2021-04-30 Circuit Won’t Oscillate At UHFs

From FB post Apr 29

Joshua E. Hrouda
I trained on Radar repair in the Army, and since then I’ve known that circuits with ‘lumped constants’ have problems with parasitic capacitance and inductance above a few hundred MHz. But I experimented with this circuit anyway.

I think Colin should say, instead of ‘tight’, that the circuit is less than optimal at UHFs due to stray inductances and capacitances. It would be better to use a quarter wavelength of coax cable for a tuned circuit.

I checked and found that a 21 nH inductor resonates with a 5 pF capacitor at nearly 500 MHz. Yet in this circuit it’s nowhere near that high. The circuit is simply being pushed beyond its practical limits and can barely perform at these frequencies. But now I can say that I’ve tried and had poor success. 👍🙄

This says it.

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