20
MDS TransNET 900 I&O Guide
MDS 05-2708A01, Rev. B
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
RSSI
command (Received Signal Strength Indicator) 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 (
KEY
command. (To unkey the
radio, enter
DKEY
; to disable the
SETUP
mode and return the radio to normal
operation, enter
Q
or
QUIT
.)
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 a 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
OFF
. This allows the radio to operate
with the lowest possible latency and improves channel efficiency. MODBUS
and its derivatives are the only protocols that should require the buffer to be
turned on. See
Hoptime Setting
The default hop-time setting is
7
(7 ms). An alternate setting of
28
is used to
increase throughput, but at the cost of increased latency. A detailed
explanation of the
HOPTIME
.
Operation at 115200 bps
Burst throughput at 115200 bps is supported at all settings. The radio will
always buffer at least 500 characters. Sustained throughput at 115200bps is
only possible when the data path is nearly error free and the operating settings
have been properly selected. For sustained operation at 115200 bps, use the
following settings:
SAF OFF
,
FEC OFF
,
REPEAT 0
,
RETRY 0
,
HOPTIME 28
.
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