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Post by kweijand on Jan 28, 2017 9:35:21 GMT -5
I do a custom cal procudure band4 100-500Mhz, smoothing off, avg=16. I use 1mtr airborne 5 with sma connectors. at the open part the SW asks if this is OK reading mag 21000 .. I say yes.. then cal till the end.
to check the procedure I run a 50 ohms load and halfway the run I remove the load. i should then see the zmag and Zre go trhough the roof, but it sticks to 50 ohms.
can figure out what is wrong, any suggestions ?
SW version VNA-UHF 628A
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Post by Bob on Jan 28, 2017 10:40:26 GMT -5
Check the VNAuhf by doing a Custom Cal over the same range without the cable. It should work ok and it should not ask you if the Open Circuit load is correct. After calibration connect another resistor around 75 ohms to 200 ohms to see if it reads correctly. If it works ok without the cable, then check the cable itself to verify the connectors are ok.
73/Bob - W5BIG
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Post by kweijand on Jan 29, 2017 15:59:19 GMT -5
mystery solved: I used an sma a calibration kit: 3 sma tops, open, short, and load, and the open was supposed to have a flat internal surface, but it became flush against the sma female PTFE and inner pin, thus shorting it. beware for this material!
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Post by Bob on Jan 29, 2017 21:29:13 GMT -5
I think you're referring to an Amphenol "open" load. These are not made correctly. There is an extra piece of metal inside that can short out. It's strange they went to the extra trouble to insert this metal when it just causes trouble. If you shake the load, you can sometimes hear the metal rattling around. The Amphenol 50 ohm load and the short load are good. We use those.
We recommend leaving the SMA female connector open for the open cal load. The cal kits that we ship with the AIMuhf and the VNAuhf don't use this Amphenol cap. They are an N-connector with a red label and the SMA is open.
We evaluated this very carefully. With some connectors, you don't want to leave them completely open. For example, the BNC cal kit makes a noticeable difference if you do not attach the open (red) load while calibrating. For that kit, it's important to attach the open load. The BNC connector makes a difference of 2 or 3 pf.
-73/Bob
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