Never more a Sigma4, 4 me 4 evermore.
How high above ground are the 1/4 & 5/8 waves in your modeling?
Is the ground effect anywhere near as serious a factor when the antenna radials are raised to 1.5-2 wavelengths above good soil conductivity ground?
The limited reading I've done with regard to ground effect has always been focused toward low band HF and considered the ground to be only 1/4 - 1/2 wavelength beneath the antenna.
I have my Penetrator atop a 4 section telescoping mast(36') atop a 20' rooftop, so the high current node is nearly 2 wavelengths from the top of my ground, and well above 2 wavelengths above the water table which is 7'-10' below the surface.
I read an extremely long strand on eham yesterday about vertical performance, ground effects, differing antenna radiation angles, etc. and found it to be more confusing than enlightening. Even Tom W8JI mentioned that he has found modeling isn't always correct, and he designs commercial antenna systems. Check out his rather impressive bio: http://www.eham.net/callbook/w8ji
"The proof is in the pudding" is often heard and in this case it means when real world tests are conducted the truth comes to light even when theoretically it shouldn't be as experienced.
Modeling is fun and can help bring ideas to life without so many errors one might otherwise experience if the simple 'trial & error' method of designing was instead employed, but it will never beat real-world comparisons, and I have done them on my roof and with the same coax, radio, mast, etc., with everything from a 1/4 wave R/S GP thru an Astroplane, Starduster, Sigma 5/8, MaCo V-5/8, A99, Imax, LW-150, Penetrator, CLR-II, Taylor GLR4, Wilson Alpha V-5/8, Shakespeare Big Stick and assorted others, (mostly short radial 1/2 wave designs) and only five stood out as superior performers well above the rest, and they were:
(in Alphabetical order)
1) Avanti Sigma 5/8
2) Hy-gain Penetrator
3) Radio Shack .64
4) Taylor Grandslammer GLR4
5) Wilson Alpha V-5/8
- and they are all ~23', four radial, .64 / 5/8 antennas.
That was here, 56' at the radials, 84' of 213 coax.
Not two different masts, two different runs of coax and two different locations on the property, no, the same mast, coax, placement, and height at the mounting bracket.
I have yet to try the I-10k but I fully expect it would mirror the other ~23' GPs in performance.
I was almost ready to blow some cash on another Sigma4 due to all of the convincing sounding hoopla surrounding it's mysteriously magical design, but I've already been there, done that, so why go back to the same results expecting them to be better the 2nd time 'round?
I'm satisfied that it is a decent, sub-.64 performer at this location.
Perhaps elsewhere, at a different location / elevation above ground / coax length / surrounding terrain, etc., it might just beat all others, but I have done my testing and the real world has favored the .64 design in my application.
And your 3.2x sleeve length numbers make sense as I remember the LW-150 being a little under 27' total length. Closer to 26' 7" - if I remember correctly. It's been well over 10 years since I sold it.
...and I don't see how anyone can experience a 1/4 wave GP as nearly as effective an antenna. Here it wasn't even in the same ballpark. Geez, even the A99 beat it.
The Starduster was the most surprising antenna I tested, beating the Astroplane, A99, Big Stick and, of course, the 1/4 wave, and it kept up with most of the other, taller, 1/2 wave GPs! - I believe it to be a center-fed 1/2 wave dipole, not a 1/4 wave GP as some have said, including me from time to time, mistakenly.
73
