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I was surfing about on the net and came across this interesting albeit mean looking vertical but cant find out much about it.
I know a fair bit about antennas but this one has me a bit stumped.
From what i can tell it probably uses the cone shaped arangement to act as a form of counterpoise while cancelling out of phase radiation from the main element, as this is 3/4 wave long.
The gamma match then provides an easy impedance match to coaxial line.
Thats a simplified version of what I recon but I'm more interested in feedback from someone out there who has used one.
How good are they? Has anyone used this ant. and compared it to the astro plane AV101?
Cheers Daz In auz.

sigma four was THE antenna over here in UK.

The basket arrangement is a sort of broadband/groundplane arrangement that worked suprisingly well. the original Avanti antenna was made entireley of aircraft aluminium and was very strong; mine survived an 80mph storm about 15 years ago.

the antenna was either a 3/4 wave or 7/8th wave; i cant remember now; but the bandwidth was brilliant; low swr accross 25-30mhz.

only drawback is they are so noticeable. If you had one, everyone knew you were on cb!

if you got one up at a reasonable height you could work over 80Miles on groundwave; it also had interesting radiation lobes allowing good dx performance too.

Unfortunately, Avanti went bust a while back; and they are VERY hard to get jhold of. That said, theres a guy who lives not half a mile from here who STILL has one on his chimney-pot!!!

if you find one KEEP IT!!

Only problems were corroding gamma bar which eventually disintegrated; but many were repaired using a bit of stainless rod, much better.

also look out for avanti PDL 2, 2 element 'quad' which wasnt really a quad as such, more of a vertical-horizontal beam with amusing 'sphere' gamma match in the centre. Absolutely huge. also rare as hens teeth!

Sirio currently produce a copy of the Antenna Specialists (Avanti) Sigma IV called the Vector 4000.

It's also a 3/4 wave monster but I suspect it's not quite as well built as the original (I had a Sigma IV way back in 1981 & it did perform incredibly well )