Originally Posted by
Owen
Penny has just dropped as to the reason why only half the length is typical.
1.8m if a full wave at VHF frequency. Therefore it has a null at the horizon if mounted vertically. The signal is like this 8
It will perform great if laid flat and used as a directional antenna in yagi or quad config but useless in a boat.
Therefore a 1/2 wave is used with the ground plane forming the other half.
Which fits exactly with the observations above re build.
So if we assume they are all half wave and if the two lengths have the same gain, measured in the same way, then height is key.
My apologies for confusing the issue.