A antenna question

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Re: A antenna question

Post by Admin on Mon May 29, 2017 4:31 pm

I think that was an interesting question, too :-)
When I read John's question I had vision of Mr Bean tying wires together to make a longer one.

I suppose it would work as an antenna, but as you pointed out Ivan, it would be unpredictable. The antenna would become capacitive, so the wire element would have to be lengthened by an unknown amount to make the inductance cancel the capacitance. there would also be phase changes so each bit of wire would be a radiator in its own right, adding other resonances.

I wonder if this technique could be used to make a sort of HF colinear antenna? A centre-fed dipole, the ends lightly capacitively coupled to two end-fed 1/2-wave dipoles? It could be practical for frequencies higher than about 14MHz. I feel an experiment coming on this weekend :-)

Very best regards, and welcome to the forum John. You are the first person to post a message using the new rules.

Very best regards from Harry - SM0VPO - Märsta, Sweden.

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Re: A antenna question

Post by Ivan on Mon May 29, 2017 1:21 pm

Hi John,
to make a small capacitor, it is enough to use a piece of twin wire or to twist two insulated wires together. A capacitor conducts RF, but stops DC. The longer the twisted wire is, the bigger value of the capacitor you get, so you can even tune the circuit by twisting and untwisting the wires. A metal connection must be avoided, as it conducts anything including DC. A knot would make a capacitor, too, but less predictable. And stranded wires will tend to untwist by themselves, therefore avoid them, too.

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A antenna question

Post by Seeker on Sun May 28, 2017 10:12 pm

Hi harry.
I followed you forum for a while but i never joined. I have a question about hf antennas.
In you 20m loop antenna you used a gimmik capacitor by twisting wires together. Does this mean i can just tie short bits of wire together with a knot to make a longer antenna? A capacitor conducts ac and rf so will it work? Or do i have to make a metal connection?
Thanks in advance John

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