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Author Topic: above groung vertical with 1 radial  (Read 3913 times)
AE5EK
Member

Posts: 53




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« on: April 05, 2013, 04:01:47 PM »

From the Stepir site I have read that 2 above ground radials (180 degrees apart) are all that is needed to get a reasonable omni radiation pattern with decent efficiency. 
http://www.steppir.com/wp-content/uploads/2011/10/radial-systems-for-vertical-antennas.pdf
Is this correct?
If I have only 1 radial, this article says that I get a null of 12-15 dB in some direction. Is this true? Do I still get the same max gain in some direction? If so what directions?
Perhaps one could select a single radial depending upon which direction they want to communicate.
I know, lots of questions but good answers come from this forum.

tks

Dennis
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N4JTE
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Posts: 1159




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« Reply #1 on: April 05, 2013, 05:17:52 PM »

N6LF and ON4UN have done extensive studies on a variation of your question.
Lot of factors effect vertical antennas.
BUT one raised radial is gonna be a dissappointment if you expect some directionailty, not to mention the matching impedance at that feedpoint, two is minimum for raised radials in my experiments.
Bob
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K0ZN
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Posts: 1562




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« Reply #2 on: April 05, 2013, 05:24:30 PM »


 A "vertical" with only one radial is a dipole !!    Basically, a dipole with one half of the dipole vertical and the other leg of the dipole horizontal (or whatever....)

 73,  K0ZN
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K0JEG
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Posts: 679




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« Reply #3 on: April 05, 2013, 05:24:42 PM »

I just took down my 28' vertical in a tree. It had 2 18' radials, 180° apart. Connected with a 4:1 UNUN it would tune on any band, and was great at picking up the S9+ powerline noise in the area.
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W6RMK
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Posts: 669




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« Reply #4 on: April 05, 2013, 05:33:08 PM »

Since it's a SteppIR, the "matching" issue isn't a big one.. you just adjust to wherever you get a decent match.

As others pointed out, with one radial, it's basically a V dipole on its side. It won't be particularly directional.  Depending on the height above ground it may or may not be inefficient.

However, it will work.
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AE5EK
Member

Posts: 53




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« Reply #5 on: April 05, 2013, 07:06:34 PM »

I do not care so much about the impedance I see as i can put an SGC tuner right at the feed point. What I care about is the radiation pattern. Has anyone simulated this with EZNEC?

tks
Dennis
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KB4QAA
Member

Posts: 2488




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« Reply #6 on: April 05, 2013, 10:47:04 PM »

From the Stepir site I have read that 2 above ground radials (180 degrees apart) are all that is needed to get a reasonable omni radiation pattern with decent efficiency. 
http://www.steppir.com/wp-content/uploads/2011/10/radial-systems-for-vertical-antennas.pdf
Is this correct?
If I have only 1 radial, this article says that I get a null of 12-15 dB in some direction. Is this true? Do I still get the same max gain in some direction? If so what directions?
Perhaps one could select a single radial depending upon which direction they want to communicate.
I know, lots of questions but good answers come from this forum.

tks

Dennis

I read the literature.  I just modeled it in EZNEC.   20m 1/4wl, 1 radial, elevated 30ft over Real Ground, it shows a slight cardioid pattern with about 5dB of F/B difference.  It's a lumpy cardioid pattern.   Bill
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W5WSS
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Posts: 1782




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« Reply #7 on: April 06, 2013, 05:58:39 AM »

The radiation is combined in the horizontal plane of the horizontal wire and vertical plane of the vertical wire it is a center fed dipole and the earth surface effects the horizontal leg pattern less than the vertical leg pattern.

The antenna can be installed with the feed point at the top and the horizontal leg will present more of it's contribution into lower angles because it is now much higher relatively speaking.

Route the feed line as far as possible at an angle of 45 degrees relative to the two antenna legs.

Yes a top fed inverted L dipole that can be pressed into multi band service as a doublet.
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W7NUW
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Posts: 40




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« Reply #8 on: April 07, 2013, 11:32:24 PM »

I have a one-radial vertical for 40 meters -- vertical element and radial each about 34'. The radial is about 11' off the ground.

At its best take-off angle of 23 degrees, EZNEC models it +1.6 dbi in the direction of the radial, and -1.8 dbi in the opposite direction. Adding a second radial (forming a straight line with the first one) produces an almost uniform pattern in all directions. Steppir is absolutely right.

I realize that anecdotal performance doesn't tell much, but this antenna got me PT0S in an East Coast pileup -- 6300 miles from my QTH near Seattle. This is a very useful antenna when space considerations dictate dimensions, and better for DX than a low dipole. Aim the radial toward where you want most to transmit, if you can.

73, Ken W7NUW

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W5WSS
Member

Posts: 1782




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« Reply #9 on: April 08, 2013, 05:48:34 AM »

Yeah to be a little more specific: the center fed L shaped dipole can be flipped, where everything the feed point, the horizontal wire and the vertical wire Central feed point is together up in the air while the vertical tip is near the ground best to hold the tip height where the tip is out of reach for safety.

This flipping adds height to the entire antenna.

The benefits of the increased height are:

The horizontal leg radiation portion enjoys lowering the power manifested TOA. of the horizontal element.

The vertical leg feed point location is also heightened.
This height increase benefits both parts vertical and horizontal effective radiated power manifested Toa is  lowered.

I have built one and the L dipole/doublet antenna is very good for multi band service is self contained, balanced, and the antenna needs no radial system.

73
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K3VAT
Member

Posts: 760




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« Reply #10 on: April 08, 2013, 07:30:58 PM »

From the Stepir site I have read that 2 above ground radials (180 degrees apart) are all that is needed to get a reasonable omni radiation pattern with decent efficiency. 
http://www.steppir.com/wp-content/uploads/2011/10/radial-systems-for-vertical-antennas.pdf
Is this correct? If I have only 1 radial, this article says that I get a null of 12-15 dB in some direction. Is this true? Do I still get the same max gain in some direction? If so what directions? Perhaps one could select a single radial depending upon which direction they want to communicate. I know, lots of questions but good answers come from this forum.
tks Dennis

I agree with N4JTE on this one: "N6LF and ON4UN have done extensive studies on a variation of your question.
Lot of factors effect vertical antennas.  BUT one raised radial is gonna be a disappointment if you expect some directionalty, not to mention the matching impedance at that feedpoint, two is minimum for raised radials in my experiments."

N6LF specifically has mentioned the need for at least 4 or better yet 8 elevated radials to get 'decent performance'.  See his website: http://www.antennasbyn6lf.com/ you'll have to scroll around to find the articles (they exist in several places).  The amount of 'return current' captured by one elevated radial is only a minimum amount, perhaps less than 10%. As Bob inferred, there are lots of other factors to consider such as near and far field ground condx; proximity to nearby objects, and height of elevated radial system above ground.

GL, 73, Rich, K3VAT

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VE3WMB
Member

Posts: 290




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« Reply #11 on: April 08, 2013, 08:54:39 PM »

This antenna idea has been around for a while and it is sometimes referred to an "up and outer",
especially if it is non-resonant and fed with parallel feeder. Normally when it is resonant it is
called an "L" or L-dipole. 

It will give you some directivity in the direction that the horizontal leg is pointing and it does have both horizontal and vertical polarization so it can be very useful at times when the band is changing. 
The key thing is that the horizontal leg needs to be off of the
ground, both for safety and to minimize ground losses but it does not have to be too far off of the ground.
I have a 30m L up at the moment, fed with Twinlead and it works quite well on 40m through 20m with the horizontal leg about 7 feet off of the ground.  This is reasonable alternative to a vertical dipole when
you can't get enough height.  Older versions of the ARRL antenna book suggest about 30 ft for both legs
fed with ladder line for multiband coverage from 40m through 20n (I have a one from the late 1970s that includes this antenna, but it is omitted from later revisions).  Like any antenna if you can get it up higher
it will perform better and provide a lower takeoff angle for the horizontally polarized component.

Cheers

Michael VE3WMB

P.S. And yes 2 elevated radials will give you an omni-directional pattern.  With sloping radials it is sometimes called a "Wye" or inverted Y, for obvious reasons and if you can elevate it,
it will most often outperform a ground-mounted vertical (unless you have a lot of ground radials down).

From the Stepir site I have read that 2 above ground radials (180 degrees apart) are all that is needed to get a reasonable omni radiation pattern with decent efficiency. 
http://www.steppir.com/wp-content/uploads/2011/10/radial-systems-for-vertical-antennas.pdf
Is this correct?
If I have only 1 radial, this article says that I get a null of 12-15 dB in some direction. Is this true? Do I still get the same max gain in some direction? If so what directions?
Perhaps one could select a single radial depending upon which direction they want to communicate.
I know, lots of questions but good answers come from this forum.

tks

Dennis

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W5WSS
Member

Posts: 1782




Ignore
« Reply #12 on: April 09, 2013, 05:45:45 AM »

Hello Ve3wmb yes well said. May I expound? I also built a wire mono band version of the Wye for 15m from a summer cottage in Tn, fed with 52 ohm coaxial feedline and it tuned very well, worked excellently from a feed point base height of about 30ft hanging from a large tree branch.All the strain was on the rope not the antenna where the vertical part was attached to as well as either radial.
The two sloping tuned and elevated radials were set at an angle of about 45 degrees traveling away from each other in opposite directions relative to the feed point and held taught with Dacron rope and insulated anchors.they were resonated indecently and determined to be optimum after some field strength measurements. The sloped tuned radials working in conjunction with the antenna vertical portion may be viewed as a center fed dipole because the feed point sets the definition from a central position and where the two tuned elevated sloping radials are radiating and contributing to the far Field sum.measured as a total ERP.
The best explanation for a better understanding of what is really defining the antenna is when we view the two actively contributing sloped radials as a sub division of the second half of a dipole split into to two equal parts. Yes a variation of a dipole and whats better is that the antenna has the potential of producing more effective radiated power manifested in the vertical plane and omni directional.than a ground plane Yes a very good antenna probably better than a ground plane that uses horizontal radials since they cancel each other and do not contribute to power transferred into the environment.except indirectly by virtue of the fact that they complete the vertical leaving the entire  burden of radiated power to it.
I like the antenna.
73
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W5WSS
Member

Posts: 1782




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« Reply #13 on: April 09, 2013, 05:48:21 AM »

Typo They were resonated independently Smiley
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W5WSS
Member

Posts: 1782




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« Reply #14 on: April 09, 2013, 06:15:03 AM »

One may ask why use two  sloped at an angle of 45 degrees when one could use just one single leg dropped straight downwards and build an elevated vertical dipole?

When we feed the mono band vertical dipole we must address the system balance that is effedted by the presence of a third conductor within the coaxial line We should not route the coaxial feedline parallel to the antennas leg,We are required to specific routing anglesaway from the antenna leg of the coaxial feed line to combat the introduction of shielding conductor becoming part of the antenna rather than a feedline conduit.
The best solution for common mode displacement currents is to use two or 4 or 6 or 8 of these sloped radials symmetrically positioned equally equidistant relative to the entire circle around the central hub of the feed position.
I made an RF choke a mono band RF choke that was wrappeed and held side to side with allot of Teflon Tye wraps.
 This 45 degree angle spreading of the two radials allowed the feedline to travel straight down from the choke to the earth and travel along the earth surface no common mode issues.



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