On 11/28/20 11:47 AM, Edward Mccann wrote:
If I use the VNA with direct input of ladder line, say nominal 450 ohm Zo, but
with measured parameters more near 400 ohms, should I not run OSL calibration
with a 400 ohm load prior to running the sweep?
The response below seems to imply that calibration with a 50 ohm load will yield “good
results for coax and two-wire line of any impedance?”
Yes, if you use AC6LA's spreadsheet. It takes care of the impedance.
Or does the creation of a reference plane with 50 ohms in the OSL calibration
yield results for a wide varieties of feed line?
Yes, you can test anything with a 50 ohm reference cal, you just have to
adjust for the non 50 ohm system you're testing.
(one can spend a lot of time arguing about whether you'd be better off
doing a cal with an impedance closer to your system impedance, but
ultimately, it's the same measurement, just different math)
Basic question.
Best from the West
AG6CX
Sent from my iPhone
On Nov 28, 2020, at 11:27 AM, jimlux <jimlux@earthlink.net> wrote:
On 11/28/20 11:08 AM, Jim Brown wrote:
On 11/28/2020 3:43 AM, Kirk Kleinschmidt via TowerTalk wrote:
I'm trying to characterize some coaxial cables and various connectors, and the
results from my two measuring methods aren't reconciling well. My understanding
of the tools is also less than complete.
First, make sure that your VNA is well calibrated. For cailbration, you will
need standard Open, Short, and 50 ohm parts.
Then, use it to make S11 measurements over the frequency range of interest. I'd
go with 1-50 MHz. Then download a copy of AC6LA's ZPlots Excel spreadsheet,
export your data to it, and follow his instructions for characterizing the
cable.
This will give good results for coax and two wire line of any impedance.
73, Jim K9YC
A bit of background: AC6LA's spreadsheet does the renormalization for the
different impedance, if your VNA doesn't have that feature.
(you're not using the NanoVNA, but for those who are, the NanoVNA-Saver python program
also has the "change characteristic impedance" feature)
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