Radio Broadcasting: Production, Transmission & Technology

Posted on Nov 26, 2024 in Electronics

Radio Broadcasting: A Comprehensive Overview

Production Units

Locutorios

Recording interviews, news discussions, and musical performances take place in the locutorio. Key features include:

  • Microphones: Common response microphones adapted to the human voice, connected to a junction box at the announcer’s table.
  • Monitoring: Speakers allow commentators and guests to listen to the generated signal. “On the air” and “open” signals indicate speaker activation.
  • Acoustic Conditioning: Walls and ceilings are treated to prevent external noise and control reverberations and echoes.

Production Control

This is where sound mixing and program creation happen. Elements include:

  • Sound Mixer: Combines sound signals from various sources into a final program signal.
  • Noise Sources: CDs, cassettes, microphones.
  • Recording Lines: Outputs from the mixing table.
  • IT Systems: Headboards, effects processors, and audio consoles.
  • External Signals: Incoming calls and other external audio.
  • Speakers: Provide audio monitoring for the sound technician.

Central Control

Manages signal routing within the station and from external sources. Components include:

  • Patch Panel: Interconnection equipment with configurable input and output connectors.
  • Communicators: Switches for routing audio signals (various input to one output, matrix switches).
  • Signal Sources: Ads, jingles, music, software.
  • Recorder: Records broadcast programs at low speed with average quality.
  • Intercommunication: Intercom systems for communication with production controls.
  • Compressor: Reduces the dynamic range of the audio signal.
  • Monitoring: Monitors the quality of the emission signal.

Transmission Systems

Emission and Signal Distribution

This dedicated room houses the radio systems:

  • Audio Encoder: Interconnects the broadcast room and links via radio or telephone links if located in the same building as the production facility.
  • Stereo Encoder: Creates the multiplexed signal for FM broadcasting.
  • RDS Generator: Generates a digital data signal for station identification.
  • Equipment Issue: The modulator creates the RF signal after the complete channel is formed.
  • Radio Links: Extend the station’s reach to transmitting facilities.

Modulation Techniques

Amplitude Modulation (AM)

AM is generated when the carrier signal’s amplitude depends on the modulator’s amplitude. Overmodulation can occur, causing the signal to vanish during negative half cycles. AM has easy demodulation but low efficiency (25%). Variations include Double Sideband (DSB) (50%), Single Sideband (SSB) (100%), and Vestigial Sideband (VSB) (80%).

Frequency Modulation (FM)

The carrier signal’s frequency is modified by changes in the modulating signal’s amplitude. The modulation index indicates the relationship between the carrier wave’s maximum deviation and the modulating signal’s maximum frequency. The audio bandwidth for FM music broadcasts is 0 to 15 kHz.

Phase Modulation (PM)

Information is stored in the phase shift between two signals, commonly used for digital modulation. Two primary states are Phase and Contrast.

Digital Modulation

  • PSK (Phase Shift Keying): QPSK uses four possible carrier signal phases (0°, 90°, -90°, and 180°).
  • COFDM (Coded Orthogonal Frequency-Division Multiplexing): Sends multiple signals mixed through a single channel, making it resistant to fading.

Stereo Transmission

Stereo transmission maintains compatibility with mono receivers (backward compatibility). The multiplex signal includes:

  • Sum signal (L+R) up to 15 kHz
  • Difference signal (L-R) between 23 and 53 kHz
  • 19 kHz pilot tone to indicate a stereo signal
  • RDS for additional information (station name, etc.)

RF Systems and Equipment

RF systems have a 50-ohm impedance. Impedance matching is crucial to prevent standing waves. VSWR (Voltage Standing Wave Ratio) measures impedance mismatch, ideally between 1.1 and 1.5.

Common coaxial cable connectors include BNC (bayonet lock), N (threaded), F (smaller), and PL-259 (larger, threaded).

Digital Radio Standards

  • DAB (Digital Audio Broadcasting): Operates between 174 and 240 MHz (up to 3 GHz for satellite). Uses QPSK modulation and includes services like station identification, weather, news, and traffic.
  • IBOC (In-Band On-Channel): Uses spectrum voids between analog channels, aiming for compatibility with analog broadcasts. Transmits a single stereo channel using QPSK modulation.
  • DRM (Digital Radio Mondiale): Aims to establish universal digital radio in AM bands (long, medium, and shortwave) below 30 MHz.

Measurement Equipment

  • Oscilloscope: Displays signal voltage as a function of time.
  • Spectrum Analyzer: Displays signal frequency components, including UHF and above. Key parameters include central frequency, expansion factor (zoom), baseline (vertical scale), and resolution filter.