I managed to get some 0.4mm diameter wire and the datasheet suggests that the enamel adds about 0.06mm to the diameter.
To get close to a 31mm former I had to wrap some masking tape around an existing former that was otherwise a bit too small.?
?
The former now measures about 30.6mm diameter.
?
When I wound 49 turns on it the coil length was 22.4mm. If I punch these numbers into my software program I get 64uH and a Q of 127 at 1.45 MHz.
?
When I measured the coil with a VNA it showed 63.1uH which is quite close. It's difficult to maintain perfectly close windings at all parts of the winding but I did try and get it very close.
?
To show how easy it is to use a VNA to find the resonant frequency when used with a resonating capacitance, I put about 185pF in parallel with it to get it resonant close to about 1.45 MHz. I then stuck a video showing this on youtube.
?
?
?
Click on the link to the Youtube video above to see how easy it is to find the resonant frequency and how the null is stable at the same resonant frequency no matter how close the test loop gets to the resonator. I used a 6cm diameter loop at the end of the VNA cable and selected an s11 measurement at 0.5dB/div. There is no need to calibrate anything on the VNA when using this method.
?
This is MUCH better than fishing about in the dark with an ancient GDO. If the cap was a variable cap you could see it tune the resonant frequency in real time. Hopefully this ends the argument against using a VNA for this test.
?
?
