On 09/21/2011 09:12 AM, Stephen wrote:
> good point -xxDbm is lower is better it is essentially a
> representation of signal loss.
> 
Well, not quite. It is an expression of a ratio against a standard value.

dBm is a measurement of power, meaning "Decibels relative to One Milliwatt".

Decibels themselves work on a logarithmic scale and express the ratio between two
values.

Examples:

If a signal is 10 milliwatts, its power level could be expressed in dBm as:

 10*log10( 10mW / 1mW) = 10*log10(10) = +10dBm

A signal of 1 microwatt is: 10*log10( 1uW / 1mW) = 10*log10(0.001) = -30dBm

1 watt = +30dBm, 1 picowatt = -90dBm, 100 femtowatts = -100dBm, etc..

A Linksys router transmitting at a power level of 250 mW, represents a power
level of +24dBm. (You won't measure this outside of the unit, of course. It
represents the power the unit is pushing into its antenna) But, I digress....

Note the importance of the sign.

Cheers,
KevinO
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