SATEL-EASy+
User guide
Version 1.33
32
6.2 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).
The radio modem constantly measures the received signal strength (RSSI) of the receiver. The
Signal Threshold setting determines the received signal level above which the search for the
radio messages is active. If the threshold is set too low (the CD LED is ON constantly), receiver
catches surrounding noise and constantly tries to receive messages. In such a case the actual
data transmission might get missed and 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 low-level 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 in generally
is not desirable since the radio network has a poor signal strength condition. 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 receiving the message. After that the value is returned to zero.
6.3 Priority RX/TX
Priority setting selects the priority between reception and transmission. The setting can be
changed via LCD UI (if device equipped with such), SL commands or configuration software. 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, it will be buffered. The radio modem will wait until the
reception has stopped before transmitting the buffered data. This will result in timing slacks to
the system but decreases the number of collisions on the air; this is particularly useful in
systems based on multiple random accesses.
If the Repeater Function has been set on, priority setting is automatically switched to RX mode.
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