I was wondering if someone could help me with this. I recently purchased an MRS Minivna Tiny and I'm observing something weird. The port terminations are supposed to be 50 Ohm, but when in reflection mode, I sometimes get different results depending on whether the 2-port device I'm measuring is terminated with a standalone 50 Ohm load and when it's terminated on the DET port. Obviously, neither termination is EXACTLY 50 Ohm, but the difference is too substantial for it to be normal variation. I observed this around 140 MHz by the way.
Is the DET not really 50 Ohm? Is there uncalibrated crosstalk between the DET and DUT ports when in reflection mode if both are connected? what's going on???