Satel EASy+ - Designing Systems; Factors Affecting the Quality and Distance of the Radio Connection

SATEL-EASy+
User guide
Version 1.33
83
17 DESIGNING SYSTEMS
17.1 Factors affecting the quality and distance of the radio
connection
• power of the radio transmitter
• sensitivity of the radio receiver
• tolerance of spurious radiations of the radio modulating signal
• amplification of transmitting and receiving antennas
• antenna cable attenuation
• antenna height
• natural obstacles
• interference caused by other electrical equipment
The transmitter power of the modems using 403 – 473 MHz frequency range is 1 W (maximum)
and the sensitivity of the receiver better than -115 dBm. Thus in a flat area and in free space with
a 1/4 wave antenna (antenna amplification 1dBi) and antenna height of 1 m communication
distances of 3 to 4 km can be achieved. Distances may be considerably shorter in situations
where there are metallic walls or other material inhibiting the propagation of radio waves.
Over long distances, increasing the height of antennas can often solve problems caused by
natural obstacles. A ten-fold increase in distance can be achieved with the use of amplifying
antennas. Frequent topographical variations over long distances may require that at least one
of the antennas be raised to a height of 10 to 20 m.
If the antenna cable is more than 10 meters long it is necessary to use a low loss cable (< 0.7 dB
/10 m) in order not to waste the antenna amplification. Adding a repeater station can also solve
problematical radio connections. In systems with many base stations the RSSI-signal can be
used to assist in choosing the base station with the best signal. A communications network can
also be built with a combination of cables and radio data modems.
Modem tolerates normal levels of interference that occur. However, exceptionally high levels of
interference can break through the safeguards and thus cause errors in data transfer. In mobile
vehicle applications the range of operation can be increased by dividing the transmitted data
into e.g. 50...500 byte long blocks and by re-transmitting the defected blocks.
A sufficient safety margin can be obtained by testing the communication path using extra 6 dB
attenuation at the antenna connection and with slightly less effective antennas than those to be
used in the final system.