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Acoustic General Purpose Modem

Product Specifications

GPM 300 is a long-range subsea communications system with unprecedented reliability in a compact, power-efficient package.

The GPM 300 acoustic modem can be used for reliably sending and receiving data and/or voice through water for communications, monitoring and remote command & control in harsh, multi path, reverberating and noisy hydro acoustic environments where other modems fail.

The leading performance of the GPM 300 is well proven. They are fitted to Triton’s Hadal Exploration System – the world’s first manned submersible commercially certified for repeatable exploration to the deepest point in the ocean. In 2019, the Hadal system was used for the ‘Five Deeps Expedition’, an around-the-world journey to dive to the deepest point in each of the world’s five oceans, and broke the world record for the deepest ever dive at 10,927m in the Marianas Trench. The modems were also used in James Cameron’s Deepsea Challenge Expedition in 2012, again, providing communications and enabling a record-breaking ‘tweet’ from the deepest point of the ocean.

The modem uses third generation MASQ (Multichannel Acoustic Signalling Quality of Service) multichannel Direct Sequence Spread Spectrum (DSSS) technology for high reliability communications, robust against multipath inter symbol interference.

To compensate for channel fading and multipath interference, the GPM 300 offers continuous channel equalisation. Communication between platforms moving at speed is supported with doppler tolerance +/-15 knots and continuous doppler correction. The network enabled GMP 300 is compatible with L3Harris ELAC UT 3000 underwater telephone and voice communication compliant with NATO STANAG 1074.

  • Third generation MASQ multichannel Direct Sequence Spread Spectrum 
  • Advanced forward error correction with error rates less than 1x10- 4
  • Supports remote configuration settings
  • Ultra reliable data rates up to 1000 baud
  • Voice communications* up to 25km
  • Digital communication up to 45km†
  • Low probability of intercept

*Voice requires optional GPM 300 Voice Interface Units.
† Assumes best case sea conditions. Actual range obtained depends on deployment characteristics, environmental noise and sea conditions.


  • Acoustic General Purpose Modem Data Sheet

    Acoustic General Purpose Modem Data Sheet

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