Avanti Sigma4: An alternative view point

[CDX-007]

CDX-007, I can't help you to accept the idea that more then one radial is active in any one direction. It is a fact take it or leave it. I've experimented with this antenna enough to know that both the shielding effect and radiation effect of the cone benefited from having the 4th radial added to the design. From your point of view as long as one radial was facing the desired direction no gain would be seen adding the 4th. This is simply not true.

Using a field strength meter at various points along the antenna would show nothing even remotely similar to the CST image. The field strength meter does not react to the maximum current point on the antenna. It responds to increases in RF voltage and shows the highest reading where the highest voltage is. Hold one up to your 102 inch whip if you don't believe me. The highest reading will be at the tip which just happens to be where the least radiation current is.

I don't question that the TOA will suffer from being mounted too low to the ground or that close proximity to other antennas would effect the pattern. I will say it shows no significant change in VSWR where many other antennas do. My point here is my roof and mast are tall enough to remove this variable.

Marconi, I'm not sure what you mean by me pausing. I only tested the GM on the ground first to confirm the antenna had a reasonable match, bandwidth, and could handle my TX power before going through the trouble to install it. I did this because I needed coverage of 10 and 11 meters. In all honestly I did not test signals on the ground but the VSWR did not change.

Unless it was raining, snowing, or your roof is metal, the roof itself really cannot effect the antenna. Asphalt shingles and plywood simply do not effect RF at HF frequencies. In the absence of those conditions during your tests, it was the height above ground that made the difference, not height above the roof. Being that it does snow, rain, and some roofs have metal in them are probably the reasons Sirio recommends 6 feet or more clearance.

No, I believe you misunderstood.

Shockwave, I agree with you that 4 cone radials is better than 3, and I'd expect that adding 20 more cone radials would certainly benefit the cone action (which you have described is performing as both a shield and a radiator) to an even higher degree than adding only 1 more, though there will certainly be a point of diminishing returns.

My point was actually regarding what we are clearly seeing in the "Full-bloom"(?) CST image of the Vector, Below.

- That being what I believe is supposed to be an accurate representative slice at any given point along the circumference of the antenna as it radiates, which shows a relatively much lower level of energy emanating from the bottom ~33% cone in comparison to that of the top ~66%, along with the heart shaped bloom around it which also seems to depict less energy by far radiating from the cone, offering me the idea that the ¼λ cone is radiating much less RF than is the top ½λ.

I would expect a ¼λ 'element' fed, or even just acting, in a collinear fashion, above or below a ½λ element would need to show an equivalent amount of peak RF radiation field, for it to be as efficient a radiating surface as that of it's adjoining ½λ 'element' before it would add the claimed ~1.5-2dB gain it is allegedly adding in the Vector.

Here it looks like only a slight coloring of the RF exited area outside the cone where the area outside the top ½λ is showing a much stronger (not just longer) RF field:

...which is what led me to believe that perhaps if we were to see the entire 360° CST Vector model it might show this is perhaps NOT the full-bloom point in the cycle, and possibly more highly energized when the cone area is not in phase, especially when noticing the red/blue colored RF energized field area around the top ½λ is considerably less pronounced than is the area around the CST model image of the SGM at full bloom, even though more power (A/m) is evidently being applied to the Vector in it's model.

When considering the fullness of the area of color around the SGM compared to the single slice sent to you of the Vector, it appears to me that it is perhaps not a slice at full bloom, suggesting something else might be happening in the cone area regarding phase when the top ½λ actually is in full bloom.

 

[Marconi]

No, I believe you misunderstood.

Shockwave, I agree with you that 4 cone radials is better than 3, and I'd expect that adding 20 more cone radials would certainly benefit the cone action (which you have described is performing as both a shield and a radiator) to an even higher degree than adding only 1 more, though there will certainly be a point of diminishing returns.

My point was actually regarding what we are clearly seeing in the "Full-bloom"(?) CST image of the Vector, Below.

- That being what I believe is supposed to be an accurate representative slice at any given point along the circumference of the antenna as it radiates, which shows a relatively much lower level of energy emanating from the bottom ~33% cone in comparison to that of the top ~66%, along with the heart shaped bloom around it which also seems to depict less energy by far radiating from the cone, offering me the idea that the ¼λ cone is radiating much less RF than is the top ½λ.

I would expect a ¼λ 'element' fed, or even just acting, in a collinear fashion, above or below a ½λ element would need to show an equivalent amount of peak RF radiation field, for it to be as efficient a radiating surface as that of it's adjoining ½λ 'element' before it would add the claimed ~1.5-2dB gain it is allegedly adding in the Vector.

Here it looks like only a slight coloring of the RF exited area outside the cone where the area outside the top ½λ is showing a much stronger (not just longer) RF field:

...which is what led me to believe that perhaps if we were to see the entire 360° CST Vector model it might show this is perhaps NOT the full-bloom point in the cycle, and possibly more highly energized when the cone area is not in phase, especially when noticing the red/blue colored RF energized field area around the top ½λ is considerably less pronounced than is the area around the CST model image of the SGM at full bloom, even though more power (A/m) is evidently being applied to the Vector in it's model.

When considering the fullness of the area of color around the SGM compared to the single slice sent to you of the Vector, it appears to me that it is perhaps not a slice at full bloom, suggesting something else might be happening in the cone area regarding phase when the top ½λ actually is in full bloom.

Steve, would you not be one of the first to claim an aperture advantage for a .64 wave radiator over a .625 wave? If so, why then do you choose to ignore the characteristic with these images. We can't even be sure of the magnitude of current represented by the color representations. We might assume the amount of red and blue bloom is a measure of the magnitude of current flowing, but in my examples of Exnec5, I can make that look anything I want too just by clicking on the elevator that makes the red line currents look greater or less. How about checking the current distribution values for the antennas represented in each image?

Unless I'm totally wrong, it's like I try to say all the time, "...we can't always know the full story of any representation...just by looking at the pictures."

If nothing else, the Vector is at least 33% larger than the GM and is very effective at radiating the whole antenna in phase in the far field. I think we may also both agree...this factor alone may be the primary benefit for the GM over other 5/8 wave radiators, with the bottom 1/8 wave for the typical end fed 5/8 wave being out of phase, providing little or no contribution to far field RF.

I guess we could also argue if the red and blue are near field or far field as well? Let me know if I'm looking at these images and data wrong, OK?

 

[CDX-007]

Steve, would you not be one of the first to claim an aperture advantage for a .64 wave radiator over a .625 wave? If so, why then do you choose to ignore the characteristic with these images.[Not sure what you mean 'ignore the characteristic'?] We can't even be sure of the magnitude of current represented by the color representations. We might assume the amount of red and blue bloom is a measure of the magnitude of current flowing, but in my examples of Exnec5, I can make that look anything I want to just by clicking on the elevator that makes the red line currents look greater or less. How about checking the current distribution values for the antennas represented in each image? [No, I'm using it's own image as a reference/ comparison to itself when I say "Look at the magnitude of the red/blue current in the top ½λ compared to that in the bottom ¼λ and you can see the bottom ¼λ field is PIDDLING LITTLE in comparison to the strong ½λ field of the top 66%"]

Unless I'm totally wrong, it's like I try to say all the time, "...we can't always know the full story of any representation...just by looking at the pictures." [Then Why bother to write the CST program if it isn't for the purpose of revealing information through visible representation, especially with regard to what it is designed to specifically visualize?]

If nothing else, the Vector is at least 33% larger than the GM and is very effective at radiating the whole antenna in phase in the far field. [I'll give it this;
The Vector is one version of a design which has effectively deleted the out of phase bottom ¼λ radiation portion of a ¾λ in order to lower the TOA to a very usable gain advantage by elevating and more efficiently feeding the upper ½λ, including adding a relatively small amount of additional radiation from the bottom ¼λ causing a slight collinear effect.]

I guess we could also argue if the red and blue are near field or far field as well. Let me know if I'm looking at these images and data wrong, OK?

No, I doubt they went to showing far field when the CST image is evidently intended to show what is as near field as possible, the RF radiation which is coming directly off the antenna skin.

I really don't know how I could be more clear about the issues presented in my previous post...?

 

[Marconi]

Originally Posted by Marconi
Steve, would you not be one of the first to claim an aperture advantage for a .64 wave radiator over a .625 wave? If so, why then do you choose to ignore the characteristic with these images.[Not sure what you mean 'ignore the characteristic'?]

007, in my words the idea of aperture is not that difficult to understand. I'm not presenting an abstract argument here. I think you refer to a consideration for the benefits of aperture improvement every time you request me to make a model or extend the length of my I-10K to .64 wavelength so I can realize and maybe even demonstrate the remarkable gain you suggest will occur.

We can't even be sure of the magnitude of current represented by the color representations. We might assume the amount of red and blue bloom is a measure of the magnitude of current flowing, but in my examples of Exnec5, I can make that look anything I want to just by clicking on the elevator that makes the red line currents look greater or less. How about checking the current distribution values for the antennas represented in each image? [No, I'm using it's own image as a reference/ comparison to itself when I say "Look at the magnitude of the red/blue current in the top ½λ compared to that in the bottom ¼λ and you can see the bottom ¼λ field is PIDDLING LITTLE in comparison to the strong ½λ field of the top 66%"]

I might not disagree with the point you raise here, that sure is how it looks. But, I'm trying to say the magnitude you see in the images may not be the best determination for the magnitude of the currents. How do you know what the input current is from these models? I assume the amperage input is fixed in the code of the software and the variations you see may have only to do with the difference in segments assigned to each model and nothing more. I seem to recall we've had this conversation before. That said though, I can't be sure, and I don't think you can be either. The best source of things related to the currents will likely be found only in the tabular list for currents and I don't that of one minute that these images are true to scale in all aspects.


Unless I'm totally wrong, it's like I try to say all the time, "...we can't always know the full story of any representation...just by looking at the pictures." [Then Why bother to write the CST program if it isn't for the purpose of revealing information through visible representation, especially with regard to what it is designed to specifically visualize?]

Because a true visual and to scale representation would be tedious to create to the minute details required. Considering the data is all that is really necessary, like a blue print looks compared to the building it will produce. A fair representation is all that is necessary. Bob has said the same, so maybe my sense of deja-vu was from a conversation with him.

If nothing else, the Vector is at least 33% larger than the GM and is very effective at radiating the whole antenna in phase in the far field. [I'll give it this; The Vector is one version of a design which has effectively deleted the out of phase bottom ¼λ radiation portion of a ¾λ in order to lower the TOA to a very usable gain advantage by elevating and more efficiently feeding the upper ½λ, including adding a relatively small amount of additional radiation from the bottom ¼λ causing a slight collinear effect.]

Sounds good for me.

I guess we could also argue if the red and blue are near field or far field as well. Let me know if I'm looking at these images and data wrong, OK?

No, I doubt they went to showing far field when the CST image is evidently intended to show what is as near field as possible, the RF radiation which is coming directly off the antenna skin.

I really don't know how I could be more clear about the issues presented in my previous post...?

All I can expect is maybe you will consider my view point as well, we are not that far apart as I see things. I think your next to last statement convinced me you understood the antenna as I do. I just consider the words and listed current data more important that the images, but again I could be wrong. I will look at Eznec5 manual to see if I can find the reference for how it applies current to the antenna and the magnitude, and what affects it. Plus I think I recall there maybe some words discussing the images produced and how they are to be interpreted. It would be nice if the images were as you imagine. I promise to follow up.

BTW, I think I understand you, I just disagree with some of your ideas.

Good discussion.

 

[BOOTY MONSTER]

"Shockwave, I agree with you that 4 cone radials is better than 3, and I'd expect that adding 20 more cone radials would certainly benefit the cone action (which you have described is performing as both a shield and a radiator) to an even higher degree than adding only 1 more, though there will certainly be a point of diminishing returns."


how about using aluminum screen to make a neatly installed cone to the 3 or 4 elements on the cone (like a faraday cage ) ? would that be the easiest way to try your idea ?

 

[CDX-007]

Sorry Eddie, I'm not tracking with your "Aperture" idea. To me an aperture is a slit, hole or opening where light or sound, (in this case RF) would be able to get through in a limited way. I don't relate to transducers in terms of apertures, that to me would be more like an area between two large buildings where normally blocked RF could sneak through.

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Any gain I've witnessed going from a .625λ to a .64λ antenna has mostly been to distant stations. It seems the further the station the more the difference. Only 10-20 miles away, maybe a needle width.

--------------------

As far as magnitude of current in the CST models, I was simply looking at the visual and noticing the lower ¼λ portion outside the cone shows a much smaller, more abbreviated amount of blue & red than does the top ½λ portion or even the area inside of the cone.

This appears to mean there's less RF energy radiated from that area, especially when considering the greater width of color in the center of the upper ½λ also corresponds to the peak current found at the center of a ½λ.

--------------------

And I'm not comfortable comparing this software to eznec. I don't see the similarity in them, but I also don't know how they're written.

I hope you can now understand why I emphasized "small" and "slight" in that statement.

 

[CDX-007]

"Shockwave, I agree with you that 4 cone radials is better than 3, and I'd expect that adding 20 more cone radials would certainly benefit the cone action (which you have described is performing as both a shield and a radiator) to an even higher degree than adding only 1 more, though there will certainly be a point of diminishing returns."


how about using aluminum screen to make a neatly installed cone to the 3 or 4 elements on the cone (like a faraday cage ) ? would that be the easiest way to try your idea ?

Aside from any severely diminishing returns, that would be a fairly effective way to create a mostly solid cone which I would imagine could increase the efficiency of the design.

 

[MrSuburban]

BTW, I think I understand you, I just disagree with some of your ideas.

Good discussion.

Your not the only one Marconi

 

[CDX-007]

Your not the only one Marconi

From what I've read in your posts, I really don't care.

 

[MrSuburban]

From what I've read in your posts, I really don't care.

Oh you Care,
At least i know my testing methods work 100 % and are repeatable evey day of the week. we can test it today tommorow or next month and get the same accurate reading, I have proven performance on my end that speaks for itself. I can read differences in antenna gain down to a tenth of a db(calibrated), you are guessing what changes you think you see on your S meter and you tell us in in tenths of S units... LOL

 

[MrSuburban]

Sorry Eddie, I'm not tracking with your "Aperture" idea. To me an aperture is a slit, hole or opening where light or sound, (in this case RF) would be able to get through in a limited way. I don't relate to transducers in terms of apertures, that to me would be more like an area between two large buildings where normally blocked RF could sneak through.

YouTube - Dr Quantum - Double Slit Experiment

 

[Shockwave]

No, I believe you misunderstood.

Shockwave, I agree with you that 4 cone radials is better than 3, and I'd expect that adding 20 more cone radials would certainly benefit the cone action (which you have described is performing as both a shield and a radiator) to an even higher degree than adding only 1 more, though there will certainly be a point of diminishing returns.

My point was actually regarding what we are clearly seeing in the "Full-bloom"(?) CST image of the Vector, Below.

- That being what I believe is supposed to be an accurate representative slice at any given point along the circumference of the antenna as it radiates, which shows a relatively much lower level of energy emanating from the bottom ~33% cone in comparison to that of the top ~66%, along with the heart shaped bloom around it which also seems to depict less energy by far radiating from the cone, offering me the idea that the ¼λ cone is radiating much less RF than is the top ½λ.

I would expect a ¼λ 'element' fed, or even just acting, in a collinear fashion, above or below a ½λ element would need to show an equivalent amount of peak RF radiation field, for it to be as efficient a radiating surface as that of it's adjoining ½λ 'element' before it would add the claimed ~1.5-2dB gain it is allegedly adding in the Vector.

Here it looks like only a slight coloring of the RF exited area outside the cone where the area outside the top ½λ is showing a much stronger (not just longer) RF field:

...which is what led me to believe that perhaps if we were to see the entire 360° CST Vector model it might show this is perhaps NOT the full-bloom point in the cycle, and possibly more highly energized when the cone area is not in phase, especially when noticing the red/blue colored RF energized field area around the top ½λ is considerably less pronounced than is the area around the CST model image of the SGM at full bloom, even though more power (A/m) is evidently being applied to the Vector in it's model.

When considering the fullness of the area of color around the SGM compared to the single slice sent to you of the Vector, it appears to me that it is perhaps not a slice at full bloom, suggesting something else might be happening in the cone area regarding phase when the top ½λ actually is in full bloom.

CDX, if you agree that adding one radial increases gain slightly, then you must connect that with the fact the additional radial combines in the far field. Therefore it is not true that only a radial facing the direction of signal will increase the signal.

With respect to the "bloom" we've gone over this before. It is in "full bloom" as you put it. I have not guessed at this. I've asked the question to the right person and at this point I even have the complete CST video version to confirm it. It shows exactly what I said. The field collapsing in on itself and reforming the same peak in the opposite phase.

To me it's self explanatory where this antenna get's it gain from. We have about 27 feet of in phase radiation surface area. It contains two independent current nodes. The CST image is as near field as it gets and does not show the combined effect of the four radials.

If you think it's possible for the bottom 1/4 wave to reach it's "full bloom" point at any other phase angle then the top 1/2 wave, you're not understanding this has nothing to do with antenna design and everything to do with the RF source.

The source is a sign wave. As with any sign wave there will be two phase angles where there is no energy into the load (0 degrees and 180 degrees) and two phase angles with maximum energy (90 degrees and 270 degrees). The Vector image is for sure shown with the source applying energy at the 90 degree phase angle.

 

[Shockwave]

"Shockwave, I agree with you that 4 cone radials is better than 3, and I'd expect that adding 20 more cone radials would certainly benefit the cone action (which you have described is performing as both a shield and a radiator) to an even higher degree than adding only 1 more, though there will certainly be a point of diminishing returns."


how about using aluminum screen to make a neatly installed cone to the 3 or 4 elements on the cone (like a faraday cage ) ? would that be the easiest way to try your idea ?

Very good idea BootyMonster. In fact, I have tried it on one VHF copper prototype using sections of brass screen. Indeed it does make a very small improvement over the four radials however, it introduces entirely new problems. First, that darn gamma match gets in the way. Moving it inwards changes the impedance. Cutting a section of screen out to go around it, makes the antenna less omni directional. Then we have snow, ice, and wind loading to consider.

 

[Marconi]

Sorry Eddie, I'm not tracking with your "Aperture" idea. To me an aperture is a slit, hole or opening where light or sound, (in this case RF) would be able to get through in a limited way. I don't relate to transducers in terms of apertures, that to me would be more like an area between two large buildings where normally blocked RF could sneak through.

007, in part I disagree with you again. It is true the slit you suggest in the image and your anecdotal statement do have apertures, but the aperture of an antenna (transducer) is directly related to the physical dimensions of the radiator and substructures involved. I don't think this is even arguable.

The only thing, in my mind, that possibly minimizes that affect would likely be any area were the currents are not in phase---causing some cancellation like occurs with both the end fed 5/8 & .64 wave radiators. And again, you might agree with me that the design of the New Gain Master seems to have mitigated its 5/8 wave radiator from being affected in the same way...allowing the whole thing to radiate RX/TX. Which in my mind may well be, in combination to good symmetry, the best reasons the GM works as well as it does.

And my trying to be clear: this is also what the Sigma4/Vector does so well - suggesting a superior aperture.

 

[BOOTY MONSTER]

Very good idea BootyMonster. In fact, I have tried it on one VHF copper prototype using sections of brass screen. Indeed it does make a very small improvement over the four radials however, it introduces entirely new problems. First, that darn gamma match gets in the way. Moving it inwards changes the impedance. Cutting a section of screen out to go around it, makes the antenna less omni directional. Then we have snow, ice, and wind loading to consider.

the screen idea was just to test the concept . over time it would be like a waste basket collecting leaves and probably a few bird nests .