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Author Topic: At what height does a ground level install turn into an elevated install?  (Read 1719 times)
KF7NUA
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« on: April 09, 2013, 08:41:40 AM »

This is something I still have not found a definate answer too.
This is pertaining to vertical antennas, in my case a S9V 31ft.
When you read about mounting or installing antennas, at what height does a ground level install turn to elevated install with elevated radials? Is it 1', 2' or Huh??
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WB2WIK
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« Reply #1 on: April 09, 2013, 09:26:03 AM »

It's not a number of feet, it's a percentage of wavelength.

Normally about 1/10-WL above earth is where "elevated" comes into play.

That's obviously only about three feet on 10m, but about 26' on 80m.
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KF7NUA
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« Reply #2 on: April 09, 2013, 09:55:49 AM »

Here is what is confusing, if it is 1/10 - WL as you say, a multiband antenna at 5-8ft off the ground should have both ground and elevated radials!

In my case I want to use a S9v 31' as a monople antenna,  and do a A/B comparrison with an R7 I also have mounted in my yard. I am not too happy with the R7 on 40m, the rest of the band is fine.
I am not sure which way to install it, I would like to use the least amount of radials as possible and still perform better than R7. I was not sure if mounting it 3-4ft off the ground meant it would be considered an elevated antenna which would need elevated radials.
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KB4QAA
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« Reply #3 on: April 09, 2013, 10:21:01 AM »

You are getting carried away in wanting absolute definitions with absolute rules of installation and then mixing and matching situations.

-If radials are not in contact with the ground, they are elevated

-If the antenna is not in close proximity to the ground it is elevated

*If an antenna and/or the radials are raised 1 inch above ground does the performance of the antenna dramatically change?   No.
 
*Do rules about the number of radials required dramatically change?  No.  It's not cut and dried that this '1 inch elevated antenna' now only requires two resonant radials per band, whereas 1 inch lower and it need 36 radials for optimum performance. 
 
It's relative.  The lower the antenna system, the more it is affected by earth. The higher it is the more it performs like an antenna system in free space.
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KF7NUA
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« Reply #4 on: April 09, 2013, 10:39:26 AM »

You are getting carried away in wanting absolute definitions with absolute rules of installation and then mixing and matching situations.

-If radials are not in contact with the ground, they are elevated

-If the antenna is not in close proximity to the ground it is elevated

*If an antenna and/or the radials are raised 1 inch above ground does the performance of the antenna dramatically change?   No.
 
*Do rules about the number of radials required dramatically change?  No.  It's not cut and dried that this '1 inch elevated antenna' now only requires two resonant radials per band, whereas 1 inch lower and it need 36 radials for optimum performance. 
 
It's relative.  The lower the antenna system, the more it is affected by earth. The higher it is the more it performs like an antenna system in free space.

Thank you, the way you explained it I can understand.....

Just to see what happens I guess what I will try is I will mount it about 3-4ft above ground and try it with 4 elevated radials, then try it at the same height and drop the 4 radials to lay on the ground.

thank you again
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RFRY
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« Reply #5 on: April 09, 2013, 10:51:48 AM »

Quote
It's not a number of feet, it's a percentage of wavelength.  Normally about 1/10-WL above earth is where "elevated" comes into play. That's obviously only about three feet on 10m, but about 26' on 80m.

Just to note that there are several AM broadcast stations in the U.S. using two or three pairs of elevated, horizontal radials installed 15 feet or less above the earth.  These systems radiate as efficiently as if they were using 120 x 1/4-wave buried radials.

Even at 1700 kHz, 15 feet is only about 9.3 degrees (0.0259 wavelengths).

Quote
Just to see what happens I guess what I will try is I will mount it about 3-4ft above ground and try it with 4 elevated radials, then try it at the same height and drop the 4 radials to lay on the ground.

Radial wires lying on the earth will have much different characteristics than when they are elevated several feet above the earth.  It will take more and longer wires lying on the surface of the earth for the antenna system to approach the radiation efficiency it can have when driven against just four elevated, 1/4-wave, horizontal radials installed at 90-degree intervals.

R. Fry
« Last Edit: April 09, 2013, 10:59:29 AM by RFRY » Logged
W5WSS
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« Reply #6 on: April 11, 2013, 07:50:30 PM »

Rfry hello that is exactly correct. I added symmetrically oriented and elevated pairs of tuned radials to my 1/4 wave to 5/8 wire vertical antenna only pressed and operated at a frequency that held the percentage to the 1/4 wave  5/8 wavelength range for excellent dx work. Yes sloped radials downwards from the feed point junction held at 5ft base height=and isolated all of them from dc earth using non conductive stakes.

An auto tuner was located at the antenna base

Strain relief was located at the feed point junction and a wander lead was utilized for earthing when away or thunderstorm potential.

Field strength measurements were evaluated and found to be proper.

These techniques are excellent and valid and incidentally the station safety ground was connected to the ac mains not to another ground rod so that a gradient potential and minimal inductance to be exposed by a lightning stroke.

This antenna was balanced and very quiet signal to noise ratio excellent and erp manifested power in the lower toa.

Loved it! 73
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W5WSS
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« Reply #7 on: April 11, 2013, 07:55:43 PM »

Tuned, symmetrically routed, sloped, Pairs (per band) radials
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KF7NUA
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« Reply #8 on: April 11, 2013, 09:59:54 PM »

thank you all for the information.... I am gathering the pieces together to try this out.   
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W4VKU
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Posts: 342




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« Reply #9 on: April 12, 2013, 05:53:40 AM »

I have seen Rudy Severns article and it states that, if the radials are attached to the vertical a few feet off the
ground and is in the shape of a gull-wing configuration, with the ends raising up to several feet, then it does not
couple to the ground.

The catch is, this is good for a mono-band vertical. For a multi-band vertical, this is an exercise in frustration
to get it all tuned up. Atleast, i found it that way for a butternut HF-9V several years ago. Since you have more
 parameters to adjust with 4 elevated radials per band.

Good luck
Krish
w4vku
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N6SBN
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« Reply #10 on: April 12, 2013, 09:47:11 PM »

  My S-9 V-31 is mounted on a pipe, attached to the side of the house.  The antenna is above the roof approximately 3'.  The overall height is approximately 18'.   The advantage to having the antenna up high is that my radials are up on the roof, out of the way.  AND, they can slope downward a bit, which lowers the feed point impedance to 50 ohms.  My strongest contacts are always on the other side of the country and Japan.    To improve matters, I put an SGC 237 at the antenna feed point.  Now, I have less RFI coming down the coax.  For my very small lot, I believe this is the best I can do. 

  Oh,  I painted the antenna sky blue and it's nearly invisible to the neighbors.

  The antenna held up well when we had 70 mph winds last week.   The antenna looked like a large fishing rod catching a large Salmon.  The tip was bent clear over.
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KH2G
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« Reply #11 on: April 15, 2013, 12:22:21 PM »

The answer to this question would depend primarily on the soil conductivity. As someone wrote previously, the minute you raise it above ground, it would technically be an elevated radial. The type antenna also matters as in is it a vertical antenna or a vertically polarized dipole.
Regards, Dick
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W4VR
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« Reply #12 on: April 15, 2013, 01:45:18 PM »

That's a loaded question.  Try the website below for possible answers.

http://www.antennasbyn6lf.com/2012/02/elevated-radial-ground-systems-some-cautions.html
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