My famous Lecher Wire demonstration

Discussion in 'Wireless & RF Design' started by KL7AJ, Dec 9, 2013.

  1. KL7AJ

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  2. WBahn

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    Definitely a nice demo.

    So, for measuring the frequency of the signal, you used the speed of light in a vacuum. Can't the speed of the waveform in a conductor be considerably less than that?

    Where are RF microammmeters available from commercially?
     
  3. KL7AJ

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    Howdy:
    With wide spacing (high Z0), the velocity factor of the Lecher Wire is about 99% of that in free space, so the error is less than the calibration of my signal generator!

    The R.F. microammeter is just a DC microammeter with a shottkey diode detector. (I actually have two of them in a voltage doubling configuration) A germanium diode will work fine too...I just happened to have a couple of nice Schottkeys. :)

    ERic
     
  4. davebee

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    Oct 22, 2008
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    Many moons ago (around 1979) I took a correspondence course in radio electronics, and it included some Lecher line experiments.

    My Lecher line was 3 foot of lengths of about 16 gauge wire stretched about an inch apart across a wooden frame. It had a little one-transistor oscillator of about 400 mHz at one end, and used a germanium diode detector on a circuit board that could slide across the parallel pair.

    It worked great!
     
  5. KL7AJ

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    Hi Dave:

    Glad to hear that! It's really hard to think of a simpler and more revealing experiment!

    Eric
     
  6. alfacliff

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    Dec 13, 2013
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    a couple of led's should ork for an indicator, they work at fairly high rf frequencies too.
    cliff
     
  7. alfacliff

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    I have been thinking of building a lecher line to use as a demonstration in my ham classes. I have been helping the local CERT team get liscensed, and I am a w5yi voulteer examiner. how about using a uhf rig, like a vx5 yeasu on very low power to generate the signal?
    cliff wa0rox
     
  8. KL7AJ

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    That works just fine. You might want to pad down the output a bit though.

    LEDs do work, but they also draw some current, which upsets the current distribution on the line. You actually want a true voltage indicator....or as close to that as you can get.

    ERic
     
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