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Re: LF: EA5DOM vertical

To: [email protected]
Subject: Re: LF: EA5DOM vertical
From: DK7FC <[email protected]>
Date: Wed, 20 May 2015 21:56:39 +0200
In-reply-to: <[email protected]cal>
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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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