Question Newbie needs help with RJ45 to fiber optics and back to RJ45 ?

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danroberto

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Oct 29, 2013
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Dear friends,
My router is working great and PCs are connected to the Internet just fine.

I have a fiber optics cable running through my wall. I'm trying to connect a computer using it. See image:

RJ45 from the router to a Fiber transceiver (number 1 in the photo), and on the other side, the same thing.

What am I doing wrong? I know the Fiber cable is ok.

Any help will be greatly appreciated!
rj45-to-fiber-optic.jpg
 
danroberto said:
Dear friends,
My router is working great and PCs are connected to the Internet just fine.

I have a fiber optics cable running through my wall. I'm trying to connect a computer using it. See image:

RJ45 from the router to a Fiber transceiver (number 1 in the photo), and on the other side, the same thing.

What am I doing wrong? I know the Fiber cable is ok.

Any help will be greatly appreciated!
rj45-to-fiber-optic.jpg
Click to expand...
Have you got part numbers for the fibre transceivers?
 
stuff and nonesense said:
The transceivers have labels for tx and rx have you got them connected such that end A tx goes to end B rx and vice versa? (Maybe misleading without more info it’s hard to help)
Have you got a manual?
Click to expand...

Thank you again @stuff and nonesense .

In both transceivers the RX side is sealed and unused. You can see it in one of the photos in the link I posted above. Only onefull-duplex port,

Is that the problem? Do I need one to be connected to RX?

The item said that it is a "Transceiver" with "Auto-Negotiation", "One 1.25Gbps full-duplex fiber port and one 1000M Ethernet port." so it should work, no?
 
What kind if fiber did you buy. You need to have single mode fiber for the frequencies the converter is using. Many times this is a has a yellow color on the fiber.

You also have to be very careful with fiber it is extremely easy to break. You wrap it around your finger a couple times and it will cause cracks in the glass core.
 
bill001g said:
What kind if fiber did you buy. You need to have single mode fiber for the frequencies the converter is using. Many times this is a has a yellow color on the fiber.

You also have to be very careful with fiber it is extremely easy to break. You wrap it around your finger a couple times and it will cause cracks in the glass core.
Click to expand...

Thank you.

It's the fiber I got from my ISP. I don't really know.

The fiber itself is fine - when I connect the router to the far side, everything works fine.
 
bill001g said:
You are going to have to explain what you mean "when I connect the router to the far side".

How so you then know it is working. What is connected to other fiber converter. Do you have a second router or something.
Click to expand...
I'll try to explain. I get fiber from my ISP. The fiber connects to the router. There is another fiber close to the router that goes through the wall into another room.

If I disconnect the router from where it is, use a female to female fiber adapter to connect the ISP fiber to the other fiber in the wall, and then connect the router in the other room, everything works fine - I can connect PCs to the router and get internet, wifi works etc. This is how I know that the fiber that runs through the wall is ok and not damaged.

Can the problem be with the green adapter - marked 2 in the image above?

Thank you.
 
Without going into great detail the media converters will support fiber that has a blue end or one that has a green end. The plastic connector itself is actually identical the difference is how the fiber is cut. The plastic does nothing other than hold the fiber strand in alignment with the ports in the equipment. The hard part with putting ends on a fiber is not the plastic connector is actually cutting and polishing the end of the fiber strand.

I have never been brave enough to buy from aliexpress.

These devices though should just work with no setup. They are basically a 2 port dumb switch.

Do you get any lights at all. Hard to say what it is suppose to do. Some device you get light just plugging in the ethernet cables others require a fiber connection. I did not see any lights so you can tell if the fiber is connecting.

Many times you can detect the light coming out of the fiber port with a camera on a cell phone, the cheaper the camera the better, good one have infared filters. Do not look into the port you can not see it with your eye but it can cause damage anyway. Not sure it really matters. We used to do this on a managed switch so we could check if the port was on or off in the software.

I am at a loss what to even try. These device have nothing to change or setup. The ethernet and fiber ports are standard. Everything should just work.
 
Another thought, a lot of the information is not in english. Does it say anywhere what the minimum distance is. They state 20km maximum. What can happen on short cable the lasers are too bright for the receiver. You need to use a small jumper that has attenuator in it...basically something that partially blocks the light.

Most the time when I did this it would still function but the risk was over the long term it would burn out the receiver optics.
 
Thank you very much. I had similar setup in the past and it worked.

After more tests it seems like the problem is with the green adapter (#2 in the image). I know it's just a dumb adapter but when I use it to connect the ISP fiber to the router, it doesn't work. When I use a female to female extender and a LC to SC fiber, everything works fine. Strange. i don't get it.
 
OK it's possible that I made myself a fool... I said I was a newbie. Maybe it will help someone in the future.

Perhaps the problem is because I used a SC/APC To LC/APC adapter, instead of a SC/APC to LC/UPC adapter, which is a bit wider.

Both adapter fits. Is it possible that this is the problem?

Thanks!
 
Everything that I have seen say those 2 terms are unrelated.

SC and LC related to the physical size and format of the plastic fiber holder. The fiber itself can actually be many different types. The common ones are single mode and multimode but there are many variations of both. This connectors only purpose is to hold the fiber the in alignment and at the proper distance from the jack. They almost touch but there is extremely tiny air gap. There are couple more like FC and ST that use round connectors.

The terms APC and UPC related to how the end of the fiber is cut. APC the end of the fiber is cut at a very slight angle, UPC is a 90 degree flush cut. You most times see APC used in applications where they are transmitting multiple light colors/frequencies over the same fiber strand. I forget exactly why but it is done to reduce the reflections that occur at ever fiber splice.

If you use a APC on one side and UPC on the other they don't quite align and you get some light loss. This matters when the fiber goes long distances, ie many kilometers, but generally does not matter for patch cables. If you were to touch the end of the fiber the finger print you leave causes more loss. They color code these with APC being green and UPC being blue.

An adapter shouldn't realy matter, they all cause a little loss because there is another point where light is being blocked and reflected. It is all going to depends on how well these are manufactured. I never actually used adapters we always had short cable with differnet end configurations and then used simple splices.
 
Thank you for the detailed explanation!

From everything you wrote it sounds like the adapter is the most likely culprit, as everything works fine with the other setup (same ISP fiber, female-to-female extender and a separate LC to SC fiber).

Thanks again
 
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