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Shorted top turn
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From: Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
Sent: Thursday, February 19, 1998 12:25 PM
To: Tesla List
Subject: Re: Shorted top turn
Gary Johnson wrote:
> To measure the top voltage, I use a capacitor divider inside the coil. I
> lay a conducting lattice over the top of the coil and connect it to the top
> turn, to form the top plate. One or more toroids are placed on top the
> lattice for top loading. The column of air in the coil is the dielectric of
> the high voltage capacitor. The lower plate is a small sphere mounted on a
> metal box centered in the bottom of the coil. The box contains the low end
> capacitor of the divider, a buffer, 9 V batteries, and a fiber optic
> transmitter to send the signal to a matching receiver in the instrument room.
I would try to put the sphere suspended above the coil. Inside it is under
the influence of the electric field of the much closer coil, and very probably
what you measure has little relation with the voltage at the top. The metal
box at the bottom would also act as a short-circuited winding there, and this
position is the worst possible in terms of immunity to interference from the
electromagnetic field generated by the coil in the measuring circuitry.
> Anyhow, what I observed when I shorted the top turn was the following:
> 1. No change in resonant frequency.
Expected.
> 2. Input impedance decreases about 10 percent. With a strong voltage
> source, this means the current and power input increase about 10 percent.
Expected, due to the added (small) load.
> 3. The top voltage increases about 10 percent, maybe even 15 percent.
I would first verify if what is being measured has really some relation to the
top load voltage. This result is really strange.
Antonio Carlos M. de Queiroz
mailto:acmq-at-compuland-dot-com.br
http://www.coe.ufrj.br/~acmq