Signal Strength (Watts) - Watchguard Firebox X15 User Manual

Signal strength (Watts)

The signal strength is set by these factors:
• Power of the RF signal that is sent and received
• Amount of directional antenna gain at the transmitter and the
receiver
• Signal attenuation (path-loss) between the transmitter and
receiver
Antenna directional gain
Antenna directional gain is calculated from the degree to which the
radiation pattern of an antenna is focused in a specified direction. A
highly directional antenna has a higher gain.
The Firebox X Edge Wireless uses 5 dBi antennas. These antennas
have a maximum 5 dBi gain pattern perpendicular to the antenna
position. The antenna gain of a laptop computer with an embedded
wireless antenna can be as low as -10 dBi.
Signal attenuation (path-loss)
This equation finds the signal attenuation (path-loss):
Loss
The "distance" is the line-of-sight distance between the transmitter
and the receiver.
The "wavelength" is the speed of light divided by the frequency.
Higher frequency signals have a shorter wavelength. Shorter wave-
length signals have a higher path-loss than signals with a higher
wavelength in the same frequency range.
In a usual office environment, the calculated loss is only accurate for
approximately 20 feet. For each additional 100 feet, 30 dB must be
added. Furniture, walls, windows, and other objects also cause inter-
ference.
Fading because of multi-path reflections also causes signal attenua-
tion. Multi-path reflections are the result of an RF signal moving
along more than one path from the transmitter to the receiver.
Multi-path occurs when a signal is reflected by surfaces in the area.
A signal with a frequency of 2.4 GHz is reflected by many surfaces.
When multi-path occurs, some reflected signals cancel each other.
User Guide
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× ×
= 20 log 10 4π
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About IEEE 802.11g/b Wireless
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dis tan ce
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wavelength
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