Two Transistors AM Radio Receiver

Using only two active components, we can build an AM radio receiver working on MW (Medium Wave) Band. The circuit uses straight receiver configuration, where an LC resonator circuit is used to filter the received RF signals and then directly rectified and further filtered to obtain the carrier’s envelope signal, which is the modulating information signal we want to hear. […]

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Tuned Transistor RF Amplifier

On the circuit below, the load resistor has been replace by a tuned circuit, C4 and L1. The tuned circuit is high impedance at resonance. The impedance is low at all other frequencies. Therefore, the signal which is amplified only at the resonance frequency. Since this type of amplifier is normally used in RF application, the capacitors can be much […]

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Varactor – The Core of Voltage Controlled LC Tuner

In hybrid system, analog system with digital control, a voltage controlled things is very important since it can be interfaced by DAC from digital system. For radio tuning with digital control, a voltage controlled LC circuit is needed. If we can turn a knob of variable capacitor mechanically, microcontroller system prefer outputting a voltage rather than controlling a variable capacitor […]

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