This project demonstrates the design, simulation, and implementation of an AM radio receiver circuit using Bipolar Junction Transistors (BJTs). The objective was to receive, demodulate, and amplify AM signals to obtain a clear audio output.
- Amplitude Modulation (AM): Varying the amplitude of a carrier wave in accordance with the audio signal.
- Demodulation: Extracting the original audio signal from the modulated carrier.
- Tuning Circuit: Selecting the desired frequency using a resonant LC circuit.
- Amplification: Boosting the demodulated audio signal for output.
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Signal Source
- V3 (550 kHz carrier), V4 (1.5 kHz audio) for AM generation.
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Mixer Stage
- Combines carrier and audio using multiplier component (B1).
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Tuned LC Circuit
- L1 (1 µH) and C1 (400 nF) form a resonant filter tuned to 550 kHz.
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Demodulation
- D2 (1N5817) rectifies the AM signal to extract audio.
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Amplifier Stage
- Q1 (BC547B or 2N2222) boosts the demodulated audio signal.
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Filtering and Output
- Capacitors and resistors filter noise and prepare signal for output.
- Input Signals: Carrier and audio waveforms.
- Mixed Signal: Modulated AM waveform.
- Demodulated Output: Rectified audio waveform.
- Amplified Output: Strong, clean audio signal.
- Real-world circuit built and tested.
- Audio signals successfully received and demodulated.
- Peak Gain observed: ~60.7x at optimal tuning.
| Carrier Freq | Audio Freq | Input Vpp | Output Vpp | Gain |
|---|---|---|---|---|
| 550 kHz | 1.5 kHz | 100 mV | 6.07 V | 60.7 |
The project successfully demonstrates an AM receiver using BJTs. The circuit:
- Tuned accurately to AM frequencies.
- Demodulated signals using a diode detector.
- Amplified audio using a common-emitter BJT amplifier.
Further enhancements could include variable tuning, multi-band support, and speaker integration.