Playing with Sonar

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  • raalst
    Junior Member
    • Feb 2003
    • 1228

    Playing with Sonar

    I found a new toy : GnuRadio. it is a set of building-blocks for (Digital) Signal Processing.
    It is created because of the interest in what is called software defined radio. Basically more and more
    of the work of transmitting or receiving a (say) FM radio station is done in a PC, which leaves a very
    minimal electrical circuit.

    GnuRadio is a collection of such digital processing tricks. you can point-and-click them together
    just like LEGO.
    GnuRadio also has the capability to use the speakers and microphone of your PC.

    So, using that you can build a sonar easy.

    the simplest one is a doppler sonar, which detects movement.

    the PC emits a constant tone. as it hits a stationary target you hear an unchanged echo.
    But when returning from a moving target, the echo has become a higher (when approaching) or lower (when receding) tone.
    with a filter the original tone is filtered away and you see the tone(difference) created by the movement of a target.

    here you see me waving frantically, then holding still and finally moving slowly


    the building blocks used for this are ]http://i625.photobucket.com/albums/tt336/raalst/Screenshotfrom2013-03-10170640.png[/img]
    It contains a signal source that is a 10kHz cosine wave, which is just a 10khz tone. It is being put on the speakers (the audio Sink).
    then from the Audio source (the mic) the signal is amplified and multiplied with the original 10Khz signal. then the bandpass filter lets
    stuff thru from 5 Hz up til 300 Hz. these frequencies are related to the speed of the target, and waving your hand is not
    very fast. so that is why the frequencies of interest are low.

    another type of sonar is the Frequency Modulated Continous Wave (FMCW)
    this one does determine the range of the target. the V pattern is my hand moving to and fro at about half a meter's
    distance to the microphone.


    the use of building blocks looks quite the same, except that the emitted sound is no longer a constant tone, but a
    chirp that first raises in frequency, then lowers again. since the echo will arrive later (because it had to travel to the target
    and back) there is in the PC a difference in frequency between the emitted chirp and the received echo. this
    difference in frequency is changing with the time delay of the echo, and hence with the distance of the target.



    If you are in to sonar, this is a toy you must give some attention to !
  • JWLaRue
    Managing Editor, SubCommittee Report
    • Aug 1994
    • 4281

    #2
    Re: Playing with Sonar

    Ronald,

    This is very interesting....could open up a whole new area of r/c sub operations.

    In looking over the web site, it looks like there are (mostly) receivers, but there does appear to be some transmitter hardware being developed. Can you determine if any of these transmitters might be in the correct frequency range for r/c subs? (e.g. 40MHz - 75MHz) If this is possible, we may have the beginning building blocks for r/c sub radio gear. Since the industry is moving (or has mostly moved) away from the traditional FM radios....this may be what is needed to keep the hobby alive.

    -Jeff
    Rohr 1.....Los!

    Comment

    • raalst
      Junior Member
      • Feb 2003
      • 1228

      #3
      Re: Playing with Sonar

      I suspect you googled for gnuradio and/or SDR. Those sites are mostly involved with reception of
      radiowaves, not sound.

      for sure Gnuradio can be used to transmit anything you like.
      This would require a small hardware transmitter circuit. Basically a fast DAC and an amplfier.
      the circuits on sale that can transmit are a bit pricy still (about 1000 USD).

      however, you will need to become a qualified hobby radio operator first.
      because transmitting without licence can ruin your whole day.

      I'm sticking with (ultra)sound, so I do not need a licence.
      I expect my trusty futaba to last a long time...

      Comment

      • JWLaRue
        Managing Editor, SubCommittee Report
        • Aug 1994
        • 4281

        #4
        Re: Playing with Sonar

        Oh, well. It was worth a thought!

        -Jeff
        Rohr 1.....Los!

        Comment

        • salmon
          Treasurer
          • Jul 2011
          • 2304

          #5
          Re: Playing with Sonar

          Oh, well. It was worth a thought!

          -Jeff
          Jeff,
          It is a great thought. We need to be thinking of the next move for our industry. 75MHz manufacturers are getting as rare as a Higgs Boson particle. I would like to see us use our computers (laptop, tablet) with a usb device that does the actual transmitting.
          Peace,
          Tom
          If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

          Comment

          • bluefish
            Junior Member
            • Mar 2007
            • 11

            #6
            Re: Playing with Sonar

            Is a license required if we only use sub-surface?
            What I'm thinking is the use of 2.4 ghz to a sono-buoy type device that would convert to a lower MHz sub-surface only... If that is even possible or practical.

            Comment

            • raalst
              Junior Member
              • Feb 2003
              • 1228

              #7
              Re: Playing with Sonar

              good question.
              maybe an american ham can answer that ?
              I only know the situation in the netherlands...

              btw, if that works then you can simply put your antenna in the water and skip the sonobuoy.
              I have seen articles about antenna's in water, but that was a long time ago...
              One thing is that the length of the antenna should be different when transmitting underwater.

              Comment

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