What shape should I make the radiator on my yagi?

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mrsvensven

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I'm building a yagi antenna for 800 band. The yagi calculator I used recommended making the radiating element a folded dipole, connected to the coax with a 4:1 coax balun. It also said that it was possible to use a regular dipole connected with a 1:1 balun. This makes sense as a folded dipole has about a 300 ohm impedance and a regular dipole has a 75 ohm impedance. I'm wondering if the other elements change the impedance of the antenna.

If I have a yagi with a folded dipole as the radiator, is it going to have a 300 ohm impedance?

Also, am I going to see any difference between an insulated and non insulated boom?
 
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BKIN

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IMO, I would use the regular dipole if you are going to use insulated elements and/or a non metallic boom.
 

nd5y

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A folded dipole is only 300 ohms and a regular dipole is only 72 ohms in free space away from all other conductive objects.
When you put them in a yagi array or very close to a metal mast like a stacked dipole array, the impedance changes.
As far as I know insulating or directly mounting the elements to the boom mainly affects how long you have to make the elements (the center of a dipole is a low voltage point and can be grounded). The calculator you used should tell you if it is for an insulated boom or not.
 

mrsvensven

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A folded dipole is only 300 ohms and a regular dipole is only 72 ohms in free space away from all other conductive objects.
When you put them in a yagi array or very close to a metal mast like a stacked dipole array, the impedance changes.
As far as I know insulating or directly mounting the elements to the boom mainly affects how long you have to make the elements (the center of a dipole is a low voltage point and can be grounded). The calculator you used should tell you if it is for an insulated boom or not.
That's what I thought, but the calculator confused me by recommending a 4:1 balun as if the impudence was still 300 ohms. Thanks for the clarification. Is a 4:1 coax balun still good enough for a receive only application?

As far as I know insulating or directly mounting the elements to the boom mainly affects how long you have to make the elements (the center of a dipole is a low voltage point and can be grounded). The calculator you used should tell you if it is for an insulated boom or not.
Thanks, that helps. I'm using a non-conductive boom now but I didn't know if I would increase gain by switching to a metallic one.
 
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