to check the phase set up the following network:
Node
1 2 C 100pF
2 0 R 1000
1 3 R 1000
3 0 C 100pF
Node 1 is connected to the signal synthesizer and Node 0 Node 2 is connected to A Channel input and Node 0 Node 3 is connected to B Channel input and Node 0
the above network will shift phase between A and B by 90 degrees -- use silver mica caps and non-inductive resistors -- should work to some 10's of MHz. This is the network described in the HP3575a phase-gain meter.