Black Box LW0050A Manual page 126

PRO 11 SERIES WIRELESS ETHERNET
• Interference
Interference may be caused by another system on the same frequency range,
external noise, or some other co-located system.
L S
INE OF IGHT
An optical line of sight exists if you can see one antenna from the other.
Clear Line of Sight
A clear line of sight exists when no physical objects obstruct viewing one antenna
from the location of the other antenna.
A radio-wave clear line of sight exists if a defined area around the optical line of
sight (Fresnel Zone) is clear of obstacles.
Fresnel Zone
The Fresnel zone is the area of a circle around the line of sight. The Fresnel Zone
is defined as follows:
Transmitter
(Site A)
√ (λ × D)
R = 1 ⁄
2
R: radius of the first Fresnel zone
λ: wavelength
D: distance between sites
When at least 80% of the first Fresnel Zone is clear of obstacles, propagation loss is
equivalent to that of free space.
124
R
Figure D-7. Fresnel Zone.
Receiver
(Site B)