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Re: Limits of the Port Extension on the Cal screen for calibrating at end of cable

 

On Sat, 28 May 2022 at 00:50, Karin Johnson <karinann@...> wrote:
I realized a couple of hours after sending the initial post, that I was incorrect with associating Calibration with the Port Extensions.
Here is, I hope a better explanation of what I am trying to do.
First off the measurement frequency is 14 MHz.? So not too beyond the capability of the 8753C.
?
A wavelength of roughly 20 m.

I want to place the measurement plane at the end of a 100 foot length of RG213.?
?
Em, wish you would work in metric! Let's call that 30 m. So your cable is 1.5 wavelengths long, which is far from unusual for a VNA.? My 20 GHz VNA has cables that are 600 mm long, so 40 wavelengths. It calibrates okay, with cables 40 wavelengths long.

So I place the SOL standards, one at a time at the
end of the cable.? Supposedly the 8753C measurement plane is now at the end of the cable.
?
More precisely, at the reference plane of the connector on the end of your cable. Depending on the connector, the reference plane may or may not be near the end of the connector. The reference plane of the connector is the outer conductor mating plane. In the case of a female N, it is well inside the connector - roughly 8 mm, as I measured with a bit of wire and ruler next to me. ????

Now I can take S11 measurements relative to the measurement plane at the end of the cable.? My question should have been
" Is there a limit in terms of how long a cable can be before this calibration technique fails."
This is probably related to the storage of the cal correction factors in the memory of the 8753C.? Is it via floating point numbers, or integer numbers?
How large or small can the calibration correction values be???
?
The calibration factors to be entered into the VNA include the offset delays (lengths) of the calibration standards. They are only of the order of mm. The fact your cable is 100 m long does not change those numbers.


I seem to be able to obtain valid data using this technique, but wanted to ask on the Keysight forum with some of the folks who actually designed
the instrument.? I think Dr. Joel it still active there.? ?

I would certainly slow the sweep speed down, and see if that changes your results. If it does, then you have a problem.
?

My rant about not being able to login to the Keysight forums still exists.? It seems their login/validation screen seems broken.
At one time I had an account over there but they have seemed to have changed the supporting vendor for the forum sites.

I wish Keysight would just use some open-source forum software, instead of all this proprietary crap, which they keep needing to change.?

As always,
Regards,
Karin Johnson
?
Dave

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