Campbell Scientific ST-21 Argos Satellite Transmitter - Manual (Page 12)

ST-21 Argos Satellite Transmitter
ArgosTransmit is used to initiate a single transmission immediately. One must
be careful because the datalogger program is totally responsible for the actual
repetition rate when using this instruction. Works well for those with multiple
ID numbers needing more data throughput and total control over the timing of
transmissions.
When multiple ID numbers are used, the ArgosTransmit() function works best.
When ArgosTransmit() is executed, the contents of the specified data buffer are
transmitted once. ArgosTransmit() gives full control of timing of
transmissions to the datalogger programmer. Special care must be taken to
avoid transmitting too often. The programmed repetition period must match
the System Use Agreement between the user and Service Argos.
2.5 ArgosError (Error as string)
Public ErrorCodes as string * 20
ArgosError(ErrorCodes)
2.5.1 ErrorCodes
ErrorCodes is a string variable. ArgosError sends the command &h09, and
then waits for the returned string plus the ACK or NAK character. The
returned string is stored in the string variable ErrorCodes. If NAK (&h15) is
returned, then ArgosError() did not receive a proper response from the ST-21.
3. ST-21 Installation
3.1 BNC Antenna Connector and Antenna
The ST-21’s BNC connector is for attaching the antenna (see FIGURE 3-1).
FIGURE 3-1. The ST-21’s BNC connector attaches to the antenna via
the antenna cable
The connector’s RF output is 50 ohm impedance at a nominal 1 watt output at
about 401.6 MHz. Frequency is dependent on setup. For the ST-21, Campbell
Scientific offers the 12022 omnidirectional, unity gain antenna (see FIGURE
3-2). An antenna with gain will perform significantly worse then an antenna
with unity gain. The 12022 antenna includes a 17 ft cable and a mounting
bracket for fastening the antenna to a mast. The antenna should be mounted
vertically and the connections kept dry.
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