Campbell ST21 User manual

ST-21 Argos
Satellite
Transmitter
User Manual
Issued 10.12.12
Copyright ©2006-2012 Campbell Scientific, Inc.
Copied under licence by Campbell Scientific Ltd.
CSL 884

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
This guarantee applies for twelve months from date of delivery. We will
repair or replace products which prove to be defective during the guarantee
period provided they are returned to us prepaid. The guarantee will not apply
to:
•Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific
•Batteries
•Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
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including those of suitability and fitness for a particular purpose. Campbell
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Please inform us before returning equipment and obtain a Repair Reference
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PLEASE READ FIRST
About this manual
Please note that this manual was originally produced by Campbell Scientific Inc. primarily for the
North American market. Some spellings, weights and measures may reflect this origin.
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
In addition, while most of the information in the manual is correct for all countries, certain information
is specific to the North American market and so may not be applicable to European users.
Differences include the U.S standard external power supply details where some information (for
example the AC transformer input voltage) will not be applicable for British/European use. Please
note, however, that when a power supply adapter is ordered it will be suitable for use in your country.
Reference to some radio transmitters, digital cell phones and aerials may also not be applicable
according to your locality.
Some brackets, shields and enclosure options, including wiring, are not sold as standard items in the
European market; in some cases alternatives are offered. Details of the alternatives will be covered in
separate manuals.
Part numbers prefixed with a “#” symbol are special order parts for use with non-EU variants or for
special installations. Please quote the full part number with the # when ordering.
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse
but sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, Campbell Park, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone] Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

i
Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.
1. Overview......................................................................1
1.1 Specifications.........................................................................................1
1.2 Serial Port...............................................................................................1
1.3 Data Buffers ...........................................................................................2
1.4 Multiple Argos ID Numbers..................................................................2
1.5 One Argos ID Number...........................................................................3
2. Datalogger Programming...........................................3
2.1 Argos Setup............................................................................................3
2.1.1 Result Code.....................................................................................3
2.1.2 Buffer Number................................................................................3
2.1.3 Decimal ID Number .......................................................................3
2.1.4 Frequency........................................................................................3
2.2 ArgosData...............................................................................................3
2.2.1 General Description........................................................................4
2.2.2 ResultCode......................................................................................4
2.2.3 ST21Buffer .....................................................................................4
2.2.4 DataTable........................................................................................4
2.2.5 NumRecords ...................................................................................4
2.2.6 DataFormat .....................................................................................4
2.3 ArgosDataRepeat ...................................................................................4
2.3.1 Result Code.....................................................................................5
2.3.2 Repetition Rate ...............................................................................5
2.3.3 Number Repeats..............................................................................5
2.3.4 Buffer Number................................................................................5
2.4 ArgosTransmit........................................................................................5
2.4.1 Result Code.....................................................................................5
2.4.2 Buffer Number................................................................................5
2.5 ArgosError (Error as string)...................................................................6
2.5.1 ErrorCodes......................................................................................6
3. ST-21 Installation........................................................6
3.1 BNC Antenna Connector and Antenna ...................................................6
3.2 Environmental Enclosure.........................................................................7
4. Satellite Orbit Patterns...............................................7
5. Antenna Placement ....................................................8

ii
Figures
1-1. ST-21 Argos Satellite Transmitter.........................................................1
1-2. The ST-21’s 9-pin connector attaches to the datalogger via the
SC12 cable..........................................................................................2
3-1. The ST-21’s BNC connector attaches to the antenna via the
antenna cable ......................................................................................6
3-2. The #12022 antenna...............................................................................7
Tables
1-1. ST-21 Serial Port Configuration............................................................2

1
ST-21 Argos Satellite Transmitter
1. Overview
The ST-21 is a certified Argos PTT satellite transmitter for use with Campbell
Scientific CRBasic dataloggers. Service Argos data transceivers fly aboard two
NOAA polar orbiting satellites. With an orbit altitude close to 800 kilometres, the
satellites are at a relatively low orbit. The low orbit allows for low transmit
power, low battery power requirements and the use of an omni-directional
antenna. The orbit period is approximately 1 hour and 45 minutes, which allows
hourly data at extreme northern and southern latitudes. Near the equator there are
about six satellite passes per day that are not evenly spaced. During the average
satellite pass, the satellite is in view for about 10 minutes.
Figure 1-1. ST-21 Argos Satellite Transmitter
1.1 Specifications
Power supply: Nominal 12 volts DC, 10 volts DC minimum,
16 volts DC maximum
Current drain
at 12 volts:
1.12 mA quiescent, 375 mA during transmit
Data buffers: 7 buffers, 32 byte each. Note: 28 bit ID numbers reduce
buffers to 31 bytes.
Operating
temperature:
-30° to 70°C
Dimensions: 19 L x 6 H x 3 W cm (7.5 L x 2.25 H x 1.25 W inches)
Weight: 224 gm, 7.9 oz
1.2 Serial Port
The ST-21 is specifically designed to work with Campbell Scientific CRBasic
dataloggers. The ST-21 serial port connects to the CS I/O port of the datalogger
via an SC12 cable (see Figure 1-2). The datalogger provides 12 volt DC power
and ground through pins 8 and 2 respectively. Communications utilize the
Campbell Scientific Synchronous Device for Communications (SDC) protocol,
which allows several devices to be connected to the CS I/O port at the same time.
Each device is addressed or pin enabled; the ST-21 is address 4.

ST-21 Argos Satellite Transmitter
2
Table 1-1. ST-21 Serial Port Configuration
Pin number Function
1 +5 volts
2 Ground
3 NC
4 TXD (data out)
5 NC
6 SDE (input)
7 CLK/HS (input)
8 +12 volts
9 RXD (data in)
Figure 1-2. The ST-21’s 9-pin connector attaches to the datalogger via the
SC12 cable
1.3 Data Buffers
The ST-21 has 8 internal data buffers. Before a data buffer can be used, a valid
Argos ID number, repetition rate and frequency must be assigned to the buffer.
The Argos ID numbers must be entered as a decimal and a Hexadecimal number.
The ST-21 uses the Hexadecimal format to determine if the ID is a 28 bit ID
number. When using 28 bit ID numbers, 31 bytes of data can be stored in the
buffer. When using 20 bit ID numbers, 32 bytes of data can be stored in the
buffer. The data buffers are numbered 0 through 7, with 7 being reserved for
other uses.
Data buffer setup can be done by the factory or under datalogger control. The
factory settings are stored in non-volatile memory. Settings that have been
changed by the datalogger are erased when the ST-21 resets.
1.4 Multiple Argos ID Numbers
The use of multiple ID numbers can significantly change how the datalogger is
programmed. 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.

User Manual
3
1.5 One Argos ID Number
The ArgosDataRepeat() function is most useful when only one Argos ID number
is used. It does not matter how many data buffers use the same ID.
ArgosDataRepeat() allows the selection of which data buffers will be transmitted,
and at what repetition period. When ArgosDataRepeat() is used to start data
transmission, the ST-21 will wait one repetition period between each transmission.
One buffer is transmitted each transmission, regardless of how many buffers have
been enabled. The maximum number of transmissions that can be scheduled with
ArgosDataRepeat() is 255.
2. Datalogger Programming
There are 5 programming instructions available for use with the ST-21 Argos
PTT: ArgosSetup, ArgosData, ArgosDataRepeat, ArgosTransmit, and ArgosError.
The use of ArgosSetup is optional. ArgosData and ArgosDataRepeat are used to
enable transmission of data. More advanced applications can use ArgosTransmit.
If the setup parameters of the PTT need to be changed, use ArgosSetup first. The
setups are maintained in memory until the PTT resets. Once the setup parameters
are set, use ArgosData followed by ArgosAutoRepeat. Data in a buffer is saved
until the PTT resets or is overwritten by another occurrence of ArgosData. If
either the ArgosDataRepeat or ArgosTransmit instruction tries to use a data buffer
that has not been setup, the instruction will fail.
2.1 Argos Setup
ArgosSetup (Result Code, Buffer Number, Decimal ID, Hexadecimal ID,
Frequency)
2.1.1 Result Code
Result Code used to determine if command executed successfully. The Result
Code is set true on success, and false on failure.
2.1.2 Buffer Number
Buffer Number is the ST-21 buffer to setup. Valid entries are 0 through 6.
2.1.3 Decimal ID Number
The Decimal ID number, and Hexadecimal ID are assigned to the Buffer Number.
Entries must be valid ID numbers or ArgosSetup will return False. The decimal
ID is not a different representation of the same number as the Hexadecimal ID.
The two ID numbers are different.
2.1.4 Frequency
Frequency to be assigned to the Buffer Number. Frequency is in Hertz. Valid
entries: 401630000 to 401656000 in steps of 2000 Hz and 401676000,
401678000, and 401680000 Hz.
2.2 ArgosData
ArgosData (ResultCode, ST21Buffer, DataTable, NumRecords, DataFormat)

ST-21 Argos Satellite Transmitter
4
2.2.1 General Description
The ArgosData instruction is used to load data to one of the 7 available data
buffers. The data buffers are numbered 0 through 7, with number 7 being reserved
for the ST-21 internal temperature. When ArgosData is executed, any data
already in the associated buffer is erased before new data is loaded. If the Argos
ID number associated with the buffer is a 20 bit ID number, up to 32 bytes of data
can be loaded. If the associated ID number is a 28 bit ID, then only 31 bytes can
be loaded. Extra bytes are discarded. The ArgosData instruction does not enable
data transmission. To enable data transmission, the ArgosDataRepeat, or
ArgosTransmit instruction must be used.
2.2.2 ResultCode
The Result Code is a numeric variable used to store the result of the ArgosData
instruction. If the result code is true (-1), ArgosData executed successfully.
2.2.3 ST21Buffer
The ST21Buffer is the number of the buffer where data should be loaded. Valid
buffer numbers are 0 through 6.
2.2.4 DataTable
DataTable is the name of the data table where data records will be read from.
2.2.5 NumRecords
NumRecords is the number of data records that will be copied from the data table
to the Argos PTT. Care should be taken to make sure the total amount of data
does not exceed what the buffer can hold, 32 bytes for a 20 bit ID number and 31
bytes for a 28 bit ID number. See DataFormat (Section 2.2.6) for details on
regarding memory usage.
2.2.6 DataFormat
There are two data formats. Enter “FP2” to use the Campbell Scientific two byte,
floating decimal point format. To use FP2, the data table (Section 2.2.4) must
store data as type FP2. Each data value will use two bytes of memory. Enter
“nnn.nnn.nnn…” to use the integer format, where nnn is an integer that specifies
the total number of bits to be used for each data value. As an example:
“5,8,16,8,3” would use 5 bytes or 40 bits for five data values. The first data value
would have 5 bits of resolution, then 8 for the next, then 16 for the third and so
forth. With the integer format, data must be stored in the data table as type Long.
When using integer format with bits/data point designator, each data point in the
data record needs to be accounted for in the DataFormat field, or the datalogger
will assume 2 bytes (16 bits) for each unaccounted for data point.
2.3 ArgosDataRepeat
Usage:
Dim BufferNumber(8) as Boolean
ArgosDataRepeat(Result Code, Repetition Rate, Number Repeats,
BufferNumber())

User Manual
5
2.3.1 Result Code
The Result Code is a numeric variable that is set true (-1) when the
ArgosDataRepeat instruction is successful.
2.3.2 Repetition Rate
The Repetition Rate will set the time between each repetition. A negative number
will cause the default repetition rate to be used. Using a value between 0 and 255
will set the repetition rate to the new value plus 42 seconds. The
ST-21 adds 42 seconds to the repeat rate with the maximum being 297.
2.3.3 Number Repeats
Number Repeats is how many times the transmission will be repeated. Valid 0 to
255.
2.3.4 Buffer Number
BufferNumber() is an eight element array of Boolean. Each element of
BufferNumber corresponds to the same buffer number -1 in the ST-21. Set the
corresponding element to true to use a buffer, or false to not use the buffer. Data
can be in a buffer that is set to false.
The ArgosDataRepeat instruction is most useful when only using 1 ID number
because time between each buffer transmission is the rep rate. When using several
ID numbers for each platform, the ArgosTransmit instruction allows the
datalogger to control the timing of each transmission.
If a buffer is set to transmit, but the buffer has not been setup with valid
parameters, ArgosDataRepeat will fail.
2.4 ArgosTransmit
Usage: ArgosTransmit(Result Code, Buffer Number)
2.4.1 Result Code
The Result Code is a numeric variable that is set true (-1) when the ArgosTransmit
instruction is successful.
2.4.2 Buffer Number
The Buffer Number designates which ST-21 buffer is transmitted. Valid entries
are 0 through 7.
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.

ST-21 Argos Satellite Transmitter
6
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 than 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.

User Manual
7
Figure 3-2. The #12022 antenna
3.2 Environmental Enclosure
The ST-21 is designed to work in a dry, non-condensing environment. A proper
enclosure should be used to keep water, dust and other environmental
contaminates away from the ST-21. Always use desiccant inside the enclosure to
keep trapped moisture from condensing on the electronics.
4. Satellite Orbit Patterns
At least two NOAA Polar Orbiting Environmental Satellites (POES) carry the
Argos transceivers and are operational at any given time. The orbits carry the
satellites over the North and South poles of the Earth in a sun synchronous pattern.
Orbit period is close to 102 minutes. The satellite foot print is about 5000 km in
diameter. At latitudes greater than 75 degrees, each satellite provides coverage
each pass. Each satellite passes over the poles 14 times a day providing 28
satellite passes per day. Coverage decreases with latitude. At the equator the PTT
will “see” a satellite six or seven times a day. The duration of the POES satellite
visibility depends on the angle from the PTT to the satellite. If the satellite passes
directly overhead, the satellite will be visible for about 15 minutes. If the satellite
passes close to the horizon, as viewed from the PTT, the satellite will only be
visible for a short time. On average, each satellite pass is visible for about ten
minutes. If using a 200 second repetition rate, a satellite pass could result in three
received messages from the PTT.
Satellite coverage must be considered when planning data collection and
transmission. Given the variability of satellite coverage, hourly data cannot be
expected unless the PTT is located above 75 degrees latitude. The number of
successful data transmissions per satellite pass will increase with a decrease in the
repetition rate.

ST-21 Argos Satellite Transmitter
8
More detailed information regarding Service Argos and satellite coverage is
available from Service Argos. On the Web, see http://www.argosinc.com/. The
Service Argos North American office can be contacted by email at
[e-mail] or phone [phone].
http://www.cls.fr/html/argos/welcome_en.html
5. Antenna Placement
The position of polar orbiting satellites relative to the PTT will change during the
satellite pass and with each satellite pass. The antenna must broadcast evenly to
all areas of the sky. The antenna is omnidirectional. Mount the antenna
vertically. Choose a location with a clear view of the sky in all directions. Any
obstruction between the PTT antenna and the sky can block data transmission
between the satellite and the PTT.

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