Designing an Acoustic Modem for an AUV

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Discussion Overview

The discussion revolves around the design of an acoustic modem for an Autonomous Underwater Vehicle (AUV). Participants explore theoretical and practical aspects of transmitting and receiving data underwater, including modulation techniques and transducer choices. The conversation includes considerations for duplex communication, data rates, and environmental factors affecting acoustic communication.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • Michael proposes modifying an existing acoustic modem design by removing the signal generator and adding a DTMF encoder, but questions the simplicity of this approach.
  • One participant suggests starting over, arguing that the current transmitter link is unsuitable for DTMF and proposes AFSK as a simpler alternative.
  • Michael acknowledges the suggestion of AFSK and asks about potential problems with his initial approach.
  • Concerns are raised about the linearity of the output stage in the proposed design, which may distort sine waves needed for DTMF.
  • Michael clarifies the project requirements for duplex communication, including specific command and value needs.
  • Another participant emphasizes the importance of data rates and suggests including error detection and preambles for reliable communication.
  • Michael indicates a target data rate of <50bps and expresses a desire to create a working prototype to improve upon later.
  • Questions arise about the optimal frequency for underwater communication, with references to various frequencies used in different contexts, including Navy submarines.
  • Participants discuss the need for a correlator in the receiver to improve communication quality and suggest researching noise sources in the ocean.
  • Michael shares his self-taught background in electronics and expresses interest in further resources and books on the topic.
  • Safety considerations regarding ultrasonic communication and potential precautions for working with ultrasonic power are mentioned.
  • One participant questions the suitability of 200kHz for communication and suggests it may be more appropriate for sonar applications.

Areas of Agreement / Disagreement

Participants express differing opinions on the best modulation techniques and the suitability of specific frequencies for underwater communication. There is no consensus on the optimal design approach or the effectiveness of the proposed methods, indicating ongoing debate and exploration of ideas.

Contextual Notes

Participants note various assumptions and limitations, such as the need for error detection, the impact of environmental noise, and the specific requirements for duplex communication. The discussion reflects a range of experiences and knowledge levels among participants.

Who May Find This Useful

Individuals interested in underwater communication technologies, acoustic modem design, and electronics projects may find this discussion beneficial.

  • #31
Berkeman,
I'm a very active diver and I can't say I've ever heard about anyone ever having trouble with depth sounders on boats which normally operate at 50, 60, 98, and 200 kHz. There is an organization called DAN, the Divers Alert Network which is free to contact and will answer diver medical related questions. You can contact them on the web at www.diversalertnetwork.org .

Michael,
Sure feel free to drop me a line. I can be reached at home at dakin@shaw.ca or at work at tom@aml.bc.ca. I'm on Vancouver island in Canada so if you are in the UK there is an 8 hour difference.

I'm in the process of designing a coded underwater comm system for divers so I'll be looking into similar stuff as well.

Tom
 
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  • #32
The circuit is right ?and it can work correctly ?
 

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