For consideration, here are my two Eznec models at 48' feet to the mounts for the old Astroplane/Top One, and Sirio's New Top One (NTO). My modeling efforts for each antenna was to try and get them as close to specs as possible.
I've added the first page as an overlay of the radiation patterns to allow for easy comparisons. The pattern in black (* Primary) is the New Top One and in blue is the AstroPlane.
I think these two are similar antennas, because according to Eznec their performance is almost identical and where differences are noted they are likely due to some height differences that I did not adjust to make equal for this project. The heights were close enough, but see note below.
I also find that these two seem to work the same in my real world testing, either side by side, and while standing alone using the same antenna system.
I think these two are basically center fed 1/2 wave antennas, not a 5/8 wave or 1/4 wave. They also perform similar to an end fed 1/2 wave model...which I've also included in this project for consideration. They look like center fed 1/2 wave too.
Personally, I consider the traditional 1/4 wave ground plane with horizontal or slanted radials a 1/2 wave antenna too.
Notes: all antennas were set at 48' feet for the mast as noted above, so due to construction differences they are all at a little different height, and that can make a subtle difference in the results you see here.
I also do not consider either antenna to be tunable as per instructions, specifications, or construction when set as instructed.
To support this idea regarding tuning, I've attached a bandwidth curve for my Sirio NTO with the gamma match feeder as well. Note that the SWR and VA1 analyzer bandwidth curves both indicate a nice flat working SWR range under 1.3:1, from 26.5 to 28.5. This is the same as noted in Sirio's specifications for the NTO's frequency range, so no tuning is necessary or needed.
View attachment AstroPlane vs. New Top One.pdf
I've added the first page as an overlay of the radiation patterns to allow for easy comparisons. The pattern in black (* Primary) is the New Top One and in blue is the AstroPlane.
I think these two are similar antennas, because according to Eznec their performance is almost identical and where differences are noted they are likely due to some height differences that I did not adjust to make equal for this project. The heights were close enough, but see note below.
I also find that these two seem to work the same in my real world testing, either side by side, and while standing alone using the same antenna system.
I think these two are basically center fed 1/2 wave antennas, not a 5/8 wave or 1/4 wave. They also perform similar to an end fed 1/2 wave model...which I've also included in this project for consideration. They look like center fed 1/2 wave too.
Personally, I consider the traditional 1/4 wave ground plane with horizontal or slanted radials a 1/2 wave antenna too.
Notes: all antennas were set at 48' feet for the mast as noted above, so due to construction differences they are all at a little different height, and that can make a subtle difference in the results you see here.
I also do not consider either antenna to be tunable as per instructions, specifications, or construction when set as instructed.
To support this idea regarding tuning, I've attached a bandwidth curve for my Sirio NTO with the gamma match feeder as well. Note that the SWR and VA1 analyzer bandwidth curves both indicate a nice flat working SWR range under 1.3:1, from 26.5 to 28.5. This is the same as noted in Sirio's specifications for the NTO's frequency range, so no tuning is necessary or needed.
View attachment AstroPlane vs. New Top One.pdf
