User Manual

MDS 05-4055A01, Rev. A MDS entraNET 900 System Guide (Preliminary) 105

Invisible place holder

Figure 5-3. Mounting Brackets 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 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 will differ from one system to

another, a Received Signal Strength Indication (RSSI) of –77 dBm 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 account for variations in

2.75˝ (7 cm)

7.25˝ (18.4 cm)