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Author Topic: Ground plane on top of windom  (Read 1679 times)
KJ6TSX
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Posts: 123




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« on: May 06, 2012, 07:26:29 PM »

I am thinking about installing a windom antenna on my roof at one end of my home would be a 13 foot mast which would be the center of the windom antenna, at the top of the mast would be my ground plane antenna with 4 - 72 inch counterpoises. Will having the counterpoises above my windom antenna cause any problems ?
Thanks
George
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KL3HY
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« Reply #1 on: May 07, 2012, 03:23:03 PM »

When you say Windom, are you talking about an Off-Center Fed Dipole?

I have a similar situation I think--I have an OCF dipole with a Dimond X300A antenna clamped to the top of the same mast as the balun for my dipole.  One of the radials for the X300 is within inches of the shorter leg of my OCF dipole, and I intend to move the dipole to a different mast.

Most of the other folks here have far more antenna experience than I do, so I'll be very curious to hear what they have to say. But in my case I'd like to get at least a couple feet separation, and preferably a lot more which is why I'm moving the dipole balun to a different mast.

Just my $0.02...
Mike
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W5DQ
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« Reply #2 on: May 07, 2012, 04:53:12 PM »

I am thinking about installing a windom antenna on my roof at one end of my home would be a 13 foot mast which would be the center of the windom antenna, at the top of the mast would be my ground plane antenna with 4 - 72 inch counterpoises. Will having the counterpoises above my windom antenna cause any problems ?
Thanks
George

I am assuming the other antenna is a vertical, since it has a counterpoise) and is a tuned antenna so I would think having a tuned antenna close to a OCFD (I am also assuming when you say windom, you 're actually talking about a Off Center Fed Dipole (OCFD) and not a true window which is simply a single wire with a single wire connected at the feedpoint intersection between the horizontal and vertical sections?) would cause some coupling and thereby mess with the radiation pattern and loading. It all depends how far above the OCFD that the couterpoises are. Also are they directly in line with the OCFD wire or perpendicular to it. Parallel will give the greatest amount of coupling, perpendicular the least.

You might want to describe the configuration in a little more detail for a better solution to be provided. Type of roof .. shingle, metal, etc.? What is the frequency of the vertical antenna (what you're calling a ground plane antenna)? How far up the 13' mast is the OCFD (or windom?) connected. What are the two antennas fed with ... coax, open wire, single wire? All this will cause different interactions.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
KJ6TSX
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Posts: 123




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« Reply #3 on: May 14, 2012, 09:24:19 PM »

Quote
You might want to describe the configuration in a little more detail for a better solution to be provided. Type of roof .. shingle, metal, etc.? What is the frequency of the vertical antenna (what you're calling a ground plane antenna)? How far up the 13' mast is the OCFD (or windom?) connected. What are the two antennas fed with ... coax, open wire, single wire? All this will cause different interactions.

First of all THANK YOU for replying.
What I am planning on doing is actually setting up a inverted V off center dipole, the peak of the antenna would be approximately 13 feet above the peak of my roof which is 20 feet high, roof is a pitched roof with composition shingles an a wood frame structure. The short wire would extend about 45 feet to the chimney about 3 feet above the roof, the long wire would slop to the back fence about 12 feet above the ground with approximately 30 feet of the eighty foot actually on top of the fence at 8 foot above the ground. (Currently I have a center-feed dipole wire total length 120 feet stapled to the top of the fence at 8 feet with fair results) The antenna I was thinking of installing above the Inverted V is a Antron 99, 18 foot vertical with 4 - 72 inch counterpoises. The counterpoises slope down approximately 4 feet. I currently have a antenna tuner, antenna are fed with coax, vertical is 11 meters
 I was also considering scrapping the vertical and raising the mast to 17 feet. My favorite frequency is 80 meters but would still like to be able to use 10 meters. Trying to get the biggest bang without upsetting the neighbors
Thanks for all the help
George
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KB4QAA
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« Reply #4 on: May 14, 2012, 11:42:38 PM »

You definitely need at least a few feet between an HF wire antenna and something a big and broad as an Antron.    Those big counterpoises/radials it has are going to interact with the wire antenna.   Two things are likely to occur: distortion of the radiation field and detuning.

I can't give you scientific numbers, but I would want to space them a distance at least equal to the length of the Antron radial length.

I wouldn't be nearly so concerned with a similar setup with perhaps 2m verticals like a Ringo or Hustler G6-144 that have minimal or no radials.

b.

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WX7G
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« Reply #5 on: May 15, 2012, 09:11:47 AM »

I ran a NEC simulation of a 10 meter ground plane with a resonant wire 1' below it. I tried 1/2, 1, and 1-1/2 wavelength wires.

Three is virtually no affect on the Antron. Your setup will work just fine.


   
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W5DQ
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« Reply #6 on: May 15, 2012, 09:18:02 AM »

I agree with 'QAA. With the drooping radials, that could cause problems. Also your far ends of the Inv-Vee are a bit low to the ground for a couple reasons. One, they are too low for safety sake. Depending on the band, the ends could present some high RF voltages and it someone of something contacts them, it could experience some nasty burns. Second, they ends will couple too much into the ground. I'd recommend the ends not be any less than 15 feet from the ground.

On the center of the antenna, 33 feet is acceptable (20 + 13 ft) but for 40, 60 and 80M this will effectively raise the primary take off angle and shorten the coverage distance. It at all possible, try to get it to at least 50'. I know this is much higher than you explained, but the improvement will be worth it. Of course 70 would be even better Smiley

Is there no way to seperate the two antennas or if you haven't acquired the Antron, check out a Ringo Ranger or similar type fed antenna. That style will easily go a couple of feet above an OCFD. One problem to watch is the lever arm torque on the top of the mast of having a long antenna above the last possible guy support. Speaking of guys, if you plan on using them, be sure to use insulators to break up the lengths to avoid coupling to the antenna.

Good Luck. Keep the forum updated as this sort of info helps others to avoid pitfalls and to learn what works.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
W5DQ
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« Reply #7 on: May 15, 2012, 09:21:23 AM »

Sorry I re-read the height info and originally thought it said 3 foot off the ground but it says 8 foot above the fence. With 8 foot and 12 foot above ground ends, that is the minimum I would go. I would still shoot for around 15 ft if possible.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
KJ6TSX
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Posts: 123




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« Reply #8 on: May 15, 2012, 08:11:05 PM »

Quote
I was also considering scrapping the vertical and raising the mast to 17 feet. My favorite frequency is 80 meters but would still like to be able to use 10 meters.

How well do you think the inverted V will work on 10 meters?? I already have the Antron 99 but could possibly find a new home for it if necessary
Thanks
George
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W5DQ
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« Reply #9 on: May 16, 2012, 02:24:12 PM »

I don't think scrapping the 99 isn't really necessary providing you can find an alternate mounting position for it. The main rule of thumb for almost any horizontal (including all variants such as Inv Vee's) is to get it as high as possible, in the clear and unobstructed by any close antennas that could couple to it and distort/disturb the antenna pattern and operations. As some have indicated by modeling your intended setup, there appears to be little to no interaction between the 2 antennas but as is discovered a lot when experimenting with antennas, the proof is in the pudding so put it up and take some measurements to see what level of performance you'll have.

I think you'll find the inv vee will work just fine on 10M. In fact depending on the overall length of the inv vee, you may find on 10M the antenna will exhibit multiple lobes and have a very good coverage both in azimuth and take off angle since you'll have it higher WRT wavelength on 10M than any other band.

Good Luck. If it were me and I could, I'd look for the alternate location away from the inv vee for the Antron to have a second go-to antenna for 10M. One can never have too many antennas.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
KJ6TSX
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Posts: 123




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« Reply #10 on: May 16, 2012, 09:28:00 PM »

Thank You Everyone for your great ideas. I will keep you advised.
Thanks

George
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