[TowerTalk] S21 to Rp & Cp - Equivalent Circuit

Jim Brown jim at audiosystemsgroup.com
Fri Jan 12 16:37:48 EST 2018

On 1/12/2018 12:36 PM, Máximo EA1DDO_HK1H wrote:
> I like to sit on the soil, or on the roof, and test the antenna. In 
> that situations a self-capable VNA is needed and Anritsu is very 
> reliable (high dynamic range and robust to in the band interference).

I understand that desire. Many of us own more than one analyzer for 
exactly that reason. My mechanical toolbox includes various sizes of 
screwdrivers, wrenches, cutting tools, a measuring tape, a micrometer, a 
small magnifier, soldering irons with two sizes of tips, and so on. My 
test equipment includes a dual trace scope, two instrumentation-grade RF 
spectrum analyzers, three instrumentation-grade audio analyzers, a 
mechanical movement VOM, two DVMs, four HP signal generators, a P3 
spectrum display, three low cost SDRs that I can also use as spectrum 
analyzers, an MFJ-259B, and a couple of ancient AEA analyzers, one for 
HF, the other for VHF/UHF. Most of this gear was purchased used. It 
would be NICE to be able to use the same analyzer you can drag up to the 
roof for bench measurement of components. Not every problem can be 
solved with a hammer.:)

My initial measurement of ferrite chokes used an HP generator and an HP 
spectrum analyzer, with point-by-point measurements transferred to a 
Quattro Pro spreadsheet. They were the tools I had available. That 
worked, but it took an hour or so to measure one part an manually enter 
the data in QPW. With the VNWA, I can make a 30-60 second sweep and 
immediately see plots of Z mag, Rs, and Xs vs either log or linear 
frequency. Another minute or two is needed to save the S21 data in 
Touchstone format and save a screen grab.

BTW -- several VNWA users are running their unit on a Windows-based 
tablet. The VNWA is powered from the same USB port used for control and 
exchange of data.

73, Jim K9YC

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