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APPENDIX D: Radio Signal Propagation
D.2 RF Terms and Definitions
dB
An abbreviation for decibel, a comparative measure of signal strength.
dBm
An absolute measure of signal strength. 0 dBm = 1 milliwatt. (See “RF Power Level”
below.)
RF P
OWER
L
EVEL
RF power level at either the transmitter output or the receiver input is expressed in
watts. It can also be expressed in dBm. The relation between dBm and watts can be
expressed as follows:
PdBm = 10
×
Log Pmw
For example: 1 watt = 1000 mW; PdBm = 10
×
Log 1000 = 30 dBm
For 100 mW, the calculation would be:
PdBm = 10
×
Log 100 = 20 dBm
For link-budget calculations, it’s more convenient to express the measurements in
dBm than in watts.
A
TTENUATION
Attenuation (fading) of an RF signal is defined as follows:
Figure D-2. Attenuation of an RF signal.
Pin is the incident power level at the attenuator input.
Pout is the output power level at the attenuator output.
Attenuation
P
in
P
out