What gives with this square wave?

[bear]

Which is the HF and which is the LF?

Both look quite normal for a transformer..

_-_-bear

 

[martyh]

This is the LF @ 100 Hz. Top trace is generator bottom is transformer

 

[bear]

Yep ur transformer is not too happy at LF... insufficient inductance perhaps, or else some other artifact of your test setup.

_-_-bear

 

[HollowState]

Your transformer would have to be flat down to 10 Hz to pass that frequency without tilting. Also, your scope input must be DC coupled...not AC.