Thanks all who have replied to my question. I am glad to hear that there are no serious detrimental effects of feeding the antenna mid way along one side rather than at a corner. I should have mentioned that I am intending to make a horizontal loop antenna rather than a vertical. Another interesting point came out of this, a delta loop may provide a better fit in the space available when the tree locations are taken into account. Again thanks for the info

73 de Mike VK3XL