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Base New V4K vs Conventional J-Pole

Second posts on page 2 of the link I posted above Eddie,

here's something else W8JI says in the same discussion,

"Another factor, feedline and mast coupling, is virtually ignored. It is virtually impossible to fully decouple a feedline without having radials at the element base.

The bottom line is this. Aside from doing something wrong to reduce gain, there is no major difference between a 1/4 groundplane with sloped radials, a 5/8th wave vertical, or a 1/2 wave vertical when all are at the same mean height for current maximums. It is where the current maximum is that matters, not the tip"
 
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freecell said:
"Another factor, feedline and mast coupling, is virtually ignored. It is virtually impossible to fully decouple a feedline without having A LARGE NUMBER OF radials at the element base."

https://www.worldwidedx.com/threads/calling-all-antenna-experts.260109/#post-748158
Click to expand...

I'm not buying this. To start with your posted image in that linked post.

gplane-png.41598


Information I can deduce from looking at this model. This is am image showing a 1/4 wavelength antenna mounted to a mast that is attached to either perfect or mininec ground. The materials for the antenna appear to be perfect conductors, and the mast diameter is significantly different that the diameter used for the antenna. The height the antenna is mounted exactly one electrical wavelength high. Further, this model was made using the 4nec2 software... ;)

The claim that you are making, and using this model to try and demonstrate is that 4 radials are not enough to decouple the mast from the antenna, and you need more to do this to do this. So, where are the models that use more than four radials to show that what you are saying is true?

The fact is, in this case the cause of the high mast currents has nothing to do with the number of radials, and is instead due to what W8JI (and later several people on this forum including myself) has dubbed an unlucky mast length. Adding radials will do very little in this case, the reason is the mast has a very low impedance compared to the radials. Even if you have significantly more radials, the mast will still have a lower impedance than each individual radial, which means it will still have most of the current flowing on it.

So you can compare the difference, I made two models at 36 feet, one with 4 radials and the other with 8 radials. They are not right at the worst possible length of the above model, but dialing the model in that way takes time I don't currently have... :(

[photo=medium]6508[/photo][photo=medium]6510[/photo]

You can click on them to make them larger if you need to. One thing I should note here is the eight radial version of this antenna actually has slightly more current flowing in its mast, according to the tabular current logs, so adding radials actually seems to be making the mast currents slightly higher, which I honestly didn't expect. When I get more of a chance later, I will have to look in to this and see why this is the case.

For a comparison I am also including two models that are at 27 feet, this is closer to what would be described as a "lucky" mast length.

[photo=medium]6507[/photo][photo=medium]6509[/photo]

As we can see, the mast length has far more effect on the currents on the mast than the number of radials. Further, in both cases, doubling the number of radials seems make very little difference, and might make a mast current problem a little worse.


The DB
 
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freecell said:
I'm not selling anything.
Click to expand...

Me neither.

freecell said:
DJ2YA Vertical Antennas, Chapter 9
https://www.fichier-pdf.fr/2014/04/21/09-1/09.pdf
Click to expand...

Here is another source for that link, only this time in .pdf format. I am 90% sure it is an ARRL publication, but it is not the ARRL Antenna Book 23'rd edition or before. I guess it can be the 24'th edition, which I don't currently have to compare. Its a good read, and I would love to know which book it is out of as I would love to read the rest of the book.

However...

Nothing in the 79 pages of the link you provided agree with your claims, unless you take something being said out of context. Every time this document refers to more than four radials, they are referring to buried in the earth, laying on the earth, or scaling to 11 meters, less than 2 feet above the earth. Nothing even comes close to the model you posted which is one wavelength (or in this case about 36 feet) above the earth. They did have a few pages on decoupling towers (all the towers in the images in this section had yagi's on top) with radials, but even then it is four radials in conjunction with a shunt wire and variable capacitor.

If I missed something here, please narrow your source down to less than 79 pages, most of which aren't directly related to the discussion at hand.


The DB
 
This is what W8JI said: "When the mast and feedline is included in the model, the "Dominator" falls apart. The exception to this is if we add a groundplane at the junction of the cone and the mast and coax."

Without wanting to open a can of worms I will simply point out nothing he said here is in alignment with the models that show the only noticeable effect of adding radials, is lower gain on the horizon with more energy in the upper lobes. The idea of adding radials was field tested long before others mentioned it and those results happen to be in alignment with the models.

The towers and feedlines used in the FM version are random lengths ranging from 100 feet to over 800 feet. I tune them with a 1 wavelength piece of cable and the only time a station had a problem with that tuning, is when they installed the top section upside down and made the radiator length wrong. This also indicates W8JI is not familiar with design and has not tested his theory regarding the need for decoupling radials.

I will add that it is somewhat disappointing to see someone so well respected, specifically make negative comments on my brand name, without even taking the time to test his theory in a model...
 
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There's a huge amount of conjecture and extrapolation of models, arguments, and bias regarding this antenna type. It is often among those who have not tested in real world environments that negative arguments thrive, all of which remain a very distant second place to empirical results. And, again, the person with an experience is never a servant to a man with an argument.
I do agree with W8JI regarding lucky/unlucky mast heights and feedline lengths contributing to CMC behavior.
I believe it was Marconi who once before did a model of the V4k with radials. The model showed a significant loss of gain from the horizon to a high angle lobe.
I quickly abandoned the idea of using radials under my antenna.
Here it is:
 

Attachments

  • NV4K with and without radials.pdf
    1.5 MB · Views: 9
Notice that model does not have a mast or counterpoise and that condition would maximize any CMC on those added radials. The current line on the radials shows an almost exact trace of the physical element, indicating whatever current is there, is just about not measurable. Unlike what you would see on something like a 5/8 wave groundplane that was dependent on those radials for decoupling.

The increase in energy at the upper lobe that these radials adds, is evidence that the low current we see in the radials, is a parasitic excitation that is reflecting upwards into the pattern and distorting it.
 
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At that point in time I was isolating my V4k from the mast by attaching the antenna to a 2' long hickory shovel handle which I attached to the top of the mast. I realize the approx. 1' separation between the mast top and antenna bottom will not prevent total decoupling like the model does, but I wanted an idea of potential behavior.
I noticed the upper lobe was the one with the most gain, and that gain was less than that of the V4k without radials. This seemed to indicate that the loss of gain against the horizon could be significant when adding radials.
 
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Instead let me quote you as you posted it. Fixed it.

Now, can you draw me that picture? I don't know what you mean in your post, and my question is honest.

We call the cone ribs radials as a convenience. They are not radials in a traditional sense. If that is what you mean, adding more ribs to the cone then that is a different conversation than actually adding radials. My understanding is that a solid cone, or a wire mesh cone, would not be any more advantageous than the four ribs, aka radials, of the cone. Perhaps someone will model that, if possible.
 
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radials are the ground circuit return path for antenna current. They constitute a radial network in every sense of the word. that applies to ground mounted as well as elevated radial monopole designs. they're called radials because that's what they do, they return antenna current to the ground terminal of the radiator.
 
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