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8753D "noise" and difference between port1 and port2

Question asked by PJU on Jan 25, 2012
Latest reply on Jan 25, 2012 by Dr_joel
I am experiencing difference between port 1 and 2 when measuring the same DUT and my measurements seems very "noisy".

1. I calibrate full 2 port, 5MHz to 3GHz, 201 points, I tried using 2 different cal-kits with the exact same result.
2. Connect Port1 to DUT input and port2 to output and measure S11 and S21, S11 is overlayed with some kind of noise,
3. Measure my DUT input return loss and gain, analyzer S11 and S21 and save traces to memory.
4. Swap port1 and port2 cables on DUT and measure input Return loss and gain now S22 and S12.

When the measured results are compared to the traces stored in memory, the traces in mem show different results but all show some "noise" and it behaves like noise, it is not "static".

I have attached a document with the traces from point 2 and 4 + a measurement of a not very good through, all show "noise" or unexpected behavior which must be from the analyzer itself.

Also I tried to calibrate to 1601 ppoints but the result is the same.

The analyzer has not been calibrated for some years but I expect there is some fault rather than the missing calibration, anyone seen this before ?  

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