I have two 1:4 voltage baluns. If I connect them together so that I have 1:4-4:1, is that the equivalent of putting a 1:1 common mode choke on my feed line?
Say you take just one of the 1:4 baluns, and connect it like so:
Since the winding ratios are not equal, then equal and opposite currents will not cancel each other's magnetic flux, so there will be a net non-zero flux in the core. Thus, it presents an inductance to common-mode currents.
Now if you add another in series:
there's still non-zero flux in the core. It simply doubles the common-mode impedance.