Paul, LF,
Tnx for the calculations. Today i again added some turn to the coil. Now it has
L = 550mH, just optimal.
My antenna has C=580pF (measured on 137kHz). When theoretically calculating the
C of a 100m vertical, you achieve almost the same. I measured the resonance
with the DDS-VFO and a series circuit of the L and a C of 570pF (470+100). Now
the resonance is @ 8964 Hz! :-) Q=82 and R(DC) 283 Ohm. Bandwidth is 109 Hz.
Tomorrow i built an additional variometer coil with about 30mH. Then i give the
rest of the wire back to the company where i have got it and have to pay abt 13
Euro/kg, pretty cheep ;-)
Then, in the next days i will apply a Amperemeter for 1A full range into the
coil :-)
About the Q you assumed that it will be worse in the field but i do not so
since if we imagine the stray field of such a coil, it was rather influenced in
the house than later in the field.
BTW, today i tried to vary the resonance by applying a ferrite rod into the
field (0,1m long and 10mm diameter) but almost nothing happend! The dimensions
seem just to be to extreme...
Walter/DJ2LF, don't you want to try to reach Markus' grabber? Would that be a
new record?
A Question to Markus: What about heat problems in your VLF coil? Since the
yoghurt cups are stacked, is there a adequate cooling possible? What could be
the maximum current in your system when increasing the power? You need a PA! ;-)
And: Does anybody of the group want to buy such a kite? A second "kite-station"
would give the chance for a 2 way QSO there! Maybe in good old CW! :-)
73, Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von Paul Nicholson
Gesendet: Mo 08.03.2010 07:57
An: [email protected]
Betreff: Re: LF: VLF TX coil ready
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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