# Folded dipole array question

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#### mvrx

##### Member
Hi guys,

I just got a UHF-DP-ARRAY-4/h antenna (Products) and plan on using it on a UHF DMR repeater. It will be side mounted on a large tower and I want to obtain the widest radius of radiation.

While the "Spacing from mast" is easy to calculate (1/2WL, 1/4WL and 3/8WL @ freq.), I am not sure about "Spacing between dipoles". On the PDF under the "TYPICAL RADIATION PATTERN" the spacing is given as 0.76 or 0.78WL. Searching for info about this type of array but different brands, I saw that the vertical spacing between dipoles is usually stated as 1WL so I'm confused, hence the following questions :

1 - Is the 0.78WL critical? If I get it wrong (.76 vs .78) it will affect the vertical beamwidth only?
2 - 3/8WL for "spacing from mast" vs 1/4WL will give me wider radius but sacrifice some gain?
3 - What about the mast? What should be the optimal distance from the tower?

Thank you!
Raz

#### prcguy

##### Member
If all the dipoles will be lined up facing the same direction you can choose the best spacing from the mast from the mfrs instruction sheet to give whatever pattern is best for you. I usually run this type of antenna in an omni pattern where each dipole is 45deg offset from the next, or imagine the top dipole pointing north, next one down pointing east, next south and bottom pointing west. For that I think 1/4 wavelength spacing from the mast is best.

For omni mode with dipoles arranged around compass headings, I would use an arm off the tower to get the antenna as far as possible away from the tower. 4ft would be the minimum in my opinion and more is better to keep the tower influence down.

For vertical spacing I would use whatever the mfr suggests and it can be critical and affect the vertical pattern and gain. To find .78 wavelength go online to a wavelength calculator, enter your operating frequency to get a length, then multiply by .78 to get your vertical spacing.
prcguy

Hi guys,

I just got a UHF-DP-ARRAY-4/h antenna (Products) and plan on using it on a UHF DMR repeater. It will be side mounted on a large tower and I want to obtain the widest radius of radiation.

While the "Spacing from mast" is easy to calculate (1/2WL, 1/4WL and 3/8WL @ freq.), I am not sure about "Spacing between dipoles". On the PDF under the "TYPICAL RADIATION PATTERN" the spacing is given as 0.76 or 0.78WL. Searching for info about this type of array but different brands, I saw that the vertical spacing between dipoles is usually stated as 1WL so I'm confused, hence the following questions :

1 - Is the 0.78WL critical? If I get it wrong (.76 vs .78) it will affect the vertical beamwidth only?
2 - 3/8WL for "spacing from mast" vs 1/4WL will give me wider radius but sacrifice some gain?
3 - What about the mast? What should be the optimal distance from the tower?

Thank you!
Raz

#### mvrx

##### Member
prcguy thanks! Actually this is the tower :

It's 114ft tall and the antenna will be mounted close to the top, 5ft away from the tower arm.
I don't need an omni pattern since the area behind the tower doesn't matter but the one facing the antenna would be great to have >180 degrees. Dipoles will be arranged all facing the same direction.
For this to be achieved will 3/8WL work better than 1/4WL for the spacing from mast of the dipoles?

Thank you.

#### prcguy

##### Member
Looks like 1/4 wave spacing will give a little more gain across about 150deg swath where 3/8 wave is a little more consistent over 180deg but with a little less gain. Use whatever best fits your needs.
prcguy

prcguy thanks! Actually this is the tower :

It's 114ft tall and the antenna will be mounted close to the top, 5ft away from the tower arm.
I don't need an omni pattern since the area behind the tower doesn't matter but the one facing the antenna would be great to have >180 degrees. Dipoles will be arranged all facing the same direction.
For this to be achieved will 3/8WL work better than 1/4WL for the spacing from mast of the dipoles?

Thank you.

#### mvrx

##### Member
Awesome! Thanks, prcguy

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