We are using VNA (E8361A with options 80, 81, 83) to measure a frequency transfer device (FTD), which has two RF and LO inputs and one IF output. In our case, all the three ports work with frequency tuned signal. For example, let’s say the RF port works with a swept frequency f1 and LO port with a swept frequency f1/2+delta (delta<<f1/2<f1), while the IF output will be accordingly at frequency f1/2-delta. Considering this measurement, we have two questions: One is how to operate a frequency offset measurement with two swept frequency stimulus and one swept frequency receiver. The other is how to calibrate the measurement.