Tuned LC oscillator is an oscillator which consists of a capacitor and a coil connected in parallel. To understand how the tuned LC oscillator basically works, let's start off with the basics. Suppose a capacitor is charged by a battery. Once the capacitor is charged, one plate of the capacitor has more electrons than the other plate, thus it is charged. Now, when it is discharged through a wire, the electrons return to the positive plate, thus making the capacitor's plates neutral, or discharged. However, this action works differently when you discharge a capacitor through a coil. When current is applied through a coil, a magnetic field is generated around the coil. This magnetic field generates a voltage across the coil that opposes the direction of electron flow. Because of this, the capacitor does not discharge right away. The smaller the coil, the faster the capacitor discharges. Now the interesting part happens. Once the capacitor is fully discharged through the coil, the magnetic field starts to collapse around the coil. The voltage induced from the collapsing magnetic field recharges the capacitor oppositely. Then the capacitor begins to discharge through the coil again, generating a magnetic field. This process continues until the capacitor is completely discharged due to resistance.

Technically this basic tuned LC circuit generates a sine wave that loses voltage in every cycle. To overcome this loses of voltage in our tuned LC oscillator, an additional voltage is applied to keep the tuned LC oscillator from losing voltage. However, to keep the tuned LC oscillator going well, a switching method is used. A vacuum tube (or a solid-state equivalent such as a FET) is used to keep this tuned LC circuit oscillating. The advantage of using a vacuum tube is that they can oscillate at specified frequencies such as a thousand cycles per second. There are several different types of tuned LC oscillators. A little off subject; one well known and entertaining oscillator is known as the tesla coil, which uses a unique tuned LC circuit using the spark gap to oscillate.

That's it for the basic knowledge about tuned LC oscillator. The last topic is about the mode of oscillation.