In class C operation, collector current flows for less than one half cycle of the input signal.
The class C operation is achieved by reverse biasing the emitter-base junction,
which sets the dc operating point below cutoff and allows only the portion of the input signal that
overcomes the reverse bias to cause collector current flow. if an input signal amplitude is increased to the point that the transistor goes into saturation and cutoff, it is then called an OVERDRIVEN amplifier.
During the positive period of the input signal (On stage)During the positiv period of the input signal the transistor will conduct (On-state). You can imagin that the transistor is a switch which connects the emitter with the collector.
What will happend now is that the current I1 (red) flow through the coil and then into the transistor and down to ground. A magnetic field builds up in the coil depending on the magnitude of the current. At the same time the voltage over the capacitor discharge through the resistor making another current flow I2 (blue) also through the transistor. The I2 current passes the resistor (antenna) which radiate the energy.
During the negative period of the input signal (Off stage)
During the negativ period of the input signal the transistor will not conduct (Off-state). You can imagin that the transistor is an open switch. No current can pass through the collector to the emitter.
The magnetic filed which was build upp in the coil will now collaps and generate a current I1 (red) which will flow through the capacitor and into the resistor (antenna).
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