Monday, April 20, 2020
LC tank review with nVNA
It was many moons ago that I learned (while studying for my General ticket, probably) that LC tank circuits offer a high impedance at their resonant frequency when in parallel. Or maybe that was for series tank circuits...?
With the soldering iron already out, I made up a couple of SMA-to-Misc adapters - at least that's what I'm calling them - that will allow me to easily connect a variety of components to the nVNA.
Then I used a toroid and an 82pF cap from the filter kit to make a parallel tank circuit. The 9 turns on
With nanoVNASaver set to sweep a wide range around that frequency, I hooked everything up and performed an S21 scan. The result: highest impedance at 31.7 MHz.
A change in capacitance of only 1pF will move resonance more than this amount, as would a change in L from the theoretical or the tiny L and C values of the pigtails used to connect everything.
I didn't really learn anything but it was a fun exercise to see a real-time graphical result of what the values specify. Theory meets reality before my very eyes - always fulfilling.
And now back to my KPA-500 amplifier powered-by-a-Sterling-engine project.....