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Author Topic: Vertical Antennas - Do Radials Radiate?  (Read 5110 times)
G0GQK
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« Reply #30 on: December 03, 2008, 01:41:25 PM »

If you feed a dipole with RF both legs radiate. If the same dipole is made into an inverted v both legs radiate. If the dipole is formed into an inverted L both hegs radiate and if you push one up in the air and one parallel to the ground it will radiate, so the answer is yes. The more that are installed the less that is radiated from them

G0GQK
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QRZDXR2
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« Reply #31 on: December 14, 2008, 10:55:37 AM »

Well they are the other side of the antenna.  So if they are not cut right the vertical will not be resonate.  Thus, one could say... YES they are part of the antenna system and represent the other half of the vertical.  Do they radiate?  Well does any gounded side of a dipole or other thing radiate?  

One needs to picture the antenna in that what we call the driven element of the vertical as being the Negative side of the battery... and the radials as being the positive side... thus the field will flow from the vertical to the ground plane.  However this is RF which is a higher form of AC and so the field is reversing by the rate of frequency.  Thus, as it does it creates a distrubance in the magnetic/electric field generated in the pool of ether...  Like a rock in the pond.. the waves travel outward from the vertical point of generation.

One also needs to remember that the ground plane side of the vertical has other issues with the elements which it is around.   If we have our transmitter grounded then not only will the ground plane of wire we string (which we hope has less resistance than other things so that our field only sees them--(path of least resistance)   In the real world that is dreaming.  The chain link fence, the sprinkler plumbing (if metal) and a whole list of other things actually come into play.  (let alone the surface skin effect on the frequency we genarate as we approch VHF/UHF)

So in short .. yes the ground plane of the vertical antenna does provide the other half.  thus they do have to resonate and as such then by deduction-- do radiate from their surface to the driven vertical element direction only.  (one can think of it as a big electrostatic cloud that forms from the vertical element to the ground plane attached only.. it does not have a mirror immage below the ground plane wires.

 One than can ask... well does any one of the ground radials have more attraction than another to the vertical element.  Answer:  Yes as we can never duplicate the lenght, its angular distance or makeup of the radial elements. Thus one element of the ground plane could in fact have more influance (resonancy lower resistance/impeadance)  than another.. but remember .. at what frequency?  It is always changing thus so also would the resonance of the radials and inversly the favored radial element would be changing with frequency.

so to answer your question in simple words.. YES the radials are the other half of the antenna.   But remember they are conditional on placement and influances from the common grounding of your radio.

 
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WE5I
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« Reply #32 on: March 04, 2009, 07:10:02 AM »

Is it fair to say that radials are the "CAUSE" of radiation rather than the "SOURCE" of radiation?

Graham Welch - WE5I
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W5DXP
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« Reply #33 on: March 04, 2009, 11:05:35 AM »

> G0GQK wrote: If you feed a dipole with RF both legs radiate. <

Point is that the currents in the two legs of a horizontal dipole are spacially in phase and constructively interfere (reinforce) in the far field broadside to the dipole yielding 2.14 dBi broadside gain in free space. Cancellation occurs off the ends.

The currents in two opposing horizontal radials are spacially 180 degrees out of phase and destructively interfere (cancel) in the far field broadside to the radials yielding -xx dBi broadside gain in free space, the opposite of a dipole. Reinforcement occurs off the ends, the opposite of a dipole.

A radiating 2x1/4WL dipole is 180 degrees different from 2x1/4WL opposing radials, i.e. they could hardly be any more different. Please do not confuse those two completely different configurations.
--
73, Cecil, w5dxp.com
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W5DXP
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« Reply #34 on: March 04, 2009, 11:22:15 AM »

> WE5I wrote: Is it fair to say that radials are the "CAUSE" of radiation rather than the "SOURCE" of radiation? <

One needs to understand superposition and interference to understand the answer to your question. The Method Of Moments analysis (MOM) method used by NEC assumes that each unit segment of a wire antenna radiates depending upon the magnitude and phase of the current in each particular segment. The separate fields generated by each of the tens/hundreds/thousands of segments are calculated at a point including all magnitudes and phase angles. The radiation field at that point is the vector sum of all the component radiation.

So the real question becomes: Was the radiation that cancels ever really radiated or not? :-)
--
73, Cecil, w5dxp.com
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KA2UUP
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« Reply #35 on: March 04, 2009, 12:56:27 PM »

No.
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W5WSS
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« Reply #36 on: March 04, 2009, 03:27:17 PM »

wb6byu Is exactly correct equidistant symmetry of a radial set even an odd number like three where two will work against the third cancel the horizontal radiation.There exists mostly horizontal radiation because the radial set is horizontally oriented irespective of the radiator tube orientation.. But the feed point being cenetered with respect to the two parts of the antenna the radial set and the radiator tube is a definition to a dipole.If' the radial set slopes then we have a different situation now the radial set becomes a 4-part second half of a dipole containing a significant level of radiation that is now depending on the slope angle mostly vertically polarized which adds to the vertical radiator tubes radiation resulting in increased feild strength as compared to a 1/4 wave ground plane the distinction is in the orientation of the radials as to whether or not we are taking advantage of this fact that radials do radiate when designed to do so and to add to the antenna. This is not rocket science we know how mutual coupling works. The radial set is driven by the feedline and the equidistance around the semi circle cancels all but a remnant of horizontal radiation because of mutual coupling so alot is happening...the best case scenario for the special antenna described here yes Tom is correct also that with elevated sloping vertical component radials 8 is about the limit either way.
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W5WSS
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« Reply #37 on: March 04, 2009, 04:07:25 PM »

yes n3ox that is an ideal definition
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W5WSS
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« Reply #38 on: March 04, 2009, 04:30:10 PM »

Another interesting point of this is base height above average earth. Take for example The 20M quarter wave radiator tube with a 4 set elevated 45 degree sloped wire radial system(really a split 4 ways second half of the dipole) when installed nearly 13-15ft up to the base of the antenna developes maximum angle of gain at a toa of apx 15 degrees and is contained in a single lobe formed by the earth surface and its height. The results are in suppressing higher secondary lobe formation. Pretty quiet really, a very good s/n ratio in this case. I have incorporated all of these techniques into one that I built and the antenna did not dissapoint me operationally. I would be bold enough to state that this version is incorporating all of the best techniques that in the end makes for as good a mono band dx vertical in its class one can design. But I do not however, state that we are finished learning how to best manipulate rf to our means Keep learning. 73
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