collapses of the entire system, due to the loopback intermittant as well, so everything goes dead, then it must be brought up in sections to determine more thn one problem and isolate them, then handed sections to fibre techs.
Selution=In the end the manageent agree its time to fork out the money(Forget about all the money already driven out on fuel over time.
Note:A new fibre can be repared when cut, but an old one that does not work reliably anymore(Grey area).

The reason I mention this is it would be interesting to see the battle in future between homeowner and Company as to when its time to replace the fibre(Costly for company).......Some charge you for callout if the fault is on your side, ...........I am refering to this age grey areas coming up.....

Edited By Chris Mate on 13/06/2022 16:27:06

john fletcher 113/06/2022 16:44:15
805 forum posts

Could short bits of fibre optic cable be useful for cleaning brass and copper electronic bits and pieces prior to soldering. I have seen any fibre optic cable, is it very thin ? i have some fibre glass cleaning sticks bought from Proops at shows years ago and they are still in regular us. John

Richard Taylor 1713/06/2022 19:08:14
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10 forum posts
1 photos

Beware of the dangers of fragments of optical fibre if using the material for anything other than commmunications. Fragments can stick to you skin and then be carried to your eyes or mouth. If your are working with optical fibre it is recommended that the work surface is dark in colout as the shards are more apparent.

SillyOldDuffer13/06/2022 21:34:29
Moderator
8898 forum posts
1998 photos
Posted by Chris Mate on 13/06/2022 16:23:55:

...

Now my experience was that the fibre works excellent for some years, then it gets older and older and start giving Age--intermittant problems....At this stage in the beginning, the scopes don't illustrate the problem clearly enough to make a new fibre replacement(Costly), so fibre faults are thrown back to techs on inside maintaining the equipment, where modules are replaced or tuned a bit, it may or may not help, its very confusing for all in the beginning of experiene with it. It escalates where problems start to cause total collapses of the entire system

...

I'm always fascinated by the different ways there are of looking at the same problem.

Much of my career matches Chris's perspective, because me and my mates spent a lot of time 'squeezing the assets', basically putting off spending big money on major upgrades until the last possible moment. With hindsight it was a bad strategy, often throwing good money after bad, and forcing the system's users to put up with an unreliable service. Didn't matter, because other budgets took the hit and their managers didn't realise or didn't care they were bleeding money due to reduced productivity.

You might think the industry was concerned about ageing fibre, but they're not. Since fibre was introduced about 30 years ago it's developed considerably, but the main driver is more bandwidth, not keeping old networks going. I think they're right: whenever a technology is rapidly improving, the smart money takes advantage of next generation stuff as soon as it's affordable. The best solution to unreliable fibre networks is to rip them out out completely, and replace with up-to-date technology. It's faster, opens the door to new opportunities because it carries much more traffic, and is cheaper per byte. During most of the 19th century marine steam engines followed the same curve, shipowners running ten year old vessels struggled to compete with more efficient new ships and their better engines.

It's important to look constantly for the break even point: given it costs x billion to lay a 5000km fibre optic cable between Somerset and Nova Scotia, and income is limited by the capacity of the cable after n months, what's the profitable life of the cable, and when does repairing it become a waste of money? Potentially rather quickly! If you own a 10Gbs transatlantic cable installed in 2000, and a competitor installs a terabit cable in 2020, he will undercut you in a jiffy. The money made from a fully working cable might not pay it's keep when other suppliers have cheap capacity to spare, and offer your customers cut-price deals.

The people who run technology see one side of the story, the people who pay for it see another. Quite easy to think all is well at the engineering level when the business is in terrible financial trouble, and vice versa. Many organisations had money in the bank, but were blissfully unaware their technology base was about to implode, and that they were dead men walking. Failure to manage change is very dangerous.

Dave

Chris Mate13/06/2022 22:43:59
151 forum posts
32 photos

Dave, something I see now where I live , I am still on ADSL, but can go over to Fibre tomorrow if I want, they call me every now and then, eventually I will have to. What I see now is our town, all the streets were dug up multiple times to lay new fibres by various companies, at least 5 it seems. Now the problem with this is, my opinion, its a waste of resources to duplication in the name of "compitition". Now as the history has shown , like with 4x cellphone companies erecting duplicate towers the same way, the cost just increased, not cheaper. If communications is considered a basic right, I would think one company, strictly controlled, no corruption could have done this for a fraction of the cost and still employed all or most of the people due to the scale of it, it worked wonderfull like that in the past. The other thing is the smaller and more the companies are, the more they stick to cities larger towns, and start neglecting smaller towns and remote areas, leaving those customers up for huge costs to have communication..............I think future banking/tax etc alone make it a basic right, and basic rights must be relative cheap, otherwise it implodes the monetary system over time.

Nick Clarke 314/06/2022 09:19:20
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1475 forum posts
64 photos

A bit more than 30 yers ago the college I was working at at the time started to network computers across the site. This meant linking two buildings which were separated by a patch of grass but the distance between them was just within the 185m limit for the technology we were using - 10base2, so a copper link was installed.

After things were set up one of the techs was changing a t-piece when they got a belt from the network cable. Both buildings had separate earth potentials and there was 70V between the coax braiding and local earth!

The most amazing thing was that it didn't seem to stop the network or harm any hardware.

Speedy Builder514/06/2022 09:51:36
2653 forum posts
219 photos

Nick, similar problem in 1976. We could not get a mini computer to RJE to a remote IBM site using modems. BT sent various technicians without success. One hot summers day another tech arrived, in shorts, sandals and long dreadlocked hair. (Some hope we thought) within a few minutes, he got his old and cracked screen AVO out of his bag, then proceeded to cut the earth wire from the modem and Bingo, the RJE link and modem connected! Our factory earth was reading +40 volts and we were an electronic equipment manufacturer !!

Don't judge a person by their looks !

Samsaranda14/06/2022 09:56:52
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1484 forum posts
7 photos

Nick, you have highlighted the problem of parallel earths where a potential can build up, historically people have died from the lethal potential built up between parallel earths, it has happened in the aviation world where ground power units and mains electricity are used on the same aircraft. I have witnessed big fat blue sparks passing across gaps between two separate equipments connected to separate earth systems.

in respect of new fibre cable systems, my local town Eastbourne is currently undergoing a complete system install, the contractors who are digging the trenches are leaving behind many problems, they backfill the trench then top it off with tarmac, unfortunately where there were nice level slabbed pavements they end up with a continuous ribbon of soft uneven tarmac and the roads now have many more potholes where the inadequate backfill and tarmac is sagging. I think that we should be careful what we wish for. Dave W

John Doe 214/06/2022 12:58:19
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100 forum posts
15 photos

I heard that BT can 'blow' fibres down their existing cable ducts, using an air source to carry the fibre along the duct without having to dig up the roads. Clever stuff.

I am just back from televising the Leeds Triathlon, where we used the fibres installed at Roundhay park for some of our circuits crossing the site. We had a lot of problems, but to be fair, it was mostly the short fibre adapters of ours at each end that were duff.

Outgoing links were on satellite, so no problems there.

 

 

.

Edited By John Doe 2 on 14/06/2022 12:58:46

Nealeb14/06/2022 13:14:29
99 forum posts
Posted by Speedy Builder5 on 14/06/2022 09:51:36:

Our factory earth was reading +40 volts and we were an electronic equipment manufacturer !!

I guess that there's a reason why ethernet connections include ground isolation!

Perko715/06/2022 02:04:17
427 forum posts
33 photos

Reminds me of this story I heard many years ago, not sure how much truth in it though.

An elderly lady with a dog called the phone company to say that her telephone failed to ring when her friends called; and that on the few occasions when it did ring her dog always barked before the phone rang. The telephone repairman proceeded to the scene, curious to see this psychic dog or senile elderly lady.

He climbed a nearby telephone pole, hooked in his test set, and dialed the subscriber's house.The phone didn't ring but the dog barked loudly and then the telephone did ring.

Climbing down from the pole, the telephone repairman found:

1) The dog was tied to the telephone system's ground post via an iron
chain and collar.

2) The dog was receiving 90 volts of signaling current when the phone
number was called.

3) After several such jolts, the dog would start barking and urinate on
the ground.

4) The wet ground would complete the circuit and the phone would ring.

Circlip15/06/2022 09:01:08
1531 forum posts

Is there some direct link between Fibre optic cables and the Silver Steel storage tubes heading this thread?

Regards Ian.

Mike Poole15/06/2022 10:45:01
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Moderator
3380 forum posts
77 photos

The picture belongs to Speedy Builder’s thread on silver solder storage, a pictorial typo I think.

Mike

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