The difference is that a 5/8~ has a lower angle than a 1/4~ thus reaching
out further. so for example take a doughnut and smash it and you have
converted from a 1/4 to a 5/8

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oups.com...
Is ther much difference in the performance of a 1/4 wave ground plane
vs a 5/8? For any freqnecy but especially vhf?