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Understanding SNR and Attenuation Rates

Mineer

Expert Member
Joined
Apr 30, 2008
Messages
3,189
#1
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
 
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sn3rd

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Jan 18, 2008
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4,294
#2
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.
 
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Mineer

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Apr 30, 2008
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3,189
#3
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.
:erm:thanks for the update was under the impression that they were the same but u are right lower speed does give a better connection :(.
 

Flippit

Well-Known Member
Joined
Aug 17, 2003
Messages
226
#5
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.
 

Mineer

Expert Member
Joined
Apr 30, 2008
Messages
3,189
#9
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
 

Strobemeister

Expert Member
Joined
Nov 27, 2003
Messages
1,163
#10
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?
 

ronald911

Expert Member
Joined
Jun 1, 2007
Messages
1,430
#12
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
 
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Gamer

Expert Member
Joined
Apr 2, 2004
Messages
2,321
#13
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
 

sn3rd

Expert Member
Joined
Jan 18, 2008
Messages
4,294
#18
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
Refer to my earlier post. Your stats indicate that your signal to noise ratio is 32dB ABOVE what you require to sync at 384kB. The required signal to noise ratio to sync at a specific rate is dependent on your attenuation. His estimate of your max connection speed is based more on your attenuation. It means you're probably a fair distance from your exchange. Remember that 3dB represents a halving of the power. So for every 3dB of attenuation the signal received by your router has only half the power of before.
 

sn3rd

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Jan 18, 2008
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4,294
#19
Does anyone know of any software to measure this? I don't have access to the router, I'm afraid.
Unfortunately if you don't have access to the actual line (which you'd have if you had access to the router) you can't measure this.

I assume you mean you're using a shared setup? i.e. You're using the connection via shared ethernet or something. If you think about it, it makes sense, because you aren't directly receiving the DSLAM signal. Instead you're receiving a (modified) relayed signal
 

timgaul

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Joined
Nov 9, 2005
Messages
11,567
#20
Unfortunately if you don't have access to the actual line (which you'd have if you had access to the router) you can't measure this.

I assume you mean you're using a shared setup? i.e. You're using the connection via shared ethernet or something. If you think about it, it makes sense, because you aren't directly receiving the DSLAM signal. Instead you're receiving a (modified) relayed signal
Its an uncapped solution, the ISP has access to the router :/
 
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