Avanti Sigma4: An alternative view point

[Shockwave]

Interesting thought. Being the Gamma Match is capacitive, I presume an inductor would throw your phase reverse of where you need it for the Vector 4000 phased collinear design to function correctly.

I also had an horrendous thought;

The Sirio Gain-Master is a center-fed, capacitive coupled radiator, 5/8 dipole,
so,
what if one were to take a...

Jo Gunn Pistol

...a gamma-fed, center-fed ½ wave dipole (read DC grounded Starduster) and insulated the radiator from DC ground along with extending the radiator & radials each to 5/16 wave, then adjusted the Gamma for ~zero reactance, (adding a cmc choke & 1:1 balun) shouldn't that function similarly to the new Sirio Gain-Master center-fed 5/8?

- Just a thought :blink:

I just wanted to mention to everyone NOT to buy that Jo Gunn pistol. You would be hard pressed to find a base antenna that would perform worse then this junk. That antenna has it's primary lobe at an elevation angle of 45 degrees and is useless for putting a signal on the horizon. It's sharp angle is also ineffective for good skywave propagation. For them to bring this antenna to market indicates that no gain testing was done whatsoever.

 

[Marconi]

I just wanted to mention to everyone NOT to buy that Jo Gunn pistol. You would be hard pressed to find a base antenna that would perform worse then this junk. That antenna has it's primary lobe at an elevation angle of 45 degrees and is useless for putting a signal on the horizon. It's sharp angle is also ineffective for good skywave propagation. For them to bring this antenna to market indicates that no gain testing was done whatsoever.

Hey Shockwave, you asked Henry for an up-to-date model of the Vector a while back. I haven't modeled the New Vector yet, but will soon. I have modeled the original Sigma 4 from Henry, and just posted some results to my album. If you email me edromans@comcast.net the Eznec model for the JG Pistol that you refer to, I'll send you my Eznec model of the Sigma 4 with a circular hoop, mast, and using original specs for length and diameters. If you don't have the Eznec file, then maybe you could send me the dimensions and/or the JG Manual.

I don't have the dimensions for the JG Pistol and would like to see the bad pattern you refer to. A good friend of mine has a Pistol and he swears how good it is. He is a trouble maker on local channel 19 and this antenna, over several others, gives him plenty of ammo to wage his battles with truckers. I don't agree with his tactics, but that is what he does and that makes me curious in light of your claim.

I haven't fiddled with the Sigma 4 yet to see if I can duplicate your's and Bob's claims for improved gain, or angle, using a longer radiator and longer radials yet, but plan to when I get the Vector 4 successfully modeled.

BTW, I don't find it impossible to model the Sigma 4 up to specs and still see some nice gain at a low angle like we thought a while back. I find that interesting and I was surprised. I can't get the gain that Henery did using the square hoop and the thin wires, but the gain seems good to me and my model shows no segment or geometry errors, since I recently got Eznec5 and can apply more segments.

 

[CDX-007]

Shockwave, I wonder why the JG is so bad, and so different from the Starduster just because they use a different type of feed? It's still a center-fed dipole, just without being insulated from ground.

Is it the Gamma match which gives it a bad angle due to the 90° capacitive phase at the feed point?

Anyway, you've both missed the point of my post,
Marconi, I did mean 5/16, but for each HALF, the radiator and the radials (5/16 + 5/16 = 10/16 or 5/8) like the Sirio GM.

[ I'm also wondering if I'd have to elevate the radials & base bracket from ground to accomplish a Sirio GM type of performance, if even at all possible. ]

And Shockwave, the reason I have a Pistol is because his signal was a weak S-5 on the Pistol where the Imax with the same mast / coax / etc. is now an S-8, 30 miles from me & 3,000' elevation ASL. You're right about warning people regarding it's performance.
- But I'm going to dink with it by trying the 5/16 + 5/16 mod and see what happens - can't perform worse than it does in factory stock configuration

If it works well enough I'll be liberating it into the top of a 90' pine in the middle of town but left for jetsam in a year & a half when my buddy sells that house.

 

[HomerBB]

It seems to me that in one of these V4k threads there was some reference to a 31.5' vertical, and less than 1/4 wave radials with a less than 1/4 wave circumference hoop on the radials optimizing the gain on horizon of the antenna; that is, if my memory serves me.
I have put the Qv4k back into the air. I needed to readjust the gamma for a match as I apparently bumped it out of adjustment moving the long-legged thing around. Owing to the fact that my homebrew version is likely not optimized to the extent that the commercial models would be, I am finding it inferior to my 5/8 GP.
I can hear farther out, and more clearly on the 5/8^ antenna. I seem to be equally well heard by each, but the increased white noise level on the Qv4k leaves me helpless on this antenna compared to the 5/8 wave. Admittedly, the more conventional 5/8 GP has become so familiar to me that I believe if I had sufficient materials around me i could have a working model up in the air and operational within two to three hours.
I am wondering if I should attempt to maximize the Qv4k by adjusting the vertical length, the hoop, and the radials to the best model discussed. If so, can someone remind me what those exact, or near exact dimensions are.

As it is now:

5/8^ GP @ 10 miles to base station 9 S units
Qv4k @ 10 miles to base station 7 S units

5/8^ GP @ 20 miles to base station 5 S units
Qv4k @ 20 miles to base station 3 S units

5/8^ GP @ 30 miles to base station 2 S units w/understandable audio
Qv4k @30 miles to base station 0 S units w/a mere whisper of sound

5/8^ GP @ 40 miles to base station 0 S units w/understandable audio
Qv4k @ 40 miles to base station 0 S units w/nothing in the receive

At this point I can only fairly assess this as faulty craftsmanship on the Qv4k.

Anyone have those other dimensions?

 

[Marconi]

Homer, as you're aware the Vector/Sigma is much more sensitive in the base of the antenna due to the radials affecting the antenna more-so that the conventional 5/8 wave. Let us know which Vector you tried to emulate. I'm sure you posted it somewhere in this thread, but that would help.

Do you recall the complaints I got from two customers some years ago that that I often talk about, and maybe even in this thread. They bought 31' foot CTE Saliut models from me. They each made their antennas as long as they could and tuned them. They complained that they talked alright, had a good match, but the receive was no good. Is that more or less what you are seeing, albeit you complaint is the white noise? They didn't specify specifically, but their problems could have been just as you described, if I read your report correctly.

BTW, that symptom can also be a clue that your common mode currents are out of control, increasing noise. I think you use a coaxial choke, but sometimes they don't work as expected, and I contend this is can happen if the choke is too long.

Since you have to take it down to adjust the gamma, check that out and let me know, so I can put the information in my bundle of good or bad stories.

Good luck,

 

[HomerBB]

When I lay it over I'll go over it. I'll check the coax again, and perhaps eliminate the choke as a possible improvement maker. As for the white noise, it seems to be a continuous problem at this location. I'll need to measure the antenna again to be sure of my model. I have a sloper dipole up that is noisier than the Qv4k, but it seems noisier than the 5/8.
Even tonight I broke to some stations on a channel I've been talking on for the past year and a half. A station I've gotten 5 S units and matching audio from on the 5/8 was received as 1 S unit and matching audio on the Qv4k. I think I'll revisit all the joints on the antenna, too. Check it real close and see what I get.

 

[Shockwave]

Shockwave, I wonder why the JG is so bad, and so different from the Starduster just because they use a different type of feed? It's still a center-fed dipole, just without being insulated from ground.

Is it the Gamma match which gives it a bad angle due to the 90° capacitive phase at the feed point?

Anyway, you've both missed the point of my post,
Marconi, I did mean 5/16, but for each HALF, the radiator and the radials (5/16 + 5/16 = 10/16 or 5/8) like the Sirio GM.

[ I'm also wondering if I'd have to elevate the radials & base bracket from ground to accomplish a Sirio GM type of performance, if even at all possible. ]

And Shockwave, the reason I have a Pistol is because his signal was a weak S-5 on the Pistol where the Imax with the same mast / coax / etc. is now an S-8, 30 miles from me & 3,000' elevation ASL. You're right about warning people regarding it's performance.
- But I'm going to dink with it by trying the 5/16 + 5/16 mod and see what happens - can't perform worse than it does in factory stock configuration

If it works well enough I'll be liberating it into the top of a 90' pine in the middle of town but left for jetsam in a year & a half when my buddy sells that house.

I'm sorry, I thought this Jo Gunn was the "Son of a Gunn" 7/8 wave model. Looking closer I see it's just a shunt fed 1/4 wave ground plane. This pistol will work just like any other 1/4 wave ground plane but it will handle more power. The Son of a Gunn 7/8 wave that looks identical is the junk with the 45 degree TOA.

 

[Marconi]

I'm sorry, I thought this Jo Gunn was the "Son of a Gunn" 7/8 wave model. Looking closer I see it's just a shunt fed 1/4 wave ground plane. This pistol will work just like any other 1/4 wave ground plane but it will handle more power. The Son of a Gunn 7/8 wave that looks identical is the junk with the 45 degree TOA.

Does anyone have the dimensions for either or both JoGunn's? I would like to model them?

I have a make-shift model I made of the SofG which may not have exact dimensions. I'll look and see if I kept it in my file. If so, I'll post what results I have, but I don't recall it only having a high maximum angle of radiation and/or no worth while gain at some lower angle that is not the maximum.

SW in case you missed it in my previous post above, do you want my new file for the Sigma 4? I know that you asked Henry for one. I have the same file and I can send you Henry's New model or my modified version that is from the same file...showing some nice gain at a low angle instead of very little gain at a high angle.

Henry says he did not work to improve the file, he is working on a new 40' co-linear monopole with some real gain at a low angle.

 

[CDX-007]

Henry... ...is working on a new 40' co-linear monopole with some real gain at a low angle.

Damn, and I was hoping I'd be the first to built a 1/2 over a 5/8 collinear I've got it all laid out but have yet to receive my fiberglass insulator rod.

What do you think I've been building with that Saliut I was supposed to try as a .82 :sneaky2:

 

[HomerBB]

I want to add to the above remarks that when I had the Qv4k on the ground I had it mounted vertical on a fence post with the feedpoint 10' above the ground not insulated from the metal pipe it was on. Whereas the SWR on ch 1 was 1:8.1, and on ch 40 1:2.1, it had some incredibly good ears. The radio it was hooked to in my shed, an old Cobra 87 GTL, lacked the power to get out as far as it was receiving, but, ironically, perhaps owing to the good ears of the Cobra, it seemed to receive better than the 5/8 at feedpoint elevation of 35'.

I have the 5/8 mounted in that spot now, so I'll attempt to see if the 5/8 has improved parked there.

Homer/Charles

 

[Marconi]

I want to add to the above remarks that when I had the Qv4k on the ground I had it mounted vertical on a fence post with the feedpoint 10' above the ground not insulated from the metal pipe it was on. Whereas the SWR on ch 1 was 1:8.1, and on ch 40 1:2.1, it had some incredibly good ears. The radio it was hooked to in my shed, an old Cobra 87 GTL, lacked the power to get out as far as it was receiving, but, ironically, perhaps owing to the good ears of the Cobra, it seemed to receive better than the 5/8 at feedpoint elevation of 35'.

I have the 5/8 mounted in that spot now, so I'll attempt to see if the 5/8 has improved parked there.

Homer/Charles

Homer, I have a A99 on a insulated 12' mast along side my AstroPlane at 45' to the tip. When conditions are good and quiet the AP is typically very quiet and hears better that some of my other antennas and for sure the A99 when it is raised up 30'-40' feet. However with the A99 lower and conditions being a bit variable at the present time, the A99 acts more or less as you describe your Qv4k. I have my antennas on a switch box and that makes this comparison easier to perceive. Were you using a switch box?

I'll also mention that in my modeling the Sigma4/Vector my pattern reports indicate the gain goes down remarkably when the mast is insulated...with the angel remaining the same. This might be something to consider in your evaluation of your Qv4k vs. the 5/8. I can't model a coaxial choke in my models, but I would think its use would be a good idea with this antenna. The model suggests that there is noticeable currents flowing on the support mast, and that may be why insulating vs not insulating shows such significant gain differences. I can't explain why that is, but that is what the reports show. As something to consider, I'll post the patterns for gain and angle below.





Notice also how the affect seems to press down on the pattern for the non-insulated mast setup. In all my models this insulating idea really makes a big difference in gain with my antenna with a 1/4 wave radiator, which really needs an effective ground plane. This also seems to hold true with the 3/4 wave Sigma4/Vector, which I believe really needs a ground plane as well. The 5/8 wave does not seem as ill-affected when I insulate its mast however. This business surprises me, because I would have thought different, but this is what I see in the models.

 

[Shockwave]

Homer, I have a A99 on a insulated 12' mast along side my AstroPlane at 45' to the tip. When conditions are good and quiet the AP is typically very quiet and hears better that some of my other antennas and for sure the A99 when it is raised up 30'-40' feet. However with the A99 lower and conditions being a bit variable at the present time, the A99 acts more or less as you describe your Qv4k. I have my antennas on a switch box and that makes this comparison easier to perceive. Were you using a switch box?

I'll also mention that in my modeling the Sigma4/Vector my pattern reports indicate the gain goes down remarkably when the mast is insulated...with the angel remaining the same. This might be something to consider in your evaluation of your Qv4k vs. the 5/8. I can't model a coaxial choke in my models, but I would think its use would be a good idea with this antenna. The model suggests that there is noticeable currents flowing on the support mast, and that may be why insulating vs not insulating shows such significant gain differences. I can't explain why that is, but that is what the reports show. As something to consider, I'll post the patterns for gain and angle below.

View attachment 3719

View attachment 3720

Notice also how the affect seems to press down on the pattern for the non-insulated mast setup. In all my models this insulating idea really makes a big difference in gain with my antenna with a 1/4 wave radiator, which really needs an effective ground plane. This also seems to hold true with the 3/4 wave Sigma4/Vector, which I believe really needs a ground plane as well. The 5/8 wave does not seem as ill-affected when I insulate its mast however. This business surprises me, because I would have thought different, but this is what I see in the models.

Marconi,

I do not have these models and I'll email you soon so I can see them. What you noticed with the masts falls inline with some of my earlier post regarding the phase of the currents where the mast meets the antenna being the determining factor on insulating the mast or not. The Sigma / Vector has currents that are in phase at this point. Take away it's mast and you lose some gain. You should actually see a slight improvement in gain when removing the mast from a 5/8 wave ground plane. Mast radiation on the 5/8 wave is out of phase below the ground plane elements.

The Sigma is also not a ground plane and adding the standard 90 degree or downward sloping radials is detrimental to it's gain. In field test did show some increased gain when a second set of upward flaring radials was added with a reduced angle. The gain increase was far from worth the mechanical nightmares. At HF frequencies you will want to choke off the coax on the Sigma. The longer wavelength makes a larger section of coax radiate before the currents diminish then I see on FM.

 

[HomerBB]

Thanks, Marconi, that's very helpful.
And you, too, SW. Your piece helps my perception of the data Marconi supplied.
The Qv4k is not insulated from a 10' top joint of pipe, and does have a coax hoke immediately below the feedpoint, however, remember the tip over tower is wood, so there is no conductive metallic connection to actual earth where it currently is. Will this make a difference? Should I bring the coax choke down farther from the feedpoint?

I did not use a switch box on the two antennas when the Qv4k was at ten feet. I walked out to the shed in the back yard and listened on the Cobra in the shed that was hooked to the Qv4k.
The Qv4k was standing where the yellow X is. The tip over tower is located where the red X is.

 

[Marconi]

Marconi,

I do not have these models and I'll email you soon so I can see them. What you noticed with the masts falls inline with some of my earlier post regarding the phase of the currents where the mast meets the antenna being the determining factor on insulating the mast or not. The Sigma / Vector has currents that are in phase at this point. Take away it's mast and you lose some gain. You should actually see a slight improvement in gain when removing the mast from a 5/8 wave ground plane. Mast radiation on the 5/8 wave is out of phase below the ground plane elements.

The Sigma is also not a ground plane and adding the standard 90 degree or downward sloping radials is detrimental to it's gain. In field test did show some increased gain when a second set of upward flaring radials was added with a reduced angle. The gain increase was far from worth the mechanical nightmares. At HF frequencies you will want to choke off the coax on the Sigma. The longer wavelength makes a larger section of coax radiate before the currents diminish then I see on FM.

SW, I think you're right about checking the current flow right below the antenna. I just checked one of my Sigma model's current reports with a non-insulated mast attached, and it shows a 1/4 wavelength of mast below the antenna that is in-phase and probably radiating a little. It is also showing more current flowing by an increase of 95% compared to the insulated mast as follows: .08123A/.004535A as an example of one segment in that area of the mast.

I agree this would make a difference if in-phase with the radiator, and that may help explain the remarkable increase noted in the patterns that I posted above...in favor of the non-insulated mast. If this 1/4 also radiates at 7* like the radiator it may show some benefits, but how do we know. Showing some gain with a model is not always the same as how it responds in the real world.

SW my stuff seems to disagrees with your claims. My models of the 5/8 wave shows much more current flowing on the mast than with the Vector. The currents right below the ground planes are also in-phase with the radials and the radiator, just like on my Sigma4/Vector models. My 5/8 wave models also show a decrease in gain when insulating the mast, but the gain difference is very slight, just as you note.

I have nothing to compare my models with except for the Gain Master model I made by adjusting a 1/2 wave dipole to simulate this new antenna. To me the output results were strikingly similar to the stuff that Sirio published in their GM Manual and they said they were using new top of the line modeling software. Seeing some modeling from others will be helpful in better understanding any mistakes I make.

 

[bob85]

HELP!
i don't understand how current in the mast below the radials can be in phase with the folded up radials, has anybody got a model that shows this, its not what ezbob predicts and makes no sense at all to me phase is denoted by color magnitude by the distance from the element