I think I can replicate some of the above here at home because I have an old and working HP8405A VVM here and my little Marconi 2024 sig gen should have similar close in phase noise (at CFs of around 10MHz) as the HP8663.
I can't easily check/verify phase noise below offsets of about 10Hz here on my old Tek RTSA but I'm only really doing casual measurements here anyway. I think if I can predict the resonant frequency within 50-100Hz on the VNA and measure the spreads across several crystals it will be good enough for this thread I think.
I earlier tried both 1 port and 2 port VNA tests on the 10MHz crystal and had agreement within a few Hz. The close in to far out phase noise response on the E5071 VNA is best described as 'strange' and when I first got mine a couple of years ago I thought it was faulty. But I checked several E5071s at work and they were the same. I don't think it has caused any issues for me yet and I'm not trying for ultimate accuracy in these tests.
I'd have to read up on how to measure a crystal with the HP8405A but my first thought would be that it would have to be a labour of love to do it across a span of maybe 50kHz to get the motional LCR of a typical crystal. I'm not sure I'd want to go there but maybe as a means to just verify where resonance occurs with a 30pF test cap it would be worth a try. But I feel I'm heading into nerdy territory here where the added value won't be worth the effort involved. I'm not sure it matters much how accurate these old 4.032MHz xtals are and they are only a small sample across countless other crystal types and specs. So the tests wouldn't prove anything conclusive (about crystal ageing) no matter what I do to vary the test methods
