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AM Directional Antenna Folks

Ai4i

Ai4i

Curious about WVOI's day and night patterns, I looked at the R-L maps, the FCC tables and polar plots, and especially the Google Earth sat views.
All four elements are used for both patterns and all four are fed with fairly close current ratios on both patterns.
The ref tower has the highest current ratio in the day (typical), but the lowest at night (atypical).
From tower one, two is southeast, four is northwest, and three is almost due north.
Neither in-line nor parallelogram, what kind of array is this?
Was each tower positioned from on a pair of computer graphs so complicated that it could never have been done manually?
 
ai4i said:
Curious about WVOI's day and night patterns, I looked at the R-L maps, the FCC tables and polar plots, and especially the Google Earth sat views.
All four elements are used for both patterns and all four are fed with fairly close current ratios on both patterns.
The ref tower has the highest current ratio in the day (typical), but the lowest at night (atypical).
From tower one, two is southeast, four is northwest, and three is almost due north.
Neither in-line nor parallelogram, what kind of array is this?
Was each tower positioned from on a pair of computer graphs so complicated that it could never have been done manually?
Click to expand...
Just a thought.

The property was chosen because of its proximity to the City of License. It would spray its signal West over the COL and out to sea. Placement would make it a little easier to increase the signal without interfering with other station in the intended direction. Plus, the property was cheap.

The antenna positions would be aligned to allow for the pattern to accomplish that.

Jeff in Sa-ra-so-ta!
 
Considering that they're throwing most of their signal into the Gulf (and what's left into the Everglades), wouldn't they be better off with 100 watts non-directional (if they could get the authorization)?
 
dwtpa97 said:
Considering that they're throwing most of their signal into the Gulf (and what's left into the Everglades), wouldn't they be better off with 100 watts non-directional (if they could get the authorization)?
Click to expand...
Is Cuban interference a factor?

Jeff in Sa-ra-so-ta!
 
"Is Cuban interference a factor?"

I doubt that it would be a factor on this frequency. Even with 100KW, daytime coverage from Cuba probably wouldn't reach Key West.

"All four elements are used for both patterns and all four are fed with fairly close current ratios on both patterns.
The ref tower has the highest current ratio in the day (typical), but the lowest at night (atypical)."

Many directional patterns which use more than two towers can be created with at least two phase/ratio combinations.
It has been my experience that the design Engineer will choose the phase/ratio combination which is likely to be more stable.
Under most circumstances, the chosen design will avoid a situation where one or more towers has an impedance which is close to zero ohms.
A very low impedance tower can make the pattern unstable if the tower impedance "wobbles" only slightly.
 
Checking Cavell Mertz, the WVOI array appears to be a parallelogram. There are three basic arrays. Inline, dogleg and parallelogram. While at first glance it appears to be a dogleg, it is actually a "double dogleg". Anything that isn't inline or a true dogleg is considered to be a "parallelogram".

I agree with frankberry's above post on very low tower impedance and stability.

Hope that helps!

-
 
frankberry said:
The array is called a "Dog Leg."
Click to expand...
This is the answer I was looking for.
iyiyi said:
...the WVOI array appears to be a parallelogram.
Click to expand...
Looks nothing like a parallelogram in that no two elements are parallel with the other two.

I do not know what a "true" dogleg is.
Why then are the vast majority of arrays laid out with perfectly spaced elements in either a line or parallelogram?
I understand about positioning lobes and nulls by phasing and current ratios and that an in-line array has the major disadvantage of being perfectly symetrical on both sides.
 
A three tower array can only be an inline or a dogleg. Example: 1260 Boston, MA has three towers located in Quincy. They "appear" to be an inline but either end tower is about 4 degrees off the azimuth of the other two. It is actually a dogleg.

If WVOI had three towers inline and the fourth is on any angle off the azimuth of the other three, it would be a dogleg. If WVOI had two towers on one azimuth and the other two towers were inline and bisect on any angle to the first two, it would be a dogleg.

Four or more towers in any configuration other than described above is considered a "parallelogram", even though they look nothing like the dictionary definition of a parallelogram.

The crazy tower layouts really came into practice when computer programs started calculating the best possible signal coverage and powers from whatever sites are practical and/or available. I believe that you will discover that the vast majority of oddball arrays have been constructed within the last 25 years. Since the FCC began allowing "designer" powers like 7.4kW or 3.5kW and stations to be "shoehorned" into the clear channels.

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I was at a station which had three towers perfectly lined up plus a fourth tower in the rear slightly off to one side.
I would assume that layout was to concentrate the beam in one direction and move the null in the back over to one side...maybe ???
 
I suggest FCCInfo.com. Enter the call letters and the search should give you the antenna array orientation and the theoretical antenna pattern.

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I agree with iyiyi.
It's absolutely impossible to know the station's directional pattern based solely on the number and position of the towers.
Perhaps the station uses a different combination of towers for each mode of operation.
 
Here's a good one for you. Four class B stations, all running DA-2 patterns, diplexed into one 7 tower array! They are: WXYG 540, WBHR 660, WVAL 800 and WMIN 1010 -- all serving St. Cloud, MN. They are all licensed, on the air and sounding good. Designed and built by an incredible AM genius. How he did it is way over my head. Run a FCCInfo.com on tower orientation and theoretical pattern for all four stations' day and night operations. That should keep you occupied trying to figure it all out for quite awhile!

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He did it using all series networks! Go to "The Virtual Engineer" website. Enter the AM forum and go to page 3. Scroll down a bit until you see the "7 tower DA quad-plex thread". Enjoy!

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Wow, but the performance has to be nothing more than acceptable, maybe just tolerable.
Nice thing about the HI state is that unless things have changed, only one DA in the whole state, and even it is or was just a DA-1. So, I guess multiplexing AM's all omni would not be toooo dissimilar from multiplexing FM's except for the L & C values.

And NO, there is no way to do anything more than guess a pattern unless one knows the currents and phases to each tower.
 
Regarding WVOI... When it signed on in the 70's, it was a daytimer on 1510 with the towers arranged in a parallelogram. At that time, the signal was good in Naples, as well as over Marco. In the early 80's, a decision was made to try for a 24-hour license. Because of WLAC, 1510 was not an option. 1480 allowed for full-time broadcasting, plus the added benefit was the ability to re-use many 1510 components. However, tower 4 had to be relocated from across from tower 2 to a point roughly west of tower 1. Because of a 1480 in Mobile, a 1480 in Arcadia, and a 1490 in Immokalee, the pattern had to be attenuated to most of the north. In reality, the night pattern covers better than the day pattern, and during a period when 1490 was dark, WVOI (then WODX) was operated on the night pattern 24/7. Not an FCC decision, BTW.

In 1999, WMIB (now WCNZ) was built on 1660 using tower 4 (the westernmost tower of the three roughly in line). It was quite a challenge and a learning experience building that setup. I was glad to have been a part of that.
 
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