User Manual

TRACER 4205 System Manual Section 2, Microwave Path Engineering Basics
612804205L1-1A © 2002 ADTRAN, Inc. 15
where the variables in the equation are defined as
P
R
received power (Watts)
P
T
transmitted power (100 mW (max) for TRACER 4205 - adjustable)
G
T
transmit antenna gain
G
R
receive antenna gain
λ carrier wavelength (c / ƒ) (meters)
d path distance (meters)
L other losses (RF coaxial cable, etc.)
The actual transmit and receive antenna gain values are strictly dependent upon the physical characteristics
of the antennas installed for each link. Typical gains are between 20 and 40 dB. For example, a 4 foot
diameter Parabolic dish has 34.2 dB of gain at 5.8 GHz. The carrier wavelength is the physical wavelength
of the main RF carrier being used for communication, and is usually approximated at the center frequency
of the band, which is 5787.5 MHz. This gives a wavelength of 5.18 cm.
The path distance is simply the physical distance between the transmit and receive antennas. For the
TRACER 4205 these distances can range up to 25 miles. The final parameter L incorporates all other
signal power losses in the microwave link, most of which are caused by antenna feed.
4. ANTENNA GAIN
Best performance will result from the use of a parabolic dish antenna. Antenna gain is determined by the
size of the dish, with typical features detailed below. Dish manufatureres will be able to supply gains for
other types of antennas.
Table 1. Antenna Gain for Given Dish Diameters
Dish Diameter
(in feet)
Gain
(in dBi)
2 28.5
4 34.2
6 37.5
8 40.7
10 42.5
12 44.2