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HF Helical Antennas: Theory and Practice

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ANTENTOP- 01- 2020, # 024

HF Helical Antennas: Theory and Practice

 

 

First bottle is original. Second bottle has removed upper part. The first original bottle is inserted to the second one with removed upper part. First and second bottles are fastened with wide scotch. Then the part inserted in the third bottle with removed upper part and so on. It is very desirable to tie each part of the form with a strong synthetic rope, stretched inside the bottles. This synthetic rope serves for installation of the antenna. The helical antenna may hang up with the rope. I did form in 5 meter length from these plastic bottles.

 

While my experiments with helical antennas I used the bottle to make a form as a temporary experimental one with short lifetime. However, one experimented helical antenna with the bottle form was live during seven years. The antenna was installed in the closed balcony and when it was removed the antenna still was fully operated...

 

Operation of Helical Antenna at Open Air

 

Helical antenna does not like open air. It is high Q antenna and any disturbing effect on the antenna, whether it is mechanical or atmospheric, can lead to complete loss of the antenna's performance on the desired band. Therefore, helical antenna should be protected from any disturbing influences.

 

What may happen with helical antenna placed outdoor? As result of exposure to the helical antenna of snow, rain, low and high temperatures, the main resonance frequency of the helical antenna may move outside the operation range of the antenna. Snow, fog, moisture from rain that covered the antenna may be lowered Q of the antenna and result of it the antenna would be not operated on the second or third harmonic and main resonant frequency may be moved unpredictably.

 

Helical antennas should be protected from such atmospheric influences. Better place the helical antenna inside- to the attic or balcony closed by windows. If the helical antenna should work at outdoor condition use design of the antenna that not exposed much by the atmospheric conditions. Follow by simple rules that placed below.

Picture 14 Experimental Helical Antenna for the 40- meter Band Made on the Form from Empty Bottles

 

Helical antenna should have large diameter of the form. Form should be ribbed to exclude the possibility of collecting moisture and snow on the form. Wire for the helical antenna should have large diameter and was fastened to the form. Helical antenna should have minimal possible shortened factor. Helical antennas with small shortening factor do not so influenced compare to helical antennas with high shortening factor.

 

Conclusion:

 

That is it. I write of here all information on the helical antennas that I have got in my experimenters. Good- or not good, right- or not right... Every one may prove it and add own practice to building of the helical antennas. Yes, a little practice better then big theory.

 

73!

Igor, VA3ZNW 

 

 

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January 30, 2021 15:22

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