Avanti Sigma4: An alternative view point

freecell said:

correction:

moving the radials upward in close proximity to to radiating element compresses the electric and magnetic charge while increasing the capacitance between the radials and the vertical element. this creates additional loss resistance.

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I tried to confirm this through modeling, intentionally removing other losses from the model. For example, I used free space to eliminate ground losses, I used perfect conductors to remove losses from materials. The results were... inconclusive.

I can say at least that this part of what you wrote sounds like it makes sense, at least at first glance, but at best I have been unable to verify this effect independently, thus far getting only inconclusive results. Because if this I have to wonder if, while the effect likely exists, is it large enough that anyone will actually ever notice it?

To put it another way, far to often the words "more efficient" and "less efficient" are thrown out there way to easily, but nothing is said about the much more important part, the degree of change in efficiency. Just saying "is more efficient" or "is less efficient" doesn't give me or anyone any real relevant information. For example, using a PL-259 to SO-239 connection is less efficient than directly wiring the coax to the antenna, but the difference in efficiency is in the range of 0.01 dB (yes, this has been directly measured by multiple people), a difference so small that you not only won't notice it, but wouldn't notice it if you had many of them chained together.

So, can you tell me how much of a difference in loss resistance angling said radials upwards to said degree makes?

Further, I'm not seeing where you are also factoring certain other changes that will happen and are relevant to this conversation, such as changes in directivity (hopefully in a benefician direction), which will also necessarily happen. Your the person I've seen talk about directivity the most in recent memory, and you actually have the concepts behind it mostly right, so what, in your opinion are it effects here? Is there enough of an increase in directivity in a beneficial direction to make up for said losses?

freecell said:

in addition, there's an instant increase in directivity of 3 dB. when any ground plane vertical is ground mounted. see logan and rockway 1997.

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As bob85 said, this is assuming a perfect ground. If the ground below the antenna is an imperfect ground, it will always add losses, and according to modeling, alot more than most people (including you by the numbers you have posted int he past) actually realize. Of course many people who model use the mininec ground, which has a nasty effect of over reporting the gain of ground mounted antennas to, actually, close to 6 dB. A recent image you posted that shows a 3/4 wavelength ground mounted antenna outperforming another antenna mounted higher has this problem...

I should also point out here that there is a very big difference in the results from modeling and direct point to point measurements. Before Henry's report, for years Marconi and Shockwave tried to say each other was wrong based on this very fallacy, and didn't actually realize that they were effectively arguing apples with oranges. When making claims like this, be careful with what you are comparing. Unfortunately I have not had the time to thoroughly read through everything mentioned due to overtime at work, so I'm just going to post a warning here to be careful and make sure any claims about modeling over or under reporting anything as per measurements are apples to apples comparison of results.

Hmm, Marconi. I haven't seen him post in a while. I hope hes doing ok...

When it comes to the conversation about "effective area", or a more common way of saying it is "capture area" of an antenna I feel is more or less moot. You have a given amount of power being fed to the antenna. All the "effective area" or "capture area" of the antenna does is change the directivity of said antenna, at least according to the evidence I have seen. If the "effective area" or "capture area" was really important, you could simply make the antenna wider to compensate for the shorter length of some antenna designs, could you not? Width is an important part of antenna design after all. Alas, we know that this doesn't actually work that way, and actually ends up having the opposite effect...

Back to the antenna in question. I seem to recall Homer posing a report where several antenna designs that he made were compared at the same tip height, and the Vector clone he made outperformed all the others when it came to local distance, with the Astroplane second if I recall? Sometimes I wish I had a link to said post for a reference as I have looked back on occasion and have yet to find it again...


The DB

I will find it... maybe.

@The DB
It may be in here. I could find nothing else

https://www.worldwidedx.com/threads/at-this-point-in-time-antenna-experiences-so-far.142772/

HomerBB said:

@The DB
It may be in here. I could find nothing else

https://www.worldwidedx.com/threads/at-this-point-in-time-antenna-experiences-so-far.142772/

Click to expand...

Thanks for looking, but this isn't it. This appears to be from before the post I was referring to.

At the time you were also posting more on other forums, it may have been one of those I remembered as I have/had accounts on other forums as well... Unfortunately this only makes it more difficult to find, if the forum even still exists...

EDIT: Actually, I think it was this one...

https://www.worldwidedx.com/threads/because-i-was-asked-best-vertical.147930/


The DB

@The DB
This?
"Because I was asked, the best vertical of those I've made:

1. 1/4 wave Ground Plane:
Smaller than many others, light weight, easy to mount, simple to build. Wide-banded, easy match. No matching network required which translates to diminished losses. Potential to handle lots of power because there isn't anything to burn out.

2. Half Wave Dipole:
Simplest to build, lightest weight, nearly infinite configurations. Power limited only by the materials of choice when building it. Most portable after # 3. Most stealthy.

3. Sleeved Dipole:
A little more work than a simple dipole, it is basically the same as and on a performance par with the common dipole. Common Mode Currents are more likely from this dipole, but the trade off is the ease of mounting it vertically compared to a center fed dipole. As a portable the coaxial sleeved dipole is the king.

4. End Fed Half Wave (EFHW):
Performance adequate, but without radials not as good as either the Dipole or the 1/4 wave GP. When the radials are added and the antenna meticulously tuned, performance is on a par with some 5/8 waves. Most complex matching section. More potential losses. More power limited due to matching network.

5. Astroplane:
Smaller in height and breadth than either a 1/4 GP, or a proper EFHW, as light as either, if not lighter, but more robust performance. Much smaller than a 5/8 GP. No matching network as the antenna design itself acts as both antenna and matcher so greater power potential than the EFHW. Works as well as any 5/8 wave I've made and used. Must have adequate height, long enough metal mast, and sufficient clearance from other conductive materials to achieve peak performance.

6. 5/8 wave/ .64 wave: All these types I've built have had radials and either an inductor coil or ring to match impedance to feed line. All of them have out performed a 1/2 wave by a little, but neither the .64 or .625 have had any detectable performance differences between themselves in my experience. Power handling I would suspect is completely dependent upon the robustness of the inductor in the matching network. Building and matching a working 5/8 wave is the effort of a single afternoon. There is nothing at all complicated about this antenna, and simpler to build and tune than an EFHW.

7. Vector 4k:
Noticeably higher gain than the 1/4, 1/2, or 5/8-.64 verticals. Taller than the others by feet, it trades off from the other vertical types by being no broader than the Astroplane - tall and skinny. The ears are the best, and it has farthest reach TX-wise than the others. Not noticeably better within 20 to 25 miles than the others, it comes into its own as the far field local work begins making communications with stations I strained to hear, or could not hear in this mountainous terrain out to 65 - 80 miles much easier by comparison.

Which do I like the best of the 11 meters verticals I've made?
a. For simplicity and portability, the dipole.
b. For classic elegance, the 5/8 wave.
c. For uncomplicated reliability, the 1/4 wave GP.
d. For shear outreach above the others and total beauty, the V4k.
e. For a mix of simplicity, size, reliability, better than most other antennas I've used, and uniquely eye pleasing appearance, the Astroplane.

The one I like the least is the EFHW, the number one pick is the Astroplane.

EFHW negatives - more prone to CMC, more complex to match, more losses by design, and less power handling.

Astroplane positives - Small, easy to build. Inherent matching without network. Greater power handling potential. Pretty. Out performs all others except for V4k, but out points it because of its ease of mounting, building, and maintaining.

These are my personal preferences/observations based on building, testing, and using each of these for a minimum of weeks on end. All of this is subjective and relies on my personal level of satisfaction, and the differences in the demands of my Ozark Mountains locality. In another place I might have to re-evaluate each of these and come to different personal conclusions."

@HomerBB Yep, thats the one, although I remember one or two bits of other info as well that I thought was included, perhaps they were in later posts in that thread or in another thread or on another forum even? I'm pretty sure they were posted in relation to that post...

Anyway, I think that thread is worthy of a sticky, and is a good reference for anyone who is interested in actual real world comparisons of these antennas. While I found it this time, there are a few times I went looking for it and couldn't find it.

Reading through the thread now, perhaps I was wrong about them being at the same tip height... It was talked about in the thread though...


The DB

@The DB , the thread from which I lifted that did not specify antenna tip height, but you are correct, those comparison were made at tip height being the same.

"as bob85 said, this is assuming a perfect ground. If the ground below the antenna is an imperfect ground, it will always add losses, and according to modeling, alot more than most people (including you by the numbers you have posted int he past) actually realize. Of course many people who model use the mininec ground, which has a nasty effect of over reporting the gain of ground mounted antennas to, actually, close to 6 dB. A recent image you posted that shows a 3/4 wavelength ground mounted antenna outperforming another antenna mounted higher has this problem..."

if anything the ground mounted vertical / monopole has been under reported from at least as far back as wolf (1966) & all that changed after 1997 with the logan rockway report that discovered the reality of the issue regarding the erroneous claim that stated that a dipole over ground has one half the effective area of a ground mounted monopole and that reality was that just the opposite has been, is and continues to be the case.

since logan and rockway wrote the original mininec program it doesn't surprise me that programs from somewhere past 1997 and on may have been updated at some point along the way with the appropriately adjusted algorithm. additional directivity is added to this initial 3 dB. depending on the adequacy of or number and length of the radials responsible for the collection of antenna current and presenting a high impedance to the shield to decouple the antenna current from the outside of the shield and connected support structures, a huge contribution to the elimination of loss resistance in the system, especially a problem as it applies to above ground vertical antennas making use of only 3 or 4 current collecting radials, wholly inadequate for the job at hand.

"the erroneous definition (postulated by Wolf, 1966) is that the effective area of the vertical receiving monopole is twice as large as that of a corresponding dipole in free space. this report shows that the effective area of a monopole is one half that of the corresponding dipole."

https://ia600105.us.archive.org/1/items/DTIC_ADA332891/DTIC_ADA332891.pdf

that's probably no error you're seeing, just a recent correction.

https://www.worldwidedx.com/threads...ernative-view-point.31799/page-45#post-766894

freecell said:

if anything the ground mounted vertical / monopole has been under reported from at least as far back as wolf (1966) & all that changed after 1997 with the logan rockway report that discovered the reality of the issue regarding the erroneous claim that stated that a dipole over ground has one half the effective area of a ground mounted monopole and that reality was that just the opposite has been, is and continues to be the case.

since logan and rockway wrote the original mininec program it doesn't surprise me that programs from somewhere past 1997 and on may have been updated at some point along the way with the appropriately adjusted algorithm. additional directivity is added to this initial 3 dB. depending on the adequacy of or number and length of the radials responsible for the collection of antenna current and presenting a high impedance to the shield to decouple the antenna current from the outside of the shield and connected support structures, a huge contribution to the elimination of loss resistance in the system, especially a problem as it applies to above ground vertical antennas making use of only 3 or 4 current collecting radials, wholly inadequate for the job at hand.

that's probably no error you're seeing, just a recent correction.

Click to expand...

The MiniNec ground I was referring to is the one that is implemented as a ground type in Nec2. This is the version of MiniNec ground for the latest version of MiniNec. There are many problems with this ground type as to fit in the basic program on the types of PC's it was intended to run on, they took many shortcuts, often simply defaulting to the settings of Perfect Ground, and it doesn't take much experimentation to show this. This is why, unlike other attempts at grounding, this type of ground that are meant to simulate "Real Ground" the MiniNec ground will always show a current maxima at the ground connection. It is the least accurate of all ground types, period, end of story. There is one seeming advantage to it, and that is the appearance of being able to connect part of the antenna to it directly, but this actually produces inaccurate results.

Using Real Ground, instead of the MiniNec ground, I can actually show the differences between the number of radials that are (in the model) just above and effectively on the earth. As I add more and more radials to this system, I can see R drop as I maintain resonance, and it drops through 50 ohms to a lower impedance. This effect has been demonstrated by multiple people with actual test antennas. With the MiniNec ground, you cannot do that. All you have is an antenna directly attached to the earth, no radials present, and it shows significantly more gain than actual real ground unless real ground has a ton of radials present, and FYI, real ground was, in part, specifically designed to show accurate results for this type of setup.

The MiniNec ground is also known to be by far the least accurate ground type available in the Nec2 engine. You say that many programs out there update this ground, and that is true, but when I refer to the MiniNec ground, I am specifically referring to the implementation in the Nec2 engine, which is the same as most recent implementation in the latest actual version of MiniNec, and the one used when you said x ground mounted antenna will outperform y antenna mounted 10 feet in the air. Its also why I gave pushback on that.

And you are treating the MiniNec program, or at least the MiniNec ground, like it is better than it actually is. There is one thing that MiniNec does better then Nec2, and that is tapering, this is actually because of how MiniNec handles segments, and in the opinion of someone who has used both modeling engines, this is the one thing that MiniNec has that I wish they implemented in the Nec2 engine. With everything else, and I mean everything, the Nec2 results are superior.

I'm not trying to talk bad about the author of MIniNec, and I'm glad that there are programs out there like Mmana-Gal that have improved on the MiniNec code. If I knew how to code at that level, I would create a version for myself.


The DB

"Using Real Ground, instead of the MiniNec ground, I can actually show the differences between the number of radials that are (in the model) just above and effectively on the earth. As I add more and more radials to this system, I can see R drop as I maintain resonance, and it drops through 50 ohms to a lower impedance."

does the program allow you to track loss resistance which increases as radials are removed or soil types are changed and just what type of an antenna (1/4 wl, etc.) are you speaking of in this instance?

logan, rockway and the NRad division of naval command used mininec professional to assist in the research overturning wolfs prior thesis. wolf was wrong.

freecell said:

does the program allow you to track loss resistance which increases as radials are removed or soil types are changed and just what type of an antenna (1/4 wl, etc.) are you speaking of in this instance?

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Loss resistance specifically, no. Radiation efficiency, however, yes, and this does change as you add radials.

freecell said:

logan, rockway and the NRad division of naval command used mininec professional to assist in the research overturning wolfs prior thesis. wolf was wrong.

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I have found the document in question... I'll link it here.

https://apps.dtic.mil/sti/pdfs/ADA332891.pdf

Its not a bad document, but irrelevant to the conversation at hand. After all, I'm not referring to models that use the:

infinite, perfectly conducting ground plane

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Or what modelers today simple call a "Perfect Ground". Every time they mention being over a ground, they are either saying or implying this "infinite, perfectly conducting ground plane" or "Perfect Ground".

I'm curious why you think something like what is written in this document relevant to anything that I have said. Its like you are using a distraction to claim that I am wrong about something.

So what if Mininec was used in a study, that doesn't change the fact that Nec2 has a superior, more accurate engine. OK, sure, someone may have updated X version of the Mininec program in various ways, but when I specifically refer to Mininec, and its Mininec Ground, I am referring to the official release, not updates others may or may not have made since. This is the specific version of the Mininec ground I was referring to in my caution above, and was used by you in another thread to make a claim about one antenna over another that is questionable at best.

And when it comes to the "Mininec Ground" and the "High Accuracy Ground" that I am talking about, neither of them are the "infinite, perfectly conducting ground plane" that is referred to exclusively in said document. Not even close. This also has nothing to do with the known issue of the "Mininec Ground" over-reporting gain.

My conclusion is either you don't understand the document fully, or your reaching for something that isn't there in the hopes that it will shut those up that disagree with you because you think they won't understand it.


The DB

you posted:
"I'm curious why you think something like what is written in this document relevant to anything that I have said. Its like you are using a distraction to claim that I am wrong about something."

"over reporting the gain of ground mounted antennas to, actually, close to 6 dB."

this is the finding and conclusion of the report:

abstract:
"the erroneous definition (postulated by Wolf, 1966) is that the effective area of the vertical receiving monopole is twice as large as that of a corresponding dipole in free space. this report shows that the effective area of a monopole is one half that of the corresponding dipole."

"thus, the gain of a quarter-wave monopole should have twice the gain of a corresponding half-wave dipole, or 5.16 dB.." (page 8) i consider this figure to be an indication of directivity instead of gain since the radiation efficiencies for the AUT have not been evaluated to make that calculation possible.

"MININEC Professional and Kraus (1950) agree on the gain of the transmitting antenna. As indicated in table 2, the transmission results of equation (18) and MININEC Professional do not agree. However, the transmission prediction of equation (18) is approximately 6 dB or four times greater than the calculation of MININEC Professional." (page 8)

additional information:
http://www.arrl.org/forum/topics/view/2112

Perhaps I should come at this a different way...

L. B. Cebic said:

Compared to a radial system over S-N ground, the MININEC system not only overestimates performance figures, but as well, provides dimensions that are at odds with those which might yield maximum gain and front-to-back ratio in the radial configuration. If optimization is performed, along with the use of additional radials, available in NEC-4, the performance of the array over radials might show better numbers, but still, nowhere near those provided by the MININEC ground analysis.

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L. B. Cebic said:

The MININEC ground shortcut to vertical array modeling should generally be avoided or used sparingly and under very limited conditions.

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A note, S-N ground, or Sommerfeld-Norton ground is what nec2 calls "Real Ground". It is by far the newest and most accurate ground system out there by any measure and standard, and this has been confirmed in real world tests.

Long story short, the Mininec ground over-reports gain compared to a ground system that has been tested and confirmed accurate in the case of ground mounted antennas. This is true even considering the document you are trying to use in an attempt to say it is false.

What J. C. Logan and J. W. Rockway are saying in that document has actually already factored into these results.

There is a saying, "Can't see the forest for the trees", but you have the opposite problem, you can't seem to see that the tree your focused on is part of a forest.


The DB

"It is by far the newest and most accurate ground system..."
which should be accurate for measuring horizontal wires down to .005 wl. ABOVE the ground. that's approximately 2.25 inches above the ground @ 27mhz..

what happens when wires are on or buried below the ground is not within the sommerfeld-norton metric for obvious reasons.

we're done here.