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ASTROPLANE best vertical antenna ever?

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

  1. bob85

    bob85
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    Eddie,

    The astroplane was designed to get an edge in height of current maxima over other antennas when you are restricted to a maximum height to the tip but its not all positive, one downside of hat loading is narrower bandwidth,

    does the hat loaded version have an edge when you place them at the same tip height due to the 4.5ft advantage of current maxima?




    Here's my take on the hat or horizontal radials on a groundplane,

    The hat has one current source which it splits radiator current 4 ways,
    each of the 4 wires has a mirror image, a wire that has current flowing the opposite direction in space making them opposite in phase with very little radiation or reception,

    [​IMG]
     

  2. Marconi

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    Bob, I agree. The link below shows what I said to nav2010 in an earlier post about the currents that I see flowing on the Top Hat elements.

    It is just as you say above, due to cancellation.

    Good point about setting the full 1/4 wave model and the shortened horizontal Top Hat model at the same tip height and comparing the results. I'll get back on that.
     
    #257 Marconi, Jan 11, 2018 at 12:46 AM
    Last edited: Jan 11, 2018 at 12:57 AM
  3. Marconi

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    Your link to photobucket.com does not work for me.
     
  4. Marconi

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    Bob, here are the models that raised the A/P with horizontal Top Hat radials up 42.803" inches to equal the tip height of the model with top radiator set to a full 1/4 wavelength.

    Looks to me raising my A/P model with a horizontal Top Hat...lowers the maximum low angle lobe down 1* degree, but it only made a modest difference in the gain.

    IMHO the reason for this possibly has to do with my starting to model using Free Space Average Gain Results to make sure the model over Real Earth is as accurate as possible to start with.

    I hope I'm right, my being able to better control the match for some of these CB type antennas also helps. I see it as improving the model even though I seldom see a model that looks to go to the trouble of matching. DB agrees that matching does not appear a popular effort in modeling we see on the Internet. He has helped me fine tune this process in models that are close to a good match.

    DB has talked about this issue several times, I think he is basically saying (I could be wrong)...that apparently matching an antenna to show a perfect or near perfect Average Gain Results...still effects the current distribution and thus we might see stark to modest differences in performance results. I've been redoing some of my older models this way, and I do see some positive results.

    When I extend the short radiator on my A/P model above I was a little surprised at the difference in gain it showed. I'm sure I have old models that did not start with an Average Gain check...that shows marked differences in results.
     

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    #259 Marconi, Jan 11, 2018 at 2:52 AM
    Last edited: Jan 11, 2018 at 4:00 AM
  5. bob85

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    When i get my layover pole setup I may try removing the loaded 1/4wave & extend the mast with a full size adjustable 1/4wave Eddie,

    vswr with the stock setup is higher than i am happy with, it would allow me to tweak vswr without butchering the avanti tubes,

    the symmetrical appearance would be a bonus to me,

    i don't know if i have any tube that will be a nice fit inside the mast.
     
  6. nav2010

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    What happens to the impedance and electrical distribution of a coil shortened quarter wave mobile antenna if you bend the whip half way so the top half of the whip is parallel with the roof of the car?
     
  7. Marconi

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    Bob. I haven't heard this claim from you before.

    You say your SWR for your A/P is higher than you like. What frequency are you getting this high SWR?

    For now, my A/P model suggest setting the top radiator in line with the mast is not as effective as what the specifications call for. I never tested the idea, but I am curious what your results show.
     
  8. bob85

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    Everywhere from 26-28mhz is above 1.5:1 with 200ft+ of genuine rg213 Eddie,
    extending the original radiator would not be strong enough for our weather.
     
  9. Marconi

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    Bob, I have an old experience with 213 that was not good. Maybe I'll share the story later.

    Thinking about your matching issue with your original Avanti A/P, I took a chance I could find some comments from other A/P owners talking about their results with their match, so I did a forum search for "AstroPlane" and went to the end of the file page #10. There I found the oldest record dated December 2014. Homer made that post and maybe you started the thread.

    Here is Homer's post. Any Astro Plane Fans? He is talking about adjusting the radial spreader to effect the match while using his 259b. I read a few more posts and I find this discussion interesting. This was deep into that old thread, but I think some of that discussion is a good read today...considering this current thread on the A/P.

    In the quote below you will see me talking, back then, about the length of the mast inside the radial cone and below.

    If you do the numbers and compare this mast length to my current models of the A/P attached below...you will see that recently I came up with exactly the same mast length 187" inches that produces the maximum gain and angle for my model.
    Here are the numbers that I think apply to this issue about the mast length below the hoop. The A/P radials are about 7' feet = 84" + 103" = 187" for the mast inside the radials. If you note in my current models, posted below, I still make this mast 187" x 1" inch...in order to see maximum gain.

    This file is long and complicated, but it basically shows 3 different methods of feeding this model at 3 different wire locations on the antenna. I added some extra antenna images just to show the antenna up close, to indicate a few of the dimensions I used for the mast inside the antenna, the length of the full 1/4 wave radiator, and the length of the mounting bracket used...which in all cases was 6" inches between the top of the radials. Some of the other detail pages were posted to complete the model for my reference.

    I also used the spacing midway between the radials to effect these matches, so in my opinion this space does exactly as noted in the Patent. This is contrary to what Homer found in his work, but I'm not surprised a bit...the differences are complicated and the changes are minuscule...even though the effects on match can be significant to the match.

    If you are curious about how accurate these different methods for matching are...then you are not by yourself.
     

    Attached Files:

    #264 Marconi, Jan 12, 2018 at 4:57 AM
    Last edited: Jan 12, 2018 at 5:05 AM
  10. Marconi

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    Bob. I would think such a long feed line would have some lowering effects on the SWR at the far end and your line reports a bit high for this antenna. Your >1.50:1 doesn't sound good and the BW seems a bit short. Could you have something that is not making a really solid connection. If this 1.5:1 goes out beyond the 26-28MHz you noted...you might check for a line that had water in it at some point in the past and has deteriorated the shield in spots.

    My Old Top One (OTO) went up more that once showing a less than desirable match or otherwise acting bad ie. noisy receive. The following construction doesn't apply to your Avanti, but my OTO model uses pre-drilled and threaded slugs at the ends that screw together. These slugs are compression fitted and they tend to get loose over time. I also find some of the old parts I collected over time have slugs that were loose. The slugs in both ends of my OTO radiator has shown this problem. I guess this was due to the wind twisting the big top hat.

    I don't know how this problem is manifested, but there is a caution note on page 10 Fig #2 about the radiator connection at the feed point. I would also make sure the two piece mounting bracket is really good and tight and the compression scheme there is working well on the element tubing. The A/P antenna shows continuity between every part of this antenna, so I would check that.

    IMO the A/P should show a near perfect match in the middle of US CB band. This is based on my recollections over the years from many guys running the A/P. This is why I went to the forum search to try and verify further what I recall.

    I have a few Antenna Work Sheets that show the bandwidth curve for my OTO, and they are all read from the radio end of a shorter feed line (maybe 70'), they show over 3 MHz on my analyzer and my inline meter.

    Good luck and keep us posted.
     
  11. bob85

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    There is a chance that my rg213 has had water damage during the 9 months it was not been used but i doubt it eddie,
    when i take it down i will test vswr with a quality dummyload, if it is damaged i have a new 100mtr reel of westflex 103
     
  12. Marconi

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    My thru-put notes for my feed lines shows: Back in the days I tested them every time I'd take them down.

    Clear Jacket RG8x 106" feet = 100 watts IN 31 watts OUT due to water damage, but after the water dried out the line seemed to work fine, low noise, low SWR, very broad bandwidth. It just didn't make a big signal.

    As Henry would say...hehe :LOL:

    RG8U Foam - 3 lines from 50' to 75' feet = 100 watts IN and 100 watts OUT
    Belden Mini8 RG8x line 160' feet = 100 watts IN and 84 watts OUT
    Davis Bury Flex 213 line 120' feet = 100 watts IN and 92 watts OUT
    TW LMR 400 91' feet = 100 watts IN and 100 watts OUT
    TW LMR 400 50' feet = 100 watts IN and 100 watts OUT

    I have a dummy load with a happy meter, but it is close when compared to and inline meter with a jumper.
     
    #267 Marconi, Jan 12, 2018 at 12:25 PM
    Last edited: Jan 12, 2018 at 12:32 PM
  13. JAF0

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    Marconi, I'm curious as to what total length the top tube of the AP would need to be from the bracket to the tip in order to tune correctly at 27.2 if it were simply a straight vertical radiator like the Maco or any other vertical?
     
  14. bob85

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    I don't know how you are measuring the loss Eddie,

    100w in 100w out is lossless & impossible with any coax,

    160ft of rg8x & 120ft of rg213 both have significantly more attenuation than your measurements suggest.
     
  15. Marconi

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    JAF0, you have to consider the tube diameter and length. So, ultimately you may have to tune this radiator length.

    If you open the last PDF file and check post #264, then go down to page #5, you will see the Antenna View with the radiator dimensions for wire #10 are 84.68" x 0.625" inches for this model.

    This is not the only dimensions I changed in the process of tuning however. With the full length 1/4 wavelength wire in the top...I also had to make slight adjustments to the insulated support bracket...space between the center of the radials and the center of the mast. I spoke about this in an earlier post.

    This antenna kit was designed fixed to tune, and was not meant to require tuning adjustments. This is why I am surprised that Bob is not getting a near perfect match somewhere close to the middle of the USA CB bandwidth.
     

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