What is the best way to measure atmospheric electric fields?

Hi DAB,

To measure the electric field inside the cloud, you have to put your probe inside the cloud.

Benjamin Franklin tried this using a kite.

To measure the electric activity around your house, a simple whip antenna, like a car antenna will do.

During a thunderstorm you can mesure DC Voltages in excess of 10 kilovolt. When the lightning strikes, the polarity of the high voltage sometimes will reverse.

Another way to detect electric activity is lo listen to a long wave radiostation. Electric discharges in the atmosphere will cause cracking sounds in the reception. Unfortunately the interference from computers and switched mode poweresupplies make the reception of long wave radio impossible in some areas.

The AC voltages are also huge. My own experiences are about radio receiving  equipment and protection  against electrical fields.

Radio receiving  equipment is often damaged during a thunderstorm. Not by a direct hit, but by the electrical fields.

I made measurements using a moving coil high voltage meter. During a thunderstorm I measured negative voltages in excess of 10 kilovolt. During the lightening, the polarity of the high voltage changes fast, then returns slowly to the original polarity.

The DC voltages are really high, but can be shorted with an inductor or even a resistor.

If a capacitor is connected between the antenna and the input transistor of a receiver, the input transistor can be damaged by the electrical field. Even if the DC voltage is shorted by an inductor.

The best way to protect the receiver input is to use a RF-transformer between the antenna and the receiver input. Additional protection can be provided using surge arrestors at the antenna side and protection diodes at the receiver side.

I think the best way to measure the fields is using a compensated divider. With a compensated divider I mean both a capacitive and a resistive divider, as is used in an oscilloscope probe.

With a Tektronics model P6015A High Voltage probe you can measure continuous voltages to 20 kilovolt and AC voltages to 40 kilovolt peak. This probe loads your detector with 100 megaohm and 3 picofarad. This probe can be used to measure frequencies up to 75 MHz.

It might be interesting to measure with the square foot detector and also with two long wires, one in north south direction and one in east west direction. The north-south wire will average differences between north and south. The east-west wire will average differences between east and west.

This way it might be possible to measure shape and movement of the fields.

The DC voltage on the detector will be caused by the electrical field, by the wind and by electrically charged raindrops. The AC voltage only by the electrical field. The detector will also receive radio-signals.

Usually for measuring the electric field due to clouds, people use a Field Mill (e.g. http://www.precisionstrobe.com/jc/fieldmill/fieldmill.html )

Chris