AM Radio Receiver Stages & Signal Processing Fundamentals

AM Radio Receiver Stages & Components

RF Amplifier Stage

The RF amplifier stage performs a small RF signal amplification and selects the radio carrier signals captured by the antenna via a tuning circuit, thereby increasing the tuner's selectivity.

Frequency Conversion Stage

This circuit is used in superheterodyne receivers, designed to eliminate instability caused by the high-frequency carrier signal. This stage consists of two main parts:

• Mixer: This block is responsible for mixing the tuned signal from the antenna.
• Local Oscillator: This block generates the local oscillation frequency, which varies in unison with the tuning knob on the RF stage.

Intermediate Frequency (IF) Amplifier

This amplifies the IF signal obtained from the converter circuit to the required level.

AM Detector

This block detects the information contained within the RF carrier signal.

Audio Amplifier

This block collects the detected audio information and amplifies it to an appropriate level.

Power Supply

The power supply comprises a step-down transformer and an AC rectifier circuit.

Understanding Modulation & Digital Signal Processing

What is Modulation?

Modulation is the process of modifying a physical quantity of a wave (the carrier) with information contained in a lower-frequency signal (the modulating signal) to enable information transmission.

Frequency Modulation (FM) Explained

Frequency Modulation (FM) is defined by the variation in the carrier signal's frequency in proportion to the modulating signal's amplitude, causing a frequency deviation.

Advantages of FM Broadcast Transmission

Key advantages include immunity to interference from other stations, high-quality reception, and immunity to background noise.

Phase-Locked Loop (PLL)

A Phase-Locked Loop (PLL)'s function is to synchronize the phase of an input signal with an internal reference signal.

Pulse Code Modulation (PCM) Signal

The Pulse Code Modulation (PCM) process converts the waveform of an analog signal into a series of binary pulses.

Quantization

Quantization is the process by which all samples obtained from an analog signal that fall within the same interval are assigned a single discrete value.

Analog-to-Digital (A/D) Converter

An Analog-to-Digital (A/D) Converter's mission is to measure the Pulse Amplitude Modulation (PAM) signal and convert it into a numeric pattern, known as a Pulse Code Modulation (PCM) signal.

Sampling

Sampling is the process of obtaining a series of samples or data points from an analog signal at determined moments in time.

Coding

Coding is the process by which a digital code is assigned to each of the quantized levels by a delivery device.

Pulse Amplitude Modulation (PAM)

Pulse Amplitude Modulation (PAM) is a double-sideband signal that requires twice the bandwidth of a baseband transmission. This modulation method involves sampling an analog signal and generating a series of pulses whose amplitudes are proportional to the instantaneous amplitude of the analog signal.