Cecil Moore wrote:

For that statement, the length of the feedline is unknown
and the load is unknown.

I was commenting on this, the subject of our conversation:

"Consider the following:

Source---50 ohm feedline---+---1/2WL 150 ohm---50 ohm load"

As I was saying, for the two boundaries as a network, and we call rho at
the first boundary r12 and rho at the second boundary r23 then
rho(network) = (r12 + r23)/(1 + r12*r23) = 0. Note that if we use your
value for r12, the network generates a reflection. I note the utility
of negative rho in this example.

Seems to me, rho
cannot both cause a voltage and be caused by a (voltage divided
by a current) which is an impedance upon which rho is dependent.

Voltages on a transmission line do not determine reflection
coefficients.
Reflection coefficients are determined by characteristic impedances, not
virtual ones.

73, Jim AC6XG