My famous Lecher Wire demonstration

WBahn

Joined Mar 31, 2012
26,398
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?
 

Thread Starter

KL7AJ

Joined Nov 4, 2008
2,229
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?
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
 

davebee

Joined Oct 22, 2008
540
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!
 

Thread Starter

KL7AJ

Joined Nov 4, 2008
2,229
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!
Hi Dave:

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

Eric
 

alfacliff

Joined Dec 13, 2013
2,458
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
 

Thread Starter

KL7AJ

Joined Nov 4, 2008
2,229
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
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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