Hi
I am building an rf transmitter for a short range data link at 433MHZ
and am almost done, but I would like to understand better exactly what
I am seeing with regard to antenna performance.

All technical notes I have read recommend a 1/4 wave whip over ground
plane as offering the best performance, statements like: "Best range
is achieved with either a straight piece of wire, rod or PCB track @
1/4 wavelength over a ground plane", I understand many factors effect
performance however I have found that a "bent" 1/2 wavelength length
of wire offers better performance.

If I use a 1/4 wavelength I need (due to case requirements) to have
two 90 degree bends in it (feed - up, across, up).
If I use a 1/2 wavelength I need to run it once around the (plastic)
case (feed - up, around the case, up).

I hope this makes some sense, anyway I have found the 1/2 wave is less
effected by polarisation and offers generally better performance.
However while more ground plane may help a 1/4 wave it seems to hinder
the 1/2 wave, I guess because it shields the loop around the case?

Regards