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If I connect to wifi AP with 1 line of strength, does it mean that I will get only 1/5 of AP's bandwidth?

I mean, do these lines tell me whether I will receive a full bandwidth or only a part of it?

Another questions, what does the dB value of signal mean? Does 100dB equal 100% of the signal? For example, I get 11 dB and 2 lines of wifi strength.

There are also the negative values of the signal, the PHY values. The value for 11dB is -77. Does this mean that the value of 0 equals to 100% of the signal?

thanks for everyone finding time to explain these things to me. I've been using wifi for years but I never paid attention to these things.

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To understand this means first of all to understand what the signal strength bars actually mean. (Content below copied from this site).

The signal strength is a combination of the actual 802.11x signal + Phone + Microwaves + other sources that might generate 2.4GHz “Noise” + Brain emissions of the user’s anxiety state (j/k), in other words it is visual representation of all the 2.4GHz in the atmosphere around the your Wireless hardware.

I.e. you might see High Signal Strength that Shows: Excellent (5 bars), but it is actually 30% signal + 70% noise.

Such a signal would be the reason for low bandwidth, and or frequent disconnection of the Wireless Network.

In contrast, a medium level Signal (3 Bars) that does not contains any noise would provide a match better connection.

Netstumbler is a free windows tool to see the signal to noise ratio.
If your router is not supported by Netstumbler, then try Kitz - DMT Tool

Db is about a relative number - a reference level if you will. So, unlike S-Unit (often used with radio operators) +db5 is literally half of 10db.

PHY is an abbreviation for the physical layer. The PHY portion consists of the RF, mixed-signal and analog portions, that are often called transceivers, and the digital baseband portion that place high demand on the digital signal processing (DSP) and communication algorithm processing, including channel codes. It is common that these PHY portions are integrated with the media access control (MAC) layer in System-on-a-chip (SOC) implementations. Other similar wireless applications are 3G/4G/LTE, WiMAX, UWB, etc. (Sourced from Wiki)

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thanks. can I somehow see the actual ration between the real signal and the noise? I am using win7, but I have ubuntu on other laptop in case win7 does not have such tool. –  JoeM Aug 10 '12 at 10:46
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Netstumbler shows the signal to noise ratio; netstumbler.com/downloads (I added this to the body as well for completeness) –  Dave Aug 10 '12 at 10:47
    
Unfortunatelly, this tool cannot use Broadcom wifi adapter which is built into my laptop. –  JoeM Aug 10 '12 at 10:54
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kitz.co.uk/routers/DMTv8.htm –  Dave Aug 10 '12 at 10:56
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Explanation of decibels: soundonsound.com/sos/1994_articles/feb94/decibels.html It works the same for RF (radio frequency) as it does for sound. –  Everett Aug 10 '12 at 12:08

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