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Thread: Understanding SNR and Attenuation Rates

  1. #1
    Grandmaster Mineer's Avatar
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    Post Understanding SNR and Attenuation Rates

    Signal-to-noise ratio
    Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering measurement defined as the ratio of a signal power to the noise power corrupting the signal.
    In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is. The concept can also be understood as normalizing the noise level to 1 (0 dB) and measuring how far the signal 'stands out'. In some instances interleaving can help raise the noise margin to an acceptable level.
    In general, higher signal to noise is better; the signal is 'cleaner'.

    Attenuation Rate
    Attenuation is the gradual loss in intensity of any kind of flux through a medium(i.e. the reduction in signal strength due to length of your phone line). For instance, sunlight is attenuated by dark glasses, and X-rays are attenuated by lead.In ADSL the signal is attenuated by length of copper lines. Attenuation is normally directly linked to the length of your line. Copper is traditionally used in the local loop and the higher gauge of copper will give the best signal, however some lines may have some aluminium or aluminium joints on the line which will increase resistance... as will oxidization of joints. Attenuation is mesured in db or noise. The more noise the weaker the data signal
    In general, lower Attenuation is better; the signal is 'stronger'.


    Heres is my table of comparisons
    SNR:

    6dB or below is very bad and will experience no synch or intermittent synch problems
    7dB-10dB is fair but does not leave much room for variances in conditions
    11dB-20dB is good with little or no sync problems
    20dB-28dB is excellent
    29dB or above is outstanding

    Attenuation:

    20dB and below is outstanding
    20dB-30dB is excellent
    30dB-40dB is very good
    40dB-50dB is good
    50dB-60dB is poor and may experience connectivity issues
    60dB or above is bad and will experience connectivity issues

    The following guide (distance vs. attenuation vs speed) gives you an guestimate what you can achieve:
    <1km should be 23-24Mbit (nice speed, but doesn't it bug you that Telkom people walk through your bedroom?)
    1.0km = 13.81dB = 23Mbit
    1.5km = 20.7dB = 21Mbit
    2.0km = 27.6dB = 18Mbit
    2.5km = 34.5dB = 13Mbit
    3.0km = 41.4dB = 8Mbit
    3.5km = 48.3dB = 6Mbit
    4.0km = 56dB = 4Mbit
    4.5km = 62.1dB = 3Mbit
    5.0km = 69dB = 2Mbit
    >5.0km (you are pretty much poked --- sorry for you)

    Really good tips can be found in this thread
    Some neat tricks for adsl lines
    by GedMarc- these tips help you improve the quality of your line.


    Sources
    http://en.wikipedia.org/wiki/Signal-to-noise_ratio

    http://en.wikipedia.org/wiki/Attenuation

    http://www.naschenweng.info/2008/10/...nd-attenuation



    more info thanks to MagicDude4Eva
    Last edited by Mineer; 24-07-2012 at 07:26 AM. Reason: more Infomation found on the subject
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    Just to add my 2 cents:

    While you're mostly right, remember that most routers report a "noise margin" which is not the same as SNR.

    Noise margin measures how much higher your signal is than the minimum required to sync at the current rate. That's why if you sync at 4Mbps, you will have a lower "SNR" than if you were to sync at 1Mbps.

    If attenuation is measured in dB (as with ALL things measured in dB), the value is actually 10 times the base-10 log of the ratio of the output to the input. Usually the input and output are power levels.
    Last edited by sn3rd; 09-08-2009 at 11:19 PM.

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    Quote Originally Posted by sn3rd View Post
    Just to add my 2 cents:

    While you're mostly right, remember that most routers report a "noise margin" which is not the same as SNR.

    Noise margin measures how much higher your signal is than the minimum required to sync at the current rate. That's why if you sync at 4Mbps, you will have a lower SNR than if you were to sync at 1Mbps.

    If attenuation is measured in dB (as with ALL things measured in dB), the value is actually 10 times the base-10 log of the ratio of the output to the input. Usually the input and output are power levels.
    thanks for the update was under the impression that they were the same but u are right lower speed does give a better connection .
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    Quote Originally Posted by Mineer View Post
    thanks for the update was under the impression that they were the same but u are right lower speed does give a better connection .
    So, that means 384k gives the best connection and 8Mbps gives worse connections?

  5. #5

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    Quote Originally Posted by Lightscribe View Post
    So, that means 384k gives the best connection and 8Mbps gives worse connections?
    8 Mbit/s requires a higher SNR to run reliably than 384 kbit/s does. If you're looking at noise margins, you can think of the 8 Mbit/s connection "taking" more of the noise margin in order to give higher speeds.

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    Quote Originally Posted by Lightscribe View Post
    So, that means 384k gives the best connection and 8Mbps gives worse connections?
    It means that if your figures suck at 384, you are unlikely to get 8Mb/s
    You only get one chance to piss off a client. After that they are an ex client ...

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    Hehe! Thx

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    <3 that my Attenuation sits at 10dB upstream and 9dB downstream

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    Quote Originally Posted by Lightscribe View Post
    So, that means 384k gives the best connection and 8Mbps gives worse connections?
    well yes the line is just more stable but 8Mbps is still possible and can be stable but the distance from exchange and quality of line is more important at higher speeds than at lower speeds
    “We know too well that our freedom is incomplete without the freedom of the Palestinians.”― Nelson Mandela

  10. #10

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    This is really interesting, guys. How do I measure my attenuation? Or does the router page inform me? Or do I need a 'gadget' like the Telkom techies have?
    Afrihost Uncapped 2mb

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    Router information page should be there
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  12. #12

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    My router status: (download)
    SNR Margin: 32.0
    Line Attenuation: 45.5

    Ok, there is definitely a lot of noise on my line, especially for a 384k line-But its VERY stable.

    So, according to the stats above, my SNR is suppose to be "29dB or above is outstanding" and my Attenuation "40dB-50dB is good"

    So, how does this work, as I asked a Telkom guy to test my line and he said I would only get a 2mbps stable connection MAX.
    Oh, im a little more than 2km's from the exchange.
    Thx
    Last edited by ronald911; 15-08-2009 at 11:09 AM.

  13. #13

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    Thanks for the cool info.
    My values are:

    Upstream 512000
    Downstream 4096000
    SNR Margin(Upstream) 14 dB
    SNR Margin(Downstream) 20.0 dB
    Line Attenuation(Upstream) 11.0 dB
    Line Attenuation(Downstream) 22.0 dB
    Latency(Upstream) Fast
    Latency(Downstream) Fast

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    Can we sticky this? Its an age old question.
    Jägermeiʃter can fix that!

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    Does anyone know of any software to measure this? I don't have access to the router, I'm afraid.
    Jägermeiʃter can fix that!

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