User Manual

36 CompactRF
TM
Operating Manual: Chapter 5 Installation
Base Height (m)
Mobile
Height
(m)
Distance (km)
When deploying your system, care must be taken to ensure the path loss
(reduction of signal strength from transmitter to receiver in dB) between
equipment does not exceed the system gain (138 dB in the above example).
It is recommended to design for a gain margin of at least 10 dB to ensure
reliable communication. Gain margin is the difference between system gain
and path loss. Referring to the same example, if the path loss is 100 dB, the
gain margin would be 38 dB, which is more than adequate for reliable
communication.
Path loss is a very complicated calculation which mainly depends on the
terrain profile, and the height of the antennas off the ground.
The following table provides path loss numbers for varying antenna heights
and antenna separation: These numbers are real averages taken from rural
environments. They do not apply to urban, non-line-of-sight environments.
Distance
(km)
Base Height
(m)
Mobile Height
(m)
Path Loss
(dB)
5 15 2.5 116.5
5 30 2.5 110.9
8 15 2.5 124.1
8 15 5 117.7
8 15 10 105
16 15 2.5 135.3
16 15 5 128.9
16 15 10 116.2
16 30 10 109.6
16 30 5 122.4
16 30 2.5 128.8
Once the equipment is deployed, you can verify the signal strength by
entering into Command Mode and reading Register S123. This register
provides the average signal strength in dBm. The minimum strength for
communication is roughly -103 dBm. For consistent reliable
communication, you should try to deploy the equipment such that signal
strength exceeds -95 dBm.