> From: Rich Measures <measures@vc.net>
> - Few designers seem to realize how much current derating of conductors
> is appropriate at 28MHz.
Few non-engineers also know how the current behaves in a conductor.
> For example: in order to carry 15 amperes at
> 50-60Hz, with reasonable loss,14 gauge wire is appropriate. However, for
> carrying 15 amperes with reasonable loss at 28MHz, a 0.5" by 0.09"
> rectangular conductor is needed.
The thickness of a conductor, once more than a few skin depths
thick, does not affect the loss. Also flat conductors have less
current capacity and MORE loss than a round conductor with the same
surface area at radio frequencies. Current bunches up at the edges of
the flat conductor, with a small amount flowing in the middle of the
wide flat area. That's why two parallel connections are much better
than one "twice as big" connection. (Of course braiding is the worse
of all, having at least three times the loss of a smooth conductor of
the same surface area.)
Loss depends on length, for "reasonable loss" a wire two inches
long can be a lot smaller than a "reasonable loss" wire 100 feet
long.
73, Tom W8JI
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