Re: 80 meter bpf toroid winding 30 turns givel 4.3 micro Henrys, not 3.8
Bob Benedict, KD8CGH
I second Kees advise on tuning by turn spacing.
I have also had to remove turns from LPF torroids. I put a small modeling study in the files section
that you can use to compare your sweep to.
One issue with a VNA is calibration. You should calibrate at the point of device test. I built a LPF test holder along with plug in calibration devices for open, short, 50 ohm load and through. Here is a post on it
and a nice commercial version here
Finally here are two posts I found helpful from Allison