Installation
Factors Affecting the Quality and Distance of the Radio Connection
36
SRL-35 Operator’s Manual P/N: 1003224-01
best way to distinguish from the other antennas situated in the neighborhood is to mount the antennas as
far as possible from each other on the altitude level. The best result is generally obtained when all the
antennas are in the same mast. With an extra ground plane between the antennas more distinction can be
obtained between the antennas in the mast.
Horizontal polarization can be used in data transmission between two points. With the polarization
attenuation more distinction is obtained to vertical polarized systems. The influence of the directional
patterns of the antennas must, however, be taken into consideration. If a distinction to another interfering
antenna is wanted with the horizontal polarized antennas there must be a good attenuation of the back
lobe. In addition to this the interfering radiator should be situated behind the antenna.
When a system does not demand the use of an omni-directional antenna it is recommended that
directional antennas are used e.g. two-element yagis in permanent external installations. Please note that
as antenna amplification increases the setting of the direction of the antenna requires more attention.
Base stations in high places should be supplied with high-Q cavity filters. Please note that the higher the
base station antenna, the larger the coverage area and in turn that the risk of interference is also increased.
Topcon recommends the use of a band-pass filter with a large Q in the antenna cable of the base station.
By using amplifying antennas (G=Gain) and by installing the antenna high, long connection distances can
be realized using the SRL-35 radio modem.
Factors Affecting the Quality and Distance of the Radio
Connection
•
power of the radio transmitter
•
sensitivity of the radio receiver
•
tolerance of spurious radiation’s 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 SRL-35 is 35 W (maximum) and the sensitivity of the receiver better than -
114 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.
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