User's Manual

MDS 05-2708A01, Rev. A MDS TransNET I/O Guide 21
Antenna Aiming
For optimum performance of directional antennas, they must be accurately
aimed in the direction of desired transmission. The easiest way to do this is to
point the antenna in the approximate direction, then use the remote radio’s
built-in Received Signal Strength Indication (RSSI) feature to further refine
the heading for maximum received signal strength.
In an MAS system, RSSI readings are only meaningful when initiated from a
remote station. This is because the master station typically receives signals
from several remote sites, and the RSSI would be continually changing as the
master receives from each remote in turn.
Antenna SWR Check
It is necessary to briefly key the transmitter for this check by placing the radio
in the SETUP mode (Page 32) and using the KEY command. (To unkey the
radio, enter DKEY; to disable the setup mode and return the radio to normal
operation, enter Q or QUIT.)
MDS TransNET 900™
Transceiver
The SWR of the antenna system should be checked before the radio
is put into regular service. For accurate readings, a wattmeter suited
for 1000 MHz is required. One unit meeting this criteria is the Bird
Model 43
™
directional wattmeter with an 5J element installed.
The reflected power should be less than 10% of the forward power
(≈2:1 SWR). Higher readings usually indicate problems with the
antenna, feedline or coaxial connectors.
Data Buffer Setting
The default setting for the data buffer is ON to accommodate virtually any data
format. However, if the system can operate satisfactorily with the buffer OFF,
we recommend doing so using the BUFF OFF command (Page 27). This allows
the radio to operate with the lowest possible latency and improves channel
efficiency.
Hoptime Setting
The default hop time setting is 7. An alternate setting of 28 is used when the
data rate is 115,200 bps.
A detailed explanation of the
HOPTIME command, and a table listing the
available selections and the channel efficiency associated with each, can be
found on Page 29.
Baud Rate Setting
The default baud rate setting is 9600 bps to accommodate most systems. If
your system will support a higher data rate, you should increase the radio’s
transmission speed using the BAUD xxxxx abc command (Page 27). It should be
set to the highest speed that can be sent by the data equipment in the system.
(The transceiver supports 1200 to 115200 bps)
Radio Interference Checks
The radio operates in eight frequency zones. If interference is found in one or
more of these zones, the
SKIP command (Page 33) can be used to omit them
from the hop pattern. You should also review Section 4.3, A Word About Radio
Interference (beginning on page 10), when dealing with interference problems.