Specifications

150 GE MDS entraNET Reference Manual 05-4055A01, Rev. D
6.1.3 Conducting a Site Survey
If you are in doubt about the suitability of the radio sites in your system,
it is best to evaluate them before a permanent installation is begun. This
can be done with an on-the-air test (the preferred method); or indirectly,
using path-study software.
An on-the-air test is preferred because it allows you to see firsthand the
factors involved at an installation site and to directly observe the quality
of system operation. Even if a computer path study was conducted ear-
lier, this test should be done to verify the predicted results.
The test can be performed by first installing a radio and antenna at the
proposed AP station site (one per system). Then visit the remote site(s)
with a transceiver and a hand-held antenna. (A PC with a network
adapter can be connected to each radio in the network to simulate data
during this test using the PING command.)
With the hand-held antenna positioned near the proposed mounting
spot, a technician can check for synchronization with the AP station
(shown by a lit LINK LED on the front panel) and measure the reported
RSSI value using the RADIO RSSI= command. If adequate signal strength
cannot be obtained, it may be necessary to mount the station antennas
higher, use higher gain antennas, select a different site, or consider
installing a repeater station.
Terrain and Signal Strength
While the 900 MHz and 2400 MHz license-free bands offer many
advantages for data transmission services, signal propagation is affected
by attenuation from obstructions such as terrain, foliage or buildings in
the transmission path.
A line-of-sight transmission path between the central transceiver and its
associated transceiver site
(s) is highly desirable and provides the most
reliable communications link.
Much depends on the minimum signal strength that can be tolerated in
a given system. Although the exact figure differs from one system to
another, a Received Signal Strength Indication (RSSI) of –100 dBm or
stronger provides acceptable performance in many systems. While the
equipment works at lower-strength signals, signals stronger than
– 90 dBm provide a fade margin of 15 dB to account for variations in
signal strength that may occur from time to time. RSSI can be measured
with a terminal connected to the transceiver COM1 port. See “Aiming
Directive Antennas for Maximum RSSI” on Page 162 for details.
A Word About Radio Interference
The transceivers share the radio-frequency spectrum with other services
and Part 15 (license-free) devices in the U.S.A. As such, near 100%
error-free communications may not be achieved in a given location, and