Figure 2-8. Initial profile before correction
4.
LOS Procedures for SHF Microwave Radio Systems.
a. The factors of VHF/UHF LOS radio planning also apply to SHF microwave radios,
with some exceptions. Due to the higher transmitting frequencies of SHF, obstacles such as
hilltops, buildings, and trees must be avoided. These obstacles can either block or significantly
decrease the signal level at the receiving antenna.
b. The Fresnel zone is defined as an area of propagation (ellipsoid in shape) that exists
between microwave transmitting and receiving antennas in which no obstacles should be
located to establish reliable communications (Figure 2-9). Additional Fresnel zones (second,
third, and fourth) exist beyond the boundaries of the first Fresnel zone. SHF microwave
radio systems have about one-half the total transmitted energy in the first Fresnel zone. The
first Fresnel zone also accounts for about one-fourth of the total received energy. Thus, both
LOS and first Fresnel zone clearance must be achieved for microwave radio systems to ensure
satisfactory communications.
c. The following procedures should be followed to determine first Fresnel zone
clearance:
(1) Step 1 - Follow steps outlined in doing a LOS profile for VHF/UHF radio
systems.
(2) Step 2 - Using the same graph paper, and at a point where the straight line (drawn
between the two sites on the graph paper) intersects the first one-kilometer/one-mile
SS0121
2-12
Previous Page
