On 7/30/19 4:32 PM, Edward Mccann wrote:
How about advice on measuring impedance offered to common mode current in coax
with a one-port and two port VNA?
Ed McCann
AG6CX
something like coax, with a choke. So you're measuring the impedance of
the outside of the coax? I would think that would be applicable to the
stuff in the article.. It was basically describing how to measure Z of
any two terminal device.
As always, fixtures are the tricky part.
If you wanted to measure a 3,4, or more terminal device, then it
probably is more complex. Devices like RF transformers especially with
a center tap on a winding often get measured on a 4 port VNA.
It is theoretically possible to make a N port measurement with a 2 port
analyzer, but it could take a while because you need to make N(N-1)/2
measurements.
A relay box with some high quality relays and some calibration would
make the process easier.
(for N ports, you'd need 2 1:N switches (to connect the 2 VNA ports to
the pairs of ports), and N SPDT switches (to connect loads to the
unmeasured ports)
One might hope that the calibration on your relay box is stable, because
doing all the SOLT calibrations would take forever.
There might be better ways to do Massive N port measurements (maybe some
form of 6 port analyzer on steroids - everything is done with precision
power measurements, no phase measurement needed)
Sent from my iPhone
On Jul 30, 2019, at 3:56 PM, jimlux <jimlux@earthlink.net> wrote:
We've discussed the measuring of things like antenna traps, and we've had
varying levels of success.
https://www.mwrf.com/test-measurement/make-accurate-impedance-measurements-using-vna
Discusses three different configurations (one port, and a couple two port
measurements), gives the math, and looks at the uncertainties.. each works best
in a particular range of impedances.
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