+ Post New Thread
Results 1 to 9 of 9
Windows Thread, Fibre backbone Noise Acceptable Limits in Technical; Fibre backbone Noise Acceptable Limits We have a fibre going to one of our buildings approx 500m run.. It got ...
  1. #1
    Grommit's Avatar
    Join Date
    Sep 2006
    Location
    Weston-super-Mare
    Posts
    1,335
    Thank Post
    31
    Thanked 54 Times in 31 Posts
    Rep Power
    24

    Fibre backbone Noise Acceptable Limits

    Fibre backbone Noise Acceptable Limits

    We have a fibre going to one of our buildings approx 500m run..

    It got tested and there was 31db of Noise ..

    Now our Network works fine and there is no issues.. but the CCTV company says that this is unacceptable

    What is the acceptable limits for fibre as I have googled it but can't seem to find a decent answer...

    Is 31db OK ?

    And does anyone have a professional link :-)

  2. #2

    Geoff's Avatar
    Join Date
    Jun 2005
    Location
    Fylde, Lancs, UK.
    Posts
    11,802
    Thank Post
    110
    Thanked 583 Times in 504 Posts
    Blog Entries
    1
    Rep Power
    224

    Re: Fibre backbone Noise Acceptable Limits

    You need an minimum SNR margin of 6dB.

  3. #3

    FN-GM's Avatar
    Join Date
    Jun 2007
    Location
    UK
    Posts
    15,777
    Thank Post
    865
    Thanked 1,664 Times in 1,449 Posts
    Blog Entries
    11
    Rep Power
    442

    Re: Fibre backbone Noise Acceptable Limits

    if the network is working fine just leave it, don't fix something that isn't broken

  4. #4
    Grommit's Avatar
    Join Date
    Sep 2006
    Location
    Weston-super-Mare
    Posts
    1,335
    Thank Post
    31
    Thanked 54 Times in 31 Posts
    Rep Power
    24

    Re: Fibre backbone Noise Acceptable Limits

    Quote Originally Posted by Geoff
    You need an minimum SNR margin of 6dB.
    Sorry Geoff.. i don't understand... is 31Db OK or not ? :?

    Quote Originally Posted by FN-Greatermanchester
    if the network is working fine just leave it, don't fix something that isn't broken
    I agree.. but the CCTV is taking 2 cores of my fibre and they say their stuff isn't working and they say it's because of the 31db, and that it has to be re spliced......

    Is this true ?

  5. #5

    FN-GM's Avatar
    Join Date
    Jun 2007
    Location
    UK
    Posts
    15,777
    Thank Post
    865
    Thanked 1,664 Times in 1,449 Posts
    Blog Entries
    11
    Rep Power
    442

    Re: Fibre backbone Noise Acceptable Limits

    I'm not to sure by self I’m not a fibre expert but I know somebody who is if nobody else knows I will ring him later.

  6. #6

    Geoff's Avatar
    Join Date
    Jun 2005
    Location
    Fylde, Lancs, UK.
    Posts
    11,802
    Thank Post
    110
    Thanked 583 Times in 504 Posts
    Blog Entries
    1
    Rep Power
    224

    Re: Fibre backbone Noise Acceptable Limits

    SNR margin is the different between the Signal strength and the Noise.

    So with a noise level of 20db and a signal strength is 30db the SNR margin is 10dB

  7. #7


    Join Date
    Jan 2006
    Posts
    8,202
    Thank Post
    442
    Thanked 1,032 Times in 812 Posts
    Rep Power
    339

    Re: Fibre backbone Noise Acceptable Limits

    What Loss Should You Get When Testing Cables?
    While it is difficult to generalise, here are some guidelines:

    -For each connector, figure 0.5 dB loss (0.7 max)
    -For each splice, figure 0.2 dB
    -For multimode Fibre, the loss is about 3 dB per km for 850 nm sources, 1 dB per km for 1300 nm. This roughly translates into a loss of 0.1 dB per 100 feet for 850 nm, 0.1 dB per 300 feet for 1300 nm.
    -For singlemode Fibre, the loss is about 0.5 dB per km for 1300 nm sources, 0.4 dB per km for 1550 nm. This roughly translates into a loss of 0.1 dB per 600 feet for 1300 nm, 0.1 dB per 750 feet for 1300 nm.
    So for the loss of a cable plant, calculate the approximate loss as:

    (0.5 dB x number of connectors) + (0.2 dB x number of splices) + Fibre loss on the total length of cable

    http://www.techoptics.com/pages/Fibe...20Testing.html

    the maximum loss the equipment can tollerate depends upon what your using, we have max 2-5db loss in any run.
    If the figure you quote is 30db loss in the run then that is far too much.

  8. #8
    Oops_my_bad's Avatar
    Join Date
    Jan 2007
    Location
    Man chest hair
    Posts
    1,738
    Thank Post
    438
    Thanked 53 Times in 50 Posts
    Rep Power
    30

    Re: Fibre backbone Noise Acceptable Limits

    Isn't it something like anything from -4dB to +4dB on multimode?

  9. #9

    Join Date
    Sep 2009
    Posts
    1
    Thank Post
    0
    Thanked 0 Times in 0 Posts
    Rep Power
    0
    It depends on the receiver. The receiving units usually have some specifications that dictate how much power they should receive to stablish proper communication. Usually 25 db is considered the limit on multimode networks. For single mode, a slightly greater loss is acceptable

SHARE:
+ Post New Thread

Similar Threads

  1. Noise from new Dell system
    By laserblazer in forum Hardware
    Replies: 8
    Last Post: 21st December 2007, 08:00 AM
  2. Printing Credits / Limits
    By phillipmillward in forum How do you do....it?
    Replies: 13
    Last Post: 2nd September 2007, 12:26 AM
  3. Procurve network backbone saturation
    By meastaugh1 in forum Wireless Networks
    Replies: 4
    Last Post: 13th January 2007, 01:15 PM
  4. Acceptable Use Policy
    By kingswood in forum How do you do....it?
    Replies: 5
    Last Post: 12th July 2006, 07:26 AM
  5. New fiber backbone and switches brainstorm with me!!!
    By ChrisH in forum Wireless Networks
    Replies: 32
    Last Post: 16th January 2006, 11:04 AM

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •