Avanti Sigma4: An alternative view point

[MisterFatty]

On a less sarcastic note...

Any testing and input which sheds further light upon this age old debate is welcome addition. However I would always be skeptical of tests such as this last one. Mainly because I've experienced first-hand how very small details can make a major difference in results.

Regardless of this thanks for taking the time to add your input wavrider

 

[wavrider]

I am satisfied with the comparison results, as I can hear both stations.

One was stronger than the other, simple as it gets, it is not perfect nor has it ever been intended to "prove" which antenna is better than the other.

On a more serious note, both are ground planes, what exactly can a ground plane have to brag about as far as gain? Both RX and TX, really one might have .25 of a DBD gain over the other one if any at all.

Throw out all the advertising hype, the inflated numbers etc. etc.

Compare each to a dipole to see how much gain it has over a dipole, not that free space crap which is a dream theory. DBI means nothing.

Ground plane is a two letter word which if looked up in Webster's book the definition should read "radiates equally poor in all directions."

A full wave loop wire antenna will have more gain than any of the two antennas compared in this thread.

If an antenna is needed with more true gain it will be a yagi or a quad.


I have "no side of the fence to be on" so the results really does not mean a hill of beans to me, a question was asked, I answered it based on my comparison, nothing more, nothing less.


An 11 meter ground plane is fun to play with, 1/4 wavelength on 11 meters is small compared to 40 meters so why not play with 11 meters antennas, find something that works and then apply it to a good long wave length band and do some real DX talking.

Thanks for the replies, comments, sarcasm, and anything else, antenna's are great fun, and will continue to be a subject of discussion, debate and controversy. The remarks in this thread are mild compared to some "on the air" discussions on 20 and 40 meters about antennas.

But it is fun to experiment, and get other opinions, pros and cons, etc etc.

No pictures of the stripper, strippers are like antennas, they are better left to an individuals imagination sort of like a 5/8 wl versus Sigma IV.

 

[CDX-007]

Definitely some Gospel truth contained within that last post.

I am still hoping to be wrong about my expectations of the modded Salute losing to the .64 & 5/8 designs, because I want it to win. I like it's appearance better than a 4-radial CB looking thing on my roof. That 'ice cream cone' looks cool and now I wish I would've kept my LW-150 just in case all the monopole hoopla proves true.

- But mostly, I would LOVE to increase my omni performance since I find it the most used antenna in my airspace.

I don't see any reason a couple of obviously sharp operators such as Bob85 & Shockwave would be interested in propagating BS, nor do they seem the type to be too obtuse to tell a better performing antenna from naught so I actually have high hopes that I simply didn't find the right tuning for my old LW-150 waaaaaaaaaaaay back in '88... dang it, but that I WILL in a week or seven for Serge, thus spurring me on to fab one for myself from what else but...

Penetrator parts!


But I admit, I still have my doubts.

- We'll see soon enough.

 

[Shockwave]

To make a long argument shorter, all I can say is if the 5/8 wave worked better, I'd be producing 5/8 wave broadcast antennas without a doubt. I could save thousands on Teflon gamma match material and extra aluminum tubing in each production run. There aren't too many applications where it is more important to have accurate gain figures then when filing a construction permit for a broadcast station.

With respect to differences in gain with ground plane antennas, there is a wide range. To say all verticals are similar and you need a beam to realize gain is false. Just going from an end fed half wave to a 5/8 wave is noticeable. Try going from a 1/4 wave to 7/8 wave.

Someone mentioned the full wave quad loop. I think it's interesting to note that the stock 7/8 wave Vector and the full wave quad loop have the same gain of 2 dbd. Except the quad is only bi-directional and the Vector is Omni. Hey Bob, sounds to me that Cebik's non apparent collinear theory may be right on.

 

[bob85]

007,
you are correct i am not the type to make bs up to look good or aid my financial situation, what i claim is what we see, i set out to understand how that can be when everybody worth their salt knows that a single element vertical longer than about .64wave provides less usefull gain on the horizon due to the formation of high angle lobes,
i dont claim to fully understand how the sigma works and i am always looking to learn,

in their defence the j-pole camp have provided nothing by way of an alternative method of operation for the sigma style antenna in 5 years of debating this topic other than the j-pole nonesense and i dont expect them to when they also dont undertsand feedlines, gammas, chokes, sleeve baluns, cm currents, ballanced/unballanced antenna currents,


shockwave

"To make a long argument shorter" lol thats wishfull thinking,

what cebik told me is what i posted,
i did not add my bit on twist to make it fit my argument or otherwise,
what he said including not wanting to get involved with pages of meanigless argument this type of antenna often generates and that what i was claiming was perfectly possible due to the none aparent colinear effect is EXACTLY what he told me,

heres my current ( no pun intended ) take on whats going on which i will update/ammend as i learn more,

 

[CDX-007]

OK, if it really does what you'ze guyz say then someone needs to come out with a collinear version, one phased on top of the other.

Can you imagine the gain?

Can you imagine the size!!

But do-able for VHF-UHF.

- I'm already scheming on how to utilize the base and radials / radiator from the Penetrator to make one.

I wonder if I could adapt the Beta matching system, with some mods...?

Edit:

One thing I'm somewhat miffed about is why you, Bob85, and you, Shockwave, end up with two different loop radial lengths, and by more 10%!?!?

That seems to me like it would be a critical measurement and something which wouldn't change radically, even with differing ground conductivity and height above ground.

 

[bob85]

007,
we end up with different radial lengths partly because shockwave is using a larger hoop and wider radial angle,
the hoop adds half the distance between a radial and its neighburs to the length of the radials,
secondly as the radials are swept closer to the central monopole impedance drops and resonant frequency of both radial sleeve and monopole goes up,
conventional maths for electrical length go out of the window as you sweep the radials up towards the central monopole,
for instance a gamma fed monopole with 90 degree radials that is electrically 3/4wave will be less than 3/4wave when you sweep the radials up,

another variable that im not sure about but have a gut feeling is that we may be manipulating radiation angle as seen in professional sleeve monopoles,

not sure about your beta match idea, i like the gamma, imho it would not be a sigma4 style if you did not use the gamma,
there is absolutely nothing wrong with gamma matching if its done correctly with apropriate tube diameters and spacing, the lossy gamma claim is nonesense,
the stock gamma is shitty but it does work ok with an ACOM 1000 full power fm without arcing or melting,
you can lower system q and loss with a fatter gamma rod but i never tried one to compare signal performance or bandwidth.

 

[CDX-007]

OK on all that, but with different loop diameters and different 'radial' lengths how can both of you still end up with the same basic length radiator (~29' 7") IF as the loop size is increased and the angle of the radials falls further away from the radiator, the radiator must grow longer to retain resonance, gain, and a low TOA...???

..........................................................

Before I build & erect mine I want to know:

1) What height above ground has been shown to be best?

2) Should the antenna be insulated from the supporting structure even though I will be utilizing a CMC choke?

3) Should the guy wires be insulated, or perhaps cut to a specific length to aid in shadowing RFI and/or adding a counterpoise?

4) If not insulated, is there a specific length of mast to either avoid or choose for best performance?

5) And lastly, should the antenna base be Earth grounded or is grounding only through the coax shield (to a grounded radio) preferable?

73

 

[multimode200]

The argument from the j-pole camp i suppose would be the measurement from where the gamma match taps into the pole back down the pole up the basket leg and half way across the basket ring against the total length of the driven element from the tapping point up (ratio of the two respective lengths), also the fact whether or not the antenna is DC grounded.

 

[bob85]

007 you got that backwards,
as the radials move away from the monopole the resonant frequency comes down impedance goes up, you would shorten it to maintain the same electrical length, i doubt that my antenna was set to a resonant length, like i said before i dont claim to understand exactly whats going on and the guys that would know dont wish to get involved with petty arguments which is understandable, LB said what he said, a second opinion would be very nice but unlikely,
its not an antenna you can just look up in any book i have seen so i look at the closest antennas to it physically,

shockwave tuned on a lower frequency with a wider radial angle,

imho the higher the better, 73feet to feedpoint worked very well at my last location with all my antennas, i never saw a situation where lower was better locally, dx is a different matter,

isolating choking grounding or not is your choice so long as its the same for all antennas, i will try it all ways and note any changes, i like experimenting when i can get my ass in gear,

i have pondered and talked about mast and feedline lengths with friends, w8ji mentions a worst case scenario mast length for cm currents,
electrical length of mast and coaxial outer shield?

if i had to use guy wires i would use phylistran or similar, i dont use metal guys with or without eggs to break them up but many people do and seem happy,

isolating the mast then running a ground wire from antenna down the mast to a ground rod would be defeating the aim of isolation,

if you isolate i would ground the coax before it reaches the house for safety.

 

[multimode200]

Half wave over a quarter wave, if the quarter wave is not in phase with the half wave and there is full cancellation then its a J-Pole I suppose, or simply a half wave linear. From the amount of gain this antenna has compared with a J-Pole it suggests otherwise, so maybe there is an element of colinear about it. Who knows, how do you know if the quarter wave section is radiating?

 

[CDX-007]

007 you got that backwards,
as the radials move away from the monopole the resonant frequency comes down impedance goes up, you would shorten it to maintain the same electrical length, i doubt that my antenna was set to a resonant length, like i said before i dont claim to understand exactly whats going on and the guys that would know dont wish to get involved with petty arguments which is understandable, LB said what he said, a second opinion would be very nice but unlikely,
its not an antenna you can just look up in any book i have seen so i look at the closest antennas to it physically,

shockwave tuned on a lower frequency with a wider radial angle,

imho the higher the better, 73feet to feedpoint worked very well at my last location with all my antennas, i never saw a situation where lower was better locally, dx is a different matter,

isolating choking grounding or not is your choice so long as its the same for all antennas, i will try it all ways and note any changes, i like experimenting when i can get my ass in gear,

i have pondered and talked about mast and feedline lengths with friends, w8ji mentions a worst case scenario mast length for cm currents,
electrical length of mast and coaxial outer shield?

if i had to use guy wires i would use phylistran or similar, i dont use metal guys with or without eggs to break them up but many people do and seem happy,

isolating the mast then running a ground wire from antenna down the mast to a ground rod would be defeating the aim of isolation,

if you isolate i would ground the coax before it reaches the house for safety.

Really? I would have sworn that it required lengthening from 3/4 wl to ~29' 7" when the loop was enlarged and radials shortened. I would go hunting and locate the post but I'm just too tired. Family issues - up 'til 5:00am.

73

 

[bob85]

are you confusing what effect the radials have on transmissionline mode impedance in a sleeve monopole and what lengths we end up with?,

from my first post in this thread,

"sleeve to monopole spacing effects impedance as does element diameter ratio, the closer spacing of the sleeve in the sigma design lowers antenna impedance"

freecells post

"conversely, as the radial elements are raised the input impedance is lowered.
as the radials are raised towards the radiating element something else interesting occurs. the
radiating element becomes less sensitive to the influence of surrounding objects and terrain
in the near field, allowing the antenna to be mounted in locations and at heights above ground
that would be extremely deleterious not only to the feedpoint match but also to the radiated
pattern emanating from the radiating element.

as the radials are swept upwards towards the radiating element capacitance between the radials
and the radiating element increases, effectively raising the resonant frequency of the system
or causing the electrical length of both the radials and the radiating element to be shortened"

further up this page

."secondly as the radials are swept closer to the central monopole impedance drops and resonant frequency of both radial sleeve and monopole goes up,
conventional maths for electrical length go out of the window as you sweep the radials up towards the central monopole,
for instance a gamma fed monopole with 90 degree radials that is electrically 3/4wave will be less than 3/4wave when you sweep the radials up"

from the arrl

If the sleeve elements were brought closer to
the central monopole such that the ratio of the spacing to element diameter was less than 10:1, then the characteristic impedance of the 3-wire transmission
line would drop to less than 250 W. At 28
MHz, ZA remains essentially unchanged, while ZT
begins to edge closer to 52 W as the spacing is reduced.
At some particular spacing the characteristic impedance, as determined by the D/d ratio, is just right to transform the end impedance to exactly 52 W at some frequency. Also, as the spacing is decreased, the frequency where the impedance is purely resistive gradually increases.

again i am not saying this IS how its working , its all i can find that seems even close at the moment, im sure theres more to it,
if you read my first post i used the open sleeve antenna as an example that just because there are currents flowing in opposite directions in the lower 1/4wave it does not mean that radiation from the radial sleeve cannot combine constructively with radiation from the upper 1/2wave to increase gain.

commercial 3/4wave sleeve antennas i have seen have the same claimed gain as the vector with radiation angles @ above or below the horizon, gain is higher and radiation angle lower than a 5/8wave groundplane, the tradeoff seems to be a small reduction in vertical beamwidth.

 

[bob85]

i dont for sure but the sleeve monopole does according to the arrl.

 

[CDX-007]

are you confusing what effect the radials have on transmissionline mode impedance in a sleeve monopole and what lengths we end up with?,

from my first post in this thread,

"sleeve to monopole spacing effects impedance as does element diameter ratio, the closer spacing of the sleeve in the sigma design lowers antenna impedance"

freecells post

"conversely, as the radial elements are raised the input impedance is lowered.
as the radials are raised towards the radiating element something else interesting occurs. the
radiating element becomes less sensitive to the influence of surrounding objects and terrain
in the near field, allowing the antenna to be mounted in locations and at heights above ground
that would be extremely deleterious not only to the feedpoint match but also to the radiated
pattern emanating from the radiating element.

as the radials are swept upwards towards the radiating element capacitance between the radials
and the radiating element increases, effectively raising the resonant frequency of the system
or causing the electrical length of both the radials and the radiating element to be shortened"

further up this page

."secondly as the radials are swept closer to the central monopole impedance drops and resonant frequency of both radial sleeve and monopole goes up,
conventional maths for electrical length go out of the window as you sweep the radials up towards the central monopole,
for instance a gamma fed monopole with 90 degree radials that is electrically 3/4wave will be less than 3/4wave when you sweep the radials up"

from the arrl

If the sleeve elements were brought closer to
the central monopole such that the ratio of the spacing to element diameter was less than 10:1, then the characteristic impedance of the 3-wire transmission
line would drop to less than 250 W. At 28
MHz, ZA remains essentially unchanged, while ZT
begins to edge closer to 52 W as the spacing is reduced.
At some particular spacing the characteristic impedance, as determined by the D/d ratio, is just right to transform the end impedance to exactly 52 W at some frequency. Also, as the spacing is decreased, the frequency where the impedance is purely resistive gradually increases.

again i am not saying this IS how its working , its all i can find that seems even close at the moment, im sure theres more to it,
if you read my first post i used the open sleeve antenna as an example that just because there are currents flowing in opposite directions in the lower 1/4wave it does not mean that radiation from the radial sleeve cannot combine constructively with radiation from the upper 1/2wave to increase gain.

commercial 3/4wave sleeve antennas i have seen have the same claimed gain as the vector with radiation angles @ above or below the horizon, gain is higher and radiation angle lower than a 5/8wave groundplane, the tradeoff seems to be a small reduction in vertical beamwidth.

OK, I believe it was this line, "secondly as the radials are swept closer to the central monopole impedance drops and resonant frequency of both radial sleeve and monopole goes up,
conventional maths for electrical length go out of the window as you sweep the radials up towards the central monopole,
for instance a gamma fed monopole with 90 degree radials that is electrically 3/4wave will be less than 3/4wave when you sweep the radials up" Which inspired me to ask, "how can both of you still end up with the same basic length radiator (~29' 7") IF as the loop size is increased and the angle of the radials falls further away from the radiator, the radiator must grow longer to retain resonance, gain, and a low TOA...???
as it appears the farther the radials get from the radiator, the resonance drops in frequency for the same length radiator.
Bob, since you have ~90" radials it would seem your ring would be smaller thus making your radials closer to the radiator than Shockwave's thus increasing the frequency of resonance in comparison to Shockwave's larger ring / shorter radials (81") and thus farther spacing away from the radiator.

I believe I meant shorter, but either way, how can both of your antennas be operating the same when your radials are longer thus making your ring smaller and closer to the same length monopole as Shockwave's?

Is yours tuned higher in frequency than Shockwave's or am I confused?