Another thing you can do to measure chokes accurately is to simply use a Vector Impedance Meter instead of a network analyzer. Like the HP 4815A. In essence, it uses the VI method, as the name implies. It doesn't care if the impedance is nowhere near 50 ohms. For really high impedances, it can be helpful to mathematically subtract the stray capacitance of the probe. I've gotten excellent results with my 4815 for years.
Rick N6RK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK