724-746-5500 | blackbox.com
Page 49
Chapter 6: Installation
6. Installation
Consider the following when preparing to deploy a radio network:
Network Topology
Section 5.0 detailed the various network topologies that the MDR100A-R5 or MDR112A-R5 will support. Determine which
topology meets your specific requirements.
Throughput
The MDR100A-R5 or MDR112A-R5 is capable of 230.4 kbps asynchronous serial data throughput. The network topology has an
effect on how this available throughput is “shared” between all nodes on the network.
Distance
The physical distance between the modems determines the required antenna performance and heights, and whether or not a
Repeater(s) is required. When contemplating antenna types and Repeater sites, keep in mind the directivity (omnidirectional or
directional) of the antennas being used, and also recall the affect of a Repeater on throughput (see Section 3.4).
Terrain
Along with distance, consider the terrain with respect to antenna height requirements. The term “line-of-sight” (LOS) refers to
being able to ‘see’ one location from another—a minimum requirement for a radio signal path. In addition to LOS, adequate
clearance must also be provided to satisfy “Fresnel Zone” requirements—an obstruction-free area much greater than the physical
LOS, i.e. LOS is not enough to completely satisfy RF path requirements for a robust communications link.
Transmit Power
Set transmit power to the minimum required to establish a reliable communications path with adequate fade margin. Required
transmit power is dictated primarily by distance, antenna type (specifically the “gain” of the antennas being used), and the
receive sensitivity of the distant modem. Also consider the cable and connector losses (the physical path from the modem’s
“antenna connector” to the antenna’s connector).
Receive Sensitivity
The MDR100A-R5 or MDR112A-R5 has exceptional receive sensitivity. This can provide benefits, including: added fade margin for
a given link, ability to use less expensive coaxial cable or antenna types, ability to operate at greater distances for a given distant
transmitter power (possibly negating the requirement for a Repeater site!). Distance, antenna gain, transmit power, and receive
sensitivity are critical “numbers” for radio path calculations. Fortunately, the MDR100A-R5 or MDR112A-R5 features the maximum
available transmit power combined with exceptional receive sensitivity—two “numbers” that will produce the most favorable path
calculation results. Only qualified and experienced personnel should install, remove, or maintain the antenna system.
Fade Margin
When all radio path numbers are considered and hardware assumptions are made, another factor to consider is the “fade
margin” of the overall system. The fade margin is the difference between the anticipated receive signal level and the
minimum acceptable receive level (receive sensitivity). The MDR100A-R5 or MDR112A-R5 performs to exacting
specifications, so the overall deployment should use the modems may be utilized to their full potential to provide a reliable and
robust communications link. A typical desired fade margin is about 0 dB, but often a 10 dB fade margin is acceptable.
