When I made the top element of my AstroPlane a straight 1/4 wave using the 43" x 1/2" top element out of my Sigma4 attached to the 46.5" x 3/4" element of my AP, I overlapped them by 1"-4" inches using hose clamps. I got the following SWR bandwidth curve. The overall top element length was only 87.5".
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I didn't sense any difference in signal when comparing these two on the same mount. If I still had my hub that I sent to Bob85, I would have built two A/P and compared them side by side too.
What kind of results did these folks get with their 102" top element? Did you ever see one? At that length I would bet they were center frequency well below channel 1. They were probably just lucky the antenna is so wide banded.
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Check out the difference that 3" made in center frequency.
By the way, when I replaced the top hat, the bandwidth match showed a much better match the entire range for CB and more. I didn't realize this at the time, but I did sensed better performance on air with the top hat model, even thought the signals were about the same. I think somewhere on WWRF I've already posted all about this project in 2009.
When I first got interested in this idea, was due to the image of this top element in the AstroBeam manual. It looked way short, but it was an artist rendering. I read the manual carefully and felt it indicated this full 1/4 wave element should be in the range near 79.5" inches long, and that is the length I started with in this project. That BW curve shows a center frequency of 28.000 to 29.750 mhz.
Your folks antenna probably worked, but I don't think they knew what they were really experiencing or talking about with a 102" element.
