The modification on the POX11 demod board has been successfully done.
I followed the procedure which had been posted in a past entry (#4554).
The home-made splitter was replaced by PSCQ-2-51W, which has a relatively wide band of 5 - 50 MHz.
The usual orthogonality adjustment will be done in the daytime.
The attached snapshot was taken when an sinusoidal RF signal with a slight frequency offset from LO was injected to the RF input.
It is clear that the I and Q output show healthy signals (i.e. almost the same amplitude and 90 deg phase difference.)
I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.