Re: LF: VLF TX coil ready

[Paul Nicholson <vlf0308@abelian.org>]

Stefan Schäfer schrieb:

> [VLF loading coil] has about 1100 turns. Average diameter is
> about 0,55m, hight about 0,5m.

I ran this info through a modelling program, with a guess that
the wire is 26awg:-

 Ldc: 482mH
 Rdc: 258.3 ohms

Resonances, unloaded, base grounded, stood vertically 10cm
above a good ground with nothing within a few metres:-

 1/4 wave : 46.56 kHz
 3/4 wave: 121.7 kHz
 5/4 wave: 195.5 kHz

Adding a 100m kite, 2m diameter, raised vertically (=560pF) to
the model, I found I needed an extra 70pF of shunt loading to
bring the system into tune.

The system resonances then become:

 1/4 wave:   8.973 kHz
 3/4 wave: 116.3 kHz
 5/4 wave: 185.4 kHz

Hopefully you can seal the coil before the thing warms up and
the turns fall out of place!

> TX power of 200W.

I bet you will need more, eg 500W.   Very hard to predict the
Q factor obtained in the field, but it is always lower than what
you hope it will be!
--
Paul Nicholson
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