User's Guide

Appendix A. Radio Signal Propagation
User's Manual A-2 BreezeNET DS.11
A.1.2 RF Terms and Definitions
dB
The dB convention is an abbreviation for decibels. It shows the relationship
between two values.
RF Power Level
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:
P
dBm
= 10 x Log P
mw
For example: 1 Watt = 1000 mW; P
dBm
= 10 x Log 1000 = 30 dBm
100 mW; P
dBm
= 10 x Log 100 = 20 dBm
For link budget calculations, the dBm convention is more convenient than the
Watts convention.
Attenuation
Attenuation (fading) of an RF signal is defined as follows:
Figure A-2. Attenuation of an RF signal
P
in
is the incident power level at the attenuated input
P
out
is the output power level at the attenuated output
Attenuation is expressed in dB as follows:
P
dB
= -10 x Log (P
out
/P
in
)