I wonder if the CMC problem is due to the SO239 being well above the ground radials, therefore placing the coax above the radials. My understanding is that the coax should connect below the radials so as not to promote CMC?
35, I can't vouch for either antenna regarding CMC's they might or might not produce, but I read GI0ZGB's comments talking about his Vector and not his new Vortex.
Bob, what is it about the coaxial stub matching setup on the Vortex that makes it seem to you to be less lossy than other impedance transformers?
I recall this is basically what Jay use to say about his trombone tuner on his I-10K. This is not the first time antenna producers have made similar claims regarding their special matching devices. They all seem to claim their idea produces a match with less loss.
Among others, both HyGain and Mosley make similar claims. I've made the claim before that my Starduster design that uses no matching device at all, and I see it produce very good results for me...even though I'm probably one of a very few around that makes such a claim.
Isn't this type of Vortex coaxial stub matcher similar to the Gain Master's stub that produces such a big bandwidth? I guess I was wrong about the bandwidth thing however, because the Vortex paperwork shows it has a <2.0:1 bandwidth of only 1.3 mhz. I think maybe we see here that a symmetrically well balanced design at the feed point is generally always better in some ways and that is what provides the added bandwidth.
I also see that this Vortex model posted producing about the same gain as my models of a similar antenna. The big difference I see beside the matching is the Vortex has the ground plan isolated from the antenna and the ground.
I've also reported for a while now that my Vector model is very sensitive to the height above ground, and that being mounted near a 1/2 wavelength multiple probably will produce a lot of CMC if the antenna is not isolated from the mast and choked well. This same model also shows me if I raised or lower the antenna to some odd 1/4 wave or close the problem of CMC is mitigated nicely. I have not tested this idea specifically with my S4, but over time with numerous installs I have noticed sometimes it is pretty bad and other times it is very good concerning CMC.
So, I think a slight change in height alone might help minimize the problems that some guys report like GI0ZGB did above with his Vector, but the idea really needs to be tested more in the real world to be sure.
I think this effect is very obvious in my models for the Vector.
That said, Sirio is an Italian manufacturer 
