[Amps] real component measurements at RF

[John Lyles]

W7IUV's recent posting makes sense as to the pitfalls of measuring L and C with the various commercial instruments. There is one other device that wasn't mentioned, but is a less expensive 
alternative and uses the Hp-optimized IV approach. But it isn't portable! The old Hp 4815A vector impedance meter has an active probe with the sampling device in it. This meter covers from 500 KHz to 110 MHz, over the HF range
and has specified accuracy from like 10 ohms to 100 Kilohms over same range. They can be found for a hundred dollars or so used, but make sure the probe is good. Also, the later 4193A digital version is superb, I use
that one at work a lot as the 4815A is prone to having intermittents from the air variable tuning capacitor in oil inside. They have been discontinued by Agilent, but these are the workhorses for amplifier component testing, once you figure 
out how to fixture the device to fit the tiny probe. That is done with copper strap and homebrewed holders and clips from N and BNC. The 4815A cannot be run through HPIB but the 4193A can. About 15 yrs ago,  I started writing a 
software calibration routine that would do OSL normalization at the probe tip, to allow the 4193A to read down to below an ohm at RF. This allows one to do a better job of knowing the Q of a series resonance and of bypass capacitors 
effects at RF. I had found a similar program in an Hp app note for the 4191A impedance analyzer. I never finished my routine due to time, but continue using the 4193A everytime i need to know what a component value is at an RF freq. ]
I have measured things like B&W chokes, Ohmite Z144s, disc caps, doorknob caps, chip components, Miniductors, tank circuit components, vacuum caps with it. I also use an ESI meter that works at KHz, and a Boonton, 
both disagree on inductors somewhat, as Larry points out the causes. 

John
K5PRO

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Message: 2
Date: Wed, 31 Mar 2010 10:31:35 -0700
From: Larry <larry at w7iuv.com>
Subject: [Amps] LCR meter & measuring components

Very complex (spelled H E A R T - A T T A C K) instruments like the
HP/Agilent network analyzers that are marketed as component test sets,
(sorry don't remember the model numbers offhand) use a system known as
RF-IV for the detectors. They actually measure the RF voltage and the RF
current at the test ports and use that to calculate the complex
impedance. Since this system is capable of accurate phase and amplitude
measurements over a VERY wide range of frequencies, these instruments
are the best there is for evaluating components, especially high Q
inductors, over a wide frequency range. The N2PK VNA has a RF-IV option.
I have the RF-IV bridge but have not yet put it together so have no
first hand knowledge, but it is reported to show accuracies similar to
the Agilent instrument (within the N2PK's normal frequency range).