User's Manual

455U Radio Modem Module User Manual
Page 28 © November 2004
and S18 (the number of bytes required to start). The override time is stored in register S19 -
this value can also be changed by the user.
3.9 Operating Problems
Most operating problems relate to an inadequate radio path, or radio interference. Before
installing a system, bench test the complete system with the 455U units near each other. This
test eliminates the radio path or interference as a factor, and ensures that the system will
operate in the way that you want. It is not necessary to connect antennas, however a small
length of wire should be inserted into the middle pin of the coaxial connector - this will act as
an antenna.
If the bench test does not give adequate performance, then you need to adjust the
configuration parameters. We recommend that you do not install the system until you are
happy with the bench test performance.
If a system gives poor performance after it is installed, check the adequacy of the radio path -
refer to the Diagnostics Section 6.
Interference will only cause a problem if the amplitude of the interference is comparable to
the radio signal from the 455U units. If the interference level is relatively small, then it will
not affect the performance of the system. If interference is causing a problem, try to improve
the normal radio level by mounting the antennas higher or in a better location. This not
always possible.
System performance may be improved by changing the following parameters :-
• If in unacknowledged mode, try Acknowledged mode.
• If configured for a radio data rate of 9600 bits/sec, reduce the rate to 4800 bits/sec.
• If large radio messages are being transmitted, reduce the maximum message length, and
transmit the data in more messages of smaller size.
Another common problem is the response time of the host software. Some hosts operate by
sending a message from one end and require a response to that message within a certain time.
If this time is less than the turn-around time of the radio modem, then the system will not
operate. It may be possible to lengthen the response time in the host software.