trying to understand a 40m vertical, my Rigexpert analyzer has Z, X, R and C.......when I measure the vertical at 7.125 (target freq) the SWR is 1.3:1, but the Z is 50 ohms, I’m told the impedance needs to be 39+j) ohms? How can I read that with my rigexpert.....I can get around 39 ohms at 7.400.....is my vertical too long, or too short?