dBm
A dBm is a standard unit for measuring levels of power in relation to a 1 milliwatt reference signal.
dBm is similar to dB, or decibel, except that where dB is relative to the power of the input signal, dBm always relates to a 1 milliwatt signal.
In other words, dB is a relative measurement and dBm is an absolute measurement.
A minus sign before the dBm indicates a loss and a plus sign or no sign at all before the dBm indicates a gain.
The dBm Formula
The dBm value of a signal can be expressed utilizing the following algorithm:
db = log10 Signal Power / .001 watt
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I did not get the formula, can you explain with example? How come strong signals show -40dBm and weak are -90?
The formulas should read dbM rather than db… jack