Schweitzer Engineering Laboratories SEL-3031 - Table 2.2 Antennas Permitted for Use with the SEL-3031

SEL-3031 Instruction Manual Date Code 20181001
Installation
Overview
2.4
NOTE: This device has been designed to operate with the
antennas listed in Table 2.2, and having a maximum gain
of 14.1 dBi. Antennas not included in this list or having a
gain greater than 14.1 dBi are strictly prohibited for use
with this device. The required antenna impedance is 50
ohms. Antennas having a gain of greater than 6 dB must
use a feedline with enough loss to remain compliant with
the maximum 36 dBm EIRP or reduce the radio
transmitted power accordingly.
For example, if you wanted to design a radio system to achieve a 32-km (20-mi) radio
path and run at the highest allowed transmitted power, one way would be to use the
SEL-3031 with 15.2 m (50 ft) of LMR 400, lightning arrestor, and the 5-Element Yagi
with 11.1 dBi of gain. The radio would transmit 30 dBm, the feedline loss is 1.95 dB,
lightning arrestor loss is 0.15 dB, and the antenna gain is 11.1 dBi. The result would be
39 dBm, which is 3 dBm higher than allowed by the FCC. You must reduce the radio
transmit power setting TXPWR to 27 dBm. This would make your EIRP equal to
36 dBm. After setting the transmit power, measure the actual power.
NOTE: To reduce potential radio interference to other
users, the antenna type and its gain should be so chosen
that the equivalent isotropically radiated power (EIRP) is
not more than that permitted for successful
communication.
Fade Margin
The fade margin determines the allowable signal loss between the transmitter and
receiver. The fade margin is a function of system gains (transmitter power, receiver
sensitivity, and antenna gain) and system losses (free space loss, losses because of the
curvature of the Earth, and coaxial cable loss). Variations in temperature and humidity
of the atmosphere with elevation causes the signals to bend more or bend less, resulting
in fading at the receiver. The longer the path, the more likely deep fades will occur,
requiring a greater fade margin. The formula to calculate free-space loss is shown
below.
Free Space Loss = 92.4 + 20log(f) + 20log(d) dB
where:
f = frequency in GHz
d = distance in km
Table 2.2 Antennas Permitted for Use With the SEL-3031
Antenna Type Maximum Allowed Gain
Yagi antenna 14.15 dBi or less
Omnidirectional antenna 9.15 dBi or less
Panel antenna 10.15 dBi or less
Preliminary Copy—Subject to Change