Roger Sparks wrote:
What is the common reference point of x,t? In other words, when both x and t are zero, where on the antenna is the zero location?

By convention, x=0 and t=0 are at the feedpoint with the same
phase as the feedpoint signal. Thus, at the feedpoint, the
current is equal, but at no other point until one wavelength
is reached.
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73, Cecil http://www.w5dxp.com