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Thread: Building a digital modem with Teensy 3.1 and the Audio Adaptor

  1. #1
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    Building a digital modem with Teensy 3.1 and the Audio Adaptor

    Hello everyone,

    I'm in the process of developing a number of digital modems for Ham Radio use; two of them will be based around the Teensy 3.1/Audio Adaptor hardware combination if it turns out to be a feasible hardware configuration. The other modems will be fully software based, and the critical requirement for one of them is that the hardware (firmware) implementation works in exactly the same way is one that my co-developer and I agreed to from the start of development. The other has the same requirement, but that is based on it being a hardware implementation of a MIL-STD (Military Standard) and a personal desire for proper interoperability.

    I know, from looking at the Audio Library web page, that the potential exists for the hardware to be able to do what I need; my main need is in assistance fine tuning things so I'm not getting more than I need to have to make this work.

    Matthew Pitts
    N8OHU

  2. #2
    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by daywalker03 View Post
    Hello everyone,

    I'm in the process of developing a number of digital modems for Ham Radio use; two of them will be based around the Teensy 3.1/Audio Adaptor hardware combination if it turns out to be a feasible hardware configuration. The other modems will be fully software based, and the critical requirement for one of them is that the hardware (firmware) implementation works in exactly the same way is one that my co-developer and I agreed to from the start of development. The other has the same requirement, but that is based on it being a hardware implementation of a MIL-STD (Military Standard) and a personal desire for proper interoperability.

    I know, from looking at the Audio Library web page, that the potential exists for the hardware to be able to do what I need; my main need is in assistance fine tuning things so I'm not getting more than I need to have to make this work.

    Matthew Pitts
    N8OHU
    I'm very sure that you can get help here, but it would be good to know what do you want to finetune...

  3. #3
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    modem like the psk31 or xpsk31 low bit rate modulation used in the low bands?

    or one of these
    http://radio.linux.org.au/?sectpat=digital

  4. #4
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    Quote Originally Posted by stevech View Post
    modem like the psk31 or xpsk31 low bit rate modulation used in the low bands?

    or one of these
    http://radio.linux.org.au/?sectpat=digital
    Steve,

    What I'm working on has some similarities to many of the modes in fldigi, including PSK31. The main thing with what I'm currently developing is that I'm doing multiple carriers and multiple bandwidths on the fly as conditions change. My main concerns are; will the hardware be able to handle generation of up to 40 simultaneous carriers (for the MIL-STD version) and do I need the audio interface board, as I don't need the high resolution stereo input or output for this.

  5. #5
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    with the right talent in programming the DAC, PSK31 should be done with the T3's horsepower. But have you learned it top to bottom using PC/Linux open source? Maybe you can adapt that code?

    Assuming you are also receiving, that'll be the hardest part, of course.

    I'm guessing that this is a rather advanced signal processing project, involving FFTs or DCTs and the like, and understanding the math.
    The Teensy 3.1 can do reasonably fast single precision floating point, but there is no floating point in hardware for 10x or more speed-up. Other ARM processors do have floating point support now, and a future Teensy may have it. But some analysis and testing may be in order to see if the algorithms you plan to use will or will not overtax the Teensy's math capabilities. It's all about algorithm optimization, not brute force hardware speed. I've seen PSK31 running nicely on a PC via its audio board. However that processor is orders of magnitude faster than the Teensy, at math.
    Last edited by stevech; 12-30-2014 at 03:58 AM.

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