Hu Luis,
Am 20.05.2015 18:34, schrieb VIGILANT Luis Fernández:
Hi Stefan
Thank you for your detailed
explanations
I can recycle 16cm diameter PVC
tube. As seen in the calculators and assuming a copper wire with
plastic cover to be 3mm diameter
can wind 300 turns in 90cm
lenght which would be 2.33 mH.
That is not a good dimension. The length of the coil should be about
the diameter of the coil or at least less than 2x the diameter.
A 16 cm PVC tube is a good choice but the 3mm diameter wire is to big.
But of course it is all your decision, i don't want to force you to do
it like i think, i can't do anyway ;-)
That can be a starting point
and the coil should be attached to the bottom support
of the vertical antenna. See and
old picture here showing the setup
Is the mast completely metallic? Or just the first piece? It can be
helpful to lift the coil a bit above the ground, say 50 cm onto non
conducting stuff, to avoid losses. Just leave the tube 50 cm longer
than necessary.
May be 5pF/m is the standard
assumption for a vertical antenna against horizontal ground plane. But
here the counter poise will be different
and probably showing much less
capacity.
Maybe the WX-station in the picture is grounded? It is a good EMC test
if it can handle 5 A of RF current ;-)
Also your horizontal loop can be a part of a counterpoise.
I can use a high voltage
capacitor in parallel with the coil to tune. The variable capacitor I'm
already using with the loop, for
example. Would it make the trick to use a smaller coil ??
It can help in first steps, when you still don't know the actual
resonance point, i.e. if you need more or less L. But in the end you
should have no C in parallel. It won't handle the voltage anyway :-) Of
cource this depends on your RF power.
If C is 55 pF and your losses are 50 Ohm and the power is 50 W, you
will have 6 kV on the antenna.
73, Stefan
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