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-   -   Wifi signal/noise etc. - acheiving optimum performance? (https://www.cableforum.uk/board/showthread.php?t=33607032)

tvout 28-01-2007 13:23
Wifi signal/noise etc. - acheiving optimum performance?
 
Hello,

Can someone explain to me what the numbers mean for signal, noise and signal to noise ratio and what is best and worst...?
I did a quick search but couldn't easily find the info to figure it out...

As an example, these are my DD-WRT details of my two wirelessly connected devices at present:

Laptop downstairs (about 6 feet across the room line of sight from router)
Signal: -52 Noise: -98 SNR: 47 Signal quality: 50%

Wireless bridge upstairs (in room immediately above router, about 9 feet away, through ceiling)
Signal: -50 Noise: -98 SNR: 48 Signal quality: 54%

Any advice on the above much appreciated...

Wicked_and_Crazy 28-01-2007 18:47
Re: Wifi signal/noise etc. - acheiving optimum performance?
 
Not sure what your looking for in the way of advice.

As you know i run the same router and same firmware.

On a laptop in a room directly under the router i get

Signal: -61 Noise: -98 SNR: 33 Signal Quality : 38% and i don't have any issues, as your signal is better your not likely to have any issues either.

You can increase the wireless power output of the router if you want to improve the signal but i wouldnt bother.

tvout 28-01-2007 19:55
Re: Wifi signal/noise etc. - acheiving optimum performance?
 
Cool, cheers. It's good to see the router seems to be performing ok. I was really aiming to find out what the noise snr values really meant with regards to what is the best and worst values as they're in minus figures? Is the lower the value lower noise etc and better or is it the other way?
I have two neighbouring routers on sky, one channel 1, the other on 6. I'd like to go to 11 but it gets affected badly by a tv sender.
Out of interest, does the logging function work with yours? It doesn't seem to with the DD-WRT firmware?

Gareth 29-01-2007 21:58
Re: Wifi signal/noise etc. - acheiving optimum performance?
 
I'm another dd-wrt user :tu:

This might be of some use to you, taken from the dd-wrt wiki:
Quote:
Originally Posted by dd-wrt wiki
How do I read signal and noise ratings?

These numbers are given in decibels (dB) and are expressed as negative numbers. So, a lesser number, like -10 dB, represents more strength than -70 dB. The values are logarithmic. A signal amplitude change of 6 dB is equivalent to a factor of two; 20 dB is a factor of ten.

Based on this Forum-post (http://www.dd-wrt.com/phpBB2/viewtop...?p=14747#14747)

Signal -> Low is good (well -10 is good, -98 is bad, mathematically -10 is higher than -98.)

Noise -> High is good (-98 is good, -10 is bad, -70 would be pretty bad in the real world)

SNR -> High is good (should be the same as difference between noise and signal, a difference of 20 would be great, a difference of 1 may barely work)

Signal Quality -> High is good (somewhat like SNR but indexed to 100 with noise as the base, percentage of the best theoretical available quality in regards to your local-noise, difficult to explain *g*)

Examples would be:

Signal Noise SNR Signal Quality

-82 -98 16 14%

Signal - Noise = SNR
-82 - -98 = 16

Signal/Noise * SNR = Signal Quality
-82 / -98 * 16 = 13.4%


Typically, noise will be -92 which means you should get a connection with a signal as low as -92. However, expecting to hold a good connection with a signal less than -85 (e.g. -90), is expecting too much. The signal can be improved by -3 dB by doubling the power setting at the transmitting radio, e.g., 100 mW increased to 200 mW would improve your signal from -85 to -82. Antennas with increased gain will also help. Say you had the standard 3 dB antenna and changed it for a 12 dB antenna, that's a 9 dB increase, so your signal would increase from -82 to -73 which would be an excellent signal, probably capable of 54 Mbps. Using the term excellent in terms of running a WISP, it would probably be only 3 bars on a 5 bar signal strength meter. Don't worry if, as a WISP your signal quality is low, like 14%. It's not really a problem since -82 is considered acceptable.

EssDee 30-01-2007 10:05
Re: Wifi signal/noise etc. - acheiving optimum performance?
 
Quote:
Originally Posted by tvout (Post 34208370)
Out of interest, does the logging function work with yours? It doesn't seem to with the DD-WRT firmware?
Mines doesn't work either. Have it enabled, etc, but nothing ever appears in the log tables. I've a WRT54G v5 running DD-WRT v23 SP2 micro.

Huge improvement on the official firmware. A v5 is definitely not a model to go for incidentally.

tvout 02-02-2007 21:24
Re: Wifi signal/noise etc. - acheiving optimum performance?
 
Cheers for the signal/noise info, that's exactly what I was looking for.
Strange, with two laptops in the same room as the router both show -98 on noise. The signal and signal quality are generally twice as good on my laptop than my gf's if we're sitting next to each other...possible just the different chips, I believe the wifi antennas in laptops are often wires that go round the screens or other areas, possible hers got messed up when she changed the casing on it...

Anyway, re the logging feature on DD-WRT, I did actually get it to work if set to high level and set to On for all three options...I suspect the other settings may not be sensitive enough?

Really interesting as it not only shows successful inbound connections but also attempted connections which were dropped by the firewall...


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