With a PNA, it's very easy. Do a "guided-calibration" and set port 1 to 50 ohms, port 2 to 75 ohms; this will prompt you to do an SOLT cal with unknown thru. You will use a 50 ohm open/short/load on port 1, a 75 ohm open/short/load and a reciprocal through device (such as your min-loss pad) as the through device. That's right, you use your min-loss pad as one of the cal devices, as long as you can assure it is linear and bilateral, which it undoubtably will be. Then, when the call is finished, you can set the measurement to whatever parameter you want, and measure the result.
With a PNA, it's very easy. Do a "guided-calibration" and set port 1 to 50 ohms, port 2 to 75 ohms; this will prompt you to do an SOLT cal with unknown thru. You will use a 50 ohm open/short/load on port 1, a 75 ohm open/short/load and a reciprocal through device (such as your min-loss pad) as the through device. That's right, you use your min-loss pad as one of the cal devices, as long as you can assure it is linear and bilateral, which it undoubtably will be. Then, when the call is finished, you can set the measurement to whatever parameter you want, and measure the result.
Easy.