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Base Have a look at this Antenna

Discussion in 'CB Antennas' started by AudioShockwav, Jan 15, 2020.

  1. Redbeard U812

    Redbeard U812 Sr. Member

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    But now days I suffer from CRS- Can't Remember Shit.....:whistle:.

    This thread has really gotten my attention. This steering issue, could be helpful for say an antenna mt top trying to talk into a valley?


     
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  2. HomerBB

    HomerBB Sr. Member

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    Yes
     
  3. The DB

    The DB Sr. Member

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    It does use the mast/feed line as part of the antenna, no argument there. But if you go back to I think that thread, or at lease one in the past where I modeled this antenna, there was what I called the "blue wire". This is a wire that, at first appearance, didn't have any current flowing on it, in spite of the fact that wires on both sides were both at peak current. One of those wires was the antenna's mast, the other was connected one side of the lower basket section and the upper vertical element. On the actual antenna, this "blue wire" was part of the metal bracket.

    When I changed the mast length from the optimal length (which, for the record, is close to an electrical half wave length if you are going to isolate it from what is below it), current would begin to flow on this "blue wire". The more you adjust the mast length, the more current would flow. This had a stabilizing effect that I have not seen in any other antenna design. It was like a built in matching system which kept SWR stable though most mast lengths. In fact, for every half wavelength beyond the optimal point, there was only a foot or so that it wouldn't be able to adjust around on its own. When I removed this wire from the model, this effect disappeared and the antenna was very sensitive to how long the mast length was.

    Further, I have worked with these antennas in the past, although not recently. I don't recall common mode currents being an issue that I had to work around.

    And for those that didn't know, Mr. Coily now makes its own version of this antenna.


    The DB
     
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  4. Redbeard U812

    Redbeard U812 Sr. Member

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    Thanks Homer,
    Explains my homebuilt GP, not sure what angle I used for radials. I know I added 5% to their length. Next time I crank down I will check it. I'm wanting to install my homebrew insulator bushing ..... 20200126_110117.jpg
    Much thicker than the original..... 20200126_110514.jpg 20200126_110123.jpg
    Having some slightly higher swr when wet/ high humidity.

    Reading all this about AP has got me wanting to build. Ain't even got the cubical quad and breakover up yet and planning another......:eek:o_O....am I suffering from RF addiction? Is there a RFA (RF Anonymous) group?:whistle:
     

    Attached Files:

  5. HomerBB

    HomerBB Sr. Member

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    There is no hope for the RF Addicted. When they get together for a meeting they end up planning, prepping, and building antennas while arguing over CMC, TOA, and the best vertical/horizontal antenna ever produced...
    BTW, really good looking bit of antenna engineering.
     
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  6. Redbeard U812

    Redbeard U812 Sr. Member

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    Oh.....? Guess WWDX is the RFA.
     
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  7. Marconi

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

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    U812, there is no other site to compare.
     
  8. HomerBB

    HomerBB Sr. Member

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    @Marconi - just for you...

    14 is the rf conducting boom/mast
    16 and 18 are the two skirt radials.
    Level B is the bottom ring.
     
    #53 HomerBB, Jan 26, 2020
    Last edited: Jan 26, 2020
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  9. bob85

    bob85 Supporting Member

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    Homer i read the patent several times trying to figure out what they were claiming,
    most of it seems to be true,
    the part about reducing the flare in the transmission-lines causing downwards tilt may not be true, i thought Eddie did a model with parallel radials some time back,

    The astroplane can have serious cmc issues as can any endfed its pitted against,
    that is no reason to avoid that style antenna, slapping a few radials on an endfed 5/8 won't ensure you have no cmc spoiling the pattern,

    they all should be isolated imho,

    i don't like gambling on been lucky with my mast & feed-line + ancillaries electrical length to ground or not as the case may be,
    id rather isolate the mast & take a smaller gamble that i won't resonate the feed-line when i wind a choke and increase cmc,

    its not a perfect antenna by any means ( its not tunable as it comes from the maker ) but installed correctly at the same tip height as the super 5/8 groundplanes in sitiations as depicted in the avanti advertising it will play just as loud or louder in my experience.
     
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  10. HomerBB

    HomerBB Sr. Member

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    That has been my experience, too, Bob. Very good antenna has made a lot of folks happy, including me.
    I don't have one, now... easy to build.

    I'd be far less likely to change the flair than I'd be to adjust the length of the mast.
    They explicitly recommend a conducting mast that is 1/2 wavelength of the operating frequency (or more), or an equivalent length of mast below the ring as the length of the vertical from the ring to the horizontal where the mast attaches, but never a shorter mast than this or the TOA is less than optimum. There doesn't seem to be an explicit call for mast isolation at the point that the recommended mast length is reached, but that is the obvious conclusion in my opinion.
     
    #55 HomerBB, Jan 26, 2020
    Last edited: Jan 27, 2020
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  11. Marconi

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

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    Thanks Homer, this is better than posting the location of the words. Now others can read these words in the patent if they wish.
     
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  12. Marconi

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

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    Bob, I have models that demonstrate heavy CMC on the A/P, just like you tell us above. I'll post them again. Just to be clear, I think you will agree that simply implementing ISO to help minimize CMC is not enough, by itself, to cure the problems. Isolation, ISO, is a complicated issue, and for Homer's question below, this may be why Avanti and others do not discuss the problems.

    Homer, I think I first heard about isolation (ISO) a long time ago from Bob. I've done models trying to specifically demonstrate the effects. So Homer I think you're right, the patent does not go into the issue and neither did the Avanti Report that I posted in my thread "The AstroPlane Another Viewpoint."

    I don't want to mess with making a model with changing the flair either, plus I have no idea what dimensions they were referring to. It requires me to remake the loop and that can get complicated. I think I may have done such a model, but it might be hard to find.

    Homer, adjusting the mast is easy, and I have a project that I did on 07/25/17 that compares the A/P with 3 different mast lengths inside the radials. I never posted it.

    1. with my idea for the radial mast length = 197"
    2. with the radial mast set at DB's 220" that he found showed maximum gain.
    3. with the radial mast set at 177.68" a model with the radial mast length set at the length below the loop = to the lengths of wire #16 and #18 in the patent.
     
    #57 Marconi, Jan 28, 2020
    Last edited: Jan 28, 2020
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  13. HomerBB

    HomerBB Sr. Member

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    @Marconi, I'd like to see the 3 models (1, 2, 3 above), if possible. . .
     
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  14. Marconi

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

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    Homer, here are the 3 A/P models that compares 3 different lengths for the A/P radial mast. There is a lot of details in these models that I use to keep in my files. I used these additional reports to try and make sure I was staying focused.

    I added antenna notes for each model.

    BTW, these models with DB handle in the title are my Eznec models where I attempted to duplicate DB's idea for the location of the Feed Point (O) in the middle of wire #2 in these 3 models.
     

    Attached Files:

    #59 Marconi, Jan 28, 2020
    Last edited: Jan 28, 2020
  15. Marconi

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

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    Homer, here I compare two A/P models where the radials space at the middle of the radials are different spacing to the mast.

    In 2017, Bob gave me some dimensions and said the insulating rod at the center of the radials was 13" inches, but over time I found my models seem to do a bit better at 10". This spacing also looked more like my Old Top One knock-off of the A/P.

    Model #1 is set at 10" inches, 5" inches to each side of the mast.

    Model #2 is set at 18", 9" inches to each side of the mast.

    You can see this in the Antenna View images where I marked the locations.
     

    Attached Files:

    #60 Marconi, Jan 28, 2020
    Last edited: Jan 29, 2020
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