Is there a program that will calculate Zin from a known Zload?

==========================================

Yes, from the same place you obtained program ZL_ZIN.

For coax lines use program COAXPAIR.
For balanced twin lines use programs RJELINE3 or 4.

These programs are to professional standards, 1% accuracy or better,
covering the frequency range from audio to UHF.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........