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I was describing the mathematics of RLC circuits to my students, and was wondering if it's possible to build an actual RLC circuit with coils of wire and an inductor and a variable capacitor. The closest thing I could find is this ferrite core circuit. But instructions are sparse, and it's not clear if I can use an amplifier and listen to it on my headphones.

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  • $\begingroup$ What are the requirements? $\endgroup$ – Mahendra Gunawardena Sep 9 '20 at 11:00
  • $\begingroup$ That I tune a basic RLC circuit to a radio frequency that I can listen to, or transmit an audio signal to a nearby radio receiver (which can be a conventional radio). $\endgroup$ – user128063 Sep 10 '20 at 12:33
  • $\begingroup$ Do you have access to DIY oscilloscope, function generator, or a spectrum analyzer, such as USB digilent analog discovery 2 spectrum analyzer $\endgroup$ – Mahendra Gunawardena Oct 9 '20 at 11:47
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I would see what variable resistors were available and using those ranges do a spreadsheet to calculate results of cycling through the resistor range with known values for L and C.

Then you can decide input voltage etc - will they be able to touch it? Safety?? 12V or 120V or 1200V?

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  • $\begingroup$ I can pick any voltage that's conveniently available in an electrical engineering lab power supply. $\endgroup$ – user128063 Sep 10 '20 at 12:31
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Sure! An LC tank connected to an antenna and coupled to a diode detector and an AC microvoltmeter - ideally one with a needle - will be fantastic. For the UHF frequencies (around 100MHz) you can build it with household materials with relative ease, although you will want to characterize your build process ie. use an LC meter to see how close are your homemade capacitors and inductors to theoretical values derived from their geometry and material properties.

Ordinary aluminum foil and polyethylene food covering wrap is good enough to make fairly decent capacitors in the ranges needed (1-100nF). Any sort of wire will work for the inductors although you may need ferrite slugs/cores to make it less painful to put together. In all cases you should start from first principles, look up material properties, and figure out dimensions/numbers of turns before you start making anything.

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