Can you send video over audio for space balloon project

  1. I am working on a space balloon project and I wanted to send video, or pictures, back to earth via walki talki. I wanted to know if this would work; I connect a composite video cable from a camera to the wires of one of the walki talki's microphone wires. Then on the other end take the wires from the second walki talki's speaker and connect them directly to a tv or monitor's video input. Would I get any sort of a picture?
  2. jcsd
  3. DaveC426913

    DaveC426913 16,534
    Gold Member

    Well, ye olde modems set data via an audio signal over phone lines so it is possible in principle. Amongst the many problems you will encounter are:
    1] Transmission rate - at 300bps (or even 1200bps), you will get about one frame per minute. Either that or your framesize will be about 8x8pixels.
    2] Codec - How will they decode the signal on the other end? They have no equipment to convert an audio to a video signal.
  4. Okay, but what would happen if you did what I said, would anything happen?

    camera ==> walki talki(mic)
    walki talki(speaker) ==> monitor(video in)
  5. DaveC426913

    DaveC426913 16,534
    Gold Member

    Well, if you're lucky enough not to simply fry something, you'd get snow.

    The signal is completely different. What you're doing is kind of like taking your TV cable and hotwiring it to your RCA_IN on your stereo, or somesuch.
  6. No. That will not work. The bandwidth requirements for the composite video are far to great for the audio bandwidth of the walki talki. As Dave said, you can only do this with a much slower frame rate. It would be like sending individual still pictures (frames) separated by a certain amount of time (frame rate). Or, the pictures would come in slowly over a certain amount of time. Amateur radio operators have been doing this for many years. They use a system called "slow scan tv". You can purchase equipment to do this, but you must have an amateur radio license to use it on the air. Also, it would be illegal to use this equipment with CB radios.
  7. sophiecentaur

    sophiecentaur 14,711
    Science Advisor
    Gold Member

    Wouldn't an mpeg codec do a lot better than "slow scan TV"? You really have to think digital for this project.
  8. I've never used the mode myself, but I'm sure most all modern setups for slow scan tv are digital now - using a computer, software, and sound card. Slow scan tv is designed for transmission via audio bandwidths. Is there an mpeg codec designed for this purpose?
  9. Thanks for the replys guys!
    What would be the most simple, cheap, small, and portable option to send pictures or video over audio, like a walki talki or ham.
  10. MATLABdude

    MATLABdude 1,723
    Science Advisor

    What the other posters above are saying is that there isn't a quick and dirty way of kludging something like this together. This sort of project isn't unique--I'd suggest doing a Google search for high-altitude balloon project and seeing what sorts of setups others have used in these sorts of endeavors.

    Heck, depending on altitude and drift, an X-11 camera hooked up to a Wi-Fi router and cantenna might be sufficient!
  11. Perhaps there is another approach?

    Why are you restricting the signal to audio bandwidth?

    The radio carrier signal used in your 'walkie talkie' is capable of supporting a much higher bandwidth than audio, it is not normally done for various reasons, but could easily be done for special purposes like this.

    You should start with a statemnt of the available carrier.
  12. I want to use walki talki's because it is cheap and small and has great range. I just need some simple, cheap, small, and portable way to transmit video from the space balloon back to the earth. My goal is to make it able to transmit 30 miles or more.
  13. If it were possible to modify a walkie-talkie easily for increased bandwidth, the range for video will not be the same as audio. Regardless of which method of encoding is used, a higher bandwidth will reduce the signal to noise ratio in the receiver.
  14. The problem you will face is that all that equipment intended to transfer audio signals filters out all the frequencies not in typical audible range. Voice transfer even more so.

    So all the high-frequency components (probably 95% of your signal) will be lost.
  15. Basically I want to make something like the kenwood VC-H1. CCD => SSTV => Audio out
    How hard would it be to make SSTV converter? Could it be done with a single AVR? I don't really care if it is in color or high res, I just want to see where the heck my balloon is.
  16. I am sure there is free software available to decode an audio SSTV signal.
  17. Ya, I know how to decode it, but how do I encode it? Could I use an arduino?
  18. I know what you want, you have already said that.

    But wanting doesn't make reality.

    I did tell you how to do it, and asked a simple question to forward the matter, but you seem to have overlooked this.
  19. I am not in the US but there are licencing issues with these.

    Note that the range stated is 2/3 your desired and Wiki suggests normal range about 1/10 of this.

    Since they are channelised at 20Khz spacing they are not suitable for the scheme I was proposing.

    There was a scheme to download pictorial information from weather satellites using Slow Scan techniques, that you could adapt to audio modulation. This was published in Wireless World. But 20 kHz will not get you a significant frame rate.

    Thre is a lot of work involved.
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