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Is my VNA broke?

Question asked by mpcengineer on Sep 13, 2011
Latest reply on Sep 14, 2011 by mpcengineer
Hi,

This is my first time making any real VNA measurements and I would greatly appreciate if anyone can just confirm my results make sense.

I calibrated my Agilent 8753 using a manual 85032B N-type cal kit. Then I used apanel mount N-type connector to act as a test fixture. Makinig an open, short and load (using two 100R 0603 resistors)

From application note AN1278-9 about test fixtures I tuned the short circuit port extension to 70.67pS, which was the point the phase response of the short was 180deg. I then measured the open as 0.2pF. The VNA gave the extension as 22mm which seemed very strange as the panel connector must have only added 3mm. But no sure what was what I carried on.

I did some measurements of some wirewould surface mount coils at 5nH with measured Q coming out at about 54 at 450MHz. Looked good except the data sheet gave Q as 100 but I wonder if I was expecting too much from my setup.

Anyhow to confirm things I remeasured the cal kit. The open and load looked good but the 85032B short showed up as 1nH inductor. This really confiused me so my question is:

1) Should the cal kit 85032B short be reading 1nH?
2) does a 70.67pS port extension seem reasable?
3) Why can I not calibrate using my standards?
4) Is there any more app notes on making real fixture calibration measurements?


PS. I also tried calibration the VNA using my panel mount calibration loads with 0.2pF open and 0mm offset, but the results obtained were no where near usable. (any ideas why?).

Photo of my cal parts attached.

Thanks.

MPCImage

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