The Avanti Sigma 4 was probably the best omni-directional base station antenna ever built.
The design was simble, robust, and extremely effective. The performance was legendary, and anyone fortunate enough to own one would probably have worked all around the world back in the '80's.
A picture of the original Avanti Sigma IV can be viewed here.
If anyone has any more original pictures of this true classic antenna, perhaps they would be kind enough to share them with us here.
If you have any pictures or information, please email us with your experiences.