Hello Warren,
Am 26.07.2012 19:39, schrieb Warren Ziegler:
Stefan,
I imagine that a LF or VLF small vertical is a relatively high-Q
circuit, how do you manage to keep the kite vertical in resonance and
matched while the kite bounces around in the wind?
Most of the time the kite was quite stable, i.e. the angle and so the C
did not change significantly. The antenna current is stable within a 10%
limit. When the wind was poor in some situations, the kite drops to a
lower angle. Then the falling ERP is rather affected by the lower
effective height than by the changing current. The current (say 1A on
8970 Hz) can easyly drop to 400 mA when the angle changes from 80 deg to
40 deg.
One method is to compensate this by turning the variometer from time to
time or you can use a working point of the variometer that uses a
slightly to low L. Then the antenna current does not reduce when the
kite falls (in certain limits of course). This is the case because the
little generator that i used (up to 550 W RF power in the best times)
can be seen as something like a constant power source. So if the kite
falls then slightly, the working point moves to the peak of the
resonance curve and the rotation speed is somewhat lowered. It was funny
to observe this effect for many hours on the field :-)
But normally the movement of the wire does not strongly change the
antenna current.
OK?
73, Stefan/DK7FC
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