Every signal is a sum of a series of sinusoids with different frequencies and phases. The square wave is a sum of an infinite number of sine waves, each with a frequency that’s an odd multiple of the fundamental frequency. In this circuit we have an ideal 1kHz square wave that feeds an LC resonant mesh. We have three capacitors that can be selected that make the mesh resonate at 3, 5 and 7kHz. Play around with the capacitors and change the square wave frequency a bit and see what happens 😎
