I'm like you Dave8, I'm not the wiser either with the Vector's shifting length that provides the best performance. At one point in time it was longer than 31' feet, and now it's less than 31' feet.
According to Shockwave, I think he reported some time back that .82% of a wavelength was the best length, at about 29' 8". Now he says a less than 31' feet, and that is a big difference.
Personally, I think it might depend a lot on your location and how much trouble you wish to go to construct, install, tune, and raising the antenna up and down while tuning again and again...in the process of trying to find that magical setup.
Bob has a lot of company agreeing that some kit models of the Vector leave a lot to be desired...regarding its durability at his high wind location in England. I think that it may be possible that Sirio changed the antenna, making it shorter, and keeping the performance about the same by adding length to the radials and making the radiator shorter for just that reason. Sounds like Sirio was truly concerned with the problem Bob suggested and maybe they were getting a lot of similar complaints. That makes sense to me and I figure big manufactures don't change old line products unless there is a problem that can be solved easily without much expense.
I don't know how much difference these guys are really saying is the difference you might expect, but Bob is probably right again...unless you plan on installing your new Vector in his garden, all bets are off regarding the performance indicators he suggested.
I can't tell you for sure, but based on what I seen the Old Vector's may have been a bit less sturdy by construction, and if so, I would choose the New Top One, set it up just as instructed and work what you can. If the Vector performance is as good as Sirio's New Gain Master, and their New Top One, then I don't think you can go wrong and I wouldn't worry my self over getting the last bit of gain out, cause that could develop to be less than a DB.
I don't find near as much difference by comparing my antennas as others find. However, my reports do indicate my old Sigma4 performs a little better than most and it only has three legs and is not supposed to perform up to par even with a stock Vector, much less a well modified and tune Hybrid Vector.
I now have some tubing material that will allow me to make my Sigma4 longer and I'll try and duplicate this remarkable difference that is reported by others...when you make that bugger about 31' feet long and tune it real well.
I recommend the New Vector 4000, but I only have Sirio's reputation and word as the bases, because I've never seen...even a modest effort given to testing and/or comparing this antenna since it was introduced. I hear some talk, but that's it.
Good luck and keep us posted,
Marconi
