Radio Inter
face
RF Interface
11
SRL-35 Operator’s Manual
P/N: 1003224-01
The Signal Threshold Level setting of the receiver determines a level, above which the search for the actual
data transfer signal is active. It is recommended that values given in the table are used. If the Signal
Threshold Level setting is set too low (the CD-LED is ON constantly), it is possible that the receiver is trying
to synchronize itself with noise, in which case, the actual data transmission might remain unnoticed.
Alternatively, weak data transmissions will be rejected, even though they would be otherwise acceptable.
Priority RX/TX
The SRL-35 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 outputs data
to be transmitted (or an SL command) it will 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.
To toggle the
Priority
setting in the programming menu, select:
1) Priority RX / TX
If the Repeater Function has been set on, priority setting is automatically switched to RX mode.
Forward Error Correction
F
orward
E
rror
C
orrection, FEC-function is switched ON (or OFF) by using the
Programming Mode
. When
activated, the FEC-function will cause the SRL-35 to automatically add additional error correction
information, which increases the amount of transmitted data by 30%. It is used by the receiving radio
modem to correct erroneous bits - as long as the ratio of correct and erroneous bits is reasonable.
Error correction improves the reliability of data transfer via the radio interface especially in unfavorable
conditions. FEC-function should be used when link distances are long and/or if there are many disturbances
in the radio channels used. The use of the FEC-function will, however decrease the data transfer
throughput of data by about 30%. The list of exact delays when using FEC-function, are introduced in
appendix B.
To switch the FEC-function ON in the
Programming Mode,
select:
1) Error correction ON
Error Checking
When the error checking is switched on, the radio modem will add a checksum to the transmitted data.
When the data is received, the checksums are verified before data is forwarded to the serial port. There are
two different options for error checking that can be accessed in the Additional Setup menu in Programming
Mode: