Also known as: Orbcomm, ORBCOMM
Orbcomm is a low-earth-orbit satellite network built for short machine-to-machine (M2M) data messages — telemetry, asset tracking, and remote monitoring — rather than voice. It is a little-LEO system: its satellites operate in the VHF band, with a downlink near 137–138 MHz and an uplink near 148–150 MHz, using store-and-forward relay so a satellite can collect a message over a remote area and drop it to a gateway minutes later.1
Overview
Orbcomm Inc. was founded in 1993 and began commercial service in 1998 with a constellation of small VHF satellites. The design deliberately chose VHF and tiny satellites to keep both the space and ground segments cheap: a subscriber terminal is a low-power modem the size of a paperback, and the low frequency means a short whip antenna suffices.1 The trade-off is throughput — the system moves short packets, not streams.
Technical characteristics
| Property | Value |
|---|---|
| Orbit | LEO, ~715 km, multiple planes |
| Downlink | 137–138 MHz VHF |
| Uplink | 148–150 MHz VHF |
| Modulation | Symmetric differential PSK (SDPSK) |
| Data rate | ~4800 bps downlink, ~2400 bps uplink |
| Access | FDMA channels, TDMA slots, store-and-forward |
The downlink uses symmetric differential PSK, a differentially encoded phase modulation whose differential decoding removes the need to resolve an absolute carrier phase — convenient when the satellite is racing overhead with a large Doppler shift.2
History
The first operational satellites launched in the mid-1990s, with full commercial service from 1998. Over time Orbcomm expanded through second-generation (OG2) satellites and acquisitions of other M2M providers, and some of its satellites carry AIS receivers to collect ship position reports from space for maritime tracking.1
Deployment
Orbcomm serves fleet and container tracking, oil-and-gas and utility telemetry, heavy-equipment monitoring, and other industrial IoT where cellular coverage is absent. Because the downlink sits at 137–138 MHz — the same VHF slice used by the NOAA APT weather satellites — it is easily received with an ordinary VHF SDR and a modest antenna, and its packets have been demodulated by hobbyists with open-source tools.
Decoding it with GopherTrunk
GopherTrunk does not decode Orbcomm. Although the 137 MHz downlink falls in a band a VHF SDR can hear, Orbcomm’s SDPSK modulation, satellite framing, and store-and-forward packet formats are unrelated to the terrestrial land-mobile trunking protocols GopherTrunk targets. It appears here as the VHF, data-only member of the LEO family alongside Iridium and Globalstar.