On 7/13/2012 6:46 PM, Richard (Rick) Karlquist wrote: > 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.
That's exactly what's needed, and is the RF I-V method that both Wes and I cited. And yes, the capacitance of the test fixture can be a major source of error -- the equivalent circuit of a typical choke is parallel RLC, where R is typically on the order of 5K and C is on the order of 2-4 pF.. 73, Jim _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK