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ASTROPLANE best vertical antenna ever?

Discussion in 'CB Antennas' started by nosepc, Oct 6, 2013.

  1. Shockwave

    Shockwave
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    I just wanted to add that modeling or field testing the lower 1/4 wave cone by itself will provide NO useful information as to how it behaves on the Sigma. Once you remove the end fed 1/2 wave from the top of this 1/4 wave coaxial cone, all you're left with is essentially a 1/4 wave of transmission line. If you think that proves it's just a 1/2 wave J-pole, you're overlooking a lot. It is the connection of this end fed 1/2 wave to the top of the cone that creates the beneficial CMC radiation on the outside of the cone. The Key difference between this and any other antenna you have seen is the 1/4 wavelength, 90 degree phase delay taking place inside the cone that feeds the upper 1/2 wave. That just happens to bring it back into a constructive phase with the CMC radiating off the cone.

    Some have been quick to quote experts like W8JI for pointing out the CMC can be a significant enough factor as to cause "the entire end fed design to fall apart once the mast and feedline are added". What do you think could happen if you provide a low impedance path to a resonant cone for the CMC to radiate off of once the top 1/2 wave has been phase shifted to line up with the cone? Why wouldn't we expect the same degree of change in a positive direction once the phase is aligned? This is what makes the Sigma IV the "non apparent collinear" antenna L.B. Cebik claimed it was.


     
    #196 Shockwave, Sep 15, 2014
    Last edited: Sep 15, 2014

  2. Marconi

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    Bob, I give these Avanti guys a lot of credit for having the know-how and understanding of what they wanted to do...and then doing it. The problem is they are humans and humans have moral and ethical failings, to say nothing about bias, and for sure with business and the advertising involved. I think this is what we see and realize in this article. I've always been skeptical of such promotional efforts.

    They also talk the talk about stuff that is even more obviously BS, like the A/P being less of a wind load and was better balanced than a typical yagi element on a beam.

    They also talk about the A/P's shortened top radiator and its benefits of top loading, and then they extend this very same element to a full 1/4 wave for the beam and eliminate the top hat.

    The distinction I tried to make in my post to Jazz was that these comments in the CB Magazine article were not related to the Vector idea.

    Since the discussion was about the AstroBeam, I'm not sure about this one, but see below.

    When I've scaled a few models using Eznec and I make a fair comparison...I don't see and changes in performance of the models due to a change in operating frequency. Of course I have to then fix the wavelength heights to compare, or else I would see differences.

    I don't know if scaling a real antenna would cause changes in the effects they made a point of warning us about however.

    Bob, those patents go way back to a time when the regular CB'er had little to no access to Patent records. I didn't start seeing them on the Internet until the 2000's maybe a bit earlier.

    I think I mentioned this above, saying they did not even use the A/P top hat setup on the beam. Just more CBBS.

    I have seen some cases where I see obvious downtilt in some Free Space models, but right of hand I cannot think if an example or why that happened. If I was ever able to see something similar over real Earth...I would think such a change would be very small. Of course I tend to take exception with most ideas that try to suggest large changes when doing most antenna work. My models and much of my personal real world experiences also shows me very small differences.

    Bob, I played with my model of the Old Top One I have...changing the angles and the top and bottom legs, and I could see no changes in maximum radiation angle. I'm a little vague about such effects on the match however. I also remember changing the length of the mounting bracket hub making it larger and smaller, and I just recall those changes had some effect. I would really have to study on the subject regarding Eznec.

    Homer made some A/P antennas. He probably can tell us more...if he made changes to angles of the radials to see if the tilt and/or match changed any.

    If you can give me links to such discussions, talking about currents, I would like to check them out. Were these discussion regarding modeling information and currents.

    Thanks
     
  3. Marconi

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    Shockwave, my days have ups and downs.

    I think I posted a response about this idea from Jazz suggesting to remove the top 1/2 wave element, but I'm not sure.

    Maybe I even posted the Eznec model I have for such a cone. If I did, then you will see it is showing minus gain, less than zero, along with and infinitely bad SWR >100 ohms. I do remember posting something similar in the long past however...with the same results.
    I'll have to go back and check for sure, but my point would still be...I agree with you on this issue.

    IMO, such a model is worthless to consider as explaining how the cone on the Vector works, and fails to show any gain as suggested. I was also unsuccessful in finding a feed point that would improved the match at the base.

    I was once curious about this idea too, so I don't find any fault with Jazz suggesting the idea.

    Just in case I didn't make the post attached is the idea that Jazz suggested:
     

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    #198 Marconi, Sep 15, 2014
    Last edited: Sep 15, 2014
  4. bob85

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    if you remove the upper 5/8wave you end up with two ends with high impedance,

    if the radiation however small or large is due to common mode caused by impedance imbalance as i think it is and cebik states in his j-pole article you have effectively removed the imbalance so no common mode radiation,
    that's the way i look at it until somebody that understands nec shows me different,

    i don't remember all the places i have read about ezmec eddie, here is one place i posted a link to in the past when i suggested you may need to add extra wires to see radiation from the sleeve,
    http://www.eham.net/ehamforum/smf/index.php?topic=32091.0

    you or somebody may understand what he is talking about and be able to tell me if eznec will show radiation from a transmission-line when it is part of an antenna using the mathematical model in eznec,
     
  5. Marconi

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    Bob, I agree.

    When I earlier thought about the idea Jazz suggested here, to check the cone with the top radiator cut off, I was thinking the cone and the center monopole would radiate similar to a setup I use to see on mobile setups...with two 102" whips mounted parallel on a bar a few inches long.

    I was thinking this would just make a very fat 1/4 wave element. I also removed the gamma tap point as the source on my S4, and set the feed point source at the base of the monopole...to no avail. I even tried setting the source on one of the radials...but nothing worked to improve the terrible match. I did not think about removing the hoop however, maybe that was a problem I'll have to check out.

    I agree with you on the part noted in bold for sure. I'm somewhat at a loss below that however. Cebik said a lot of things in that article which is maybe 50> pages long. I have it here, printed out as a reference.

    I understand. I read the link the other day, but all I remember off-hand was - IMO the guy with the question did not get a specific or constructive answer. I noted that some agreed one way and other's suggested the opposite was true. Some argued to do it one way or another, but were not specific. I'll go back an read it again, but I wasn't impressed with the efforts there.

    This may be off point with what you are thing, but you do have to add a wire in order to use the Eznec Transmission Line feature, but I can't make a sleeve per se. I would have to make a cage of sorts using a lot of wires, and that would be a beast to model. I think 4Nec2 provides a utility that will make a cylinder however, but I don't know what can be done inside.

    Are you suggesting that I don't see any currents or radiation from the S4 cone?

    Maybe DB can help with you sleeve idea.

    Sorry, I'm lost again. I'm not sure who he is.

    Bob, have you seen Roy's instructions in the Eznec Manual on transmission lines? If not, I'll email it to you. I tried to attach the 6 pages here, but the new forum gave me an error message...saying the file was too big. Let me know.

    I got the file to work Bob, but I had to split the file into 3 smaller groups. You will see on page three a note where I copied the Transmission Line data information from a default model that came with Eznec.
     

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    #200 Marconi, Sep 17, 2014
    Last edited: Sep 17, 2014
  6. bob85

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  7. bob85

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    i have had a quick look years ago eddie, i don't pretend to understand it but i am willing to take another look.
     
  8. Marconi

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    I don't understand much of it either.

    Maybe you will see some discussion of the question the guy on the forum had about non-radiating Feed Lines and those that do radiate.
     
  9. bob85

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    eddie, this is what i have been talking about for a long time,

    right at the start it tells you that transmission-lines in the model always have equal and opposite currents and don't radiate, the link i posted says the same thing ,

    the arrl open sleeve article tells us they do radiate but not why, i think it is likely due to unbalanced currents as cebik tells us,

    maybe the solution to the model is adding those extra wires i asked about so that the numerical model allows the transmission-line to radiate if there are unbalanced currents as there are in the vector,

    it is visible in donalds cst vector plot, i pointed it out to nosee in my edited image, and in my minds eye with the astroplane,

    how much i don't know but it is certainly not balanced with one side connected to the bottom of a 5/8wave and the other well spaced out there is fresh air,



    interesting what it tells us about phasing stubs in the model with balanced currents vs real world with unbalanced currents
     
  10. Marconi

    Marconi
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    Don't stop reading Bob.

    There is nothing wrong or revealing in the statement you noticed in the beginning of the article. That is true. In the text you posted above you left out some important words on the topic. Here it is complete as stated.
    The distincion here is he is only talking about the two conductor feed line.

    IMO, what he is saying is Eznec models follow the rules for coaxial transmission lines and do not radiate. However, if we have an imbalance at the coaxial feed point the feed line will radiate, so we have to add a wire to the model for the outside of the shield.

    I labored over this understanding in the beginning too. It is no wonder that one of the guys in the link you posted was claiming that Eznec models of the coaxial feed lines do not radiate, which is true. It doesn't radiate unless we have an imbalance at the feed point.

    IMO in the beginning he was strictly talking specifically about Transmission Lines rules, the equal opposite idea and cancellation.

    Then read the topic entitled: "Modeling Coaxial Cable" on page 83, the last topic "Using Transmission Lines." Here he tells us how to model coaxial cable, and explains a lot more about Eznec.
     
  11. bob85

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    that's what i am trying to understand eddie,

    the way it sounds to me is he says it won't radiate because transmission-lines in the numerical model always have equal and opposite currents and do not recognise that coax is a 3 conductor affair unless you add the extra wire to simulate the outside of the coaxial braid ,

    the cone is a transmission-line and part of the antenna structure, it should act similar to a tapered coaxial cable,
    the radials can be replaced by a tapered solid cone according to avanti,

    the arrl article tells us transmission-line currents flow and are responsible for radiation in the lower 1/4wave in phase with the upper 1/2wave,
    the arrl does not tell us that there is no radiation due to cancellation even though the conductors are parallel to the monopole, what am i missing ?

    if i remember correctly your models show very little imbalance in currents at the top of the radials,
    is that because it sees the cone as a none radiating coaxial cable with equal and opposite currents ?

    to my eyes if im understaning donalds cst animation correctly shows some imbalance with virtually no current at the top of the radials out there in fresh air and some current at the bottom of the 5/8 monopole it is connected to, it also shows some radiation in phase with the upper monopole,

    will the cone radiate in necs numerical model or not ?
    if the answer is no, can it be fixed with extra wires to simulate the outside of the coaxial transmission-line ?
     
    #206 bob85, Sep 18, 2014
    Last edited: Sep 18, 2014
  12. Marconi

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    You may be right Bob. Maybe this is why Sirio calls their Vector a coaxial J-Pole.

    I'll wake up more, and do some more reading. I'll get back on the rest of the interesting ideas you posted here.
     
  13. Marconi

    Marconi
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    Bob it has been a while for my getting back to your long post above. I have some responses to some of your comments, but there are still a few I would like to consider.

    I'll make a new thread in order to get our discussion about the S4/NV4K out of this thread on the AstroPlane. If I have time I'll leave a link here in case some want to follow the posts on this subject.

    Here is the link: http://www.worldwidedx.com/threads/follow-up-with-bob-on-the-sigma-4-new-vector-4000.174340/
     
    #208 Marconi, Sep 21, 2014
    Last edited: Sep 21, 2014
  14. booksbenji

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  15. Needle Bender

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    The only way the radiator could be directly driven & short to ground at the 1/2 wave point (high current node, near zero voltage) is if it were a 3/4 wave with the bottom 1/4 folded upright to correct the phase inversion. Anyone remember your gain factors for differing antennas? How about a 3/4WL? If I remember correctly, it's right about 4.65dBi. Hmmm ;)
     
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