Radio Field Strength - Satel SATELLINE-1AS User Manual

SATELLINE-1AS and SATELLINE-2AS
amplifying antennas. Frequent topographical variations over long distances may require
that at least one of the antennas needs to be raised to a height of 10 to 20 m.
As the placement of the antenna at the base station is more than 10 m from the modem it
is necessary to use a low loss cable (< 0.7 dB /10m ) in order not to waste the antenna
amplification.
If the antenna at the base station must be placed near other radio transmitter antennas (eg.
NMT, GSM etc.), an antenna filter should be added between the modem and the antenna.
Problematical connections can also be solved by adding another intermediate station for
relay. In systems with many base stations an RSSI-signal would assist in choosing the best
receiving base station. A communications network can also be built with a combination of
cables and radio data modems.
The SATELLINE-1AS/2AS radio data modem operates in the 450 MHz band where
interference caused by human beings is insignificant. Long distance interferences need not
to be taken into account even in special weather conditions.
The SATELLINE-1AS/2AS eradicates normal levels of interference that occur. However,
exceptionally high levels of interference can break through the safeguards and thus cause
errors on transmssion. In mobile vehicle applications the range of operation can be
increased by dividing the transmitted data into e.g. 50...500 bits blocks and by
retransmitting defected blocks.
A sufficent safety margin can be obtained by testing communications using an extra 6 dB
rejection at the antenna connection and with slightly less effective antennas than those to be
used in the final system. Saterm test program can be used in the communications testing. If
there is a need to measure RSSI signal during the Saterm test transmission, a message long
enough must be used eg. File Logo.TXT
4.2

Radio field strength

A successful radio transmission depends essentially on the radio field. Where field strength
is over a certain level the operational results are very good. Below this level, a few dB
marginal areas may occur in which errors begin to be generated by noise and interference
which will eventually lead to loss of connection.
Whilst in an open space, the field strength is at its optimum level although it will still be
reduced by distance. It must also be remembered that one open space has different
environmental and external factors to another and that the effects on transmission quality
must be taken into account when planning the system.
Ground, ground contours and buildings cause attenuation (loss of energy through
absorbtion) and reflections of radio waves. Buildings reflect radio waves and therefore the
effects of attenuation are not as acute when transmission is over a short distance.
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