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Re: Terry's New Plane Wave Antenna



Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>

Dmitry quoted R. Hull:

> Often at 8 feet from the 30 watt coil the voltage slams
> to minus 200 volts (limit of the Keithley in a fraction
> of a second ...

Dmitry wrote:

> how about this?

This is overload of the instrument.  If an input half-cycle
is high enough to activate the instrument's input protection
device (zener, or whatever), then after the pulse is over,
the input circuit will be left with a residual charge of
opposite polarity to the overload, likely to be close to
or exceeding full scale deflection.

Hull:
> ...while the coulombmeter reading takes a few seconds to climb
> to 10^-7 coulombs of collected positive charge on the 12 pf
> sphere.

In this mode the instrument must be grounding the sphere and
integrating the current flowing to ground (otherwise, with
that amount of charge, the sphere would be at several kV,
and the input range is only 100V or so).

Consequently, this is probably a more reliable measurement.
It would be interesting to repeat these experiments, to witness
the space charge collecting on an electrode over a period
of seconds or longer.   Naturally, Terry's plane wave antenna
would make a good charge collector!

Terry wrote:
> my perhaps ill named "plane wave" antenna was meant to pick
> up a large "current area".

And it should work for this collected charge just as well as
for induced charge.

I see the reasoning behind 'plane', and as you say, much better
than a wire electrode from the point of view of source
capacitance.  I can only continue to object to 'wave'.

> Insulators are like batteries

Too right!  In some of my experiments the charge that happens to
reside on the *outside* of the insulated connecting leads of a test
circuit becomes a problem, and I have to switch to using bare wires!

Are we going to see a thread 'How to build an electrometer' now?
--
Paul Nicholson
--