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AMfone's Online AM Handbook => Antennas => Topic started by: PA0NVD on March 03, 2018, 07:45:44 AM



Title: low radiation angle vertical for 40 and 20
Post by: PA0NVD on March 03, 2018, 07:45:44 AM
I am designing a verical for DX for the 40 and 20 meterband. In order to get a low radiation angle, I decided to use an end fed 1/2 wave vertical. That also solves some problems of big radial fields needed for a 1/4 wave in order to get a good efficiency. The nice fiber poles of Spider beam will be the basis of the antenna. In order to predict the performance, I downloaded MMANA.

But, for 20 there is a problem. it is a full wave vertical and the radiation angle is quite steep, not a good DX antenna at all. So I simulated a non-connected half wave wire for 20 meters along the lower half of the antenna at a distance of 15 cM. That should break-up the antenna in two half wave verticals above each other, a vertical array for 20. And that did the job. MMANA predicted a radiation from 8 degrees to 50 degrees (-3dB) above real ground, almost constant and, 4 dB gain above a 1/2 wave vertical!!
The wire did not influence the 40 meter behavior at all.
At the base of the antenna I will put a box with two parallel resonant circuits and a link to the coax. The band selector just switches the antenna and the coax to the appropriate circuit
When my house is ready, this will be the first antenna I will make, a low cost simple and a nice DX antenna.


Title: Re: low radiation angle vertical for 40 and 20
Post by: KD6VXI on March 03, 2018, 11:57:32 AM
Can you post your mmana files?

I, too, use mmana.

--Shane
KD6VXI


Title: Re: low radiation angle vertical for 40 and 20
Post by: PA0NVD on March 03, 2018, 06:07:44 PM
Here they are.
As you see, I have put a 12 pF in series at the base.
DON'T do that, it just was an experiment
It tunes the antenna for the 20 meterband, but it is better to tune the antenna with the parallel LC circuit. That will give you a higher impedance, less ground current
The LC circuit for 40 should be approx. 90 pF // to 5.5 uH
For 20 meters it should be approx. 50 pF // to 2.2 uH
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