Mike W wrote:
Many years ago I used a car windscreen wiper motor and gearbox to do
just this. IRRC the boom was monted in two ball races and there was an
operating arm , set at 45 degrees to the main polarisation, which was
attached to the wiper motor and the boom. Sorry but I really can't
remember any further details but ISTR that I had to make the motor
operate in "one wipe" mode by frigging the switch.
hth and seasons wotzits, Mike W, G8NXD

Yep, that's an idea.

I could buy 2 yagis, it's not really the expense, but a question of loading
on my scaffolding pole mast! :c)

Or I figure a peice of string and some kind of mechanism.