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Signal to noise

jabb0
Grafter
Posts: 716
Registered: 18-09-2007

Signal to noise

hey folks,

this is a networking question but anyone who has a grasp of maths shud be fit to help me out.

in relation to the Signal-to-noise ratio the following formula is used to claulate decibels.
The thing is, in my ignorance, i cannot figure out how to use it correctly

Quote
D = 10 log10(S/N)


just to be certain here is a linky to the same equation on wikipedia.

its the 10log10 bit i am having problems with, a dummies guide to typing this into a calculator would be most appreciated.
3 REPLIES
Community Veteran
Posts: 1,229
Thanks: 1
Registered: 30-07-2007

Signal to noise

the log10 bit is to specify that it's a logarithm to base 10 (rather than an exponential logarithm to base e) ... I think if you have a scientific caclulator or even windows Calc.exe then the "normal" log key rather than the one marked log(subscript e) is the one you're after.
do your bit of division, press the log key, multiply by 10.

I might of course be talking out of my rectal passage as it is 3 decades since i was at school and i failed maths Cheesy
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Signal to noise

madswitcher
Grafter
Posts: 235
Registered: 01-08-2007

Signal to noise

The exact definition of SNR depends on whether you are dealing with voltages or power measurements. Usually, the signal you get down the telephone cable is measure in milliwatts (power) relative to 1mW into 600 ohm - dBm.

For this SNR = 10Log ( (S+N) / N). which can be approximated to
10Log(S / N) for low values of noise compared to the signal power.

Log means logorithm to base 10. If it was to base 'e' it will be called 'Ln' instead of 'Log'. Ln is mostly used in mathematical functions and not used a lot in electronics.

Regards, Mike