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Friday, January 29, 2010

Quiz Question for Knack Victims

Hey Bill,

I know you have the knack . . . so I'm coming to you.
I've got 31 years of ham radio experience, on top of 16 years experience in the Wireless Telecom industry, that said I have a tech question that has really got me stumped. Maybe the answer is just too obvious.

Here it is: About 2 years ago an electrical engineer/ham radio operator/nuclear engineer threw the following question by me (I've yet to get back to him with my answer). Maybe you, or some of your listeners know the answer.

Knack Question: For yagi antennas only one (yes, sometimes two) element is electrically driven/xmit. Instead, why aren't all of the elements (simultaneously) electrically driven/xmit (vs parasitically driven)? Now the stumper - according to the engineer supposedly the answer excludes the following as the answer(s):

  • Impact to antenna gain,
  • The need to have any type of phasing harness
  • Impact to transmit horizontal beam width (directivity).
Any idea what the answer might be? What am I missing?


  1. It made me think of the HB9CV design. Witch is not a Uda Yadi!
    A beam indeed but based on all elements driven by a phasing harness. Characterized by beaming front to back with deep nulls to the side and also narrower pattern than the Yagi. Therefor I think the third answer does not apply.

  2. The mutual impedance between elements already provides the optimal feed impedance with a simpler design. Phasing harnesses would only make the feed to all elements complex and depending on line balance could contribute to sidelobe production.


  3. Becase a Yagi with all the elements driven is called a log periodic :-) ?


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