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Modified Vector 4000

Discussion in 'CB Antennas' started by bob85, Oct 3, 2009.

  1. Marconi

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

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    I placed a 1 pF capacitor as close to the top of the radiator as possible. I did not physically isolate (ISO) the mast from the antenna. This only simulates the mast to showing no common mode in this case, it is not an actual choke.

    If I add a Feed Line and isolated (ISO) the mast, that might be more similar to your antenna, :unsure: so I'm not sure what you did in this new 6 meter setup.

    If you have been successful at fixing the CMC on your real Vector I would try the same setup.

    If you are isolating your 6 meter were the mast would attach to the antenna, let me know the distance and I will play with getting the model to working with a feed line, ISO, and a simulated choke.

    I'm not positive, but I seem to recall that DB, some time back, said he was using a coil choke at this point, but I've never seen this included on one of his models and I he didn't explain to me, what he did instead.



    Maybe you could ask him.

    I plan to try and get the physical gamma to work on your 6 meter model and I will start by using the 27?" x 1/4" inches that you suggested. I might take some guessing and trial an error. Maybe Bob has already shared or can share how he does his new project. I'll have to go back and see if Bob posted those dimensions already.

    I might also find some need to correct some of the dimensions I calculated too. Sometimes with wires close to other wires the raw dimensions don't consider these effects.
     
    #721 Marconi, Jan 6, 2021
    Last edited: Jan 6, 2021

  2. HomerBB

    HomerBB Sr. Member

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    I think my gamma rod is over all 27". The gamma tube is 1/2". The rod is 1/4".
    My coax was wrapped as a choke 18' down from the feedpoint.
     
  3. Marconi

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

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    Homer here is the model adjusted to your location for the choke on the feed line and it shows a tad less bandwidth but more gain as noted in the overlays below.

    I added a + in the title of the model after the wC+ for choke.

     

    Attached Files:

  4. HomerBB

    HomerBB Sr. Member

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    Interesting. Thanks. One never knows how a little thing can have influence on antennas. . .
     
  5. bob85

    bob85 Supporting Member

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    I only posted my starting dimensions Eddie,
    its back on the short pole sporting 3/8wave radial cone like a Vortex q82 mk2,

    IM tuning for 50mhz starting at 180" which I think is electrically a little long

    vortex's claims seem too good to be true, as if their version acts like a 3/4wave center fed dipole,
    I think my scaled versions are close enough to see if there's any truth in the higher gain at low angles.

    m0ogy posted a review on YouTube that includes a vswr plot using his analyzer that shows a much wider bandwidth than any of the other versions of this style antenna,

    either his coax is very long/lossy, or the antenna does have the wide bandwidth vortex claim,

    I had a look around earlier,
    all I need to make an identical test antenna using the 1/4wave radials for comparison is another hub with an in tact gamma bracket which I think I have at the old place,

    I found radials hoops gammas & spare monopole sections.
     
  6. freecell

    freecell Member

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    "either his coax is very long/lossy, or the antenna does have the wide bandwidth vortex claim."

    or there are higher than normal values of radiation loss resistance, usually the case when bandwidth is excessively wide.
     
    #726 freecell, Jan 6, 2021
    Last edited: Jan 7, 2021
  7. Marconi

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

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    For the folks that missed the thread on the Vortex antenna that Bob mentioned here. Bob is working on a test on the Vortex design using a 6 meter antenna he is going to install soon. I posted the models again when Free Cell commented about losses maybe causing the very broad bandwidth.

    I tend to agree with his suggestion, and I've talked about my experience that suggested a similar condition...when I was using an old 100' foot lossy RG5x feed line, that was found to be contaminated with water in the feed line when hooked up to an A99 for about 5 years.

    I can't tell for sure why the Votex preforms like my models suggest, but in this case, I think the very long radial cone is causing the losses that Free Cell is talking about. The current distribution on these long radials does not look right.
     

    Attached Files:

    #727 Marconi, Jan 7, 2021
    Last edited: Jan 7, 2021
    freecell likes this.
  8. bob85

    bob85 Supporting Member

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    My 3/8 cone vector is tuned near enough for a quick test,
    between 1.1 & 1.2 :1 on my old kenwood sw200a meter, i ran out of gamma rod so i will change it later,

    bear in mind the 1/4wave cone version was tuned to about the same vswr, neither been perfect,

    they are the same monopole on the same short pole, same coax, same position,
    i only changed the radial length from 1/4wave to 3/8wave & adjusted the gamma for low vswr,

    Nav was using the same radio /coax / antenna / tx power
    & he's at the same asl as me,

    the results are not at all what i expected

    right away he said i was stronger on tx to him,
    so i hooked the coax to the sdr for a look at signal strength at my end in more detail,

    1/4wave cone without radials = -89.7dbm
    3/8wave cone without radials = -86.1dbm o_O

    the test was not ideal been on different days but signals are stable on the dbm meter,

    the last test with & without radials we did multiple times over a length of time proved to me that signals don't vary enough for the dbm meter to register a change between me and Nav providing we do it in a timely fashion,

    i never saw any change in his signal apart from that caused by adding the radials,

    my results tell me i must build an identical 1/4wave cone version so i can test by swapping them within 20 seconds to eliminate any change due to not been done at the same time,

    if when i test at the same time the 3/8 cone version holds an advantage the fun begins.
     
  9. nav2010

    nav2010 Active Member

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    Technically it should be worse than the quarter wave because increasing the basket length reduces the length of the upper element akin to increasing the braid length of a coaxial dipole and shortening the upper element.......but - it's not a dipole and it doesn't deal with the same characteristic impedance of coax.
    But think about this:- If you overlap the basket above where the half wave node is located on the monopole and you increase the basket length electrically there is a strong possibility that in phase radiation is using the top of the basket to form the missing lower phase of the half wave. In other words if you increase the length of the lower stub of a J-pole so that it shortens the electrical length of the main element to below half wave, the antenna will take the increased electrical length of the stub to replace the missing lower part of the half wave and keep in phase. You are moving the location of the half wave node onto the top of the stub and it will change the angle of radiation completely.
     
  10. freecell

    freecell Member

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    all antennas are dipoles.

    https://ocw.mit.edu/courses/electri...s-and-signals-spring-2003/readings/ch3new.pdf

    see page 113, the two "dipole" diagrams just under the top of the page.

    the vortex q82 mk2 is just another off center fed full wave dipole antenna just like the av174, lw150, saliut27 and the v4k. they are also referred to as elevated 1/4λ radial 3/4λ vertical monopoles.

    pay particularly close attention to the current distribution in both diagrams. max current zero voltage equals low impedance, max voltage zero current equals high impedance. these values are inverted every 1/4λ.
     
    #730 freecell, Jan 7, 2021
    Last edited: Jan 7, 2021
  11. nav2010

    nav2010 Active Member

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    Like thus
    node.jpg
     
  12. Marconi

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

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    Bob, how about the remarkable bandwidth this Vortex extended cone version is supposed to produce?

    My real Earth model shows <2.00:1 SWR = 5.3 Mhz.
     
  13. bob85

    bob85 Supporting Member

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    i just got back from my old place with more vector parts,
    I need to clean them up then make another 1/4wave cone version to test against.

    i won't believe it until i test both versions within a short time of each other multiple times with the only change been the radial length,

    Eddie
    can't tx below 50mhz with this radio to see how wide vswr bandwidth is, my analyser is not calibrated,

    im more interested in what caused the difference in signal when all esle is the same apart from radial length & the day we tested on.
     
    #733 bob85, Jan 7, 2021
    Last edited: Jan 7, 2021
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  14. Marconi

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

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    Here is Vortex with a promise for the future. Apparently they scrubbed all their old sites.

    They also say they are in maintenance mode.

    http://www.vortexantennas.co.uk/
     
    #734 Marconi, Jan 7, 2021
    Last edited: Jan 7, 2021
    freecell likes this.
  15. freecell

    freecell Member

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    saw that yesterday.
     

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