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Author Topic: DB224e Antenna  (Read 12337 times)
K6ECS
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« on: February 24, 2014, 10:34:06 PM »

I am getting conflicting information regarding the DB224e antenna. I've seen it free standing with all elements pointed in one direction and no tower behind it. Is it directional? Or does it need a tower behind it? If it has no tower behind it and all elements are facing one direction what would the pattern be?

Thank you.
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WB2WIK
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« Reply #1 on: February 25, 2014, 10:14:36 AM »

I've installed several of these over the years, it's an old design.

The DB224e, specifically, has the radiation pattern shown here when all four elements are installed facing the same direction (look under "DB224e" and not "DB224" -- the "e" is "elliptical): http://www.repeater-builder.com/db/pdfs/db-224-data-sheet-%28andrew%29.pdf

The mast that supports the four dipole elements is part of the antenna -- no tower needed behind it.  In fact, most of the ones I've installed were at the tops of towers, not the sides, so the only thing behind the elements was the 20' mast.
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NJ1K
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« Reply #2 on: February 25, 2014, 12:59:07 PM »

Be careful with that E suffix.  A DB-224E means bandwidth is 138-150.  A DB-224E-E means 138-150 eliptical.

Read further down the page Steve sent you to. 
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K6ECS
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« Reply #3 on: February 25, 2014, 04:03:48 PM »

I think you're both dead on! When I called Commscope he told me that I should call a consultant instead of asking him. How rude! He is Tech Support!!! Basic antenna design suggested to me that the mast was the reflector. I like the antennas but I'm not so happy with Tony (?) in support.
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K6ECS
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« Reply #4 on: February 25, 2014, 04:08:02 PM »

By the way, how well do they manage the top of a tower in wind? No snow on this baby but desert winds for sure.
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W9GB
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« Reply #5 on: February 25, 2014, 04:18:01 PM »

Quote
By the way, how well do they manage the top of a tower in wind?
ANY Antenna installation, in a desert environment, should be prepared for:

WIND: Sand Blasting
SUNLIGHT: UV Degradation
WEATHER: Water and Lightning

Yes, antennas taken down, after 10 to 20 years of service (desert environments),
would have pitting on metal (sand blasting) and metal coatings or plating was usually gone.
Professional installs examine these as part of Regular Maintenance (when climber on tower).

Quote
I am getting conflicting information regarding the DB224e antenna.
Sounds like you don't understand the data being presented to you.
Steve, WB2WIK provided the Andrew/Decibel Products DB224 Brochure.

1. You know what a Dipole/Folded Dipole is, and its Classic radiation pattern. That's FCC license material.
2. Are you aware of the Phasing of Identical Dipoles? Antenna Handbooks cover
3. The DB-224 antenna is FOUR Dipoles, In Phase.
4. The Overall Pattern is dependent on the Orientation of those Dipoles (and spacing from mast/tower face).
5. For the Professional / Commercial Radio Tech (and knowledgable Radio Amateur), the antenna can be configured to meet specific geographical  or coverage requirements.
6. In the 1970s, a Radio Amateur had to do these antenna and HAAT calculations for FCC Repeater License Applications (old "WR#xxx" callsigns).
« Last Edit: February 25, 2014, 04:39:06 PM by W9GB » Logged
K6ECS
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« Reply #6 on: February 25, 2014, 05:18:02 PM »

Hmm, I don't see that you've answered my question in any way. That makes me feel bad.
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K6ECS
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« Reply #7 on: February 25, 2014, 05:50:11 PM »

@W9GB,

I understand completely. I understood Tony at Tech Support for Commscope incorrectly tell me that the tower is what provides the pattern. I understood correctly when he told me that I should be calling a two way radio consultant. I Understood completely his abject rudeness just as I understand you telling me that I don't understand the data Steve [provided. You quoted my message written before Steve provided data. In other words, sir, please, lighten up and participate in a meaningful way.

I understood correctly that Tony was wrong.
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WB2WIK
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« Reply #8 on: February 26, 2014, 09:23:40 AM »

Sorry to hear about "Tony."

I have no idea who he is.

Commscope is the "new" DB224 series company, but these are old designs dating back to Decibel Products many years ago and their tech support was very good (way back when).  You could actually talk to the antenna designers!

I'm sure that's not the case today, and the original designer might be dead. Tongue
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AD4U
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« Reply #9 on: February 26, 2014, 11:05:12 AM »

FWIW - At the site where my 146.670 repeater is located there is a DB224 4-bay antenna on top of the tower with the antenna base at 360 ft.  The folded dipole elements are arranged for 360 degree coverage.  My Station Master antenna is side mounted with its base at 340 ft.  

When the tower and radio systems were being put on the air the first time, I wondered if or how much better an antenna on top of the tower would work when compared to my Station Master side mounted some 20 ft lower.

We arranged for several hams located 20-30 miles from the site in all different directions to meet us on the air for the tests.  We first connected my repeater to the side mounted Station Master and the hams listening made signal strength notes.  As quickly as possible (2 minutes maximum) we disconnected my repeater from the side mounted Station Master and connected it to the DB224 4-bay antenna on top of the tower and ran the exact same signal strength tests.

In every case and in every direction the signal from the side mounted Station Master antenna was noticeably stronger.

Of course this was not a perfect comparison between the two antennas and it does not mean that the Station Master is a better antenna than the DB224 types, but I thought the results were interesting.

Dick  AD4U

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K6ECS
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« Reply #10 on: February 26, 2014, 02:47:50 PM »

Dick, that sounds like a perfectly reasonable test! How far away from the tower did you mount for omni coverage? I noted that using the standard 24" side-mount the elements were just too close to the tower.

In our case the valley that we need to cover is about 100 miles of desert and the repeater site is at the far end. I need the cardoid pattern! We've made an agreement with he site owner to mount the DB224 at the ends of the cross arms at 160 ft. and 180 ft. with all elements pointed west. We're hoping for clean 9dB pattern. The tower will be 20-30 feet away from the antenna.
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K6ECS
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« Reply #11 on: March 06, 2014, 03:37:34 PM »

If I may ask, how was your omni-directional performance with the elements spaced around the tower? Was it equal to or better than a Station Master? Or was the Station Master better? I'll switch if I need to. Could the DB224e handle no top support in moderate winds?

Thank you.
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WB2WIK
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« Reply #12 on: March 07, 2014, 11:16:29 AM »

If I may ask, how was your omni-directional performance with the elements spaced around the tower? Was it equal to or better than a Station Master? Or was the Station Master better? I'll switch if I need to. Could the DB224e handle no top support in moderate winds?

Thank you.

The DB224e is rated 80 mph wind survival when self-supporting by only the bottom clamps.  It is normally supplied with a 2" diameter aluminum hollow bar seamless mast with .187" wall thickness at the bottom (where the clamps go) and it's very strong.

I've never used a top support for one, and have installed them atop tall towers in windy areas.  The 80 mph rating is "no ice."  With 1/2" radial ice coating, the "self supporting" wind rating decreases to 55 mph.
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W8JI
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« Reply #13 on: March 08, 2014, 05:19:12 AM »

If I may ask, how was your omni-directional performance with the elements spaced around the tower? Was it equal to or better than a Station Master? Or was the Station Master better? I'll switch if I need to. Could the DB224e handle no top support in moderate winds?

Thank you.

Be really careful with that idea. It is NOT a good idea at all.

If the tower is 15 inches on a face it will put the DB224 elements in spatial phase quadrature. You will have 90 degree shift in the fields between elements. While the azimutal pattern is not bad, the gain goes away pretty fast as the pattern spreads elevation wise. It gets worse with wider face towers, and starts to create nulls.

I have a DB224 above my 318ft tower. The bottom element is below the tower top, and pointed away from the tower. The upper elements fill in the tower and other direction.

Look at the photo:

http://www.w8ji.com/Rohn%2065G%20project.htm
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W8JI
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« Reply #14 on: March 08, 2014, 06:36:10 AM »

If I may ask, how was your omni-directional performance with the elements spaced around the tower? Was it equal to or better than a Station Master? Or was the Station Master better? I'll switch if I need to. Could the DB224e handle no top support in moderate winds?

Thank you.

To expand on this a little, I pulled some old antenna models up from my model archives and ran them.

On a 15 inch wide face triangular tower, staggering the dipoles around the tower reduces gain about 3dB over having the antenna omni and above the tower, or the way I mounted my antenna. It is exactly like I thought, it softens the pattern focus for elevation, so you lose significant collinear gain.

I'm positive it becomes even worse with a larger face.

A collinear is only collinear when the elements are in line on one axis, or nearly so. When you start spreading the axis offset  beyond around 1/8th wave, all sorts of things quickly go wrong very quickly.
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