5% is 1.45uH so 0.6uH is well within tolerance. I've been analysing a 20m LPF with my NanoVNA and I found I had to remove a total of 4 turns off the 3 toroids to get a decent return loss and minimise the insertion loss. How tight the turns are and how spaced they are makes quite a difference.
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73
Richard
G4TGJ
