AM Superheterodyne Radio Receiver

An analog superheterodyne receiver designed to tune, demodulate, and play commercial AM broadcasts.

AM superheterodyne radio receiver

Story

This project connected analog circuit design, signal processing, and communication systems in a complete AM radio receiver.

The signal path combined a frequency mixer, intermediate-frequency filter, envelope detector, and operational-amplifier stages. I designed, measured, and debugged these circuits before integrating them with the RF front-end.

The finished receiver converted a selected broadcast to a fixed intermediate frequency, filtered it, recovered the audio signal, and amplified it for playback through a speaker.

Design

Envelope Detection

An RC envelope detector with a germanium diode recovered the low-frequency message from the AM carrier. Its time constant balanced carrier-ripple suppression against the response speed needed to follow the audio signal.

Audio Amplification

Multiple 741 operational-amplifier stages buffered and amplified the recovered audio before driving the speaker. I measured gain and tested saturation behavior while debugging the signal path.

Intermediate Frequency Filter

An active band-pass filter centered near the receiver's 14 kHz intermediate frequency isolated the selected signal. Frequency sweeps and oscilloscope FFT measurements verified its bandwidth, cutoff frequencies, and out-of-band rejection.

Superheterodyne Receiver Integration

The final receiver combined an RF front-end, local oscillator, mixer, IF band-pass filter, envelope detector, and audio amplifier. The mixer translated the selected AM station to the fixed IF, where it could be filtered before demodulation and playback.

Incoming AM signal → frequency mixer → intermediate frequency → band-pass filter → envelope detector → audio amplifier → speaker

After integrating and debugging each stage, the receiver successfully tuned and played commercial AM broadcasts.

Results

  • Built and characterized RC envelope detector circuits
  • Designed multiple op-amp amplifier stages
  • Designed and analyzed an active IF band-pass filter
  • Measured frequency response using oscilloscope FFT tools
  • Integrated the analog subsystems into a complete receiver
  • Received and demodulated commercial AM radio stations

Skills Demonstrated

  • Analog Circuit Design
  • OP Amps
  • RC Networks
  • Envelope Detection
  • Band-Pass Filters
  • Fourier Analysis
  • Frequency Response
  • Oscilloscope Measurements
  • FFT Analysis
  • Signal Processing
  • Amplitude Modulation
  • Superheterodyne Receivers
  • Communication Systems
  • Hardware Debugging
  • Electronic Prototyping