SATELLINE-EASy / SATELLINE-EASy 869
User Guide, Version 3.0
27
5.2
Receiver
The sensitivity of the receiver depends on the channel spacing of the radio modem (=data
speed of the radio interface) and on the mode of the FEC (error correction).
Receiver sensitivity
Radio Modem
Channel Spacing
FEC OFF FEC ON
SATELLINE-EASy
25 kHz
-108 dBm -111 dBm
20 kHz
-111 dBm -114 dBm
12.5 kHz
-111 dBm -114 dBm
SATELLINE-EASy 869
25 kHz
-108 dBm -111 dBm
The radio modem measures the received signal strength (RSSI) of the receiver constantly. The
Signal Threshold setting determines the received signal level above which the search for the
radio messages is active. It is recommended that values given in the table above are used as a
basis. If the threshold is set too low (the CD LED is ON constantly), it is possible that the receiver
is trying to synchronise itself with noise. In such a case the actual data transmission might remain
unnoticed. If the threshold is set too high, the weak data transmissions will be rejected although
they could be otherwise receivable. Signal threshold should only be changed for a reason - for
example in the following cases:
Continuous interference is present and the desired signal is strong. In this case the signal
threshold can be increased to prevent the modem from synchronising to the interfering signal(s)
and /or possible noise.
Maximum sensitivity should be achieved and the desired signal is very weak. In this case the
sensitivity could increase by decreasing Signal threshold. This type of situation is usually a sign of
a poorly constructed radio network / contact. Bit errors and momentary loss of signals can be
expected in this kind of a situation. Some data might be successfully transferred.
The radio modems equipped with an LCD display show the RSSI of the last received message in
dBm units. The RSSI can be requested also locally by using a special SL command (SL@R?). The
RSSI value is available 7s after the receiving the message. After that the value is returned to zero.
5.3
Priority RX/TX
SATELLINE-EASy offers a Priority setting, which selects the priority between reception and
transmission. The setting can be changed in Programming Mode. By default, transmission has
higher priority than reception i.e. the default value is Priority TX.
Priority TX means that a terminal device attached to a radio modem decides the timing of the
transmission. The transmitter is immediately switched on when the terminal device starts to
output data. Should reception be in progress, the radio modem will stop it and change to a
transmit state. There is no need to use any handshaking for the control of timing.
Priority RX means, that a radio modem tries to receive all data currently in the air. If a terminal
device outputs data to be transmitted (or an SL command) it will buffered. The radio modem will
