Inmarsat-D(D+) Downlink

Inmarsat-D/D+ Downlink

Frequencies	1525 MHz,1559 MHz
Frequency Range	1525 MHz - 1559 MHz
Mode	USB
Modulation	MFSK
ACF	—
Emission Designator	—
Bandwidth	640 Hz
Location	Worldwide
Short Description	Inmarsat D+ (and it's predecessor, Inmarsat D) was Inmarsat's satellite paging system. The main use of the technology was in tracking trucks and buoys and SCADA applications.
I/Q Raw Recording	Download file
Audio Sample

Inmarsat D+ (and it's predecessor, Inmarsat D) was Inmarsat's satellite paging system. The main purpose was for tracking trucks and buoys and SCADA applications. The original Inmarsat-D terminals were one-way (to mobile) pagers. The newer Inmarsat-D+ terminals were the equivalent of a two-way pager. This signal is the downlink from satellite to mobile station. The infrastructure is now rendered obsolete by the newer IsatData Pro service.

Characteristics

The downlink comprises a 32 MFSKMultiple Frequency Shift-Keying signal at symbol rates of 4 sym/s or 8 sym/s for data rates of 20 bpsBits per second (bps) and 40 bpsBits per second (bps) respectively. Reed-Solomon (31,15) FECForward Error Correction is used on downlink.

The 4 sym/s signal has shift of 20 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). for each tone. The bandwidth of the signal is ~640 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)., but the channel allocated to the downlink is 2.5 kHzKiloHertz (kHz) 10^3 Hz wide to account for doppler shifting interference. There is a frequency shift of 20 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). for each tone.

Samples

Inmarsat Downlink @ 4 sym/s:

(Sample contributed by RAPIDBIT)
(Sample contributed by UHF-SATCOM)

IQQuadrature signals form the basis of complex RF signal modulation and demodulation, both in hardware and in software, as well as in complex signal analysis. Sample contributed by RAPIDBIT

Frequencies

• Rx (Downlink): 1525.0 to 1559.0 MHzMegaHertz (MHz) 10^6 Hz
• Tx (Uplink): 1626.5 to 1660.5 MHzMegaHertz (MHz) 10^6 Hz

See Also

• Inmarsat IsatM2M

Additional Links

• UHF Satcom Inmarsat D
• DMR200 Specs (Inmarsat D+ compatible)
• Inmarsat-D identified, Reddit
• FCC Public Notice
• LXE Inc. FCC Form 312 – Notification of Minor Modification

Additional Images

Inmarsat-D MFSKMultiple Frequency Shift-Keying downlink channels seen from AOR-W Satellite (American Ocean Region, West). We see on the left one IsatM2M channel, with the other channels on the right being Inmarsat-D/D+ channels. Inmarsat Band, with 5 IsatM2M channels with traffic and 2 Inmarsat-D/D+ idling channels Wireless Characteristics of Inmarsat-D/D+/IsatM2M Transceiver, SkyWave SureLinx 8100. Analysis of Inmarsat-D/D+ MFSKMultiple Frequency Shift-Keying waveform by USA-Satcom.com.