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Question on the Vector

Discussion in 'CB Antennas' started by The DB, Sep 15, 2014.

  1. The DB

    The DB Sr. Member

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    It has been described that the basket area of the Vector acts in some ways like a coaxial feedline with separate currents on the inside and outside of the basket. That is fine, but...

    What keeps the currents on the inside and outside of said basket on their respective sides?

    With a coax, or a t2lt/gainmaster design for example, you have shielding that completely surrounds the center conductor, and currents riding on the separate surfaces of the shielding, each clinging to its own surface. They don't interact because they can't, there is the metal of the shielding keeping that from happening.

    However, with the Vector, you don't have separate surfaces, you have four round tubes, and both of the currents are on the outside of the tubes. In *every* other situation I am aware of the currents aren't locked to one side of the tube, so why the exception for the Vector basket area? Why wound the currents present not use the entire tube as they do everywhere else?

    My Maco V5000, for example, has a bar feeding the signal to the bottom tube of the main vertical element, and is bolted to one side of said tube. The current flowing on the tube portion of the antenna are not limited to that side of the antenna, they use all of it, all the way around the tube.

    Another question is where else in the world of antennas does this happen?




    The DB
     
    Marconi likes this.

  2. Shockwave

    Shockwave Sr. Member

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    The door on your microwave has thousands of small holes through the metal shield yet you're safe on the other side of it too. The cone forms a tapered skeleton sleeve and the four radials are close enough to confine most of the lower 1/4 wave radiation on the center vertical inside the cone as a result.
    In this case you have to avoid the idea of looking at the aluminum tube as a single element on the cone.

    You must view all four radials as a single element that RF interprets as a virtually complete tapered cone without voids. It really appears as simple as coax with a good deal of CMC flowing on the outside braid. The differences are this braid is a tuned 1/4 wave cone that provides an ideal low impedance path to attract the CMC. The tapered shape allowed some impedance transformation to occur inside but it mostly allowed for a 90 degree delay feeding the top 1/2 wave. This is nice since it brings the top into phase with the CMC already on the outside of the coax or cone in the case of this design.
     
  3. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    That is a good question DB.

    I have argued this issue before, to no avail. IMO the currents flowing on these radials are NOT CM currents, as I think you suggest.

    In my S4 model's tabular currents report it shows the minus (-) current magnitude on the radials noted to be a fraction of an amperage difference greater than the (+) current magnitude on the 1/4 wave section of the monopole radiator in the middle. Pretty simple idea for cancellation.

    As the model also shows these two currents cancel almost completely leaving a small (-) current flowing into the far field. This current is constructive with the top 1/2 wave radiator, and in my opinion this is where the non-apparent collinear idea came from. I simply claim that this current contribution is miminal at best.

    IMO, the group consideration here justifies their idea based on the cone being coaxial. Like you suggest the cone is arguably not a feed line.

    There might be CMC's flowing on this antenna from the termination point of the coax (the feed point), but they will be flowing down the coax...not on the cone.

    CMC's are described to flow in every other situation, where we have currents flowing down the feed line from the unbalanced feed point, instead of flowing on the attached radials as we would prefer.
     
    Shadetree Mechanic likes this.
  4. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    DB, you model in 4Nec2, right?

    Do you have a model of the Sigma4?

    If so, does 4Nec2 provide a tabular report of currents amps per segment similar to what Eznec does?

    If you don't have such a model can you import and Eznec file?
     
  5. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Donald, where is the shield of the coax attached to the sleeve on a sleeved dipole?

    Is the feed point at the bottom or at the top of a sleeved dipole?

    Does the bottom of a sleeve dipole come in physical contact with the shield or anything else on a sleeved dipole antenna?
     
  6. The DB

    The DB Sr. Member

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    I think you are misunderstanding my question. I am not talking about the signal from the central element here, where the faraday cage explanation is a good example. I'm talking about the currents flowing on the elements of the cone from the antenna itself. I don't know that treating the separate elements of the cone as a whole is adequate for such currents, and the three dimensional RF fields they create. I think what I'm saying is, I need more...


    The DB
     
  7. Shockwave

    Shockwave Sr. Member

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    I fail to see the point since the collinear effect only becomes useful once the radiator is longer than 1/2 wavelength. The sleeve dipole has no phase delay between the source and the main vertical radiator since it's directly connected to it, appearing more like a center feed antenna to RF. Not the case at all in the Sigma where we have delay between the source and the upper 1/2 wave.
     
  8. The DB

    The DB Sr. Member

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    I was simply asking about something that is being applied to the radials that I have never seen applied to any other antenna system in existence in that way, that being said, I'm not aware of any other antenna that would have a need for it either. The explanation of where the extra gain comes from has always seemed rather convenient to me. It also makes me feel uneasy, and that uneasiness, when I feel it, exists for a reason. I have learned to question things that make me feel that way. I waited till now because I didn't really have the understanding of antenna theory when I first came to the board that I have now...

    Mind you, I'm not questioning weather or not the gain from the come area of this antenna exists, I have no reason to disbelieve the people who are hopefully more knowledgeable than I on this topic. I am simply seeking understanding.


    Currents to many people are an ending point when it comes to antennas, and I used to be that way to. More recently I began using currents to try and imagine the three dimensional RF fields they create and how they interact, and what I'm seeing is sometimes counter-intuitive to what the currents, by themselves, will tell you. The rf fields the currents create are not simply plus or minus to me. NEC based software simply likes to add these currents and call it a day, but that is not what I see happening with this antenna...


    Respectfully, I think the direction I am trying to go is very different than the direction that you think I am going, and what I am asking about really isn't weather cancellation exists on this antenna (I am of the current opinion that it does not). I am asking a question and seeing what responses I get in the hopes I get an answer that I am satisfied with. If such an answer does not come I will search elsewhere. Perhaps what I think I'm seeing is wrong, perhaps not. If only it were easier for me to describe the three dimensional fields I'm seeing with words on a two dimensional screen...


    The DB
     
  9. The DB

    The DB Sr. Member

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    I do use 4NEC2, I have attempted to model the sigma, I was just playing around with a theory earlier today in an effort to model the common mode currents on the radials that ended up being a bust...

    I can get the segment data but I have to know where to look, which I do. It isn't in a convenient form like it apparently is in eznec. I prefer the color chart for currents that 4NEC2 provides...

    I'm told I can import from eznec, but I haven't tried to import anything yet, mainly because I don't have anything from exnec that I'm interested in. I know someone gave instructions in a previous thread on this forum somewhere...


    The DB
     
  10. Shockwave

    Shockwave Sr. Member

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    Consider the broadband dipoles used in the old Russian Over The Horizon radar system. The dipoles are all tapered out from the source and formed from individual elements in a cadge type design. To RF this appears like one solid element that is getting wider but with much less wind load.
     
  11. The DB

    The DB Sr. Member

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    Are you talking about the Russian Woodpecker, officially called the Duga (and a number) in the Chernobyl area I think it was? I will have to do some research on that antenna... I am aware of its existence, and seen a picture or two, and a video clip on the History Channel I think it was, but that is about it...


    The DB
     
  12. Shockwave

    Shockwave Sr. Member

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    That is the example I was thinking of.
     
  13. Shockwave

    Shockwave Sr. Member

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    [
    Consider antennas like the 2 meter Isoploe that uses 1/4 wave tapered sleeves to very effectively address CMC issues. The only difference is the direction the cone is folded in with respect to the antenna and source. If the sleeve or radials are folded up, it turns the portion of the vertical radiator inside, into coax while the outside of the cone still bleeds off the CMC. Always try to remember the EZNEC software you are basing your opinions on has fibbed to you. Today we have 100% proof of this 90 degree inaccuracy on the phase indicated in the program through my collinear experiments. I'm still willing to debate this topic with anyone who understands the collinear phasing experiments in order to show how it proves all of the EZNEC models we have seen were completely misleading.
     
  14. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    DB, this wasn't some trick questions.

    Here is a page from my Eznec Manual where Roy discusses Currents. Maybe it will give you a better sense as to how 4Nec2 might work with currents as well, since it too uses the NEC2 engine.

    IMO, the problems you might be finding with the current magnitudes and their phase signs might have to do with how NEC handles the current data reported out.

    Roy built his interface for ease of use for the novice and the professional alike. Since I'm sure this is a problem with NEC, I figure that 4Nec2 did something similar with their utility programs.

    Some of Roy's ease of use utility routines like Create Radials, Connect Wires End to, and others violate NEC rules for data entry...if we want to correctly see the proper phase and current magnitudes per segment for our model. That said, all other performance details reported out for a model with such violations will be correctly reported. Otherwise NEC will require strict conformity to the rule for connecting wires, and IMO that can make its use far more difficult.

    To be clear, these utilities do serve the user to do work to produce accurate performance results, within the scope of the limitations, even though the tabular currents indicated may be skewed if the rule on page #97, below is not followed. This skewing of current data only happens when all wire definitions for the model do not conform to the rules noted near the middle of page #97, else you cannot depend on the tabular currents data report as noted. If you correct the errors in your Eznec model the currents and phase details will be corrected, while all reporting for performance, match, and far field pattern, etc., will remain unchanged.

    Read the rest in the attached image below.

    DB you can check this out using a simple two wire 1/2 wave dipole. Just connect wire 1 end 1 to wire 2 end 1, and add you source.

    The model should report out performance data correctly just like a dipole for match, gain, angle, SWR, etc. However, if I'm right, and you check the tabular current data...you should see that wire one will show a (-) current phase while wire two will show a (+) current phase. We know that a dipole has two poles that are in phase in order to radiate. The currents may look wrong, but the details will remain correct if you 4Nec2 works like my Eznec does.

    I prefer the current indicator red line in Eznec too, but if I want to know the specific magnitude and phase segment by segment...I find it better to check out the tabular currents report. I can also turn the currents on or off. In the on position you can also get a sense of the phase as well. That said, there is more information in the details.

    This is a test to see if I can still edit this post.
     

    Attached Files:

    #14 Marconi, Sep 16, 2014
    Last edited: Sep 16, 2014
  15. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Donald the info about the Isopole is interesting, but could you give me a brief answer to the questions above.
     

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