This video shows a simple circuit that was shared by N4TMI in 73 magazine (no defunct, and archives freely available online). It shows a simple 2-transistor oscillator that can be used to test the resonant frequency of an unknown coil / inductor when paired with a known capacitor, as well as the resonant frequency of parallel tuned circuits like IF transformers. This is especially handy for folks that work on old radios and need to identify IF transformers, or want to figure out what value of capacitance to use to resonate with an inductor at a chosen frequency. I show a very handy “slide calculator” that can be used to quickly calculate LC resonant circuit values and frequencies. I made a small modification to the values in the circuit because I used a different N-channel JFET than was used in the article. Here is a link to the original article in 73 magazine from September 1990:
http://archive.org/stream/73-magazine-1990-09/09_September_1990#page/n49/mode/1up
And, here is a link to where you can find the handy L/C/F slide calculator:
http://www.arrl.org/shop/L-C-F-and-Single-Layer-Coil-Winding-Calculator/
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