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ST-21 Argos Platform Transmitter Terminal
Services Available
Repair No
Calibration No
Free Support No


Campbell Scientific’s ST-21 is a Service Argos-certified Platform Transmitter Terminal (PTT ) that transfers data from the data logger site to the Argos Data Collection and Location System via NOAA polar orbiting satellites. This transmitter is well suited for remote meteorological and environmental data collection applications, including mobile and high-latitude installations. The ST-21 is compatible with our newer data loggers.

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Benefits and Features

  • Well-suited for remote meteorological and environmental data-collection applications, including mobile and high-latitude installations
  • Provides uplink capability for up to eight unique ID codes, frequencies, and repetition periods
  • Supports up to seven independent Argos data buffers that can be populated in real-time
  • Transmits variable-length Argos messages with either 20- or 28-bit ID codes
  • Allows researchers to forgo a rigorous certification process
  • Includes an autorepeat feature that allows the ST-21 to repeat data without host intervention
  • Provides a fail-safe feature that alerts users upon communication link or host failure
  • Allows the ID and repetition rates to be set in real-time or by Campbell Scientific


Detailed Description

While Campbell Scientific's ST-21 Argos PTT is based on Telonics' ST-21, they are not equivalent; our ST-21 includes a case, voltage regulator, and our SDC communication interface.

Please note that when ordering the transmitter, the customer needs to provide Campbell Scientific with the number of buffers, repetition rate, decimal ID, Dex ID, frequency, and fail safe information.

To use the Argos system, you must receive formal permission from Service Argos and pay a fee. The data must be used for environmental purposes. Examples include meteorological/hydrological stations, ship tracking, volcano monitoring, and seismic data.

Platform Transmitting Terminal (PTT) Equipment

  • ST-21 Argos transmitter (includes an SC12 cable)
  • CR800, CR850, CR1000, or CR3000 Datalogger
  • 12022 antenna (includes antenna cable and mounting bracket)
  • Environmental enclosure
  • Power supply consisting of our BP12 12-Ahr or BP24 24-Ahr battery pack, CH100 or CH200 regulator, and SP10 10-W or SP20 20-W solar panel

Retrieving Data from the Ground Receiving Station

Choose one of the following methods:

  • Phone modem with MNP level 4 error correction (most Hayes-compatible modems contain this error-checking protocol; check the operator’s manual for your modem) and user-supplied communication software (e.g., Procomm Plus, Crosstalk).
  • Internet
  • Telnet
  • Email


Operating Temperature Range -30° to +70°C
Supply Voltage 12 V (nominal)
Output Impedance 50 Ω
High Power Level 800 mW typical (27 to 31 dbm)
Argos Transmission Frequency 401.618 to 401.680 MHz
Modulation (BPSK) -1.1 to +1.1 ±0.1 radians
Spurious Emissions -45 dB
Transmission Distance or Area Worldwide
Current Drain
  • 1.12 mA (at 12 Vdc, quiescent)
  • 375 mA (a 12 Vdc, transmitting)
Service Requirements Must receive formal permission from Service Argos and pay a fee. Must use data for environmental purposes.
Dimensions 19.05 x 3.18 x 5.72 cm (7.5 x 1.25 x 2.25 in.)
Weight 224 g (7.9 oz)


Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Data Loggers

Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR295X (retired)
CR3000 (retired)
CR5000 (retired)
CR800 (retired)
CR850 (retired)
CR9000X (retired)

Mounting Equipment

Product Compatible Note

Additional Compatibility Information

Data Logger Considerations

Our data loggers can format the data as bits per data point, allowing the user to select the resolution used for each data point.

Enclosure Considerations

The ST-21 requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. Grommets and screws are provided to attach the ST-21's flanges to the backplate of our enclosures.

Subscribing to Argos

To subscribe to Argos, the following steps must be completed:

  1. Obtain a Program Application Form from the Service Argos website ( or from one of the following offices:

    North America
    CLS America, Inc.
    1441 McCormick Drive, Suite 1050
    Largo, MD 20774
    Tel (301) 925-4411
    E-mail: useroffi

    CLS/Service Argos
    8-10, rue Hermes
    Parc Technologique du Canal
    31520 Ramonville Saint-Agne, France
    Tel +33 (0)5 61 39 47 00

  2. Fill out and submit the application form to the appropriate Service Argos office. Service Argos will send you a program review stating whether your program has been approved.
  3. Following approval, send a Technical File that describes the required data processing and type of results to the appropriate Service Argos office.
  4. Complete and return a Service Agreement to the appropriate Service Argos office.

Frequently Asked Questions

Number of FAQs related to ST-21: 5

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  1. The ST-21 is not used via wire. The ST-21 is only used for one-way data transmission via radio frequency to polar-orbiting spacecraft. Limited data throughput with very low power requirements works best at high latitudes. 

  2. No. The ST-21 is designed for one-way communication only. 

  3. Data throughput is dependent on latitude. The spacecraft are polar orbiting, which creates more frequent satellite passes at higher latitudes. Each satellite pass can provide 15 to 90 data points, depending on cost.

  4. Email delivery or web-based access.

  5. Fees are set by CLS (Argos). Generally there is a fee for each day the service is used. For details, contact Argos

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