Keith Dysart wrote:
Open circuit 46.6 degrees of 600 ohm line attached
to 80 degrees of 100 ohm line. The drive point impedance
will be 0 ohms. And the impedance at the junction will
be the same -j567. Using your arithmetic, there is
90-46.6-80 - -36.6 degrees of phase shift at the
junction. The physical length is 126.6 degrees
while the system is 90 "electrical degrees".

Yes, you have just discovered that a 100 to 600 ohm
impedance discontinuity *loses degrees* when the 600
ohm end is open. That's why a center-loaded mobile
antenna takes more coil than a base-loaded mobile
antenna. Think about it.

Hint: if the stub is open, the low Z0 needs to be
placed at the open end to make the stub physically
shorter.

If the stub is shorted, the high Z0 needs to be
placed at the shorted end to make the stub
physically shorter.

You seem to be surprised at that. One wonders why?
--
73, Cecil http://www.w5dxp.com