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Wifi Signal Strength in Decibels of miliwatts


Lost In Cyberia
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So I noticed that all wifi analyzers, and readers, display the signal strength of wireless hotspots, and wireless connections in decibels, but in miliwatts. Furthermore, no matter what signal I look at it's always a negative number. I've seen ranges all the way from -23 down to -78 dBm. At first this confused me as I never saw any positive numbers, I assumed that the negative was bad no matter what... But thinking about it.. One the receiving end of an analyzer..the signal strength must ALWAYS be negative right? If I put it like this, you can't hear something louder than it was originally sent. So if the wifi router is sending a signal out at 0dBm, and my analyzer picks it up at 0dBm, then it received a 100% signal, but more likely it'll be reduced, hence the negative numbers.. So my main question is if the wifi transmitter was sending out a signal at like 6dBm, and my analyzer picks it up reasonally well, would it still have a positive like maybe 3 dBM? How would the receiver know that the transmitter was sending it at 6dBm in the first place? It doesn't know the transmitters starting power so it would assume that anything that the transmitter is sending would be 0dBm right?
Does this sound about right?

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http://www.tomshardware.co.uk/forum/9782-43-read-signal-strength

 

" Absolute power of a signal is measured in wattage. The bel or decibel
system can only describe relative power- a gain of 3 dB means your
signal is 2 times as strong as it was before, but the dB scale doesn't
define where you're starting from or what your 'zero' is. So, we
specify dBm, indicating that our scale is relative to 1 milliWatt of
power. 0 dBm = 1 mW.

The reason you see negative values is that you're representing small
but positive numbers, on a logarithmic scale. In logarithms, the value
indicated represents an exponent... for example, under a log 10 scale,
a value of -2 represents 10 to the -2 power, which equals 0.01.
Likewise, a negative dBm means that you're applying a negative
exponent in your power calculations; 0 dBm equals 1 mW of power, so
-10 dBm equates to 0.1 mW, -20 dBm equates to 0.01 mW, and so forth.
It's a lot easier, and more useful in some calculations, to describe a
weak signal as -100 dBm as opposed to 0.0000000001 mW. "

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5 hours ago, haze1434 said:

http://www.tomshardware.co.uk/forum/9782-43-read-signal-strength

 

" Absolute power of a signal is measured in wattage. The bel or decibel
system can only describe relative power- a gain of 3 dB means your
signal is 2 times as strong as it was before, but the dB scale doesn't
define where you're starting from or what your 'zero' is. So, we
specify dBm, indicating that our scale is relative to 1 milliWatt of
power. 0 dBm = 1 mW.

The reason you see negative values is that you're representing small
but positive numbers, on a logarithmic scale. In logarithms, the value
indicated represents an exponent... for example, under a log 10 scale,
a value of -2 represents 10 to the -2 power, which equals 0.01.
Likewise, a negative dBm means that you're applying a negative
exponent in your power calculations; 0 dBm equals 1 mW of power, so
-10 dBm equates to 0.1 mW, -20 dBm equates to 0.01 mW, and so forth.
It's a lot easier, and more useful in some calculations, to describe a
weak signal as -100 dBm as opposed to 0.0000000001 mW. "

 

What the hell?? So...how is this even possible? The network in my house, is reading -63 dDm... So according to the wiki, that's about 1 nanoWatt. I'm not an electrician obviously, but how on earth can my wifi router only put out 1 nanoWatt?? That sounds microscopically small? Doesn't the radiating antenna need lots of power to pump out that wifi frequency throughout my house?   It sounds really bizarre that the power from the wifi router is only operating with such a small weak signal.

Infact looking up on the chart on the wiki, it shows that WiFI bands b/g/n use about 200 miliWatts. and cell phone transmitters put out 500 miliwatts. That's a pretty significant jump over the reading of 1 nanowatt that I'm reading from my router Why such a huge difference?... Just a bit confused as how the range can be so wide.

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