im waiting for the 1/2wave endfed j-pole camp to post ANYTHING that makes sense,
lets look at some of the things they have claimed over the years of posting nonesense without ever showing us where this info came from,
1/2wave endfed
radials that restrict radiation to make it act like a 5/8wave
radials that solve the problem of feeding a high end impedance 1/2wave
lossy gamma feed
sigmas are difficult to tune for a low vswr compared to the i10k
raising a sigma higher causes the vswr to go through the roof
sigma4's are weak antennas that need drilling and bolting together
the sigma works like a slot antenna
aperture is a slot or opening not related to antennas,
Effective Aperture
where are the links to anything factual,
a book to go look at, an alternative method of operation??
i am keen to learn IF what is been claimed can be shown to be true or even possible from a respected source,
speculation and personal none factual ideas mean absolutely nothing 
jazz,
antennas such as the sigma do have two current modes,
some call them transmissionline mode and antenna mode ( arrl ) while others call them transmissionline and common mode.
