sigma4 article is online

[Shockwave]

For many years I've seen field results that can only be simulated by collinear antennas. While I see several discrepancies in this report I'll address the most significant first. There has been strong evidence that this design is capable of downward beam tilt and with Henry's recent models we can now prove that manipulation of the two collinear elements can provide both upward and downward beam tilt.

You can see Henry's free space Sigma model shows an upward beam tilt of several degrees which would be a disadvantage to distant gain on the horizon. The only reason for that upward TOA is that Henry's model has not taken advantage of the "non apparent collinear" effect with respect to the element lengths on the Sigma's TWO radiators.

I ask Henry to lengthen the cone elements or shorten the top element and then report what happens to the TOA? As soon as we provide more delay to the top element the TOA drops BELOW 0 degrees! If the Sigma did not function as a collinear antenna any manipulation of a single element length could only cause the TOA to reach angles higher than 0 degrees.

Downward electronic beam tilt requires the array to have more than one active element and that the signal driving the upper element be delayed through the transmission line (cone) by a few degrees. If you take my field test results and apply them to your models, you will quickly see my description is accurate and accuracy is all I truly care about here.

 

[Shockwave]

I also have to mention that Bob has seen similar effects with distant gain regarding these element lengths. Although, Bob has indicated the optimum lengths would vary from one installation to another. That was not lining up with my field tests where one design consistently outperforms all center fed dipoles.

Further consideration forces me to see every one of my broadcast antennas have been installed on towers above the height of average terrain. Making downward beam tilt a noticeable advantage to my clients. I can see where this would not be as attractive if the antenna were located in a valley or location lower than the target area but consistently works well in my application.

 

[Henry HPSD]

@ homer bb, Especially cause you used the words "overall" I tend to think you understand rather well

@ Eddie, pse allow me to reply a bit later...kids to bed.

@ Shockwave, You are searching in the wrong direction.
This is what Sirio does as well with the provided plot of the Gainmaster antenna.
It is a free space plot, it is MEANINGLESS in real live.
It is often used to confuse future buyers.

You will have a reflected wave from earth.
Now if you're angle is "too"" low...the reflected wave will reflected high
(think of snooker or eight ball) .
In order to "achieve" maximum distances...you want that angle as close to zero as possible. A centre fed dipole is rather good at doing so, that's one reason why it is relative hard to beat.

There are situations where down ward tilting is rather common.
And that's with cellphones...or broadcasting or HAM repeater applications etc
but then only cause the area of interest is underneath the antenna
(for example a highway)
And they do that most often by tilting the antenna.

Your impression of what a "collinear" can do..
(move the TOA)
You are asking me to change the length of the radiator.
Well..imagine a long wire....with additional length to the wire the main lob will become You will know that the lobs will become more along the ax of the antenna ?
heck ...we all know that "long verticals" have the radiation pattern for most upwards to the sky.
Why would you think that has anything to do with "collinear" in this case ?

You could look up things like pseudo Brewster angle etc
That will lead to the sum of resulting fields

Kind regards,

H>

 

[The DB]

The article is a good read. Thanks for the work you put into it Henry.

I ask Henry to lengthen the cone elements or shorten the top element and then report what happens to the TOA?

I did part of this, namely changing the length of the central vertical element. I was able to get its pattern to drop below the 0 degree mark in freespace, although it took shortening the antenna to near 1/2 wavelength long to do, which is counter to the real world Sigma 4/Vector 4000 design. Also shortening the central vertical element steadily causes impedance to rise, which does make sense with an antenna of this length, however, it has risen far above what a real world Sigma 4/Vector 4000 feedpoint impedance.

I have not yet played with the radial length or ring height/diameter yet. When I get time I'll likely play with the ring height first, then play with the ring width second. The reason is it isn't as easy to adjust the size of a ring configuration then simply changing its height. Radial lengths will of course be adjusted with the ring height/diameter modifications...


The DB

 

[Marconi]

You can see Henry's free space Sigma model shows an upward beam tilt of several degrees which would be a disadvantage to distant gain on the horizon. The only reason for that upward TOA is that Henry's model has not taken advantage of the "non apparent collinear" effect with respect to the element lengths on the Sigma's TWO radiators.

Donald, are you referring to the Eznec Pro/4 image on the top of page #30, showing 2.27 dbi gain at 23* degrees?

 

[Henry HPSD]

Donald,

Almost forgot...thank you for joining the conversation !

perhaps its best to visualize a yagi beam..
Normally we rotate the antenna in "azimuth"
But now rotate it in "elevation"

Im sure you can imagine the "downward" main lob if we point it towards the ground.
And upwards (vica versa eme work for example)

Think logical...
Why would we all "set" the antenna in a exact horizontal position ?
Cause we want maximum gain at distant horizon.
The earth will "interact".

You seem to have the impression if a free space plot provides downward tilting it will provide "extra" in real situation in the far field im afraid that isnt the case.

Oke...model a dipole antenna in free space.
Now set the source say 20 percent from the top.
You will notice it has a downward tilt...
Now we set the source at 50 percent (as a true centre fed halve wave dipole)
That downward tilt is gone and is 0 degrees...just like we want to.
And that one will provide "maximum gain at distant horizon".

Doing that simple test will also show you that your statement:
If the Sigma did not function as a collinear antenna any manipulation of a single element length could only cause the TOA to reach angles higher than 0 degrees.
Is not accurate, turn any end fed halve wave vertical upside down and it will show a "downwards tilt"

Hope it is of use..

Kind regards,

H>

 

[The DB]

I just played with ring height, and I was able to, again, get the angel to drop below 0 degrees. This also raised the feedpoint impedance, but not as much as shortening the vertical element.

As the ring height adjustment had more of an effect on the radiation pattern, and less of an effect on impedance for a given length of change, I think I can make changes that will both increase gain, and lower the radiation angle, while keeping the changes in feedpoint impedance relatively close to the starting points of GHZ's model.

Both of the changes (the vertical element length and the ring height) I was able to increase the gain of the antenna overall, and significantly increase the gain at low angles. I'm not sure what GHZ's goal was with this antenna model.

It looks like GHZ made the ring adjustment easier as well. I may or may not modify this as the current system is based on a multiplier, and the system I would want to use would be based on a direct length. I guess that depends on how well and to what accuracy I can make the current system work. I need to run some calcualtions.

I have to give GHZ props on the design of this model. It is easy to make all of the adjustments necessary to explore the design.


The DB

 

[Henry HPSD]

@ Marconi,

I had to re read your post several times as i did get the wrong impression.
But after reading it again, im happy ! Cause you are saying it "violates" any rules etc.

That means: You understand some of the precautions mentioned.

And that makes me happy, cause it will lead to "better" overall results.
As (not in a bad way) but sometimes i see results from modellers who are not accurate.
Not so long ago you were in a conversation about a trombone match with the "designer" of the antenna.
He said something in the line of...he didn't use to many segmentations as that would influence the outcome. That should ring alarm bells big time !

Looking at other manufactures there are those who have delta loops
A strong aluminium Vshape and a single thin wire on top...that is a large difference in diameter...that will lead to large errors.
We now have:Alarm bells and we must hide in the shelter.

"those" situations lead to people saying : well modeling isnt accurate.
They fail to realise they are who is wrong.
Having a Ferrari doesn't mean you are a good driver.
(ps your model too had some issues hihi)

For some reason manufacturers seem to "dig in".
Not so long ago i was in a conversation with another manufacturer.
I explained the theory, he said something in the line of:
He could "see" what I was saying, but he didn't agree as he noticed in the "field" something different.
Instead of going on a search what went wrong in the field..
He went on searching in what way the theory is wrong.
And that is of course his right to do so....but it will fail each time.

Anyway..

I think you fail to realise why that GHZ 24 model is there.
And that is of course because I havnt been clear.
Its meant to be a "working" model....

Please notice what DB is now doing (see post above or below i don't know)
That is why it is there....

That GHZ24 model is easy for changing something, its his model...he deserves credit. Are you aware of how easy it is to change something with that model ?

Now, obviously after "work' has been done you will need to apply the "pre-cautions" You will have to "verify" the provided data and adust in order to make it accurate.

Kind regards,

H>

 

[bob85]

Donald,

I think height above ground was an important factor when i was experimenting with the vector, mine was very low, when i raised it i had to re-tune it,
i put that down to the detuning effect of proximity to ground, your antenna on your test pole is significantly higher relative to the wavelength of operation,

Your Dominator's wavelength / diameter ratio is also significantly different to my old style vector 4000's with their skinny upper tubes and tuning tips,
i would not expect to end up with the same physical .82wave even though the electrical length could be about the same,
They will all be electrically shorter than their physical length would suggest due to the cone raising the resonant frequency of the monopole the closer the radials get to the monopole,

i have no doubt i can manipulate signals,
its working out what is causing it that is the problem, all i can think of is common mode,

I 100% agree with Henry that a stock sigma4 or vector can out perform any 5/8wave at typical installation heights,
and that the quoted gain for 5/8 and the open sleeve antenna is dependent on having very good ground under them, I asked about the ground under the open sleeve several times, Henry was the only person to answer my question,

There are no decent 1/2waves with low loss matching networks on the market to compare to other antennas at the same tip height,
if such an antenna was available it would very likely give a 5/8wave a hard time.

 

[Shockwave]

Henry, with all due respect I'm searching in the direction 15 years of real world experience working with this design leads me to go. Areas that have been providing repeatable results from qualified professionals like the chief engineer from Clear Channel and the VP of engineering from the same company long before we started seeing modeling work done in this area.

I'm aware that the ground reflection has a strong influence over the TOA but I'm also acutely aware that the Vector design can be manipulated to steer the TOA up or down even over real earth. If you took a pair of stacked dipoles and delayed the feed to the top bay, it would show a TOA below 0 degrees in free space and still be above 0 over real earth just the like the Sigma collinear you think is acting different.

When I can lengthen the cone and monopole with a matching network that adds capacitive reactance, see signal increase as white noise decreased, and easily change the TOA by 10 degrees or more in a free space model, it's not reasonable to expect me to consider this as meaningless just because the effects are reduced with ground reflections.

Marconi, that is the figure I'm referring too of Henry's Sigma model on page 30 of the report. All of that high angle energy is easily refocused to a much more effective angle by adjusting the lengths of the two radiators and would be required before the model could be considered a Sigma.

DB, I only mentioned the option of shortening the top radiation because that's the easiest one to change in the model and see the effect. For sure it's the lengthening of the cone structure that provides the best gain in the distance. It is the one area Sirio, Bob and myself all agree on.

This of course shortens the electrical length of the upper section and requires it be made longer too. Since the cone must be similar to an electrical 1/4 wavelength, lengthening the 4 radials requires the loop be smaller and the upward angle to be sharper.

Seeing how these lengths were able to focus the primary lobe on the horizon should make it apparent that we haven't produced exceptional gain but just "nudged" the beam down to where it can make a significant improvement in distant coverage.

Neither of the two radiator lengths can be extended without the use of a capacitive matching network. Whatever gain people assume is being lost in that gamma match is insignificant in comparison to the gain that can be achieved in the distance with a gamma match. Understanding that's only possible since the gamma allows us to extend radiator lengths beyond resonance.

 

[Marconi]

@ Marconi,

I had to re read your post several times as i did get the wrong impression.
But after reading it again, im happy ! Cause you are saying it "violates" any rules etc.

That means: You understand some of the precautions mentioned.

Henry, that might be a first...that someone would actually take time to read what I've said over again. When I saw the wires description of GHZ24's model I knew it was a Free Space model, because it was on the ground. When I uploaded the model and saw the Antenna View, I knew he did not allow for the radial offset at the base of the radiator. I also realized the radial length was way short of being a 1/4 wavelength at 27.185 mhz. The model is so far off from the real model...that I wondered why anybody would consider it a reasonable representation for a Vector 4000, and then I posted why I think GHZ24 did the model that way. I did not think he was just stupid or did not know how to model...I figured he had some reason.

Bob raked me over the coals recently for making models that did not represent the best ideas to be included in the model, and now we see another member doing something similar, but in this case everything is just fine.

I've spent a lot of time, a lot of study, and a lot of words trying to prove what Bob reported to us all some years ago in his thread "The Sigma4: Alternative View," but my Eznec models did not support those ideas so the battle to discredit Eznec and me was on.

Now I feel better reading this report from you Henry, but I think "My Goose" is cooked.

Anyway..

I think you fail to realise why that GHZ 24 model is there.
And that is of course because I havnt been clear.
Its meant to be a "working" model....

Please notice what DB is now doing (see post above or below i don't know)
That is why it is there....

That GHZ24 model is easy for changing something, its his model...he deserves credit. Are you aware of how easy it is to change something with that model ?

Now, obviously after "work' has been done you will need to apply the "pre-cautions" You will have to "verify" the provided data and adust in order to make it accurate.

Kind regards,

H>

No Henry, I won't be the one fixing GHZ24's model. If DB is going to use it to try and optimize it to check out Donald's idea here...then he will be the one to fix the model, and it does need some fixing. I am a little surprise however, that DB is using the Optimizer feature in 4Nec2, because I recall him claiming the feature was not reliable and maybe even a waste of time.

DB, am I wrong again?

BTW, Henry could you email me the Eznec Pro model that you used for the top of page #30? I would like to see how your Eznec Pro/4 model, done right, compares to my Vector model below. I want to see where I went wrong.

1. GHZ24 Free Space model per the wire descriptions you posted in the introduction of your report.

2. My model of my New Vector 4K in Free Space per the Bob's dimensions and the Sirio manual.

 

[HomerBB]

Bob raked me over the coals recently for making models that did not represent the best ideas to be included in the model, and now we see another member doing something similar, but in this case everything is just fine.

Now that's funny, I don't care who you are.
Don't feel too bad, Marconi. It's like being married. If it's her idea, it's good, but if it's my idea, it's bad.

 

[Marconi]

Now that's funny, I don't care who you are.
Don't feel too bad, Marconi. It's like being married. If it's her idea, it's good, but if it's my idea, it's bad.

Homer, I wonder about you sometimes.

That was not meant to be funny. Even though I explained why I made a couple of models at 36' feet over average Earth and they showed a lot of current flowing on the mast.

I was really surprised when Bob took me to task with that set of models I did trying to duplicate some model results that DB told me he had done earlier. When Bob and I get to talking about lucky or unlucky heights for antenna installations, and that was what that discussion was all about...I think guys looking in typically get the wrong impression.

I think Mr. W8JI started all that concern and did not wish to explain further on the idea so he coined the term "lucky height." He wasn't even talking about height as it turns out...and therefore all of the CBBS comes to the surface like cream on sweet milk.

You'd really have to be there to understand I guess. The Internet will never replace our communicating face to face...try as it might.

 

[HomerBB]

@ Eddie,
I understood completely. I just found a lot of humor in you being so perturbed over the difference in how you saw you and GHZ being handled. . .

Still funny

 

[Marconi]

Your astroplane models showed that mast length is important and that isolation 1/4wave below the hoop fixes it,
The coax needs isolating too if you want to minimise the chance of rfi in the shack and common mode ruining the pattern,

I think the Avanti guys had an idea that really big antenna tuning devices attached to a metal radiator, even if the ratiator had to be either real long or real short, might help produce the propagation of RF into some areas around the antenna that a CB'r might find useful.

Bob, if this is even close to the truth...then I'm concerned that if you eliminate all of the errant currents from flowing only on the radiator portion of the antenna some might deem desirable...then that little old A/P might not talk worth a hoot.

If this is not the case...then I have a question for you...I'll ask you one day.

To me the A/P is so out of balance at every turn...but to me it is still beautiful in its own way. I'm surprised it works at all, but head my warning...if you stop the transmission line mode currents here, and that antenna mode current there, and/or instead place a fiberglass isolator here or there...the old gild may work out like a blind-date with a gal that plays the violin and a mouth organ...all at the same time.

I was hoping we were going to do another avanti bulk buy so i could have one astroplane unopened and one to play with plus a couple of 6ft moonrakers mobile antennas, but im not sure what's happening on that front,

I got my order of 15 at last count, in too, and I'm counting the days.

The new top one was never going to be popular here, the astroplane and cte clone were never popular either,
Installing them at the same tip height = more wind load and more of an eyesore than your typical end-fed,

They use to sell like hotcakes here, but the source for Coppers dried up. There use to be about 3 AstroBeams in my neighborhood, and maybe 25 A/P that I personally knew of in the area.

My idea for making a collinear 2 x 1/2wave is the drawing i called the topsyturvy,
In no way is it related to Donald's collinear design which would be a huge antenna @27mhz.

I never did quite get what you were expecting us to understand on that issue Bob. I don't recall it ever relating to Donald's idea either. I thought you were saying the other day...the idea of a real collinear was the next project on your agenda. I guess wrong again.

I did recently see a fellow post an image of a paper weight on FaceBook that looked like an A/P.