hi guys,

After an hour or more of pushing and twiddling various buttons and
knobs on my VNA I have at least established two standards: I connect a
short and the (polar) spot flys off to the extreme left-hand-side and
sits stably on the central horizontal axis. I then remove the short and
replace it with an open and the spot jumps across 180 degrees to the
extreme right-hand side on the same plane. All well and good so far.
Next, I replace the open with a lab-grade 50 ohm termination and I wind
up with an arc on the outermost circle of the polar chart at about
two-thirds of the way round the circumference (clockwise) from "12
o'clock" as opposed to a spot in the dead center of the display as I
would expect. What have I done wrong? I have checked this with 3
different 50 ohm loads and they all show an arc at the 'south west'
corner of the chart. What's goin' on here, guys??
confused
Paul