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
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