Avanti Sigma4: An alternative view point

[MrSuburban]

Do you believe the cone radiates a significant amount of power, or mostly acts just to contain the lower reverse phase energy with only negligible additional in-phase radiation?

I think he addresses that issue here


Toll Free wrote:
"THEREFORE!!!! The model that shockwave posted, the modeling I've seen and performed myself, and the theory of slotted antennas and others points to this: The BOTTOM section (the basket) works on the principle of a transmission line, and it transforms the impedance seen at the halfwave feedpoint (which is at the basket) down to a MUCH lower feedpoint impedance which is also slightly inductive.

Proof in the pudding you say???

OK, here ya go!

Get some GOOD ferrite beads and put them JUST below the basket attachment point to the 'radials'. This will prevent radiation, JUST LIKE A BALUN OR CHOKE ON A COAXIAL FEEDLINE!!!. Do NOT try this with full power, you'll crack'em good! The INSIDE of the basket will STILL contain the radiation pattern (and the 4 radial version does better than the original siggie design), BUT you will get LITTLE 'feedline radiation' from the OUTSIDE of the basket, or as Shockwave had put it, the colinear effect....

The antenna BASICALLY performs just like the marketing BS from the Antron.... It's a half wave over a quarter wave... The ODD thing that makes this NOT apparent and nobody takes into account one thing (in the basket): VELOCITY FACTOR. Because the basket flares out and is a transmission line, the internal conductor will HAVE to be shortened to maintain ELECTRIC length.

 

[CDX-007]

I think he addresses that issue here


Toll Free wrote:
"THEREFORE!!!! The model that shockwave posted, the modeling I've seen and performed myself, and the theory of slotted antennas and others points to this: The BOTTOM section (the basket) works on the principle of a transmission line, and it transforms the impedance seen at the halfwave feedpoint (which is at the basket) down to a MUCH lower feedpoint impedance which is also slightly inductive.

Proof in the pudding you say???

OK, here ya go!

Get some GOOD ferrite beads and put them JUST below the basket attachment point to the 'radials'. This will prevent radiation, JUST LIKE A BALUN OR CHOKE ON A COAXIAL FEEDLINE!!!. Do NOT try this with full power, you'll crack'em good! The INSIDE of the basket will STILL contain the radiation pattern (and the 4 radial version does better than the original siggie design), BUT you will get LITTLE 'feedline radiation' from the OUTSIDE of the basket, or as Shockwave had put it, the colinear effect....

The antenna BASICALLY performs just like the marketing BS from the Antron.... It's a half wave over a quarter wave... The ODD thing that makes this NOT apparent and nobody takes into account one thing (in the basket): VELOCITY FACTOR. Because the basket flares out and is a transmission line, the internal conductor will HAVE to be shortened to maintain ELECTRIC length.

Exactly why I asked that specific question, he sounds like he's saying "LITTLE" as in not very much, or 'negligible', which would make it more of an efficiently fed elevated ½λ without much energy in the, "over ¼λ" dept.

 

[Shockwave]

It's become clear that the cone effects many things and serves more then one function. It's a tapered transmission line that transforms impedance. It's a shield that confines out of phase radiation. It emits it's own in phase radiation supporting the collinear claim.

Some things that are not so clear is that the antenna performs well with it's top section close to 5/8 wave. Even though changing the top section from 1/2 wave to 5/8 wave would seem to cause a large change in it's drive impedance, the antenna tunes well in either case.

What wavelength radiator works best is still open for debate as far as I'm concerned. The new Vector suggests that 3/4 wave has the best far field gain. Test's that Bob and myself have conducted in the field suggest closer to 7/8 wave produces more far field gain.

The last thing I question is if there is any effect of the hoop playing a part in acting as a counterpoise or ground plane for the upper section. The addition of the loop itself has little impact on the gain of this antenna. It does improve bandwidth and virtually eliminates any directional characteristics from the radials.

With respect to how much productive radiation is coming from the cone. There is no reason to speculate. Refer back to the CST model and you can see exactly how intense this radiation is. Granted it's not as strong as the upper portion of the radiator. However, keep in mind the current is divided into the four radials.

 

[Shockwave]

I've also used enough center fed vertical dipoles to know the advantage of the Sigma design goes well beyond efficient feeding of an elevated end fed 1/2 wave element. I work with this everyday and know it's not a few feet of height or efficient feeding alone.

In my applications the antennas are typically installed 10 wavelengths or more above ground. Ten feet either way here makes little difference. When we remove a single center fed vertical element and replace it with the Sigma design, we pick up about 3 db in every case.

 

[BOOTY MONSTER]

im no where near you guys in antenna knowledge ..........
it looks to me like the color pic shows the cone acting kinda like the shield on coax with there being a different signal/polarity on the inside and outside of the coax/basket .
is that right or wrong ?????

 

[Shockwave]

You are correct with the polarity / phase being reversed inside the shielded cone (tapered transmission line) from what is being radiated on the outside.

 

[bob85]

i agree the radials form a transmission-line that radiates constructively with the upper 1/2-5/8wave of mono-pole,

IF the mono-pole was isolated from the radial sleeve and direct fed at the base you would have two impedance's, transmission-line mode and antenna mode impedance seen in parallel at the feed-point,

transmission-line mode impedance would be the high end impedance of the tapered open sleeve transformed to a low impedance through the electrical length of the transmission-line formed by the radials around the central mono-pole,

antenna mode impedance and resulting antenna mode current in the portion of mono-pole above the radial sleeve is determined by the electrical length of the mono-pole in open sleeve antennas,

the sigma style antennas are not fed at the bottom of an open sleeve, they need not be 3/4wave to have significant current flowing in the mono-pole above the sleeve,
sigma's work fine with or without radials over a wide range of mono-pole lengths,
me and a local both ran 3/4wave gamma fed scaffold poles years ago, they are a bit of a cloud warmer without the radial sleeve but they work ok,

i looked at velocity factor/dielectric constant in sleeves, sleeve baluns, isopoles, and much more while the j-pole camp peddled their 1/2wave endfed diatribe,

adding the radials has the effect of electrically shortening the mono-pole and radials, raising the resonant frequency,
you will have to lengthen the elements to maintain the same resonant frequency,

avanti realised that they could add upswept radials to the gamma fed extended monopole to constrict dissonant radiation from the lower 1/4wave of monopole while adding constructive radiation from the radial sleeve creatng a 1/2wave over 1/4wave co-linear effect that does exactly what the patent claims vs a 5/8wave groundplane,

the cst plot shockwave posted should remove any doubt about how sigma style antennas work, that picture is worth a thousand words and more,

when i swapped my beatup vector hybrid for the i10k i saw a reduction in local signal strength and a notable reduction in how far i can talk without skip,
at the same time i saw short hop high angle skip improve and lost out on real dx 12,000 miles into australia

 

[Marconi]

i agree the radials form a transmission-line that radiates constructively with the upper 1/2-5/8wave of mono-pole,

Bob, are you suggesting that the top half wave is part of what looks like a 5/8 wave radiator above the Sigma4/Vector hoop? That is what it looks like to me and I think CDX007 has also suggested that, but maybe I'm wrong. Personally I think the Vector makes more sense described as a 5/8 wave over a 1/4 wave that happens to be a 3/4 that measures 7/8 wave. That said however, you may be referring to the top of the stock Sigma4 antenna being 1/2 wave and the modified Vector type being the 5/8 wave radiator.

IF the mono-pole was isolated from the radial sleeve and direct fed at the base you would have two impedance's, transmission-line mode and antenna mode impedance seen in parallel at the feed-point,

transmission-line mode impedance would be the high end impedance of the tapered open sleeve transformed to a low impedance through the electrical length of the transmission-line formed by the radials around the central mono-pole,

antenna mode impedance and resulting antenna mode current in the portion of mono-pole above the radial sleeve is determined by the electrical length of the mono-pole in open sleeve antennas,

the sigma style antennas are not fed at the bottom of an open sleeve, they need not be 3/4wave to have significant current flowing in the mono-pole above the sleeve, sigma's work fine with or without radials over a wide range of mono-pole lengths, me and a local both ran 3/4wave gamma fed scaffold poles years ago, they are a bit of a cloud warmer without the radial sleeve but they work ok,

Isn't this what the open sleeve antenna in the ARRL you refer to does so well?

i looked at velocity factor/dielectric constant in sleeves, sleeve baluns, isopoles, and much more while the j-pole camp peddled their 1/2wave endfed diatribe,

adding the radials has the effect of electrically shortening the mono-pole and radials, raising the resonant frequency, you will have to lengthen the elements to maintain the same resonant frequency,

avanti realised that they could add upswept radials to the gamma fed extended monopole to constrict dissonant radiation from the lower 1/4wave of monopole while adding constructive radiation from the radial sleeve creatng a 1/2wave over 1/4wave co-linear effect that does exactly what the patent claims vs a 5/8wave groundplane,

I think you are right on the money here, no matter what tall-tale says about the I-10K. Did you notice that he didn't respond to my request to share his Eznec model of the Sigma4? I think he's scared.

the cst plot shockwave posted should remove any doubt about how sigma style antennas work, that picture is worth a thousand words and more,

Yep, and any CB Goober should be able to sense that about what he sees in that image if he ain't color blind.

when i swapped my beatup vector hybrid for the i10k i saw a reduction in local signal strength and a notable reduction in how far i can talk without skip, at the same time i saw short hop high angle skip improve and lost out on real dx 12,000 miles into Australia

I don't know about DX yet, but I see a little less signal with my I-10k vs. GM, albeit the GM is maybe 2'-3' feet higher at the mount. I just ran out of energy yesterday trying to push that big old GP all the way up. Yesterday, while I still had my A99 up I was able to talk to an old buddy in Limestone county Texas which is a little over 130 miles NW of me with a 2+ signal on the GM and 2 on the A99. Both antennas made it TX'ing too. We haven't had much if any DX for a day or two, but the A99, TO, and the GM have been making it to Australia and Hawaii, just fine. I can't be sure, but my experience seems to suggest that the TO is a bit more reliable with DX at about all ranges.

 

[bob85]

Originally Posted by Marconi
Bob, are you suggesting that the top half wave is part of what looks like a 5/8 wave radiator above the Sigma4/Vector hoop? That is what it looks like to me and I think CDX007 has also suggested that, but maybe I'm wrong. Personally I think the Vector makes more sense described as a 5/8 wave over a 1/4 wave that happens to be a 3/4 that measures 7/8 wave. That said however, you may be referring to the top of the stock Sigma4 antenna being 1/2 wave and the modified Vector type being the 5/8 wave radiator.

eddie,
im saying that in the stock sigma you have about 1/2wave above the
radial sleeve and on the old style vector you have aboout 5/8wave above the sleeve,

"Isn't this what the open sleeve antenna in the ARRL you refer to does so well?"

yes it is, which proves to me YOU bothered to read what i asked people to look at,
go to the top of the class


"I think you are right on the money here, no matter what tall-tale says about the I-10K. Did you notice that he didn't respond to my request to share his Eznec model of the Sigma4? I think he's scared."

i have no idea why toll-free did not share his model info with you, im not sure he used eznec, you know my feelings on eznec and the sigma style antennas, i will stick with ezbob

"Yep, and any CB Goober should be able to sense that about what he sees in that image if he ain't color blind."

that depends on how much 5/8wave snakeoil they ingested,

desert snakeoil is powerfull stuff my friend, at first i thought it was just a case of lack of understanding, people looking at antennas through the eyes of an electrician where ohms laws rule resistive losses, kirchoff's laws are a puzzle to ohmies,
the longer its gone on i realise it can only be scullduggery, nobody can be that dumb as to keep arguing without looking at the evidense or posting anything at all to backup their claims in over 6 years,

it does not surprise me that j-pole jay thinks a hairpin match gives 3db gain over a gamma or that he don't know where the other half of a gamma fed element gets its energy and never shortened an element when converting from gamma to hairpin feed,
i mean its common sense aint it, if a gamma only feeds one half of an element and a hairpin feeds both halfs it MUST have 3db more gain eh lolol,
if people took the time to look at whats been said they will realise that its not restricted to the sigma4, almost everything he posts is cb hogwash,
my signature explains my feelings,


"I don't know about DX yet, but I see a little less signal with my I-10k vs. GM, albeit the GM is maybe 2'-3' feet higher at the mount. I just ran out of energy yesterday trying to push that big old GP all the way up. Yesterday, while I still had my A99 up I was able to talk to an old buddy in Limestone county Texas which is a little over 130 miles NW of me with a 2+ signal on the GM and 2 on the A99. Both antennas made it TX'ing too. We haven't had much if any DX for a day or two, but the A99, TO, and the GM have been making it to Australia and Hawaii, just fine. I can't be sure, but my experience seems to suggest that the TO is a bit more reliable with DX at about all ranges."

i can't comment on the i10k vs gm yet

 

[Shockwave]

Bob, I find both your knowledge and humor refreshing. When I first got into electronics I use to think the hunk of metal the coax plugged into outside was the simple part and all the circuits inside the radio were the hard part. Thirty years later and I can honestly say I had it backwards. Truly understanding what RF does once it hits the antenna and begins to radiate has taken more effort.

It's what I've done everyday for the last decade and I still wish I knew twice what I do because I'm sure there is at least that much more to learn. The question is from who do we learn because much of the missing information is covered over by those who promote misinformation. Be it willingly or by accident. Sometimes it's just too hard to let go of old ideas that were wrong. I know because I'm stubborn too but realized that gets in the way of the learning process.

 

[CDX-007]

I'd sure like to see the entire 360° CST on the "New Sirio Vector 4000 ¾λ Coaxial J-Pole" - as Sirio refers to it.

- Seems odd they would send only a single slice of the CST, ...and one that's not even in full bloom.

Back in '88, the LW-150 (same basic dimensions as the new Vector) didn't keep up with the Penetrator or I would have kept it.

I liked it's appearance better than the Penetrator,

Twice the weight of the P500.

It was the newest,
Latest,
Greatest thing at that time.

Gold annodized

Heavy wall construction

CNC machined radiator section couplers, no screws or hose clamps

Taller for a higher vantage point

Longer for more capture area...

Yep, I sure had high hopes for it.

I remember thinking, (when on the ladder, screwing on the coax connector to the base of the gamma) "I wonder how much I can sell the Penetrator for and who will want it?"

Alas the "¾λ Coaxial J-pole" didn't keep up with the P500 so down she came and off she went, down the road.

Empirical experience is hard to ignore or forget, still, I'm tempted to get that Saliut together using Sirio dimensions just because you guys, Bob85, Shockwave & Marconi are having such good luck with yours.

But it sure looks like minimal current bloom from the cone to me, especially in comparison to that of it's upper ½λ bloom.

Hey Shockwave, dare you ask for the entire CST and post it here? :drool:

 

[Shockwave]

I considered myself quite fortunate to get my hands on the CST image that was offered to me. Maybe the next time I place a stock order I may ask for the entire file however, I do not want to become a nuisance to these people. Perhaps comparing the Vector image to the other active CST files on their website may help you to understand the Vector CST plot is shown at one of the two phase angles that does indeed produce the current maxima. She is in full bloom!

When I look at that plot it's hard for me to understand how you don't see there is reasonable constructive energy radiated from the cone. Notice the color on the outside, left hand side of the cone is still in red while the right side is in blue? These are the colors of most intense current. For sure the currents in the cone are less then the top of the radiator but lets not forget that one source is being divided into four radials here.

I also had the gold LW-150 and was not convinced it worked as good as the other similar models. The way it tuned with it's fixed dog bone tap point to the main radiator did not impress me. It wasn't until I replaced the gamma and modified the radiator tap point to be adjustable that I felt this antenna was working up to par. That forth radial does make an improvement too. More so then on a 5/8 wave because here it's used for shielding also.

 

[CDX-007]

I considered myself quite fortunate to get my hands on the CST image that was offered to me. Maybe the next time I place a stock order I may ask for the entire file however, I do not want to become a nuisance to these people. Perhaps comparing the Vector image to the other active CST files on their website may help you to understand the Vector CST plot is shown at one of the two phase angles that does indeed produce the current maxima. She is in full bloom!

Really, full bloom? That's hard to believe when I compare it to the much fuller SGM bloom, or perhaps I'm seeing the extra gain of a 5/8 over a 1/2...?

When I look at that plot it's hard for me to understand how you don't see there is reasonable constructive energy radiated from the cone. Notice the color on the outside, left hand side of the cone is still in red while the right side is in blue? These are the colors of most intense current. For sure the currents in the cone are less then the top of the radiator but lets not forget that one source is being divided into four radials here.

I see it but I see only a sliver of color not a nice thick bloom, which to me shows only a little energy, as in minimal added gain and definitely not the level I'd want to see if I was designing it for noticeably superior performance, - compared to the SGM, for instance.

I also had the gold LW-150 and was not convinced it worked as good as the other similar models. The way it tuned with it's fixed dog bone tap point to the main radiator did not impress me. It wasn't until I replaced the gamma and modified the radiator tap point to be adjustable that I felt this antenna was working up to par. That forth radial does make an improvement too. More so then on a 5/8 wave because here it's used for shielding also.

Makes me wish I still had it so I could measure the X to see if X=0 at 1:1 SWR.

 

[Shockwave]

You're comparing apples and oranges because the GM produces a single current maxima while the Vector has a pair of collinear current maxima points. The only reason I recommended looking at them was so you could visualize how the pattern changes through the different phase angles. You keep zeroing in on a single radial and fail to recognize you are only looking at 1/4 of the total radiation currents in the cone.

This plot gives no indication of how all the constructive currents in the 4 radials and the top of the main radiator combine in the far field. Which happens to be indistinguishable from the GM and quite an accomplishment for a fiberglass stick. Notice how the manufacturer claims the GM has more gain then all other 5/8 waves that include their own but stopped short of comparing it to the Vector? That's because this company tells the truth.

 

[jazzsinger]

This plot gives no indication of how all the constructive currents in the 4 radials and the top of the main radiator combine in the far field.

Donald this seems to be the biggest difficulty most people have,people see a 2d plot of the near field and can't translate that into what is happening in reality 3d in the far field.

That's because this company tells the truth.

That wasn't always the case Donald, i have sirio catalogues from the early 2000's that show some incredible gain figures on base antennas and outrageous claims for mobile antennas. it's only in very recent years they realised the folly of misleading buyers.