User's Manual

MDS 05-2806A01, Rev. E.1 MDS iNET 900 Series User’s Guide 131

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Figure 5-3. Mounting Bracket Dimensions

5.1.2 Site Selection

Suitable sites should provide:

• Protection from direct weather exposure

•A source of adequate and stable primary power

• Suitable entrances for antenna, interface or other required

cabling

• Antenna location that provides as unobstructed a transmission

path as possible in the direction of the associated station

(s)

These requirements can be quickly determined in most cases. A possible

exception is the last item—verifying that an unobstructed transmission

path exists. Radio signals travel primarily by line-of-sight, and obstruc-

tions between the sending and receiving stations will affect system per-

formance. If you are not familiar with the effects of terrain and other

obstructions on radio transmission, the discussion below will provide

helpful background.

5.1.3 Terrain and Signal Strength

While the license-free 900 MHz band offers 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 remote site

(s) is highly desirable and provides the most reli-

able communications link.

Much depends on the minimum signal strength that can be tolerated in

a given system. Although the exact figure will differ from one system to

another, a Received Signal Strength Indication (RSSI) of –77 dBm (–80

dBm for iNET II) or stronger will provide acceptable performance in

many systems. While the equipment will work at lower-strength signals,

signals stronger than – 77 dBm provide a “fade margin” of 15 dB to

2.75˝ (7 cm)

7.25˝ (18.4 cm)