Thread: Low VHF antenna designs View Single Post
1-Dec-2019, 6:20 PM   #39
Tim
Senior Member

Join Date: Nov 2014
Location: Acworth, GA
Posts: 238
Quote:
 Originally Posted by eggman531916 So, I've decided to start gathering materials needed for a 5 element Yagi found on the Yagi calculator page that GroundUrMast posted earlier. I decided to go with the folded dipole calculator as well. All to the tune of 86 MHz. Now this causes me to ask a question or two. The main question is, how important is it that I stick to the rod diameter for the folded dipole? It's calling for a diameter just a hair under 1/2" and I was wondering if 3/8 would work just as well? I ask because benders can get a little pricey. Also, I've seen folded dipoles now with both a curve on the end and squared ends. So my next question is, could I just keep the same distances (with the exception of the curves) and simply use 90 degree elbows and square it off? Or, in my ignorance, am I missing something here? Thank you in advance for any wisdom you all can bestow upon me.
I can't answer your question about diameter with a formula or antenna modeling facts, but from practical experience building ham radio antennas, I would suspect that making your tubing diameter smaller would change your resonant frequency by 2 or 3 MHz at a design frequency of 86 MHz and that technically you would have to change the element length a small amount to compensate. It would also technically affect what your spacing should be between elements. From a practical viewpoint, I suspect that it would have very little effect on the performance of your antenna for receiving purposes.

As far as the folded dipole driven element, from a practical perspective I suspect that either curved ends or squared ends will work fine as long as you keep the relative dimensions the same.

Another thought to keep in mind is that an antenna is usually more broad banded when it is constructed of larger diameter elements.

There are many, many variables in yagi antenna design. Someone with antenna modeling software could probably give you some more specific answers than my general ramblings and observations.
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Last edited by Tim; 1-Dec-2019 at 6:24 PM.