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Question on the Vector

Henry HPSD said:
Marconi,

I am under the impression we are talking about the 5dBI model of "DB"
from page 10.


If so...pse see my comment above.
Click to expand...

Henry I have not tried to open this file in 4Nec2 or Eznec yet. I think I heard it reported that DB's model showed a >6.0dbi gain. If it really shows on 5.00dbi instead, then I would not have taken the time to try and look for a mistake. I would have been trying to duplicate his model using Eznec, adding the wires and whatever it took to get similar results.

I have compared some of my results to DB's and we always reported results that were very close.

DB, does the model you posted on page 10, only show a gain of 5dbi like Henry says?
 
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No, im afraid it shows less.. if you include material losses we are somewhere around 1,5 dBI (give or take 0,5 dB ..i forgot)

You can upload that file in enzec by the way...
And just to have it said, was the first time i saw the model with "two wires"
(u know what i mean) really like the "out of the box" thinking DB !

of to bed, before im deeper in :)

Kind regards,

H.
 
The DB said:
At 90 degrees of difference between the sources above instead of a peak between the sources you see a valley, although not a deep one.

The DB
Click to expand...

I think you're on the right track DB. I noticed the same thing when I introduced an additional 90 degree shift between the two sources, forming the "valley" in the middle. It appears the 90 degree offset is a simple function of the sources being at opposing ends of a 1/4 wave radiator. To me the CMC source at the top of the cone is logical since it should start at the end of the 1/4 wave transmission line and flow back down the outside of the cone.
 
Here is the plot, the Vector experimental model is seen in relation to a center fed dipole who's center is near the center of the Vector model.

vector-plot.jpg


Now the image showing the currents.

vector-currents.jpg


And the phase data.

vector-phase.jpg


Just a note, the currents and phase data is not showing the full height of the antenna, I was focusing in on the basket areas.

One thing to note, if you actually check the URL you will see a date as a folder, 9-20-14. That is when this version of the model was created.

Now looking at the plot, it is easy to see that this model is not over perfect ground, if it were the lowest lobe would be at ground level. For further evidence I here is a screenshot of the screen that shows the ground information.

grounddata.jpg


For those who aren't familiar with this modeling software look in the Environment section next to Ground / Free-space. The box is where Perfect Ground would be chosen from. Also, when Perfect Ground is selected, the options in the Main Ground are all greyed out, and Average Ground is not selectable.

Now to follow Henry's suggestion...


The DB
 
Shockwave said:
I think you're on the right track DB. I noticed the same thing when I introduced an additional 90 degree shift between the two sources, forming the "valley" in the middle. It appears the 90 degree offset is a simple function of the sources being at opposing ends of a 1/4 wave radiator. To me the CMC source at the top of the cone is logical since it should start at the end of the 1/4 wave transmission line and flow back down the outside of the cone.
Click to expand...

I agree that that is logical. The only other thing that I can think of that would affect those currents, or perhaps an apparent source, is an induced current from the main radiator also acting on the radial, although I would imagine any such induced current would be small. I'm also not sure how it would affect the source at the top of the radial.


The DB
 
DB, I have to agree with you now, the model does show to be over real ground, and thus my claim that your model was incorrect is wrong. Good work DB, I think this answers the questions about the S4 design that Donald and Bob have been claiming for a long time

I took a chance on what I though you might have done, and I obviously thought wrong, and in the course of this debate...I said some bad things about my friends.

My apologizes for questioning your work DB.

I am now convinced that you guys solved the mystery about the S4 design, and it does look to have currents on the added wire that would added gain due to CMC...just like Donald has been telling us, and Bob told us about a long time ago.

I also agree that Eznec may not be able to generate a model that shows us what 4Nec2 clearly does. I banked my whole conclusion about an error on the fact that I felt confident that DB had the environmental ground type set on Perfect and not Real ground.

Sorry guys, Old Grampa was wrong.
 
Well, now is as good a time as any to apologize to you too Marconi. I must admit I was not expecting this response and it says a lot about you as a person. Certainly some of the thing I've said to you were not appropriate and came out of frustration. I can also say without you Marconi, I don't think we would have had the incentive to put as much effort into figuring out how this antenna works.

I think we should ALL be proud of that since there is NO OTHER forum that contains as much useful information about the design. I for one have learned the most about the Sigma from thoughts generated here. Thanks to everyone.
 
Don't fret Eddie, we all make mistakes. Thank you for the apology, I do appreciate it.

I'm not so sure it is the solution to the problem for several reasons, and weather or not it is a step in the right direction, it is something new to talk about and experiment with. There are some aspects that has me concerned, however.

Did you by chance take a look at the aluminum version of the antenna model above? When I change the elements to T6 aluminum losses go to hell, but that is just one more thing to look at now. The model wasn't complete to begin with as there are a few things I still want to do to it, such as adding a gamma match instead of a typical feedpoint.

Thanks Henry for the suggestion and instructions for using other materials. That is something I will be looking at more in future models I make. It is one step closer in my efforts to simulate real world results.


The DB
 
well i hate to be the party breaker...
but I think we are missing the point....
What i tried to point out yesterday:

Im afraid the model is inaccurate.

When done as one should...the gain is drops with say 3 to 4dB

I allready told you both where the main part of the error is.
Besides that error, your trying to model closed spaced wires NEC4 is the one to use.
Although i can understand not everyone using nec4.
And besides those two....as soon as you "run" the model 4nec2 generates a segmentation warning
(at least my version does)

Marconi was inaccurate about where the mistake was, but he was on track by claiming that the gain was too high.

Kind regards,

Henry

edit: Ill post the DB model including aluminium losses using nec4 later...first kids to bed.
 
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It's agreed the model is still flawed. I'd like to see it represent the 90 degree phase shift in a collinear model and I believe DB said it does not. I still see success in learning about more than one current on the cone. Seeing we can form a 1/4 wave current with a peak in the center using a pair of currents. Learning that when extra wires are added around the cone for CMC to radiate in the model, gain goes up. I suspect as time permits we may see DB's model get closer. In the meantime these models have given us food for thought and opened insights to others that may not have been apparent before.
 

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