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New Design Technology

Discussion in 'Electronic Design' started by RST Engineering \(jw\), May 27, 2007.

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  1. I am thinking about creating a new design for transceiving audio over a
    range of a couple of meters. The criteria are as follows:

    1. Up to four audio sources each of which must hear all of the other three
    stations. (Headset-microphone-earphone) Although I'm not ruling out any
    scheme, what I think would work is a "base station" that could be mounted
    somewhere in the vehicle, receive up to four separate frequencies, and
    retransmit the detected audio over a common transmit channel.

    2. Fairly high electromagnetic intensity environment ... tens of watts of
    RF at 120-140 MHz. at a meter or so range. Hundreds of peak power watts
    (average 5 watts or so) at 1 GHz. also at a meter or so.

    3. Entirely possible that in some instances the device will have to operate
    in direct sunlight. I'd prefer not to use opto techniques.

    4. Whatever the technology and power source, the device will have to be
    worn on the head for several hours at a time. It may be possible to mount
    the device on the chair the person is sitting on but I'd like to keep my
    option open to mount the whole works inside the individual headset.

    5. Moderately high noise environment made a little more liveable by the use
    of noise-cancelling microphones.

    6. If at all possible, I'd like something that will work in an amateur
    radio band...the device will only be marketed with proof of amateur license.
    2 meters might work, as would 220 or 440. 220 is so quiet that I'd really
    like to operate in that band if possible.

    I'm not so much looking at a design per se, but more a technology or
    device(s) that I could research and see what is available and preferable.
    Comments appreciated.

  2. John Larkin

    John Larkin Guest

    I was thinking about a system wherein all car drivers within
    line-of-sight would be able to converse, sort of full duplex CB. The
    social evolution of that would sure be interesting. I figured it would
    be RF or optical. Preferably received sound level would not vary with
    distance, at least until the range limit was hit.

    I was thinking that everybody would transmit random carrier-modulated
    pulses, with pulse density carrying the audio modulation. The receiver
    is then just a limiting bandpass amp, a comparator, optional one-shot,
    and a lowpass filter.

    You could also do some fancy digitized burst packet things, I guess,
    with overlapped packets straddling each group of samples, so
    collisions could be mostly corrected for. More work.

  3. Nordic semi has some stuff, such as nRF24Z1, but not exactly suitable,
    it might give you some ideas

  4. Gibbo

    Gibbo Guest

    I like the idea, very much. If you can get it to work then good luck. I
    think you could be on to a winner.
  5. Ben Jackson

    Ben Jackson Guest

    Bluetooth does this (with digital audio) in the ISM band at 2.45G.
    There are probably appnotes out there for the phone/headset sides
    of a BT link, eg:
    Seems like the GHz range has size advantages for that, even if you
    want to homebrew.
  6. joseph2k

    joseph2k Guest

    AFAIR Ham radio is not allowed to be operated just like that. To be part 97
    compliant each transmitter would have to have its own frequency and each
    user would have to have multiple (or multichannel) receivers. Some "900
    MHz" ISM band radios can do this directly. Moreover, you should consider
    motorcycle usage as well. Range should be about 100 m line-of-sight at the
    standard 1 W.
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