shockwave,
the sleeve monopole article is interesting and may shed light on how the sigma operates, since its the only source of detailed information of an antenna with that layout and dimentions i can find at this time its the only idea i can come up with untill somebody finds an alternative,
one version described has a 3/4wave monopole and about 1/4wave sleeve, look what happens when the central monopole to sleeve ratio exceeds about 3.2:1,
this could be the none aparent colinear array that CEBIk told me was possible when folding the radials up towards the central monopole,
if you have any different articles that you think answers how the sigma works i would like to read them,
you will find several more sigma4 threads on this forum, i think some older ones may have been lost in the forum changeover, check them out, i think you will enjoy reading them,
id like to see the 15 degree radial setup to give me an idea of what mine would look like@ 27mhz
