Vivint SR1410, Инструкция по установке и эксплуатации, Страница: 33 / 38

SR1410 Installation and User Guide Page 33
SR1410 Installation & User Guide Ver. 0.01
2.4 GHz 12.5cm
5.8 GHz 52cm
2.2.2 The Decibel
The decibel (dB) is a ratio, measured in logarithm, used to measure quantity. A dB has no dimensions.
The decibel is used to compare one power (or voltage level) to another.
Ratio in dB = 10log10 (Power Ratio) = 20log10 (Voltage Ratio)
(Power is proportional to the voltage squared)
20 dB means a power ratio of 102 to 1 or 1,000:1
10 dB means a power ratio of 10 to 1 or 100:1
0 dB means a power ratio of 1 to 1 or 1:1
Because the dB is a ratio, it is dimensionless, however many times reference is made to the unit that is
made as a ratio.
e.g. dBm in the case of milliwatts 20 dBm means 100:1 over 1 milliwatt or 100mW
e.g. converting 4W into dBm 10log10 4000mW / 1mW = 36 dBm
Later on we will see that if an antenna has twice the power gain of a half wave dipole (an antenna used
as a standard reference), that is a power ratio of 2 over the 1/2 wave dipole, then the antenna is said to
have a gain of 3dBd. (3db over the1/2 wave dipole)
10log2=3
A +3dB gain represents a doubling of power while a -3dB loss represents 1/2 of the power
2.3 Align Antenna
After wireless router units have been mounted, connected, and their radios are operating, the antennas
must be accurately aligned to ensure optimum performance on the router links. This alignment process is
particularly important for long-range point-to-point links. In a point-to-multipoint configuration the
SR1410 uses an omni-directional or sector antenna, which does not require alignment.