If you have a 6dB attenuator just ad it directly on to the RF IN port, then perform CAL.
Now should the KC901 read 0dB IL with 6dB attenuator 2 cables attached.
After this perform your measurements of the balun again and you will get more correct measurements.
But the balun is 4:1 = 200:50 so you would have at mismatch when doing S21.
To test preformance of the balun you should use following setup.
Mode = S11
Format = VSWR
Center frequency = 20MHz
Span = FullSpan
SweepPoint = 3150
Now connect the input/coaxial side of the balun to SOURCE port of the KC901.
Connect a 200Ohm non inductive resistor to the output/antenna side of the balun.
Now should you be able to see how close/good the balun is transforming 200Ohm to 50Ohm/1:1
I would normally expect a result ranging from 1:1 to 1:1.6
I have done som testing
The fault is not on the TF card but on the KC901S.
If you start by saving a measurement then the KC901S recognize the TF card and you can afterwords save the calibration.
If you only try to save a calibration after bootup the file is corrupted.
Please opdate firmaware!
Next issue is the insufficient returnloss of the RF IN port wich make the KC901S useless for S21 measurements!
The VSWR of the RF IN port is abouts 2:1 and therefore do I get funny readings due to mismatch ! 2017-03-29