Technological University of Panama
Laboratory
Analysis of Analog Filters
Sergio Reyes 8-960-939
Matthew Irish 8-960-939
Bryant Ojeda 20-70-7398
Group 1EE131
Instructor: Cristal Cáceres
2024
Introduction
Frequency modulated radio (FM) has revolutionized the way audio signals are transmitted and
received, offering significantly better sound quality compared to other methods such as amplitude
modulation (AM). FM receivers play a crucial role in this process, as they are responsible for
capturing, tuning, amplifying, and demodulating the carrier signals transmitted from radio stations to
convert them into audible sound.
The design and operation of an FM receiver are based on key principles of electronics and
telecommunications, such as resonance, amplification, and signal filtering. These devices include
specialized circuits that allow filtering of specific radio frequency signals within the FM spectrum
(usually between 88 MHz and 108 MHz), eliminating interference, and extracting the
frequency-modulated information that contains the audio content.
The purpose of simulating a homemade FM receiver is to understand these basic concepts and
apply principles of electronics and physics to capture radio signals and convert them into usable
audio.
Operation
The FM radio receiver operates through three fundamental stages:
1. Tuning:
Tuning is achieved by adjusting a resonant circuit composed of a coil and a variable capacitor. This
circuit allows the receiver to select a specific frequency within the FM range. When the circuit's
frequency matches that of a radio signal, it is amplified, making it easier to detect.
The coil and capacitor work together to filter out unwanted signals. The variable capacitor serves to
find the correct frequency.
2. Detection:
At this stage, the audio signal is separated from the carrier signal using a transistor or diode, which
demodulates the frequency-modulated signal. The goal is to translate variations in the carrier
frequency into voltage variations that represent the original audio. This process requires precise
design to avoid distortions.
3. Amplification:
The audio signal obtained after detection is weak and cannot be directly heard. Therefore, an
operational amplifier, such as the LM386, is used to boost its power. This component increases the
amplitude of the signal without altering its content, resulting in a clear audio signal that can be
played through a speaker or headphones.