Walter, W2DU wrote:
"The first reference I can give you is in "Theory and Problems of
Transmission Lines" by Robert Chipman, in Schaum`s Outline Series, page
128 Eqs 7.9a and 7.9b."

Alas, I don`t have Chipman`s book. Another source is Terman`s 1955
"Electronic and Radio Engineering". He solves the differential equations
for a transmission line, starting on page 84 for solution of traveling
wave problems.

Best regards, Richard Harrison, KB5WZI