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Base Ground Mounted Verticals

Discussion in 'CB Antennas' started by freecell, Apr 24, 2021.

  1. freecell

    freecell Active Member

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    blue pattern: 10 meter 1/4wl. vertical @ 1/4wl. above ground.(at the feedpoint)
    red pattern: 10 meter 1/4wl. vertical @ ground level.
    green pattern: 10 meter 3/4wl. vertical @ ground level.

    34wgmv.png



    the distance between the "circles" in the elevation display grid represent a
    change in directivity of 3 dB. along any radius or specific angle of radiation.
     
    #1 freecell, Apr 24, 2021
    Last edited: Apr 24, 2021

  2. freecell

    freecell Active Member

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    the flattening of the upper portion of the pattern of the antenna represented in blue is caused by the re-radiation of antenna current from the outer shield of the feedline.
     
    tecnicoloco likes this.
  3. NZ8N

    NZ8N Well-Known Member

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    So the difference between the 1/4 wavelength and 3/4 wavelength at ground level is about 6dB.
     
    freecell likes this.
  4. freecell

    freecell Active Member

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    directivity of the gm 3/4 wl. over the gm 1/4 wl. is 7.5 dB. @ 45 degrees above the horizon while outperforming both the other antennas at all angles down to less than 5 degrees.
     
    #4 freecell, May 22, 2021
    Last edited: May 23, 2021
    tecnicoloco likes this.
  5. barefootindian

    barefootindian Supporting Member

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    Would a ground mounted 11 meter 1/4 wave antenna work as well? or would it have to be mast or pole mounted to achieve the same results or better?
     
  6. freecell

    freecell Active Member

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    "Would a ground mounted 11 meter 1/4 wave antenna work as well?"

    a ground mounted 1/4 wl. vertical will outperform the same antenna with 3 or 4 radials elevated to any feedpoint height up to 54' and demonstrate a clear advantage in directivity of better than 3 dB. using a minimum of 16 radials, either laying on the ground or buried. it is also immune to the re-radiation of antenna currents flowing on the outside of the shield, eliminating any necessity for rf chokes, current baluns and doing away with the requirement for isolation from any conductive, elevated support structures. antenna radiation efficiency is also about 20-25% greater than its elevated counterpart, which directly results in higher levels of power radiated by the antenna and increased gain.
     
    #6 freecell, May 31, 2021
    Last edited: May 31, 2021
  7. Shockwave

    Shockwave Sr. Member

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    The only thing I'll add is that antenna gain doesn't always transfer directly to signal gain. If the ground mounted antenna has a much more obstructed line of sight, you may not see a benefit here.
     
    barefootindian and HomerBB like this.
  8. freecell

    freecell Active Member

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    every expression in decibels (voltage) directly correlates to a unique power multiplier ratio.

    dB. gain = 10 log (power out / power in)
    dB. loss = 10 log (power in / power out)

    unfortunately, gain cannot even be calculated until the radiation efficiency of the antenna has been determined. until then, directivity is all that can be discussed. the same could be said in regard to system losses.

    gain = radiation efficiency X directivity.

    gain and directivity are differentiated. you can have an antenna with 3 dB. of "directivity" (at some angle) but if the radiation efficiency of that antenna is only 50% then "gain" is only 1.5 dB.. directivity does not automatically equal "gain" unless all antennas are assumed to be 100% efficient. i promise you that is not even the case, particularly where commercially manufactured antennas are involved.

    you're right about the terrain but the gm 3/4 wl has maximum directivity at 45 degrees above the ground and the -3dB. beamwidth is over 40 degrees wide. comes in handy for working dx in and out of valleys if there is any distance between the antenna location and the surrounding hillside/s.

    they perform extremely well (at lower angles) at a mile above sea level over flat desert plain composed of "poor soil."
     
    #8 freecell, May 31, 2021
    Last edited: May 31, 2021
  9. freecell

    freecell Active Member

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    every "gain" figure that you've ever seen stated in any advertising is not the "gain" of the antenna advertised. it is the directivity of the antenna prior to the determination of the radiation efficiency of that antenna and the "gain" is not known. i don't ever remember any manufacturer making any claims as to antenna radiation efficiency. either they are not aware of this fact or like i said earlier, the unspoken assumption is that the radiation efficiency is 100%. that never happens.

    the typical radiation efficiency of your favorite, commercially manufactured 3/4 wl. vertical antenna is < 70%. ground mounted verticals approach levels of radiation efficiency (over average ground) of 96% and slightly higher over poor soil, then salt water and reaches maximum efficiency over fresh water, about 98.65% which is indicative of an overall loss of 0.1 dB. relative to what would be considered an ideal system.
     
    #9 freecell, May 31, 2021
    Last edited: May 31, 2021
    tecnicoloco likes this.
  10. Shockwave

    Shockwave Sr. Member

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    I like how the ground mounted vertical removes all of the nulls that get added into pattern as height increases.
     
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  11. freecell

    freecell Active Member

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    the flattening of the upper portion of the pattern of the antenna (null) represented in blue is caused by the re-radiation of antenna current from the outer shield of the feedline that occurs because of increased loss resistance due to the lack of a sufficient number of radials to decouple the feedline from the antenna.
     
    #11 freecell, May 31, 2021
    Last edited: May 31, 2021
  12. TheBlaster

    TheBlaster Well-Known Member

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    Interesting post... can we assume the 16 radials are 1/4 wave as well ?

    I have tried ground mounting a few antennas for 11m, the Gain Master and a 1/2 wave vertical without radials both mounted just on a a 1.5 meter pole as an anchor, they were the worst DX antennas I have ever used. Neither of them working properly.The GM just became unbalanced despite a low SWR and the 1/2 wave vertical was probably radiating 1/2 the power into the earth below.
     
    #12 TheBlaster, Jun 3, 2021
    Last edited: Jun 3, 2021
  13. The DB

    The DB Sr. Member

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    As someone who uses the modeling software of the model posted above, I had concerns on the accuracy of how it was being presented and what was being said about it.

    I noticed right off the bat that its not the full image of the models output, but cut off. Then statements were made since that I was also concerned about, so I tried to duplicate the models in that image, although I used the CB band as that is more relevant here. As long as I adjust the lengths of the modeled antennas for the CB band it won't make much of a difference in the output.

    This is closer to what it should look like before it was cut off. (20 radials were used, not the 16 claimed by the op)

    modelcomp

    Now, normally I would let something like an image being cut off pass, just assume that it was due to inexperience or lack of knowledge of the person posting it, but the op has a recent history of misrepresenting things to try and say what he is saying is true. For example, in another thread he used a quote from M. Walter Maxwell's "Another Look at Reflections" to say something, but conveniently left out an important line of context that that changes the entire meaning of what the M. Walter Maxwell was actually trying to say. Further, much of the document itself actually disagrees with the op's position on the subject. Additionally, the op posted a link to an album I made on this forum to claim something that the models clearly showed the opposite of as evidence of what he was trying to say. Because of these and other things the op has posted recently, I find myself being suspicious whenever something he posts strikes me as out of place.

    So with this I decided to do some modeling and came up with the above models.

    There are two things to talk about when it comes to claims made and the models in question.

    When it comes to the elevated 1/4 wavelength antenna requiring the mast to produce that pattern, my model almost perfectly duplicates said pattern without the mast. I added a mast just to see, and while it did increase gain (very slightly), it made effectively no difference to the shape of the pattern. You do not need a mast to ground with this antenna for the pattern in question to exist.

    Initially, when it comes to the number of radials, I was curious as to the number needed for the op's models, but this was not mentioned, so based on the results and prior experience I assumed that it took something like 60 radials to get that strong of a signal as compared to the elevated antenna that was 1/4 wavelength up. This is plausible as adding radials on a ground mounted antenna has the effect of increasing its gain. However, it was then claimed that this is the result with just 16 radials???

    In the models that I posted I used 20 radials, and both ground mounted antennas showed a weaker signal comparatively speaking than the op's model which supposedly used 16 radials? Based on, again prior modeling experience using this software, I would estimate that you would need something like 60 radials, give or take, to get the results that the op is posting.


    The DB
     
  14. freecell

    freecell Active Member

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    "Interesting post... can we assume the 16 radials are 1/4 wave as well ?"

    no we cannot as the velocity factor of a conductor either laying on the ground or buried beneath the surface is substantially shorter than a physical 1/4 wl.. the velocity factor is modified by the increased inductance between the soil and the radial conductor/s (insulated or not) coupled with the unique conductivity and dielectric permittivity (R=100, K=12) of the soil present at the antenna site.

    "I would estimate that you would need something like 60 radials, give or take, to get the results that the op is posting."

    if you're assuming that the increased directivity is produced in large part due to the effect of the number of radials then your assumption is wrong. the radiation efficiency of the antenna when moving from 16 to 60 radials produces only a 0.36% increase in radiation efficiency while reducing rf loss resistance in the ground electrode system by a mere 0.3 ohm. there's not enough difference there to justify all of the extra wire and labor.

    no where did i state that there were 16 radials used in the ground mounted verticals represented in the graphic appearing in the op.

    read it again.

    a ground mounted 1/4 wl. vertical will outperform the same antenna with 3 or 4 radials elevated to any feedpoint height up to 54' and demonstrate a clear advantage in directivity of better than 3 dB. using a minimum of 16 radials, either laying on the ground or buried. it is also immune to the re-radiation of antenna currents flowing on the outside of the shield, eliminating any necessity for rf chokes, current baluns and doing away with the requirement for isolation from any conductive, elevated support structures. antenna radiation efficiency is also about 20-25% greater than its elevated counterpart, which directly results in higher levels of power radiated by the antenna and increased directivity and yes, now we can talk about gain.

    radiation efficiency X directivity = gain
    radiation efficiency is 95.96%
    .9596 X 7.5 dB. directivity = 7.197 (7.2)
    dB. gain @ an ert angle of 45 degrees.

    the difference in directivity between the two grids with respect to the comparison between the ground mounted 1/4 wl. and the ground mounted 3/4 wl. verticals is less than .7 dB.. the distance between the "circles" in the both of the elevation display grids represent a change in directivity of 3 dB. along any radius or specific angle of radiation.
     
    #14 freecell, Jun 3, 2021
    Last edited: Jun 4, 2021
  15. freecell

    freecell Active Member

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    i understand why they didn't work.
     

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