AM/FM Radio Stage Analysis: Antenna, IF, Audio, and Demodulation

Posted on Jan 25, 2025 in Electronics

AM Receiver RF Stage Conclusions

An AM antenna, typically a fine enameled copper wire with a ferrite core, receives signals. These signals are then classified through a resonance system. A tank circuit, consisting of a variable capacitor and coil, disperses the signals in various processes.

The AM antenna can be considered a transformer with a primary and secondary winding.

A tank circuit, formed by a coil and a capacitor, resonates and acts as a signal classifier.

IF Stage and Demodulator Conclusions

The Intermediate Frequency (IF) signal is obtained by mixing the carrier signal with the local oscillator signal.

The IF stage is crucial for the receiver’s selectivity. It includes amplifiers and filters to purify the signal.

The IF stage prepares the signal from the mixer for demodulation and amplification.

Filters and amplifiers in the IF stage process the signal from the mixer.

The Automatic Gain Control (AGC) system provides feedback for accurate wave demodulation, delivering audio information.

The detector demodulates the signal, rectifying it, removing the carrier, and providing audio information.

The signal transmitted by the carrier is picked up by the antenna and transformed without altering the message.

The mixer combines the RF carrier and local oscillator signals, using the difference to obtain a purer signal.

AM Audio Stage Conclusions

  1. The audio stage amplifies the audio signal, correcting any weakness or differences.
  2. The audio signal from the detector is sent through a coupling capacitor, which moderates the signal.
  3. Information about integrated circuits can be found online, including schematics and technical characteristics.
  4. The audio stage often uses operational amplifiers.
  5. Working with radios helps memorize steps, making it easier to work with unknown radios.

FM Stage Conclusions

  1. The local oscillator frequency is always 10.7 MHz higher than the carrier in FM.
  2. FM antennas are typically telescopic.
  3. An FM resonant circuit, consisting of a capacitor (C1) and inductor (L2), acts as a signal classifier.
  4. The signal transmitted by the carrier is picked up by the antenna and transformed without altering the message.
  5. Information about integrated circuits can be found online, including schematics and technical characteristics.