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Davemade groundplane / birdcage antenna

Discussion in 'CB Antennas' started by bob85, Mar 21, 2020.

  1. bob85

    bob85 Supporting Member

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    Has anybody seen one, 2 versions, one like a higher power vector 4000 & a similar antenna with 8 radials & 4 hoops spaced along the radial sleeve,
    that would be a headache to model.


     

  2. 711

    711 Well-Known Member

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    4ACA430E-A5E5-4AA4-98C3-D0A6867A7ED4.jpeg This one?
     

    Attached Files:

  3. Redbeard U812

    Redbeard U812 WDX-1030 / U812 South Texas

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    Oh yes, see why they call it bird cage now. Plenty of roosting places, and can conveniently be used by Raptors needing a nest.
     
    S&W357, G GOLLY WAlly and Slowmover like this.
  4. Shockwave

    Shockwave Sr. Member

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    Now this is something I had not seen before, but may have thought about. Does anyone know some approximate measurements for this antenna? The one I'm most interested in is how long is the entire antenna? If it is noticeably longer than the Sigma, Dave and I had the same idea about how to maximize the effectiveness of the cone. If this is what I think it is, I'll explain in detail what the differences are and why it is showing more gain in EZNEC.
     
    G GOLLY WAlly likes this.
  5. Marconi

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

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    I had to raise my model of the NV4K to specs up from 36' to 48' feet at the feed point in order to see 4.95 dbi gain over Average Ground. However, the maximum angle was at 7* degrees and the files associated with the image antenna shows its maximum gain at 5* degrees.

    The cone does look to be noticeable taller relative to the overall antenna length, so that and the 3 added hoops could possibly account for the lower angle we see. I don't believe it, but I could be convinced.

    Bob is right, it will be an additional nightmare for me to model with all the extra wires needed, to say nothing about the slim chances of getting some good dimensions. Plus my NV4K model is already using 500 segments...which is my limit. So, I likely won't be doing this model.

    The only thing I'm pretty sure about, is this antenna will have to be a lot higher than the image antenna...if it will show the 4.97 dbi gain at 5* degrees above the horizon and remain modeled over Average Earth settings.

    It is claimed to be a Dave Made, but I believe this is just eye-candy. Here is a link to the original post:

    Need base antenna advice
     
    #5 Marconi, Mar 24, 2020
    Last edited: Mar 24, 2020
  6. Slowmover

    Slowmover Sr. Member

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    Africanized honey bees.

    .
     
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  7. bob85

    bob85 Supporting Member

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    CCM did build a vector style antenna years ago,
    I have seen several of Daves creations, most were elaborate affairs compared to your average homebrew antenna & this one reminds me of those,

    its claiming full wave but that could be 3/4wave monopole + 1/4wave radial sleeve,
    looking at proportions if it is a full wave monopole the sleeve would have to be much longer than 1/4wave,

    for a long time I believed that the longer monopole increases unbalance at the top of the cone because its not level with the high impedance point on the monopole 1/2wave from the tip,
    which transmission-line theory tells us will increase radiation from the outside of the sleeve,

    Lockdown means i can't get started on my sigma with full length sleeve & 1/4wave radials,
    probably make a hub so i can add/remove them to see if they give the sigma the ground-plane it needs according to some respected people,

    are radials the key to making radiation from the cone compress the pattern,
    I will find out,

    i can also move the fiberglass isolator from the base of antenna to 1/4wave below the antenna to see if having that part of the mast radiate is of benefit or detrimental.
     
    Marconi likes this.
  8. Marconi

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

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    I don't remember CCM.

    I looked at the Dave Made website, and I see 1 antenna that looks similar to a S4/NV4K, but it was fuzzy and looked far away. However, I can tell it is not the one in the picture above.Here is the site I was looking at: http://rfjunk.com/Davemade-Ground-Plane-Antenna-_p_63.html

    I also did not find any of the info on RF Junk site for Dave Made like the information we see presented in post #2 by 711. Maybe he can give us his source.

    I don't see any claims that this Bird Cage antenna is a full wavelength either. I could have missed it though. I will ask 711 where he got his details.

    Bob I might try and figure out some antennas in an image, but I often find it difficult to simply look at an image and figure out the dimensions or the proportions accurately. Besides that, IMO all of these pictures so far are not real clear or close enough to really tell much.

    I don't know about the longer monopole etc .................but I just looked at my NV4K with a physical gamma match on the model and it shows the 107" inch radials positioned near the bottom high voltage point very close to the radial loop. My Simga 4 with a gamma match has 90.6" radials and this one positions the high voltage point at the bottom too, but it is much higher above the radial loop. This is obvious when comparing the antennas patterns. Is this basically what you are getting at? I think this shows the NV4k showing more gain and a better pattern than the S4. If I'm close to what your thinking here, I will publish the models below.

    Just keep me posted when this mess is over and you can get to the project.

    I think that is what the models will show but I have to check closer,,,so the models are similar in construction. I think you are probably right though.

    I don't know about this aspect with my models, but Shockwave claims his commercial antenna does not require any CMC mitigation if the match tunes on the money and I don't think he uses any insulators.

    Good luck and keep me posted.
     
    #8 Marconi, Mar 24, 2020
    Last edited: Mar 24, 2020
  9. Marconi

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

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    [​IMG]

    711, can you give us a source for the jpeg files you added to your original post #2, that were below this image?

    Bob says he heard this antenna is a full wavelength tall. Can you confirm that information or give us a link to the source?
     
    #9 Marconi, Mar 24, 2020
    Last edited: Mar 24, 2020
  10. Slowmover

    Slowmover Sr. Member

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    DIY: Stop by Homers Deepot and grab some metal tubing plus hit the Garden Department for a tomato plant cage to bend into shape.
     
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  11. 711

    711 Well-Known Member

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    This was pulled off of Facebook from DavemadeNJ

     
  12. bob85

    bob85 Supporting Member

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    Yes Eddie that's what im getting at, 1/4wave cone & 3/4wave monopole puts the hoop close 1/2wave from the tip where current is lowest & voltage is highest,

    pictures can be misleading as we have seen in the past,
    the cone looks to be more than 1/2 the length of the radiator above it, could it be a full wave radiator with 3/8wave cone,

    VORTEX use a 3/8wave cone.
     
  13. Marconi

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

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    I see that the Vortex has a 3/8 wavelength radial cone. I never did try and model that one because I could not clearly see the matching area, and no way to know the overall length. If it is a full wavelength it looks like it will be about 434" inches or 36' feet tall. That is really tall.

    Have you ever seen a discussion from an owner of either of these antennas...anywhere?


    I will plug in the 3/8 wavelength radial cone and the full wavelength tall radiator and see where the match is without the physical gamma.
     
  14. bob85

    bob85 Supporting Member

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    The dimensions are on VORTEX website Eddie, 834cm for resonance @27.500
    mk1 Q82 was 860cm @27.500,
    The only VORTEX i have seen & talked about are the Q64 groundplane & mk1 Q82
     
  15. Shockwave

    Shockwave Sr. Member

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    I had this idea years ago but never got past the matching part. This antenna absolutely appears to have dimensions closer to a 1/2 wave or more, over another half wave cone. The 1/4 wave cone has already displayed ability to shield the undesired, out of phase radiation coming from the 1/4 wave inside the cone and replace it with in phase radiation folding back over the outside of the cone.

    The only thing preventing this 1/4 wave of in phase radiation from being replaced with a longer 1/2 wave, was matching the feed impedance back to 50 ohms. As you can see from the closeup pictures, this is easily done by adding an insulator and folded shunt inductor at the base. Testing of this design in the VHF spectrum will begin soon.
     

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