Avanti Sigma4: An alternative view point

[CDX-007]

That sounds plausible - that the bloom size / appearance is variable by the user, as is the amount of power one programs into the simulation.

So it appears it has "a little" additional current in the cone but that ~75%-80% of the radiated RF energy is from the top ½λ.

 

[Marconi]

That sounds plausible - that the bloom size / appearance is variable by the user, as is the amount of power one programs into the simulation.

So it appears it has "a little" additional current in the cone but that ~75%-80% of the radiated RF energy is from the top ½λ.

007, I don't think the input amperage that the NEC model assumes is user controlled, but the number of segments are, so more segments will show less amperage/X than fewer segments will. This is per model only.

BTW, I see the RF as 100%, indicated by the in-phase action for both the bottom and top sections increasing the capture area by about 50% over a typical 1/2 wave radiator...rather than the bottom just acting to raise the top 1/2 wave section a bit and contributing little to nothing in the standard end fed type 5/8 wave.

For me this is also true of the GM to the degree it can and I think this is what makes the differences I see, albeit they are smaller than others report. The important part is that the GM does show more gain regardless of why or how.

 

[jazzsinger]

Another problem i see with the cst images of the vector 4000 and gainmaster is no-one here really understands how cst works,myself included, so they are trying to translate those images of two of the most complex cb verticals ever made with absolutely no grounding on this software from basic antennas.

What would help immensely is plots of a basic 1/4 wave gp like a starduster m400 and a couple of half waves,one centre fed and one end fed for comparison purposes along with a basic 5/8 wave with and without radials .you have to learn to walk before you start trying to run.

just my tuppence worth,

it would be nice if sirio could post these plots of all the different antennas on their website side by side for easy comparison, would probably end one hell of a lot of arguments on cb verticals.

 

[mackmobile43]

Another problem i see with the cst images of the vector 4000 and gainmaster is no-one here really understands how cst works,myself included, so they are trying to translate those images of two of the most complex cb verticals ever made with absolutely no grounding on this software from basic antennas.

What would help immensely is plots of a basic 1/4 wave gp like a starduster m400 and a couple of half waves,one centre fed and one end fed for comparison purposes along with a basic 5/8 wave with and without radials .you have to learn to walk before you start trying to run.

just my tuppence worth,

it would be nice if sirio could post these plots of all the different antennas on their website side by side for easy comparison, would probably end one hell of a lot of arguments on cb verticals.

Antenna manufacturers should be required by law to provide this type of information with each model produced and sold.

 

[jazzsinger]

Antenna manufacturers should be required by law to provide this type of information with each model produced and sold.

if that was the case many would go out of business immediately when the facts exposed their bullshit snake oil claims.

 

[Shockwave]

Many others could not afford the investment Sirio has put into research and development.

 

[CDX-007]

007, I don't think the input amperage that the NEC model assumes is user controlled, but the number of segments are, so more segments will show less amperage/X than fewer segments will. This is per model only.

BTW, I see the RF as 100%, indicated by the in-phase action for both the bottom and top sections increasing the capture area by about 50% over a typical 1/2 wave radiator...rather than the bottom just acting to raise the top 1/2 wave section a bit and contributing little to nothing in the standard end fed type 5/8 wave.

For me this is also true of the GM to the degree it can and I think this is what makes the differences I see, albeit they are smaller than others report. The important part is that the GM does show more gain regardless of why or how.

I was tossing this around in my mind earlier tonight while I was helping a friend set up for home brewing.

- If the cone area bloom (visual representation of the RF radiation) appeared to be as 'healthy' as it does in the top ½λ I would venture an inspired guess that it would add about 50% more active area thus providing perhaps 1.5dB gain over a ½λ.

As it appears the cone has only about 15%-20% of the level of energy of the top ½λ, I will hesitate to give it more than .3dB gain guesstimate with equivalent minimal ability to lower the TOA.

There appears to be far too little energy in that region for me to believe it is anywhere near close to the upper ½λ in performance enhancement.

- And as far as the current being split between 4 cone radials, if it appears weak in one direction, it's weak in all directions. There's 360° to cover so each radial is responsible for 90°, and it shows what it shows.

I am not surprised the SGM provided only equivalent gain to your Vector, Shockwave, considering how low it was overall in comparison to the Vector, and the fact it is a balanced dipole which I believe needs to be considerably higher above the roof, ground, etc., for it to 'shine' as intended.

I would have no fear of placing a sizable wager on the SGM to outperform the Vector if both were erected at, say, 72' above ground, transmitting 500w pep over flat ground with the receiving station at, say, 75 miles.
- That's a statement, not a challenge, though such a challenge would be very interesting and the possible outcome rouses my ardent fervor.

The one seriously disappointing feature of the SGM is the low power handling handicap.

Only 125w AM...???

 

[HomerBB]

The one seriously disappointing feature of the SGM is the low power handling handicap.

Only 125w AM...???

There is something to be said for this, and while many seem to wonder why Sirio introduced it before they made a high powered version, something about it makes sense for some of us.

Not all CBers are ready or able to join the ranks of the mega-power users. Getting stepped on, or out performed routinely by a couple guys running high dollar antennas and large wattage takes the fun out of radio far too often. With a reasonable cash investment, and a reasonable height, this antenna levels the playing field just a little. So far, were I to look at a production antenna for a low powered or barefoot station that could help me hear and be heard a little better, this would be my choice. The antenna system continues to be the most important part of the setup. And this looks like a new and better choice. There's a definite market for these. Perhaps a more high powered version is on the way.

 

[CDX-007]

There is something to be said for this, and while many seem to wonder why Sirio introduced it before they made a high powered version, something about it makes sense for some of us.

Not all CBers are ready or able to join the ranks of the mega-power users. Getting stepped on, or out performed routinely by a couple guys running high dollar antennas and large wattage takes the fun out of radio far too often. With a reasonable cash investment, and a reasonable height, this antenna levels the playing field just a little. So far, were I to look at a production antenna for a low powered or barefoot station that could help me hear and be heard a little better, this would be my choice. The antenna system continues to be the most important part of the setup. And this looks like a new and better choice. There's a definite market for these. Perhaps a more high powered version is on the way.

I hope so, on 10m it's legal for me to run 1500w pep.

 

[HomerBB]

Me, too. I hope to join the ranks of 10 meter users, also.

 

[Shockwave]

I was tossing this around in my mind earlier tonight while I was helping a friend set up for home brewing.

- If the cone area bloom (visual representation of the RF radiation) appeared to be as 'healthy' as it does in the top ½λ I would venture an inspired guess that it would add about 50% more active area thus providing perhaps 1.5dB gain over a ½λ.

As it appears the cone has only about 15%-20% of the level of energy of the top ½λ, I will hesitate to give it more than .3dB gain guesstimate with equivalent minimal ability to lower the TOA.

There appears to be far too little energy in that region for me to believe it is anywhere near close to the upper ½λ in performance enhancement.

- And as far as the current being split between 4 cone radials, if it appears weak in one direction, it's weak in all directions. There's 360° to cover so each radial is responsible for 90°, and it shows what it shows.

I am not surprised the SGM provided only equivalent gain to your Vector, Shockwave, considering how low it was overall in comparison to the Vector, and the fact it is a balanced dipole which I believe needs to be considerably higher above the roof, ground, etc., for it to 'shine' as intended.

I would have no fear of placing a sizable wager on the SGM to outperform the Vector if both were erected at, say, 72' above ground, transmitting 500w pep over flat ground with the receiving station at, say, 75 miles.
- That's a statement, not a challenge, though such a challenge would be very interesting and the possible outcome rouses my ardent fervor.

The one seriously disappointing feature of the SGM is the low power handling handicap.

Only 125w AM...???

CDX-007, You are not really understanding what is happening in the cone section. You're theory assumes the radials are highly directive and only radiate energy over a narrow radius. Thereby only one radial serves a single direction. The worst possible direction of signal would be having only one of the four radials blocked by the out of phase currents in the main radiator. Still leaving the combined currents of three radials adding to the signal. Just one radial has coverage well over 180 degrees. Each radial can only be blocked by the location of the main radiator. Meaning it's only possible to block one in any direction.

I did test my GM very low to the ground at first. In fact right on the ground before going over 40 feet on the roof and it worked fine. I'm not sure where this idea comes from that the GM is highly sensitive to it's surroundings. If you read my reports you would see I had the Vector originally mounted on the same 10 foot mast before the 15 foot was installed. That made little difference in my location as I've recorded those signals too. To make a long story short, I'm very surprised the GM can hang with the Vector with the GM having 6 feet less in phase capture area.

 

[CDX-007]

CDX-007, You are not really understanding what is happening in the cone section. You're theory assumes the radials are highly directive and only radiate energy over a narrow radius. Thereby only one radial serves a single direction. The worst possible direction of signal would be having only one of the four radials blocked by the out of phase currents in the main radiator. Still leaving the combined currents of three radials adding to the signal. Just one radial has coverage well over 180 degrees. Each radial can only be blocked by the location of the main radiator. Meaning it's only possible to block one in any direction.

Are you certain the simulation program wasn't given, and doesn't take into account, the number of radials and the cumulative current gain?

It appears to show two of the four radials, one on each side, left & right, and being that it is designed to show a flat slice from one side for a visual representation of the actual radiation currents, it sounds like you're presuming that the program is making the same mistake you think I am, and not taking into account the parameters you mentioned.

- I have a hard time accepting that idea.

I believe we are seeing exactly what a field strength meter would show regarding the radiated field strength in each area of the antenna's vertical plane.
I just can't accept that the designer of that program would leave a large hole requiring mental gymnastics in order to correct it's 'flaws'.

I did test my GM very low to the ground at first. In fact right on the ground before going over 40 feet on the roof and it worked fine. I'm not sure where this idea comes from that the GM is highly sensitive to it's surroundings. If you read my reports you would see I had the Vector originally mounted on the same 10 foot mast before the 15 foot was installed. That made little difference in my location as I've recorded those signals too. To make a long story short, I'm very surprised the GM can hang with the Vector with the GM having 6 feet less in phase capture area.

It's common knowledge that the pattern of any balanced antenna will be distorted by the introduction of near field articles, especially when those articles are of a nature to resonate or reflect RF.

Even Sirio recommends keeping it ~6m above the roof.

When I first installed my SGM I was immediately disappointed.

I was an S-7 to Phil where the Imax had been showing an S-8.5 and the Penetrator ½λ away showed an S-9, all with his attenuator on.

After simply removing the Penetrator from the near field, the SGM came alive and was an S-9+2 on Phil's Pro3, and his signal increased ~3dB on my 751A.

(A line drawn from mine to Phil's QTH is almost directly perpendicular to a line running between the two antenna masts, which are ½λ apart.
With both antennas up there were up to 3 S-units difference off to the sides favoring either antenna depending on which side, so I discount those directions when testing and remain with signals only perpendicular to both.)

No doubt the SGM will function reasonably well when installed too close to another article or the ground, but I wouldn't expect the nice flat TOA or gain pattern to remain intact.

 

[Marconi]

This antenna should change conventional thoughts on fiberglass antennas. The Gain-Master replaced my Vector last week. Before the antenna arrived I didn't intend to install it on my roof. Some back yard testing of the bandwidth made me give it a try. I'm glad I did. It is working every bit as good as the Vector with much wider bandwidth and simple appearance. RFI is non existent.

I see signs that this antenna with it's virtually parallel 0 degree TOA is performing better then I expected in the distance. It does exactly what Sirio advertises. I think this will be the antenna I recommend to most people seeking a good vertical omni. The only possible drawback is the power rating. Do not exceed the advertised ratings. I intend to investigate the possibility of replacing the capacitor with a Semco metal cased mica and attempt to convince Sirio to do the same.

Shockwave I probably started this issue about the GM being sensitive near the bottom, and I believe CDX007 agrees with me for his own reasons. Your quote above is what you said the week you received your GM and tried it on the ground before raising it up on your roof. You said; "Some back yard testing of the bandwidth made me give it a try. I'm glad I did."

To me, this sounds like something happened that caused you to pause... instead of finding the GM being fine like you claim below. I don't understand the seeming contradiction. Can you tell us what happened back then that caused you to pause, because in your post below you suggest something different, or am I just wrong?

I have explained before why I found the GM sensitive and now you question my claim? It not a big deal, because for me these are just opinions, but I would like to hear your side of this delima. I made a further explaintation below.

BTW, I raised the same issue with one of the guys in Europe that tested his new GM and reported it working poorly. He too had his mounted low to the Earth for some reason not explained. His pictures showed it mounted down below the two story homes surounding the area. I asked him why, and after a while I just figured he didn't have a clue what the hell this Yank was talking about...and he never responded.

I did test my GM very low to the ground at first. In fact right on the ground before going over 40 feet on the roof and it worked fine. I'm not sure where this idea comes from that the GM is highly sensitive to it's surroundings. If you read my reports you would see I had the Vector originally mounted on the same 10 foot mast before the 15 foot was installed. That made little difference in my location as I've recorded those signals too. To make a long story short, I'm very surprised the GM can hang with the Vector with the GM having 6 feet less in phase capture area.

I can't dispute your claim that you're GM worked fine on the ground, because I wasn't there. You claim here that it worked fine, but in your original post on the GM's arrival you seemed unsure for some reason for how it was working on the ground. I remembered your statement, so when I got my GM I took careful note of what happened when I installed it low on my new mount next to my radio shack. I mounted it on my 12' foot P/U pole that was totally collapsed. So, the antenna was close to the roof in that situation and it didn't show a bad match I don't think, but it worked just like other antennas I have when put in the position, its performance was attenuated. I raised it up about to 17', which is near the top of the peak on my roof...and it was still attenuated. So, I raised it up the full 9' for the 2nd section to about 21' feet, and then I noticed the attenuation was gone. The stations up north were coming in loud and clear at that point. That is the only reason I made my claim...about the GM being sensitive to stuff near the base of the antenna. I might be wrong, because I think the problem is due to blocking that Avanti referred to as "Shadow" in their patent for the AstroPlane. That said though, I still think I would try to keep stuff away from the fine working choke at the bottom as best one can.

How say you?

 

[Shockwave]

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.

 

[CDX-007]

And don't forget water and gas pipes and electrical, phone and TV wiring.