Hi there,

depending on the type of omni you want, have a look at the mobile omni at http://www.frars.org.uk/cgi-bin/render.pl?pageid=1071

The main problem with stacked antenna's like the colinears is feeding them efficiently. As the antenna length and number of elements is increased, the signal being fed into the radiator descreases etc.

So when you see a 1.1m long antenna with say 10db gain, and a 2m long antenna with 11db gain, this is why.....

regards,

Paul.