Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>We made a plane wave antenna for high voltage peak potential measurements by using a 30 x 30 inch piece of sheet copper. Near the center portion we suspended another smaller 4 x 4 inch piece of sheet copper on 4 small ceramic standoff insulators. This center section fed the center of a 50 ft long coax cable which the large copper piece fed the outer sheath. This was all supported on a few corner insulating pieces of PE which held the copper sheet 1/4 inch off the supporting wood 2 x 4 structure. We put it on wheels for easy mobility around the lab.
Termination was into a precision 50 Ohm resistor. I suppose one could also use a trim pot and trimmer capacitor if absolute accuracy is required but since we are performing a calibration with a HV DC power supply on each type of terminal we test (toroid, sphere, or oblate) we didn't feel this extra work necessary.
We did the calibration using a 75 kV DC power supply and also did a separate calibration with a 200 kV DC power supply with similar results. We usually run a separate calibration for small coils with a 30 kV DC supply calibrated to NBS standards and use the 75 kV supply for the larger coils and Van de Graaffs.
We operated this approx 12-25 feet away from larger coil and 6-8 feet away from smaller coils and obtained very consistent and reliable results.
It measures the peak AC potential and the peak DC potential. To keep the load small we also experimented with a small electrostatic field mill voltmeter but due to the high impedance of modern oscopes there was not a detectable difference.
We tested our "simple contraption" against one of Terry's earlier plane wave antennas and there was no noticable difference. With a small op amp inserted we were even able to measure charge on passing clouds on a non-stormy day. During a storm the op amp was not necessary.
Dr. Resonance
Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hey All,If nothing more than a sheet of copper is required, then that is nice and easy. Easy enough for those with planewaves to test. But not until after the holidays, at least for me!Take care, Bart Tesla list wrote:Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx> Hi, > Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx> > > HI Terry and Bart and others, > > Im just curious. Seems like the H field from the toroid is tangental > to the plane wave antenna. If so, it seems like eddy currents are > not an issue. Terry, have you noticed a difference with the "fractal" > version of you antenna vs the solid copper version?? > > Gerry R, > > Not sure what the H field direction would be at either the toroid or the antenna. The antenna is working in the near field of the coil that contains a supposition of normal (probagating) EM waves such that most of the H fields cancel leaving a large H field. So its hard to say what direction the H filed is from simply knowing what the E field is. The whole near far field/impedance thing was discussed adnorsium in connection the power transmission thing. Its does not do much plane wave detecting so its misleading to call it a plane wave antenna. I more accurate term would be a capacitive probe. I agree it very unlikely that anything more than a sheet of copper is required anymore so than the plates of a capacitor. Robert (R. A.) Jones A1 Accounting, Inc., Fl 407 649 6400