[SI-LIST] Measuring characteristic impedance of transformer

Hi,
 
We are measuring the characteristic impedance of transformer.(TDR)
Path is
 
SMA- 50 ohms trace- 1:1 transformer- 1:4 transformer- 200ohms (resistor 
soldered across)
 
We find as soon as the co-ax is connected to the SMA, immediately a standing 
wave exisists on the co-ax i.e insteAd of measuring 50ohms measures the 174 
ohms)
 
And the complete wave(volt ) even at the transformer, pcb traces shits upwards.
Can anyone explain this phenomena.
We also tried measuring a 68 ohms inductor alone+pcb trace.
the co-ax measures 50ohms , no standing wave on the co-ax.
 
Would like some input from anyone who tried this.
 
Thanks,
Padma
 
 

      
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