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ilkogd
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Minimum fibre length between S-3553LC20D

Tue Aug 06, 2019 3:13 pm

Hello. I'm plan to connect CRS326 and HEX-S with S-3553LC20D kit. Before put them "in production" I want to run them in lab with short LC patch cable, 1 meter or 2 meters to make all the configuration and tests. In this case is there any risks for SFP modules, can they be burned because the distance is very short? Also when I put them "in production", the distance will be about 250 meters. Is this a problem too? In spec. they wrote "to 20km" so maybe the lasers are very powerful and can damage SFP modules when used with short fiber lengths.

Thanks for help.
 
bds1904
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 5:33 am

I have a very similar SM fiber link that has been in production for a few years. I actually used SFP’s from FS.com because they were the only ones that I could find 10km rated BiDi SFP transceivers they weren’t crazy expensive. The transmit power on the pair I use is -5db and they are currently running at at -5.7db receive with no issues ever. I max out the 1Gb link quite often and never get any errors. I’ll link the 2 transceivers I use below.

https://www.fs.com/products/75335.html
https://www.fs.com/products/75336.html

To actually answer your question, I don’t think it’ll be in issue. The actual specifications for the transceiver module are not published on the website. I deal with single mode links on a regular basis and I believe the 40km links I deal with have a transmit power of +2db and the transceivers get upset if the receive power is above -3db. The GPON links I deal with are a whole different animal. Anything hotter than -15db to the OLT SFP results in problems.
 
savage
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 9:44 am

The SFP's will automatically increase/decrease power as needed. There's no minimum distance for a fiber cable. Maximum limitations are provided as there is loss / fade over long cable runs.
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Chris
 
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skylark
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 10:57 am

The SFP's will automatically increase/decrease power as needed. There's no minimum distance for a fiber cable. Maximum limitations are provided as there is loss / fade over long cable runs.
Maybe there are transceivers with auto-power adjustment, but definitely not all of them. Maybe you can mention some specific model which does that? Never seen that before..
 
ilkogd
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 1:59 pm

Maybe someone from MikroTik support should give us answer, this is important question. At the moment opinions are 50:50 and there is not full technical data on product page.
 
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skylark
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 2:15 pm

For S-3553LC20D and such a short-range like 1-2 meters, you have yo use attenuators. Our SFP transceivers do not have auto-power adjustment.
 
ilkogd
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 2:39 pm

Thank you @skylark. What should be the value of attenuators?
 
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skylark
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 3:35 pm

5dB will be enough.
Will work with 10dB aswell.
 
ilkogd
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Re: Minimum fibre length between S-3553LC20D

Wed Aug 07, 2019 4:39 pm

I understand. One last question - in the schemes attenuators should be on receiver. In my case sender and receiver is the same (only one fiber between SFP modules). So I should put attenuators only on one of SFP modules or on both? Also should I keep them "in production" - the real fiber link will be 250-300 meters?
 
tdw
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Re: Minimum fibre length between S-3553LC20D

Mon Aug 12, 2019 5:29 pm

According to the datasheet https://i.mt.lv/cdn/rb_files/SFP2-131002143606.pdf attenuators are not required as the maximum RX power accepted is at least 0dBm and the TX power will be between -3 and -9dBm.

If support say attenuators are required is the datasheet incorrect?
 
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skylark
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Re: Minimum fibre length between S-3553LC20D

Tue Aug 13, 2019 8:38 am

If support say attenuators are required is the datasheet incorrect?
You only have to use attenuators when you use transceivers for a distance of couple meters. S-3553LC20D range is 20 kilometers, for example, if you use them to interconnect two devices with range 10km, attenuators is not necessary.

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