RF Gain/Loss
WiFi uses RF to transmit data.
The signals amplitude decreases as it travels away from the source. Think of
the area of the wave increasing. As the area increases, the amount of signal
that hits the receiving antenna is decreased (most of the signal spreads out in
other directions). The rate of decrease is affected by the material the wave
passes through. Even if the wave hits no obstructions, it will still decrease.
This is called Free Space Path Loss. The free space path loss in dB can be
calculated according to the following equation:
FSPL (dB) = 20log 10
(d) + 20log 10 (f) + 32.44
As you can see, the loss is
proportional to both the distance and the frequency. The higher frequencies (of
the 5GHz band) will be attenuated more than lower (2.4GHz) frequencies. This is
one reason why 2.4GHz WiFi bands cover a larger area than 5GHz bands.
When an RF signal passes through
other materials such as walls, windows and people, the annuation is greater
than the FSPL.
Antennas are used to amplify the
signal. Remember antennas amplify both the transmitted signal and the received
signal. So an antenna on an AP will improve the reception of WiFi signals as
well as the transmission.
The link budget is the
combination of gains and losses between the transmitter and the receiver. It is
the transmit power – cable loss + transmit antenna gain – path loss + receive
antenna gain – cable loss.
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