Hello Lowfers
there is an interesting article written by Ralph Holland, VK1BRH named
"Spiral Top Loading of a Short Vertical" on the internet, check
http://www2.dynamite.com.au/vk1brh/SpiralLd.htm
for details.
Best 73
Geri, DK8KW (W1KW)
Longwave homepage http://www.qru.de