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ASTROPLANE best vertical antenna ever?

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

  1. The DB

    The DB Sr. Member

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    I referred to example 6 which, in the context of the article, is a combination of a top hat and a central load. They also mentioned that for a small amount of shortening a top hat by itself may be best. I was specifically comparing an antenna with a top hat to a full length antenna, which we seem to agree on...

    How much gain will be decreased depends on how much it was shortened. Further, it is on an exponential scale, which means the more you shorten the antenna the losses get significantly worse.

    I was just looking at a 6 foot long 40 meter ham radio antenna that uses both a top hat and a loading coil. It is in the 13'th Edition ARRL Antenna Book. That being said, I don't think it was as efficient as the builder thinks it was (my opinion). Luckily, if conditions are right you don't need a particularly efficient antenna to make contacts...


    The DB

     
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  2. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    DB

    It may have been on this site, I am not sure where i sen the models.

    there was a 5/8wl, 1/2wl, 1/4 wl, the astro plane and the merlin antenna.

    All eznec modeled.

    The top hat seemed for lack of a better term to "force" the radiation down to the horizon per say.

    http://www.worldwidedx.com/cb-antennas/158801-take-off-patterns-cb-antennas-we-use.html

    Marconi modeled the astro plane in the above link. Notice how the astroplane does not have the high angle lobe?

    The top hat loading works, as long as it is not TO MUCH top hat where the vertical radiator is severely compromised.
     
  3. nosepc

    nosepc On Vacation

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    This very interesting.

    Actually the difference between antennas is negligible, and it is there where other factors come much or more important, ...

    which is the signal to noise ratio.

    If an antenna receive a station with "signal 4" but has 3 of noise signal,..

    and another antenna only receive "signal 2", but has signal noise 1 ......

    Which is better antenna? :pop:
     
  4. The DB

    The DB Sr. Member

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    I looked through the models listed, and I can't deny that the two models that had more significant top hats didn't seem to have a high angle lobe. The problem is, those aren't the only antennas in that file that had little to no high angle lobe. Because of that I will limit myself to saying that there is a definite possibility that the top hats could at least play a role.

    Taking it a step further, there are two other antennas with much smaller top hats in the file, and those top hats don't seem to have made any difference at all to their high angle lobes. Therefore, if top hats can help either eliminate or minimize that high angle lobe there is likely a minimum effective size of said top hat to have such an effect. Odd, this line of thought disagrees with your statement on top hat size...

    And actually thinking further, the two antennas that have the larger top hats, and also have little to no high angle lobe, are not full length antennas because of said top hats. Is it possible that their physical length was short enough to simply not have cause the high angle lobe to form in the first place?

    I'll have to mull over this for a while to see where I come out...


    The DB
     
  5. The DB

    The DB Sr. Member

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    You won't notice much of a difference between those scenarios. In either case the signal will be about 1 S-Unit (or 6 dB) above the noise. Of course this assumes your S-Meter is accurate, which in the real world very few actually are...


    The DB
     
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  6. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Same thing I Noticed in Marconi's models.

    The ones with larger top hats did not have the pronounced high lobe per say.

    I did say top hats were useable as long as they are not TO LARGE, taken up to much of the vertical radiator. I,E the 40 meter 6 foot whip both top hat and base loaded.

    Just lucky that when RF is transmitted it has to go some where.

    Scenerio.

    If the antenna can not be installed at 1 w/l or even at 1/2 wl above ground will the top hat type antenna still put the radiated RF at the horizon 12 to 30 degrees?

    Homer may be able to add some insight into this scenario.

    This is, if it is indeed true, may be the reason so many say the astroplane is a great antenna.

    Friend of mine, an old timer (70's plus yrs. old) Swears the best antenna he ever had was the astroplane.

    He has never had an antenna installed above 30 feet high and admits most of his antennas were on a piece of pipe 20 foot tall.

    I dunno what or why that astro plane works as good as it does, There sure has been decades of ops praise the performance of that unusual antenna.

    I have never owned one, and probably never will unless one falls into the back of my truck.


    The smaller top hats on the antennas may just be there to make the antenna look cool(y)

     
  7. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    If you are using your receiver S meter for comparing two different antennas.

    The results you described above lead me to believe that one antenna has a higher gain than the other by TWO S UNIT or 12DB.

    That is like comparing a vertical ground plane to a five or 6 element yagi.

    There is no comparison, apples and oranges.

    If one antenna receives 12db more of signal than the other then it will usually transmit 12DB more of radiated RF.

    The law of reciprocity.

    Copy and Paste from Wikipedia

    ***Forms of the reciprocity theorems are used in many electromagnetic applications, such as analyzing electrical networks and antenna systems. For example, reciprocity implies that antennas work equally well as transmitters or receivers, and specifically that an antenna's radiation and receiving patterns are identical*****
     
  8. HomerBB

    HomerBB Sr. Member

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    I mounted the AP lower down simply to tune it. I ran it as an antenna at heights ranging from 29' at the cap hat to 54' to the cap hat. What I eperienced with the antenna was that the Avanti design concept for the antenna of making it so that it could compete with other antennas when the top, or cap hat, of the AP was at the same height of the larger (longer) antennas proved to have merit. Working on it below those mounted heights it seemed no better than any other antenna near the ground with similar bottom heights (One exception to that would be the Vector4k/SigmaIV types, which displayed significant performance improvement over all other antennas mounted as low as 10' from the bottom of the antenna to the ground). However, when I began to lift the AP upward from the ground attempting to get its Cap Hat to elevations the longer antennas had been due to their greater length it began to demonstrate equal performance to the longer half and 5/8 wavelength antennas. When I managed to lift it up to a tip top height of 54', still slightly lower than the V4k the tip of which went on up to 61' at that time, the AP came nearer mimicking the performance of the V4k than any of the others. It clearly had better ears to the horizon than the other 1/2ƛ & 5/8ƛ I had put in the air, and handily worked stations I struggled to hear with them. DX was worked to destinations I could not manage with those antennas. Only the V4k was showing its ability to talk through the Ozarks to distances of 80 miles that left the AP behind with roughly 60 mile range, and the others which achieved up to 50 maximum miles of range line of sight in these hills.

    Now to your question - I feel that, as I said, at lower heights the AP was no better than, but equal to most any low mounted antenna. The theory of the antenna I believe is fulfilled in the location of the current maximum being higher up the vertical height of the antenna than longer verticals have. That said, when the bottoms of the antennas are mounted at the same height, the maximum radiation of the AP, 1/2ƛ, and 5/8ƛ are within 6' of each other, and the difference would be negligible in terms of difference between them, while to the user of the antenna it would seem that the antenna was better because the performance was on a parity with longer more expensive models. Whether or not the antenna maintains its lower TOA to the horizon down low I don't know except to say it seemed to maintain performance equal to the longer antennas which may indicate that as much as they are affected by low mounting it is too, but not more.
    Modeling at low heights may offer clues . . .

    Clearly I have a love affair with the two Avanti creations I have built and flown, as well as the original AP I had. Perhaps it is because only beam antennas have proven superior to them while I have reasons to believe other verticals struggle to do as well.

    A fellow with an experience is never the servant of a fellow with an argument. ;)

    Smaller top cats, as opposed to true/large cap hats, have never given me significant performance enhancements, nor required large antenna length adjustments. I believe the size matters, but I haven't deliberately tested various sizes of cap hats and their empirical effect upon antenna length and performance. Maybe a field test for the future . . .
     
    #68 HomerBB, Oct 31, 2013
    Last edited: Oct 31, 2013
    Oldme likes this.
  9. Shockwave

    Shockwave Sr. Member

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    Stop paying so much attention to the model pictures and start looking at the numbers. Realize they are all in isotropic format (that means subtract 2.15 db to compare with dipole) and they all have ground gain added in at 32 feet.

    That also means all but the last few models on that page are well below unity gain. Some of the poorest performers in gain on the horizon were the top hat loaded antennas. Both showing highest gain in the secondary lobe above the horizon.

    The reason you don't see the familiar high angle lobe in the top hat antennas is because three individual lobes have all blended together to form one big low gain "blob". The highest angle lobe is nearly straight up on these antennas.

    It's when these lobes become more clearly defined by taking power away from the areas that will form the nulls at undesired angles, that we produce needed gain on the horizon as seen in the Vector 4000 model at the bottom.

    The reason the Astroplane works well in many common applications is that it's center of radiation is in a more confined area do to the top hat loading. That makes it easier for the antennas center of radiation to clear more obstacles at average mounting heights.

    Go below average height with top hat loading and the advantage is lost because the entire antenna is blocked with obstacles. Go much higher and the entire center of radiation on the longer antennas will be in the clear and the top loading lost the advantage there too.

    Put the Astroplane higher in the model at like 45 feet and watch the high angle lobes sprout up. It will also start to produce nulls. Unfortunately since it couldn't produce gain over a dipole at 32 feet, the power transfer from the nulls to the primary lobe will be proportional. In other words it's still less than unity gain at any height.
     
  10. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Homer, Shockwave thanks for the posts.

    Homer's experience sums it up.(y)

    Shockwave's explanation explains it.(y)
     
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  11. Marconi

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

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    Bob, I hear you describing the A/P as a 1/2 wave, and I agree. Then you go on to suggest something about a 5/8 wave idea. I use to believe the A/P was a 5/8 wave also, until I was able to model it...and then I realized it looked more like a 1/2 wave radiator. There are other reasons for my ideas that the A/P style is an excellent 1/2 wave antenna too.

    I like my real world results using my A/P style antennas, but I don't think it is because it is a 5/8 wave. And, since Avanti made their AstroBeam using an AstroPlane...I figure that nails the fact that it is a simple 1/2 wave radiator that radiates like a 1/2 wave. It's just short and maybe its current distribution is a bit compressed and maybe that is a bit of an advantage to gain. I think Sirio makes a similar claim. So, I can't imagine a 3 element beam would be effective using a 5/8 wave radiator for the driven element...even if it was a 5/8 wave and we were using CST to model it.

    There is also an advantage with the A/P style antennas in the very low noise level they tend to manifest, but the only gain advantage I think we're likely to ever see using this antenna is when we get the tip up as high as the comparison antenna...just like the Avanti design idea suggest.

    I suggest that very few can really appreciate the features this little antenna has without having owned and worked one. I don't even think most can really appreciate the low noise level idea without having two antennas connected to a switch box to really see the difference. I'm not saying here that if the noise level around this antenna or any other antenna is really bad at any point in time...that the A/P will give you a very low noise level, but I find it is always lower that my other longer antennas that I've compared. I find about the same is true with my Starduster and my Marconi 5x antennas too. I believe their symmetry and good balance in antenna design does that, and I think we can see that in operations...even if we don't see the big signals other longer antennas can produce. I think nospec wrote about this the other day, but that idea was trashed before the his idea even got started.

    The gain results from my Eznec model of my A/P does not suggest anyway that it is a 5/8 wave, but it would be nice if it was a 5/8 wave and could produced results like a 5/8 wave when compared to any other antenna at the same feed point height...which it won't.

    I only see a real world advantage using my A/P or the New Top One when I compare it to another antenna with the tips are close or equal in height...just like Homer has reported. I also see a similar advantage using my Starduster under similar conditions.

    I think I also recall you stating that Avanti said making the A/P shorter with a top hat made the bandwidth wider, but I did not find that to be true when I compared two Top Ones side by side with one having a full 1/4 wave radiator. I recall those results were the opposite, and at the very best the difference was very small. That said however, I was testing the BW using a long feed line, so that might show more difference if tested at the feed point like my models do. The Eznec models don't exhibit much difference either, and I also find the issue of bowing the two radials closer of farther away from the mast does have some effects on match, it too is not much, and I see no difference in radiation angle either while the gain does change a bit. This part of the Avanti patent looks to me like the old story when folks tell me there is a difference when we do in this or that...it often works out to be almost insignificant, and hard to really tell. I have said, maybe they are talking about technical differences which tend to be very small and specific.

    Bob, I also think you suggested above that the Avanti engineers did not know how the A/P antenna worked. That is not how I read what was said in the article noted below. The article was about the AstroBeam, and what was said was the engineers did not understand the special added effects they claimed when using the A/P as the driven element in their new creation for the AstroBeam. In due course, however, they discovered and claimed that the A/P coupled better with the parasitic elements, and that is what caused the unexpected results in their claim for gain and rejection.

    I'm not so categorical as to believe that puffing is not going on in CB advertising back in those days even by Avanti engineers...and even on very small points like this antenna may be noted as being of benefit to users. Magic always plays on human nature and mystery sells too.

    Here is the article which is not very legible so I typed the pertinent text below: View attachment 11518

    I think you also claimed that the shadowing effects that Avanti claims regarding their A/P was poppycock, but in my simple testing of the idea I found this factor to be remarkable in its ill effects on RX responses. I've said for a long time that topography and Earth conditions play a part in how and why antennas in different locations respond differently. I think you would agree that getting our antennas above the typical surrounding structures is probably a good idea too. I take it that you might also agree that if we were able to really do professional field testing we would make sure all the transmitting and receiving antennas were basically at or near the same elevation, with the absolute mimimal of obstructions in the way, right?

    Since the world around me is more like a flat plane by nature...this may be why I see more similarities in results with the CB antenna tests and comparisons. How do you evaluated antenna comparisons in your area being as it is hilly? For example, say 10 to 20 miles with a station to the north of you that sits on land 200'> higher than your station, compared to a contact south that is 200'> feet below you, or does that matter in your observations?

    Among other things, could this possibly account for some of why you tend to see very little shadowing in your experience, while in my experience the ill-effects are remarkable. The idea is easy to test and detect? Could this also account for why we might hear reports of 1-3 sunits difference is some signals at times. Homer as mentioned his topography before and I think he sees some results similar to what you see at times.

    I've often suggested to guys in Europe that have their antenna mounted very low to Earth, and set among two and three story buildings that they are likely to suffer from attenuation (shadow effects), but now I think that may be I was wrong and because of the general hilly terrain, like in your area, those problems with being low are not always so noticeable. I have never lived with hills around.

    I'm late getting into this thread, but I've had a cold bug for over a week now.
     
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  12. Marconi

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

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    Bob, according to my Eznec model here is the difference in feed point impedance...with and without the mast. It does raise the impedance a little bit.

    View attachment AstroPlane with and without mast.pdf
     
  13. Marconi

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

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    Homer, you may be right. I think my models typically show better results over poor soil conditions than over good soil...excepting when over sea water.
     
  14. bob85

    bob85 Supporting Member

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    i never said the astroplane was a 5/8wave eddie, it looked like a hat loaded 1/2wave to me when you posted the 5/8wave idea on freecell's site years ago,

    i never said the reduced shadowing was bs only the magnitude of advantage depicted by the adverts, they are not telling the truth about where other antennas radiate from,

    avanti tell us in the patent what effect the hat has, i have not tested it but i have seen other sources who have taken measurements claim the same things about hats,

    maybe i read the article wrong, i remember saying if they don't understand the atrobeam how can they understand the astroplane when you sent me the article and you not pointing out the error of my reading into what they meant at the time, i won't be satisfied with how it works until i see it in cst,

    i know how well the astroplane works for a short antenna, i owned one and did plenty of tests vs other antennas in the 80's,

    its lighter with much lower windload, easier to get in the air and safer if it falls down in high wind to use a vector on a short mast than it is an astroplane/starduster on a longer mast at the same tip height,
    that won't stop me testing my homebrew astro against the 10k at the same tip height,

    i explained how we test multiple times, why i don't use two 36ft poles and a switch anymore,

    most of my own tests were done at my parents in a field with flat land Vale of York - Wikipedia, the free encyclopedia for 55-60 miles to the east coast and small hills to the west, more than half of the stations would be on a similar elevation to me,

    we also took antennas out to high ground up the pennines to the west where you could talk coast to coast easy, or we would drive 58miles north up sutton bank,

    at this location i have hills but nothing close to 200ft higher or lower than me for 20 miles or more, its enough to give the longer antennas an advantage when mounted on the same pole no doubt.
     
  15. W5LZ

    W5LZ Crotchety Old Bastard

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    :) :)

    And if you could define all that rock/sand/dirt/metal/etc, under that antenna in terms a modeling program would find acceptable you could see the results of including all those variables!
    I ain't going there, I like hanging out on street corners and bars too much. Have fun.
    - 'Doc
     

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