Re: Coil forms, Q, and instruments
ALso, I'd like to see your STL
file for the spreaders.
David Martin - NA1MH - Mountain Home, Ar. -----------------------------------------
Wherever I go, there He is.
On 7/22/2021 2:25 PM, Jim, N5IB wrote:
With too much free time for my own good, I did an experiment with 3D printing some spiral grooved coil forms. I was curious if the PLA plastic material used to print would degrade the Q of the coil. 16 turns AWG24, about 1" diameter, about 1" long on a hollow, grooved PLA tube Short answer, no noticeable Q degradation when I inserted a rod of the PLA material into the center of the coil. The effective inductance of a coil wound on the form is a few percent lower than the "air wound" formulas predict. prediction: 5.6 uH, measured: 4.8 uH But that's to be expected because of the increased inter-winding capacitance due to the dielectric constant of the form's PLA material (about 3). We see the same effect with toroids when spreading/squeezing turns - changing the spacing changes the inter-winding capacitance. Made a series trap with the test coil and a 200 pF dipped mica cap, and measured the 3 dB frequencies. The interesting finding is that when I did the Q measurement with a $1000+ spectrum analyzer, I got Q=185. The on a whim, repeated the measurement with a $65 Nano VNA , and got Q=180 Darn ! 2.7% low ! I think there is a lesson hiding here LOL Jim, N5IB