The DC offset is a result of the balun, MABACT0039, only providing a DC short
to the IN pin while the IP pin is connected to a 50 ohm load (as well as 90.9
We now recommend using a balun (see attached) that has an extra tertiary
winding that provides DC short such that both IP and IN remain at 0 V bias.
Note,a balun (or transformer) has a lower cut-off frequency hence should only
be used for ac applications where reconstructed signal falls within its 1 dB
I also attached some more information on the output stage of the AD9739 below.