Inmarsat-C TDM

Inmarsat-C TDM

Frequencies	1537.7 MHz,1539.585 MHz,1539.685 MHz,1539.525 MHz,1539.555 MHz
Frequency Range	1537.7 MHz - 1539.685 MHz
Mode	USB
Modulation	PSK
ACF	135 ms
Emission Designator	—
Bandwidth	2.5 kHz
Location	Worldwide
Short Description	Inmarsat C provides two-way data and messaging communication services to and from virtually anywhere in the world. The low-cost terminals and antennas are small enough to be fitted to any size of ship.
I/Q Raw Recording	Download file
Audio Sample

This signal identification is from Inmarsat 3-F4. This is a 1200 bpsBits per second (bps) DBPSK Network Control Station Channel (NCSC).

The Inmarsat C maritime mobile satellite system has an inherent capability, known as Enhanced Group Call (EGC), which allows broadcast messages to be made to selected groups of ship stations located anywhere within a satellite's coverage. Four geostationary satellites provide worldwide coverage for these types of broadcasts. Two types of EGC services are available: Safety NET and Fleet NET. Fleet NET is a commercial messaging services offered by Inmarsat, and is not recognized by the Global Maritime Distress & Safety System, or GMDSS. Safety NET, along with NAVTEX, is recognized by the GMDSS as the primary means for disseminating maritime safety information. Ships regulated by the Safety of Life at Sea Convention travelling outside areas covered by NAVTEX must carry an Inmarsat C Safety NET receiver by 1 February 1999.

Frequencies

Check UHF Satcom for frequencies.

For the TDM NCSC channels, they are fixed for the following Ocean Regions (OR):
AOR-W: 1537.70 MHzMegaHertz (MHz) 10^6 Hz

IOR: 1537.10 MHzMegaHertz (MHz) 10^6 Hz

AOR-E: 1541.45 MHzMegaHertz (MHz) 10^6 Hz

POR: 1541.45 MHzMegaHertz (MHz) 10^6 Hz

View This map to see what each ocean region used to cover in 2015. Use a sat tracker (e.g. G-Predict) and look for birds in geostationary orbit (zero inclination; not changing longitude) to find the (likely) currently operating satellites. The ORs maybe inferred from the 4 main ground footprints.

Decoding Tutorials

• RTL-SDR Tutorial: Decoding Inmarsat STD-C EGC Messages

Decoding Software

Hobby Level Software

• EGC std-C decoder
• Scytale-C EGC Decoder
• stdcdec - CLI decoder for linux, based on Scytale-C source

Professional Equipment/Software

• go2DECODE
• go2MONITOR
• Hoka Code300-32

Additional Links

• Inmarsat Worldwide Satellite Services: Today and Tommorow, 1993
• WAVECOM Database: SAT-C TDM

Additional Images

Inmarsat-C TDM IF Spectrum of Inmarsat-C TDM DBPSK Phase Plot Inmarsat-C TDM Baudrate from Quadrature AMAmplitude Modulation Detector.