3e–525C–3 Wireless Access Point
Chapter 2: Hardware Installation
16
29000171-001 A
3e–525C–3 Wireless Access Point
Chapter 2: Hardware Installation
29000171-001 A
17
Bridge Transmit Distance
Normally, the bridge need transmit RF signal to another bridge device
at long distance. You may need to calculate the RF link Budget as refer-
ence. The equation of RF link budget is:
Fade Margin = received signal – receiver threshold
Where
Received signal = Transmitter power – Transmitter cable loss + Trans-
mitter antenna gain – free space path loss + Receiver antenna gain
– Receiver cable loss
Received threshold = Received sensitivity
Free Space Path Loss
Using below Free Space Loss Formula to calculate free space path loss
Where
L
P
= free space path loss between antennas
F = frequency in GHz
D = path length in miles
Bridge Antenna Location
When as bridge device, the 3e-525C–3 may need to be mounted out-
doors on a high place to achieve the best bridge result. The Fresnel zone
and Earth bulge dominate to decide how high that the unit’s Antenna
need be put. The total antenna height equals the width of Fresnel zone
plus the height of earth bulge.
The Fresnel zone is the area around the visual line-of-sight that radio
waves spread out into after they leave the antenna. This area must be
clear or else signal strength will weaken. The rule of thumb is that 60% of
the Fresnel zone must be clear of obstacles. Typically, 20% Fresnel Zone
blockage introduces little signal loss to the link. Beyond 40% blockage,
signal loss will become significant.
