User Manual

108 MDS entraNET 900 System Guide (Preliminary) MDS 05-4055A01, Rev. A
Table 5-2 outlines the minimum lengths of RG-214 coaxial cable that
must be used with common MDS omnidirectional antennas in order to
maintain compliance with FCC maximum limit of +36 dBm.
5.1.5 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 underway.
This can be done with an on-the-air test (preferred method); or indi-
rectly, 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 Access Point (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 sim-
ulate 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 Access Point
station (shown by a lit
LINK LED on the front panel) and measure the
reported RSSI value. (See “Antenna Direction Optimization” on
Page 97 for details.) 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.
To prepare the equipment for an on-the-air test, follow the general
installation procedures given in this guide and become familiar with the
operating instructions found in the CHAPTER-4 TROUBLE-
SHOOTING & RADIO MEASUREMENTS section Page 85.
5.1.6 A Word About Radio Interference
The transceivers share the radio-frequency spectrum with other 900
MHz services and other Part 15 (unlicensed) devices in the USA. As
such, near 100% error-free communications may not be achieved in a
given location, and some level of interference should be expected. How-
ever, the radio’s flexible design and hopping techniques should allow
adequate performance as long as care is taken in choosing station loca-
Table 5-2. Minimum Feedline Length versus Antenna Gain
Antenna Gain
(dBd)
Antenna Gain
(dBi)
Minimum Feedline
Length (Loss in dB)
Power Level
@ Minimum Length
Unity (0 dB) 2.15 dBi 3 meters (1.0 dB) +31.15 dBi
3 dBd 5.15 dBi 3 meters (1.0 dB) +34.15 dBi
5 dBd 7.15 dBi 3.1 meters (1.2 dB) +35.95 dBi