Bart Rowlett wrote:
Z0 = SQRT(L/C)[1 + j(G/2wC - R/2wL)]

is an approximation of the well known exact formula:

Z0 = sqrt( (R + jwL) / (G + jwC)) which can be found in any treatise on
transmission lines.

The equation just introduced from Ramo & Whinnery consists of the first
two terms of a particular series expansion of the exact formula for Zo,
and is therefore an approximation to Zo.

Thanks, Bart, that answers my question. I jumped to the conclusion that
since [(G/2wC - R/2wL) = 0] satisfied Reg's equation, it followed that it
must be part of the approximation mentioned by Ramo and Whinnery. I just
didn't read far enough: "For many important problems, losses are finite
but relatively small. If R/wL 1 and G/wC 1, the following approximations
are obtained by retaining up to second-order terms in the binomial expansions ...
it is often sufficient to retain only first-order correction terms ..."
which is what the above equation does.
--
73, Cecil http://www.qsl.net/w5dxp