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ASTROPLANE best vertical antenna ever?

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

  1. W5LZ

    W5LZ Crotchety Old Bastard

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    Nice try, but power has very little to do with it.
    - 'Doc


     
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  2. nosepc

    nosepc On Vacation

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    Then any piece of wire works well??

    The best antenna is fiction?

    nosepc = notpc (my normal language is Spanish)
     
    #32 nosepc, Oct 15, 2013
    Last edited: Oct 15, 2013
  3. Shockwave

    Shockwave Sr. Member

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    Sorry but you're making the same modeling mistakes that made you think the Top One had any gain over a dipole. You must stop using the fake perfect ground option. It is not the antenna that produces this low angle null in the pattern. It's the ground reflection from the infinite perfect ground option you have selected in your model.

    The specific height you have chosen above ground is also responsible for the angle the null is placed at. Changing the height will move the null. If you model over real ground you will see the null closest to the ground is going to be at a much higher angle that would not effect DX propagation the way your model shows it.

    PS: The Vector and Gain-Master are not 5/8 wave ground planes like the one you have modeled. Their radiation currents are significantly different in both cases.
     
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  4. nosepc

    nosepc On Vacation

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    Well, then you can show me that good or design diagrams antennas and irradiation at 40 feet?

    thank you!
     
  5. Marconi

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

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    Donald, I agree that we need some minimal understanding of the ground use available in modeling or we might get the wrong impressions from such results.

    Here is what my Eznec suggests regarding the difference in patterns between the center fed GainMaster and the end fed Imax.

    I also modeled the Imax over Perfect Earth at 36' and 18' feet to compare the differences, but I don't think the difference we see here are due to the difference in height. If height really was effecting the model, I would expect we'd likely see a difference in the angle. I also don't think the feature over Perfect Earth is a fake consideration. I think there is probably some accepted scientific theory that applies when Perfect Earth modeling is considered. IMO working your TX'r over sea water, being well into the clear you will see a very big difference in contact range vs when over real Earth anywhere, and sea water is much closer to Perfect Earth. So I think this suggest that Perfect Earth is feasible as a technical reference.

    View attachment Imax vs. GainMaster.pdf

    View attachment How height effects models over Perfect Earth.pdf
     
  6. Shockwave

    Shockwave Sr. Member

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    When the antenna was moved from 18 feet to 36 feet, the angle of the lowest null also moved down several degrees. The use of perfect ground in an attempt to demonstrate an objectionable null is highly misleading and completely inaccurate.

    In fact the angle of the null we see in perfect ground would just about perfectly line up with the actual primary lobe if it were over real earth. Just about none of us will ever have a situation where the real ground mimics an infinite perfect groundplane.
     
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  7. W5LZ

    W5LZ Crotchety Old Bastard

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    Any antenna will -->react<-- differently at different heights above ground, it's normal. Part of how it -->reacts<-- is expressed in the 'field' it produces, it's shape, right? Why the emphasis on -->react<-- ? Think about it...
    - 'Doc
     
  8. Marconi

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

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    Donald I went back and looked closer at the models and you're right.

    The Perfect ground feature does consider the height above ground. The difference in 18' and 36' is just close.

    I also noted that it seems the higher the antenna above the ground the worse the pattern looks when using the Perfect Ground feature.
     
  9. HomerBB

    HomerBB Sr. Member

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    Maybe we should throw all kinds of junk under the antenna, with stones and sand being predominate so as to create the imperfect ground and have a better pattern . . . :blink:
     
    Needle Bender likes this.
  10. nosepc

    nosepc On Vacation

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    :laugh::laugh::laugh:

    (y)
     
  11. ghz24

    ghz24 Member

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    Take off angle is no myth

    No, it's a fact .
    Keep in mind this is a CB /11 meter antenna thread.
    On 11 meters the signal wont arrive at high angles
    I posted this before herebut it must have been missed so I'll repeat it

    Critical angle is directly related to critical frequency.
    Critical frequency can be found in "near real time" here

    Then you can use Snells or Secant law F = Fc / ( sec θ )
    Where :
    Fc is critical frequency
    F is a higher frequency (~27.1 for CB)
    θ "is the angle of incidence, measured from normal to the plane of the layer".
    that is the angle that a radio wave would make to a vertical line.(angle to the horizontal is 90- this angle)

    This site gives a better description that I can at the end of chapter 2 see figure 2-3 and previous paragraph.

    So the angle above which CB frequency waves are lost into space and your antenna doesn't need to put sensitivity/gain can be calculated from the critical frequency using the formula (solved for θ ).

    θ =90-(Inv cos Fc/F)

    Feel free to check my math.

    Watching the real time map for a few days the highest critical frequency I saw was 12 MHz in the tropics.( 5 was the best in temperate North America at my 20)
    (although I have seen 15 MHz reading {in E. Africa} since I first posted this)

    From that optimistic value of 12 MHz I get a max angle of arrival of just over 26 degrees.
    (only 3 degrees off my earlier estimate)
    @ Fc = 5 the max angle was 10 degrees, much lower than even I expected.

    Critical frequency of 15 MHz gives 33 degrees

    What antenna did you have in mind?
    Just because the main lobe is pointed above the actual angle of arrival doesn't mean you have no gain at the that angle even negative gain is gain and will work DX.
    Just because some people are overly infatuated with TOA and give it too much value doesn't mean that it's a myth or that it's irrelevant (depending on the frequency in question)
    Personally I'd prefer "angle of arrival" instead of take off angle .
    Because what the exact angle where the maximum gain occurs (TOA) is not as important as the gain at the angle that the signal is arriving.
    But take off angle is the norm, so imho the 3 Db down beam width (beam height) should quoted (in lieu of a graphic pattern ) so nulls within the "area of interest" can be determined and not hidden from users/consumers.
     
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  12. W5LZ

    W5LZ Crotchety Old Bastard

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    What antenna? Pick any antenna that doesn't have a very low TOA. One type that comes to mind are the so called NVIS antennas, of which a full wave horizontal loop is one.
    - 'Doc
     
  13. ghz24

    ghz24 Member

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    A horizontal dipole at one quarter wave above moderate (default ground in 4nec2) shows -5 dBi at 8 degrees and 2.1 at 22 degrees.

    Consider mobiles that get much less than unity gain and far from favorable TOA but still work DX.
    Not optimal but it can work.
     
  14. nosepc

    nosepc On Vacation

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    Well I think that is a coaxial antenna ASTROPLANE
    with a top hat to increase the gain horizontally.

    Extra capacitances top hat and skirt, help it to gain.

    No more ;)
     
  15. W5LZ

    W5LZ Crotchety Old Bastard

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    A 'top-hat' has no effect at all on 'gain'. It does have an effect on the resonant frequency. It also has very little, or nothing, to do with an antennas 'TOA' or shape of it's radiation pattern, doesn't 'lower' it's pattern except in efficiency maybe.
    - 'Doc
     

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