Dave wrote:
however, once you change the
reference Zo to 50 ohms inside the meter there is no reflected power to
measure since the load presented at the end of the 75 ohm line is 50 ohms.

The question remains: Does the MFJ's physical design ensure the
*physical* reference Z0 is 50 ohms or would it perform just as
well in a 75 ohm enviornment simply by recalibrating it for
75 ohms?

In other words, it is sampling a voltage and current completely
divorced from any *physical* reference Z0. The actual reference
depends upon an arbitrary setting of a calibration cap which
has no effect at all on the *physical* reference Z0.
--
73, Cecil http://www.qsl.net/w5dxp