Though the design is still somewhat of a mystery to me, I have a feeling you will see an overall loss in performance in comparison to the 5/8 -.64, not only because of the AP design's inherent handicap of loss of overall height above mast, but because when I tried one out (many decades ago) I also tested it with the top height equivalent to my Penetrator and it had less overall performance, especially on distant signals.
I presume the AP has a higher TOA than a 5/8 -.64.
I will be interested in your findings.
007, summer before last I did several comparison trials using my Top One antenna, among others that are posted in my album. They were staged at various heights where I then recorded RX signals from a group of radio buddies around the Houston area. I didn't plan too well, so I didn't end up really being able to make good cross comparisons for test to test.
I thought I was making all the tests pretty equal, but when I finished and recapped everything I could see I missed the mark. I also compared the antennas side by side, a practice where many operators object. So, the reports that I posted will have to be considered in this light.
007, my results differ from your results using your modified P500.
I found in every case except one while comparing my Top One to several other antennas, where the tips were at the same height, that the shorter antenna will always show...an equal or better signal at the distances noted in my reports.
I didn't notice anything particular during testing, but on recapping my results it suggested that the antenna with the highest feed point in the test almost always showed the better RX signal. There were a few exceptions, but signals from a majority of local points out to maybe 60 miles were mostly stronger on the Top One in similar situations. I tested at various miles, but I can't argue about long range vs close range. If you want to look at that however, my reports do show approximate miles between stations.
I also have a recap report that shows the Top One performing quite well with its tip as much as 10' feet below the tip of my I-10K, for example, where I tried to get the current maxima's at equal heights and I have a test with my Top One setup with a full 1/4 wave radiator on top instead of the shorter top hat configuration.
I will mention that I'm limited to what I can do regarding height, because I can only test within a range above ground of about 40'. With 23' - 27' foot antennas this gets the bottom of the longer antennas below a 1/2 wavelength when trying to keep the tips equal heights. Then the houses in this area that are a minimum of about 18' at the peaks can interfere and I find that can be important to understand and consider when testing. I find getting any part of an antenna below the peaks of my house for sure, and maybe even neighbor's homes seemed to me to show determinately effects on the signals I saw using the antenna below 18' feet or the peaks of the roofs.
Avanti raises this issue and refer to it as "shadow," in their ad work or the AstroPlane Patent. I therefore consider the old CBBS stories about the AP's only benefit being "...it works real good only when installed low to the ground, suggesting that it's crappy when raised up higher" ...is just plain CBBullS.
I consider the AP to be a very effectively fed center fed 1/2 wave antenna that does show a little skewing in the pattern, similar to the skew noticed in 1/2 wave j-poles favoring one side.
If the Top One antenna is assembled well with all connections nice and secure, whether threaded or compression, then IMO the antenna is relatively free of common mode currents. I believe this is due to the very high voltage in the bottom hoop that creates a high impedance field around the antenna mast and coax which is known to help minimize CMC below like a choke. However, it any of the parts of this antenna are the least bit loose, you will likely see RFI and TVI problems.
Take special note, I discovered this problem by accident having bad TVI with my Top One: this can be a problem that isn't always easily noticed with some of the threaded connections by the way. One area of note in this case is a hub with a threaded stud in the end of an element is loose and can turn, or the hub that holds the top hat radials in the Top One. These hub parts are compression fixed in the tubing and can be loose. This problem may not show up on a continuity test. When I fixed the problems on my Top One the TVI went away. If you notice these fittings are loose, you will see problems if not fixed even if the antenna works normally otherwise.
I don't think the original Avanti will have this issue, because the tubing is all compression fit in the hub I think. Except maybe for the radial section that fits at the feed point. That one, I'm not sure about how it fits. I do know that Avanti gives a installation warning somewhere regarding this area however. They warn to be careful when inserting the radial into the insulator at the feed point. The warning is, that you can break a ring clip inside and the antenna won't work. Such info is in the original AstroPlane manual by Avanti.
