SNR / Signal / Noise Units?

clentz · 03-13-2003

Does anyone know what units Netstumbler records SNR, Signal, and Noise?

agentgrn · 03-13-2003

decibels.

bumpus · 03-19-2003

Actually, they're in two different sorts of units. The signal and noise measurements are in decibel milliwatts and the SNR is in plain decibels. dB is a meausement scale that's only useful for comparing one value to another. In the case of the signal and noise measurements we choose 1mW to be 0 dB and measure from there (hence, these measurements are usually a negative number). In the case of the SNR we are comparing two values directly and it doesn't matter what value is used as a zero for each measurement as long as it was the same. The difference gets lost in the subtraction.

For example:
Signal = -38dBm = 1mW - 38dB
Noise = -96 dBm = 1mW - 96dB
SNR = 38 dBm - -96dBm = (1mW - 38dB) - (1mW - 96dB) = (1mW - 1mW ) + (96dB - 38dB) = 58 dB

But nobody but a hardcore radio geek is going to call you on it if you just refer to everything as dB.

03-13-2003	#1 (permalink)
clentz Registered Member Join Date: Feb 2003 Location: Hanover, NH Posts: 8	SNR / Signal / Noise Units? Does anyone know what units Netstumbler records SNR, Signal, and Noise?

03-13-2003	#2 (permalink)
agentgrn KB1JQO - Packin' Heat Join Date: May 2002 Location: Worcester, MA Posts: 517	decibels. __________________ -A.G.-

03-19-2003	#3 (permalink)
bumpus Registered Member Join Date: Jul 2002 Location: CR, IA Posts: 1	dBm Actually, they're in two different sorts of units. The signal and noise measurements are in decibel milliwatts and the SNR is in plain decibels. dB is a meausement scale that's only useful for comparing one value to another. In the case of the signal and noise measurements we choose 1mW to be 0 dB and measure from there (hence, these measurements are usually a negative number). In the case of the SNR we are comparing two values directly and it doesn't matter what value is used as a zero for each measurement as long as it was the same. The difference gets lost in the subtraction. For example: Signal = -38dBm = 1mW - 38dB Noise = -96 dBm = 1mW - 96dB SNR = 38 dBm - -96dBm = (1mW - 38dB) - (1mW - 96dB) = (1mW - 1mW ) + (96dB - 38dB) = 58 dB But nobody but a hardcore radio geek is going to call you on it if you just refer to everything as dB.

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