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Author Topic: DB224 Mounting / Interference  (Read 8722 times)
AF6D
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« on: April 15, 2011, 04:01:27 AM »

Now that the snow has stopped and melted away... we hope.

I have a DB224 that is scheduled to go up in the next week onto an 80 foot guyed tower. I have a 24" standoff kit for it. The original plan was to side-mount the entire antenna but that would lose considerable height. Trees and such. A person sharing the tower has a 440 receive antenna at the top and is concerned that if I mount the DB224 a few feet from his antenna 1) it will get into his 440 machine (even though I have a 440 isolator,) and 2) it will considerably alter his pattern.

Frankly, I don't know the answer.

But looking at the Andrew plots I see that if I side-mount the entire antenna 24" off the flat side of the 12" face tower (EXTREMELY well guyed!) and point all elements in towards the tower I will get a slightly elipitcal pattern but close to omnidirectional. With this said, suppose I compromise and point the bottom two elements towards the tower and the top two out away from the tower -- what kind of pattern should I expect. Should I half side mount but place the elements 90 degrees apart for omni-directional? Or should I say screw it, mount the antenna omnidirectional up along side the 440 antenna. His little dinky 5 footer would be dwarfed by my 24 footer. Smiley Do the dipole loops receive broadside so that if I face the bottom two in towards the tower but bow-tie the top two above the tower...?

I want to play nice.
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N5BEW
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« Reply #1 on: April 15, 2011, 01:12:06 PM »

I prefer not to reinvent the wheel on antenna plots as Andrew/Decibel tested all that out years ago on patterns. If you are seeking the closest thing to an omni pattern point your elements in. Slightly lower on the tower will lessen your lightning exposure a little. Your frequency separation of 440 vs 147 Mhz will help some as far as interference depending on cavities used
etc.
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AF6D
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« Reply #2 on: April 15, 2011, 08:18:05 PM »

Umm.. umm... that didn't really answer my question Sad
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K1CJS
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« Reply #3 on: April 16, 2011, 06:56:06 AM »

The antennas can be mounted at the same height, they just have to be separated by a set distance.  I believe that distance is about six or seven feet.  (has to do with the wavelength)

There are boom kits that can be had that will allow antennas to be top mounted, side by side.  It just depends if the other fellow will agree to it or not.
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AF6D
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« Reply #4 on: April 16, 2011, 02:15:33 PM »

That's an answer I was looking for! The trick is getting the other guy to agree even if I spend the $$$.
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N5NPO
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« Reply #5 on: May 10, 2011, 08:49:25 PM »

If that DB224 is less than 12 years old, you might want to weather proof all the molded joints with scotch-kote before you put it up. They have been having a devil of a time with water getting into the harnesses.
If you decide you are going to mount on the side of the tower and you want the most omni pattern, you should mount the antenna so that no dipole points to the nearesr tower leg. In other words, the closest to pointing at the tower for any of the dipoles is 45 degreess. That seems to give the best results as far as least interference from the tower.
73
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