GHZ24 what is your opinion of the Sigma 4?

[Shockwave]

In my best effort to cover new ground I have to ask the forum one question. Is there anyone here who understands what I'm talking about when I say EZNEC miscalculates the phase by 90 degrees?

How this relates to the construction of a collinear model and what the electrical length of its phasing network means in terms of the electrical length and phase of the radiation currents on the stock antenna below this phasing network?

That this test reveals the cone has contributed significant radiation over the entire 3/4 or 270 degree wavelength? That this would require some mechanism of phase correction to go beyond a 1/2 wave or 180 degree radiator?

That this phase correction taking place in the lower 1/4 wave radiator also effects the phase correction required to drive another 1/2 wave collinear section? That if the cone were not an effective 1/4 wave radiator, a collinear version would require a standard 180 degree phase delay between sections?

I know we have some bright minds here that can follow. I'd love to elaborate on this rather than the not so "humble opinions".

 

[bob85]

read the arrl open sleeve article again eddie, it explains the difference between antenna mode and transmission-line mode currents,
you should be able to figure out how to model what they show and claim,

i don't think your a fool eddie, your just losing the plot.

 

[Marconi]

In my best effort to cover new ground I have to ask the forum one question. Is there anyone here who understands what I'm talking about when I say EZNEC miscalculates the phase by 90 degrees?

Donald, in answer to your question above, I don't think you will get any comments at all, execpting maybe this one from me, but if you do you'll likely be told your idea is completely clear and easily understandable.

Donald, my response to your first comment above is, if you get any responses at all, you will likely be told they understand completely every thing you are saying, but I don't think you will get any response to this question at all...excepting this one from me.

How this relates to the construction of a collinear model and what the electrical length of its phasing network means in terms of the electrical length and phase of the radiation currents on the stock antenna below this phasing network?

That this test reveals the cone has contributed significant radiation over the entire 3/4 or 270 degree wavelength? That this would require some mechanism of phase correction to go beyond a 1/2 wave or 180 degree radiator?

That this phase correction taking place in the lower 1/4 wave radiator also effects the phase correction required to drive another 1/2 wave collinear section? That if the cone were not an effective 1/4 wave radiator, a collinear version would require a standard 180 degree phase delay between sections?

I know we have some bright minds here that can follow. I'd love to elaborate on this rather than the not so "humble opinions".

Donald, I know you have something in mind that makes total sense to you. I also have some understanding of the terms you use, but I miss your idea that you have in the big picture. I tend to think this is pretty normal when we're trying to understand some complex issues.


This is just like when Bob reminds me, we've talked about the issue of the Sigma4, before. You and I have also discussed this before regarding our individual ideas about Eznec, and we were maybe talking about the same subject, but from two totally different points of view. I see this process as follows.


I see me trying to discuss Eznec based on why the currents on both sides of a simple dipole are not in equal phase on both sides, which is not what I would expect. I showed you that I can fix the problem just by entering the wire descriptions in a different order.

This causes me to wonder if this happens in my more complex model of my Sigma4, where I have wires connected and running in both directions, where wire 1 end 1, is connected to wire 2 end 2, rather than having wire 1 end 1, connected to wire 2 end 1.


This stimulates you to think about how Eznec went wrong in your mind at a much more complex point in your experience, and then you proceed to discuss that issue, while I over here listening and missing every point you make, because I'm thinking about the simple dipole example in my mind.


I've heard you describe how you see this issue with Eznec before I think. I have an email you sent me once that speaks in similar terms. I've read it many times. I wish it was clear in my mind however, but it is not. I think I get the gest maybe, but I don't get the relationships like I think you intend. Remember I'm thinking a simple dipole here.

So, I can't be sure that there is not some hard and fast order with which Eznec does not handle a model well...unless that strict order in data entry is always applied.

I've read that this idea for the order of wires placement is not important as to Eznec overall results, but it will certainly confuse the results we see in the important area of understanding the currents for the model.

I can only assume that Roy made some conscience decision that most users of his product would not be interested in the currents issues...as long as the results were close.

Or, in the case where currents were deemed important to some aspect for a particular model the modeler could apply is data entry in the required hard and fast format.


There are no two other gentlemen on this forum that I would be more pleased to agree with on this issue, as you and Bob among a group of others I won't name.


So Donald, I have similar feelings that I'm possibly being misunderstood as well.

I've said this before, "...when I present current information or the current data log on WWDX, everybody's eyes cross at the sight of all those numbers. And, what do I get from some folks? I get the following: "... here we have ole' Marconi calling all CBr's stupid."


I think this is sometimes the cost of bearing our souls, and speaking out on some issue we are passionate about, but can't quite get across to others Donald.


I want to understand and be understood, but sometimes just trying to make a point or raise an idea that is different or controversial...over the roar of protestation, insinuation, and sometimes even misdirection...this may be the best we could expect.

Sorry for the large type guys, I have trouble seeing.

 

[Marconi]

read the arrl open sleeve article again eddie, it explains the difference between antenna mode and transmission-line mode currents,
you should be able to figure out how to model what they show and claim,

i don't think your a fool eddie, your just losing the plot.

Well Bob, you may be right. I guess the problem here is I never consider this idea or discussion as a plot. I may be off the script that this group likes however

Thanks for the heads up.

 

[Shockwave]

The serious discrepancy that I've discovered with the Sigma modeled in EZNEC may be difficult to explain but it couldn't be any easier to demonstrate. All you have to do is add another 1/2 wave whip on top of the stock Sigma and experiment with the length of the phasing network to see where the free space gain peaks.

When you get the free space gain peaked with the length of the phase delay in EZNEC, build the collinear prototype for field testing. It will have less gain than a stock Sigma until you remove 8 feet of electrical length from the phase delay. Those 8 feet EZNEC is off by, are the 8 feet of phase corrected radiation present on the cone.

 

[Marconi]

The serious discrepancy that I've discovered with the Sigma modeled in EZNEC may be difficult to explain but it couldn't be any easier to demonstrate. All you have to do is add another 1/2 wave whip on top of the stock Sigma and experiment with the length of the phasing network to see where the free space gain peaks.

When you get the free space gain peaked with the length of the phase delay in EZNEC, build the collinear prototype for field testing. It will have less gain than a stock Sigma until you remove 8 feet of electrical length from the phase delay. Those 8 feet EZNEC is off by, are the 8 feet of phase corrected radiation present on the cone.

Could you email me your Eznec file of the setup you note above? It would help me not have to experiment trying to find a proper phasing stub. I would just like to see what I can see with such a model, and maybe that way I could get a better understanding of what is in your minds eye with this Eznec problem.

At my age 76, I doubt you have much to worry about that I'll build a Sigma4 collinear prototype...just to find out that it doesn't work as it should. But if I did, I would not think using a stinger above your Sigma would produce anywhere near the same load as you would get with a fully assembled couple of Sigma's in a collinear setup. Just trying to figure out what you did based on your brief descriptions. I have your email of a year ago that also describes this setup. Would that be the same now?

When you actually build the collinear Sigma did you put the tips together or the feed points?

 

[Shockwave]

I've checked my files and I have modified the original collinear file from a simple folded phasing section to a helix coil without saving the old file. This type of phasing network is too difficult to calculate the actual electrical length of and is not appropriate for this experiment.

The picture below shows the four wires I propose you add to the top of the stock Sigma. The top wire is the added collinear 1/2 wave element. The other 3 wires make up a simple folded phasing section.

The entire point of this is to experiment with the length of this folded section so you can observe that EZNEC will show a peak in free space gain when the entire electrical length of this phase delay is 180 degrees or 1/2 wavelength.

That in itself proves that EZNEC views the stock Sigma as nothing more than a 1/2 wave antenna. It sees the cone as tapered coax and the effective radiation beginning in the 1/2 wave above the cone. That's why it wants to see the next 1/2 wave confined in the phasing section because it mistakenly thinks the next 180 degrees are non constructive.

In reality the cone has already produced a significant amount of radiation over its 1/4 wave length. It also shifted the normal phase that is radiated by the main radiator by 90 degrees since it confined the first 1/4 wave of radiation.

This is the key reason adding another 1/2 wave to the top of the Sigma only requires a 90 degree phase shift in the field. That brings it into phase with the 1/4 wave cone and the first 1/4 wave of the exposed radiator above the cone.

Using a 180 degree shift causes half of the added collinear section to buck the phase of the cone, destroying gain in the field. If the cones radiation were not significant, we could buck its phase and only be concerned with matching the phase of the existing 1/2 wave above the cone. The fact this idea can't produce gain in the field suggests radiation is stronger from the cone than some may think.

EZNEC completely overlooks the fact radiation above the cone has been offset by 90 degrees from the source since that radiation was confined within the cone and replaced with what may be CMC in phase along the outside of the cone.

That's why you only need a 90 degree phase shift to feed another 1/2 wave element. Currents allowed to radiate in the 1/2 wave above the loop have already been shifted 90 degrees from the source.

If the phase shift feeding the collinear section is allowed to reach the 180 degrees EZNEC suggests, the added top 1/2 wave would repeat the same current and phase distribution we see in the first 1/2 wavelength of the main radiator. With it's out of phase currents in the first 1/4 wave allowed to radiate since they would no longer be confined within a cone.

Am I making any sense yet?

 

[Marconi]

Well I just stacked two of my Sigmas together like I thought you did with the prototype.

 

[Marconi]

Here is the performance results

View attachment Sigma4 collinear detaisl.pdf

 

[Shockwave]

I think if you remove everything above wire # 38, you will have a similar model to what I've described. We are just adding another 1/2 wave element and phasing section, not another Sigma on top.

 

[Marconi]

Here is the same antenna Donald with a 1/2 wave only in the top. I made real Earth and in free space. How does this compare to what you have for this configuration?

View attachment Sigma4 collinear with .50w.pdf

 

[Shockwave]

Here is the same antenna Donald with a 1/2 wave only in the top. I made real Earth and in free space. How does this compare to what you have for this configuration?

View attachment 11212

The basic model is very similar to what I had in mind. You may notice the free space pattern is horribly distorted too as it should be with the folded phasing section hanging off to one side.

That's because the currents in the top half of this phasing section are not equal in magnitude and opposite in phase to the currents in the lower half of the fold as seen in other collinears. They radiate and skew the pattern.

This is bringing me to the conclusion that plot generated in EZNEC may be more accurate than the currents it displays on the Sigma. How does EZNEC display the current through the folded 1/2 wave section? Are they inverted from top to bottom in your model?

Keep in mind the phase shift we see working in EZNEC is twice as long as what works in the field. The working 1/4 wave phase delay would surly radiate if it were formed in the folded design since the currents can't cancel.

To keep EZNEC happy, I gave it the incorrect 180 degree phase shift it wants to see in the model below. The main difference is that I've minimized any non constructive radiation in the folded phasing section by replacing it with a tighter, multi turn helix coil.

Notice how much cleaner the pattern is? The cone in this model covers the entire 1/4 wavelength of out of phase radiation on the main vertical where I can still see about 15% exposed in your model.

The part that drives me nuts and keeps me skeptical using EZNEC modeling the Sigma, is I have to lie to the program with respect to making the phase shift 100% greater than it should be.

I need to see EZNEC work with a 90 degree phase delay in this case so it matches what works in the field.

 

[Shockwave]

I would not think using a stinger above your Sigma would produce anywhere near the same load as you would get with a fully assembled couple of Sigma's in a collinear setup.

I wanted to comment on this specifically and say you're absolutely correct! Much of my spare time over the course of two years went into investigating what the best way to obtain collinear gain in my application would be.

The best field tests of the collinear design being discussed here, struggled to produce half the gain that simply phasing a pair of stock antennas together on the tower with proper spacing will produce.

The reason being is you can't get enough separation between the current maxima points on one multi section antenna to achieve the full 3 db of extra gain. That requires separate antennas properly spaced apart.

 

[Marconi]

I wanted to comment on this specifically and say you're absolutely correct! Much of my spare time over the course of two years went into investigating what the best way to obtain collinear gain in my application would be.

The best field tests of the collinear design being discussed here, struggled to produce half the gain that simply phasing a pair of stock antennas together on the tower with proper spacing will produce.

The reason being is you can't get enough separation between the current maxima points on one multi section antenna to achieve the full 3 db of extra gain. That requires separate antennas properly spaced apart.

Well Donald, being interested and active in CB antennas only, I know very little about real stacked collinear antennas. I know the CB BS that started many years ago, probably by HyGain with their idea for a 5/8 wave vertical for CB. They actually took credit for this antenna being collinear because it had currents in the bottom of the antenna below the active radiating 1/2 wave radiator. In those days they also glaumed onto the idea about that effect of raising the current distribution higher up the radiator, because of the same wasted portion of the radiator at the bottom, but IMO that was at the very least a better representation of the truth of the matter than calling the design a collinear. This all happened during the peak of the business, and back then anything goes.

This and other stories that have been repeated over and over until they are said to be facts. This is what got me into the study of CB antennas, and my passion has been to try and lend some semblance of reason, as I saw it, to those I could reach in conversation. I never imagined that the Internet would open this quest up to such a larger group however.

Does this sound familiar.

It looks like we might not get back to the collinear models, but I want to tell you that the models you saw, every one of them did not show the currents right until I set the wire #38 connections as MOM probably is intend to see in the definitions file, with wire #1, end 2, connected to wire #2, end #1 and visa versa.

IMO Roy wrote code to allow the wires to be connected both ways so he could avoid writing some more code that created error interference at the point of data entry or with an attempt to scan the antenna. It is likely that he had a choice to choose some features like I note below however.

Again, I suspect that the licensees have options to select the level of accuracy and demand that controlled the accuracy and speed at the data entry point. I think they wish to deal with this to expand the availability for their customers base. I think Roy was intent of his product being user friendly.

I have read a quasi bio for Roy that I think was written by Cebik. Roy suggest this in he manual maybe. He may not have been as specific to why however.

I've also read snippets on the MOM original progress work, and there they discussed their desire to create tables and algorithms for different levels... where they could recover more of their development cost with higher fees.