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Discussion in 'Electronic Basics' started by Roger Dewhurst, Mar 22, 2007.

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  1. I want to feed a single pulse of, let us say, 10 to 100 microseconds
    duration, into a short length of waveguide and detect that pulse upto 1000
    metres away in another short length of waveguide set to be more or less
    co-linear with the first piece of waveguide. Can anyone suggest how I might
    implement this?

  2. Gareth

    Gareth Guest

    Please can you supply a bit more information, in particular:

    What exactly are you trying to do?

    Is there a good reason why want to use waveguide?

    What is the carrier frequency of this pulse?


  3. John  Larkin

    John Larkin Guest

    That probably can't be done. No reasonably sized waveguide (smaller
    than Central Park, say) will propagate signals that slow.

    Why do you want to do this?

  4. Transfer instantaneously a start signal to some mobile electronic equipment
    which is in line of sight upto 1000 metres away.
    I do not want interference by or to other radio transmissions but other
    options are possible. It is just too inconvenient to run a wire except for
    the shorter distances. For short distances the start signal by wire is a
    momentary low triggering pin 2 on a 555.
    Flexible but around 2 gigahertz. The waveguide can be of any size that is
    reasonably portable and aimable and the carrier wave should match it. For
    preference it will be just outside any recognized band.

  5. The 'pulse' might be a brief period of carrier wave or even a brief gap in
    the carrier wave. Pulse was probably a poor choice of word on my part. It
    has to start some other electronic equipment which measues time intervals in
    milliseconds (not microseconds!).
    See above.

  6. Gareth

    Gareth Guest

    Apologies if I have misunderstood your post, but I don't think waveguide
    does what you think it does.

    Are you thinking that you can confine your pulse to a narrow beam so
    that it can only be picked up by another bit waveguide of 1km away which
    is carefully aligned? If that is what you are thinking it doesn't work
    like that. a signal from an open ended waveguide will have a beamwidth
    of ~60 degrees.

    If you want to confine your signal to a narrow beamwidth you need a
    large antenna. The beamwidth, in radians, of an antenna is
    approximately the wavelength divided by the antenna diameter. at 2 GHz
    the wavelength is ~6", so you need a very large antenna if you want a
    narrow beamwidth.

  7. I would like to explore all options.
    Very interesting but it might require telescopic sights on the light source
    and receiver.

    The transmitter moves every few minutes.

  8. John  Larkin

    John Larkin Guest

    Oh. If you modulate a microwave carrier it becomes feasible. At 1km
    distance, horn antannas or parabolas might be better, or yagis for UHF

    Line-of-sight optical is interesting, too.

  9. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst" <

    ** Sheep Shagger Alert !!

    ** Err - where did you get the mad idea that a wave guide will create a
    narrow beam beyond the guide ?

    See anyone do it ?

    Or have you just decided in your infinite Kiwi ignorance that the name alone
    tells you that.

    Baaaahhhhhhhhhh ....

    ....... Phil
  10. John  Larkin

    John Larkin Guest

    You can buy wireless modems, with small whip antennas, that will work
    that far.

  11. Bob Masta

    Bob Masta Guest

    If you modulate the start signal instead of using a simple pulse,
    you could easily make it such that only the matching receiver
    can demodulate it properly. True, it won't be as "instantaneous"
    since you may need to send several symbols to generate a
    decent code, but at 2 GHz you ought to be able to send quite a few
    in the time windows you mention.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
  12. Rich Grise

    Rich Grise Guest

    You could build waveguide feedhorns, but you probably wouldn't get enough
    gain to go 1 Km. Get a couple of parabolic dishes, and use the feedhorns
    to drive them, and it should be a snap.

    Good Luck!
  13. How easy is it to feed the signal into one feedhorn and get it back from the
    other? Are there easier ways to achieve the required end result? Long
    lengths of cable will do it but they are a nuisance to move around. The
    signal is required to start a seismograph. The first part of it is a 555
    acting as a Schmitt trigger and timer.

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