| signal to noise graph Can anybody tell me what this graph indicates. I am new to the telco business and am learning this piece of equipment. I dont understand what this graph means. Thank you in advance |
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guppy_fishPremium
join:2003-12-09
Lakeland, FL
kudos:1 | As the frequency increases, the ratio to signal to noise decreases as the signal gets attenuated. Eventually with increasing frequency the signal can't be recovered. |
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| would low dsl speed like 1.5 meg mean low frequency, and higher speed like 5.5 meg equal to higher frequencys. Is that graph saying at the frequency about 1800 mean it wont recover. If so, what uses the frequency higher than 1800. |
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guppy_fishPremium
join:2003-12-09
Lakeland, FL
kudos:1 Reviews:
 ·Verizon FiOS
| The graph shows the higher frequency's get attenuated more, so it can only go shorter distances. 1800 in actually 1.8mhz
That looks like a typical graph, if your at 1.5mbs, its likely your far from the central office or remote terminal and nothing can be done about that
»www.kitz.co.uk/adsl/images/adsl_···cies.gif |
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 tschmidtPremium,MVM
join:2000-11-12
Milford, NH
kudos:8
 ·G4 Communications
·Fairpoint Commun..
 ·Hollis Hosting
| reply to hemoon4
DSL rate vs attenuation |
ADSL and ADSL2 use frequencies up to 1.1 MHz and ADSL2+ up to 2.2 MHz. ADSL2+ is able to deliver much higher speed but only to nearby customers.
As guppy_fish  posted attenuation increases with distance and frequency. This is why folks further from the central office get lower speed.
There are many things that affect speed. The first thing to do is determine the modem sync rate and the SNR. That indicates if the line is maxed out of if higher speed is possible.
/tom |
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 whizkid3Premium,MVM
join:2002-02-21
Queens, NY
kudos:9 | reply to guppy_fish
said by guppy_fish:As the frequency increases, the ratio to signal to noise decreases...
Really, that is all one can deduce from the graph. While what guppy_fish & Tschmidt are saying are true (about distance, attenuation, etc) - the graph shows the results of that; but one can not simply deduce that from the graph.
The graph does show that the SNR is lower at higher frequencies. While the graph does not show why; it is exactly because of what guppy_fish & Tschmidt are saying. The noise is not greater at higher frequencies (in general). So the 'signal' part of SNR, must be lower at higher frequencies. As the signal travels along the cable, it is attenuated greater at higher frequencies. At the same time, noise continues to be induced in the unshielded cable; replacing any noise that has been attenuated by traveling along the cable. End result is that the SNR is lower as the frequency increases.
Here is a very good place to start:
»en.wikipedia.org/wiki/Decibel
then...
»en.wikipedia.org/wiki/Signal-to-noise_ratio
If you really want to understand the graph and what the euqipment is measuring (and why its important), one must have a real good graph on what SNR is; why it is important in communications system design & operation; and the math behind it. |
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