Yes, you need to place the choke in its position ON THE INTENDED AMPLIFIER chassis. In this manner the exact distributive affects of shunt C are properly noted.
And with all do respects to the VNA, I would much rather do this measurement with a GDO.
Or... convert your vna into the equivalent of a GDO by exciting the ch 0 port into a small link coil which would utilize the measurement system as a coupled transformer. Not unlike the GDO, coupling must be kept to a minimum so that reduction in Q affect of the choke under test is minimized.
Note, you will need to measure both the anti resonate as well series resonate points as you described. In the series mode, the choke is shorted. Again, a direct connect of this arrangement to ch 0 would seem problematic. Consider the vna system is placing 50 ohms in series with the choke under test!
I would encourage you to correlate the measurements with the vna and with the GDO technique before applying 4000 volts to that nice tube!
I would also consider if you have one... the classic chokes like the old National Radio R175 which had strong series resonate problems in the 15 meter band. They would burst into flames! See if the vna points out the alarm. You should be able to pick up both the series resonate and parallel resonate signature on the vna-Smith plot. I know the GDO does pick up these signatures and I have modified those chokes based on the GDO results to fix their problems.
Alan
