The measurement only tells you that the plugs are correctly fitted. The important measurement is the choking impedance - if this is not maximum at 70MHz, this choke can do more harm than good. 'Ugly baluns' like this can worsen feedline radiation if they are not resonant in band. It also occurred to me that using a Vf factor of 0.66 is actually wrong. That is the velocity factor of the coax in differential mode, you are trying to create common mode impedance, so Vf is only the outer skin of the coax braid - so a Vf factor of 0.95 is probably nearer the mark. Vf is pretty irrelevant since the choke works by achieving resonance in the middle of the 4m band. The inductance of the loop, combined with stray capacitance creates the resonance. So the number of turns and the diameter of the coil, and the length is related to that, not a notional half wave. When you measured the SWR, you showed the SWR increasing towards 150MHz, still minimal, but rising. What contribution to the SWR is the dummy load making? One of my dummy loads used to get to 1.5:1 at around 50MHz!
Is it not as good to make a "loose" coil by wrapping turns around each other, as it were, rather than obsessively keeping them parallel? And is there a test using a nanoVNA that would be useful here?
The measurement only tells you that the plugs are correctly fitted. The important measurement is the choking impedance - if this is not maximum at 70MHz, this choke can do more harm than good. 'Ugly baluns' like this can worsen feedline radiation if they are not resonant in band.
It also occurred to me that using a Vf factor of 0.66 is actually wrong. That is the velocity factor of the coax in differential mode, you are trying to create common mode impedance, so Vf is only the outer skin of the coax braid - so a Vf factor of 0.95 is probably nearer the mark. Vf is pretty irrelevant since the choke works by achieving resonance in the middle of the 4m band. The inductance of the loop, combined with stray capacitance creates the resonance. So the number of turns and the diameter of the coil, and the length is related to that, not a notional half wave.
When you measured the SWR, you showed the SWR increasing towards 150MHz, still minimal, but rising. What contribution to the SWR is the dummy load making? One of my dummy loads used to get to 1.5:1 at around 50MHz!
Is it not as good to make a "loose" coil by wrapping turns around each other, as it were, rather than obsessively keeping them parallel? And is there a test using a nanoVNA that would be useful here?