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Author Topic: Yagi Design Does it work?  (Read 876 times)
KC0FDE
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Posts: 122




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« on: May 14, 2003, 05:03:03 PM »

I was using yagi max the other night playing around with antenna designs for a basic 3 element yagi for 2 meters. However,I have found that I guess I am not sure how to tell when looking at the antenna on the E plane if it is a good design or not. Which plane is the best to look at when deciding if you deminsions are the best? The H plane or the E plane? Since I wasnt sure I just went to look at the 3d plot of the antenna on a free space design. As far as I can read the plane graph I just look at the normalized dbi gain that the program shows and decide from there if my antenna is good. I wish I had a photo of what a good plane looks like for a 3 element gain. Someone clear me up on this please oh btw the design shows it normalizes at 8.58dbi gain. Here is how the program shows the antenna to look at various frequencies...

Freq.     Gain (Dbi)   F/B (Db)   Impendance
146.000   8.58       11.72     33.41+j46.72
146.500   8.59       11.32     33.91+j50.93
147.000   8.60       10.96     34.39+j55.23


Ps. So far the antenna design is using .1875" diameter elements the boom is 3 foot long the reflector is 40" back 16 inches from that is the driven element that is 39" and 22" back from that is the director which is 35 inches long. I want to keep the element diameter but if my design isnt functional from the numbers I gave how far then should each element be spaced from the reflector and how long should each be? Thanks.
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K5DVW
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Posts: 2193




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« Reply #1 on: May 14, 2003, 05:18:39 PM »

Here is a website that you might want to read on 3 element yagi design.

http://www.cebik.com/3lyg2.html
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AC5E
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Posts: 3585




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« Reply #2 on: May 14, 2003, 10:38:32 PM »

Let me put it this way - the numbers you quote are pretty much typical of a decent 3L Yagi design. The tradeoffs from where you are are slightly more gain, slightly better F/B, and feedpoint impedance.

Of the three,  feedpoint impedance is probably the most important - because a little more gain or slightly more F/B are nice but if you cannot obtain a reasonable match to the feedline you essentially have a dummy load.

So plan on building it just the way you have it but before you build it research how you are going to feed it.

73  Pete Allen  AC5E
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