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Understanding SNR Signal to Noise Ratio on Netstumbler.

Posted on 2006-06-25
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Last Modified: 2012-08-14
I would like someone to explain to me how SNR can tell me which AP provides the best signal strength.  Ex.  I have to AP's.  
AP1 has:  SNR: 36 Signal -52 Noise -100 SNR+ 48
AP2 has:  SNR: 36 Signal -62 Noise -100 SNR+ 38

I would like to understand what is the optimal state I am looking for.

Thanks
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Question by:kapara
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by:fredshovel
fredshovel earned 75 total points
ID: 16979867
I can only relate this to SNR in audio, which is a similar principal -- and the most simplistic explanation is that a higher number represents how much higher the signal stands out from the noise -- thus the higher the number the better. It's a ratio based on a reference level between clean signal and the noise -- you want your signal to climb as high as it can above the noise floor.
You don't want noise 'up there' with your signal. You want to bury your noise as low as you can.

Cheers.  
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by:Rob Williams
Rob Williams earned 50 total points
ID: 16979960
To add to fredshovel's comments, below is a link to a brief explanation.
http://www.pcmag.com/encyclopedia_term/0,2542,t=signal-to-noise+ratio&i=51330,00.asp
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by:XY_GT
XY_GT earned 50 total points
ID: 16980414
AP1 has the best signal strength.

The better signal is shown by the signal value. When the signal value is lower it is better. This is also indicated by the signal to noise ratio, higher is better.

A good resource for this is WikiPedia. http://en.wikipedia.org/wiki/Snr
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by:ded9
ID: 16982168
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skaap2k earned 75 total points
ID: 16982896
SNR = Signal to Noise ratio,

It is generally the difference between Noise and Signal,

The less noise you have, and more signal, the higher the SNR.

ie, you could have a signal of -63dbm and a noise level of -82dbm, giving you a SNR of 19.
SNR is only an indicator of the quality of the link, and does not guarantee a good connection.

Kind Regards,
Rob
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by:kapara
ID: 16985211
The reason I want to know is I have to get 2 wireless bridges pointing at each other from 1 mile away.  They are currently working but I have a feeling that they are not positioned for the best possible reception.  I was thinking of taking a wifi card with an external antenna and position it in front of Bridge 1 and tring to change the position to find the best reception.  

Thanks
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by:Rob Williams
ID: 16985255
If you can actually measure, it is well worth doing. Some commercial wi-fi units have built-in diagnostics to do this.
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by:skaap2k
ID: 16985272
Hi,

Theoretically, you should have equal signal levels on each end (that is the -52 and -62 bit) - All is not fair with wireless though, most cards have a sensitivity of up to -90dbm (-95dbm if you have a good chipset!) so you have plenty of headroom for weather factors to come into play.

Any signal level between -50 and -70 is good, anything lower and you'd want to either look at alignment / antenna size.

Rgds,
Rob
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by:Rob Williams
ID: 17172784
Thanks kapara,
--Rob
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