VHF yagi

[Planeguysexploration]

Put thus thing together in less than 30 minutes, works great. Just got to find a place to store it.

 

[Ubbe]

It looks as if you have connected both the left and right dipole element to the center lead of the coax and nothing to the braid. They work in opposite phases to each other so it will probably work even better if you pull out one of the elements and instead attach to the ground of that T adapter. Then you'll have to use a balun or ferrite cores over the coax to stop the coax from being the antenna.

/Ubbe

 

[prcguy]

Seeing that makes me wonder what else might be overlooked. Like where did the dimensions and spacing for the elements come from?

When you have two similar elements connected to the same feedpoint but running in opposite directions it cancels radiation. That antenna should be very quiet.

It looks as if you have connected both the left and right dipole element to the center lead of the coax and nothing to the braid. They work in opposite phases to each other so it will probably work even better if you pull out one of the elements and instead attach to the ground of that T adapter. Then you'll have to use a balun or ferrite cores over the coax to stop the coax from being the antenna.

/Ubbe

 

[Planeguysexploration]

Off of some calculator online, I'll try to fix the feed problem

 

[Planeguysexploration]

Off of some calculator online, I'll try to fix the feed problem

Te calculator was KN9B-YAGI

 

[Planeguysexploration]

In fact, I think I will change the driver element to a folded dipole, I have some 4/1 balums around that should work.

 

[KB4MSZ]

Here is the feed point of a design I use for experimentation. One model is shown with a full render, the other is in transparency view. My connectors are different, but the concept is the same. On the SO-239 connector you will see the brass rod soldered to the center conductor and turning 90 degrees to continue to the end of the element. The other side of the dipole has a lug soldered to it, and it in turn is bolted through the PVC fitting to the body of the SO-239 connector to achieve the counterpoise for the driven element (the machine screw is not shown, I didn't feel like creating it in AutoCAD at the time).

 

[Planeguysexploration]

Here is the feed point of a design I use for experimentation. One model is shown with a full render, the other is in transparency view. My connectors are different, but the concept is the same. On the SO-239 connector you will see the brass rod soldered to the center conductor and turning 90 degrees to continue to the end of the element. The other side of the dipole has a lug soldered to it, and it in turn is bolted through the PVC fitting to the body of the SO-239 connector to achieve the counterpoise for the driven element (the machine screw is not shown, I didn't feel like creating it in AutoCAD at the time).

View attachment 120625View attachment 120626

I have some SO 239s, I'll try this out

 

[Ubbe]

In fact, I think I will change the driver element to a folded dipole, I have some 4/1 baluns around that should work.

That's probably the best solution for you. 4:1 baluns are the ones in TV antennas that has folded dipoles.

/Ubbe

 

[Planeguysexploration]

I have decided to go with the folded dipole with the 4 to 1 balun, I was wondering is I would need to adjust the directors and reflector At all with this being folded, the yagi was built for 160MHz as is the folded dipole. Could I just attach the folded in place of the old driver element or is some adjustment required?

 

[prcguy]

How did you determine the size and shape of the folded dipole? Do you have a way to check for resonance or VSWR? If its the correct size and resonant for your frequency it should work fine in place of a regular dipole driven element.

I have decided to go with the folded dipole with the 4 to 1 balun, I was wondering is I would need to adjust the directors and reflector At all with this being folded, the yagi was built for 160MHz as is the folded dipole. Could I just attach the folded in place of the old driver element or is some adjustment required?
View attachment 120631View attachment 120632

 

[Planeguysexploration]

To determine the size I compared the results of various calculators and did some math on my own, I do not have a way to check resonance or VSWR but I hope that the math is somewhere in the ballpark, as I only plan to RX on this anyway.

 

[prcguy]

I would stick to the Yagi calculators original dipole size, it should be close and easy to duplicate.

To determine the size I compared the results of various calculators and did some math on my own, I do not have a way to check resonance or VSWR but I hope that the math is somewhere in the ballpark, as I only plan to RX on this anyway.

 

[MDScanFan]

One thing you have to watch out for is the electrical length of bare wire vs wire that is coated. Looks like you are using coated. The online calculators are likely using bare metal. When using coated wire the length of the element will need to be shortened vs bare metal.

 

[Ubbe]

...is some adjustment required?
View attachment 120631

It's too high. Make it 2 inch between the bottom and upper part. I've also seen that folded dipoles sometimes are not exactly in line with the other directors and reflector elements. Best thing would be if you could just hold the balun and move the dipole vertically and try and find maximum signal level. You could at the same time move it along the boom forward and back to find a maximum.

/Ubbe