Date Code 20181001 SEL-3031 Instruction Manual
Installation
Overview
2.3
Obstructions in the Fresnel zone may also cause multipath interference because of
reflective or refractive signals that may arrive at the receiver out-of-phase with the
desired signal. The Fresnel zone should be 60 percent clear of obstructions for reliable
radio communications. Large objects outside the Fresnel zone can cause reflections
that may also affect reliable radio operation.
Transmitted Signal
According to FCC and IC, the maximum transmitted power allowed out of an antenna
is 36 dBm EIRP (Equivalent/Effective Isotropically Radiated Power). This is the
amount of equivalent power transmitted equally in all directions using a theoretical
isotropic antenna. EIRP takes into account the power output of the radio, line feed
losses, and the gain of the antenna.
EIRP = SEL-3031 Power Output (dBm) – line-feed loss (dB) + antenna gain (dBi)
NOTE: Antenna/feedline configurations with net gains
(antenna gain minus cable loss) greater than 8.0 dBi must
have their output power limited to 341 mW. After setting
the transmit power, measure the actual power.
Calculate the EIRP so you can set the proper output power on the SEL-3031 to stay in
compliance with FCC and IC regulations; maximum power output from the antenna
must not exceed 36 dBm. The SEL-3031 can transmit as much as 1 W or 30 dBm from
the antenna port. If the calculated EIRP exceeds 36 dBm then you must reduce the power
transmitted by the radio by reducing the transmit power setting TXPWR (see the TXPWR
description in Radio Settings on page 4.12 for more information). The radio is shipped with
TXPWR set to 30 dBm by default and can be reduced to 20 dBm. Look up feedline loss in
Table 2.5. After setting the transmit power, measure the actual power.
Table 2.1 Fresnel Zone Diameter
900 MHz
Distance Between Antennas Fresnel Zone Diameter Freespace Loss (dB)
304.8 m (1000 ft) 4.9 m (16 ft) 81
1.6 km (1 mi) 11.6 m (38 ft) 96
8 km (5 mi) 25.9 m (85 ft) 110
16 km (10 mi) 36.6 m (120 ft) 116
24 km (15 mi) 44.8 m (147 ft) 119
32 km (20 mi) 51.8 m (170 ft) 122
40 km (25 mi) 57.9 m (190 ft) 124
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