Band III

Lore & Background

Band III came into use for radio broadcasting at the turn of the 21st century and is used for DAB (Digital Audio Broadcasting). It is subdivided into a number of frequency blocks used for multiplexes; grayed frequencies are not used for DAB, and some countries like Germany do not use channel 13's frequencies to prevent interference with aviation frequencies. In the UK and part of Ireland, Band III was originally used for monochrome 405-line television, discontinued by the mid-1980s. Other European countries (including Ireland) continued to use Band III for analogue 625-line colour television. Digital television in the DVB-T standard can be used in conjunction with VHF Band III and is used as such in some places. The use of sub-band 2 and sub-band 3 for Digital Audio Broadcasting is now being widely adopted. Sub-band 1 is used for MPT-1327 trunked PMR radio, remote wireless microphones and PMSE links.

Reader's Guide

Band III holds significance as a transitional bridge between analog and digital broadcasting. In North America, its favorable propagation characteristics and reasonable power limits (up to 65 kW for full-power digital television, versus 20 kW or less on VHF Band I) led many US broadcasters to move their full-power ATSC stations from UHF frequencies to Band III VHF when all full-power NTSC analog television services shut down in 2009. In Europe, the band's allocation varies by country, with channel widths of 7 or 8 MHz, and it continues to support both DVB-T digital television and DAB digital radio. Australia has allocated 8 channels in Band III for digital television, each with 7 MHz bandwidth. Russia and other former members of OIRT use System D with 8 MHz channel bandwidth for analog television. Amateur (Ham) radio has a small allocation in the band, known as the 1.25-meter band, from 219 to 220 MHz and 222.0 to 225.0 MHz for communications. The band's legacy includes its role in the transition from analog to digital services across multiple continents.

Did You Know?

• Band III is also called high-band VHF, in contrast to Bands I and II.
• In North America, the band is subdivided into seven channels for television broadcasting, each occupying 6 MHz.
• Amateur radio has a small allocation in Band III known as the 1.25-meter band.

Defining the Spectrum's Boundaries

The radio spectrum occupies the lowest-frequency portion of the electromagnetic spectrum, stretching from 3 Hz up to 3,000 GHz (3 THz). The ITU formally defines radio waves as electromagnetic waves of frequencies arbitrarily lower than 3000 GHz that propagate through space without an artificial guide. At the upper end, the boundary with infrared is somewhat arbitrary and shifts depending on the scientific discipline in question. The terahertz band, spanning 300 GHz to 3 THz, sits in a gray area: the ITU classifies it as the highest radio band, while spectroscopic researchers treat those same frequencies as part of the far or mid-infrared. At the lower end, there is no true physical floor—radio waves simply represent the lowest-frequency electromagnetic radiation that exists. This convention-based boundary means the exact edges of the spectrum are not dictated by fundamental physics but by human agreement across different fields of study.

Regulation, Allocation, and the Congestion Problem

Because the radio spectrum is a finite resource shared by an ever-growing number of users, its use is tightly governed. National laws control the generation and transmission of radio waves, while the International Telecommunication Union coordinates these regulations on a global scale. The ITU's Radio Regulations define roughly 40 distinct radiocommunication services, each assigned to specific frequency ranges. In many cases, portions of the spectrum are sold or licensed to private operators such as cellular carriers and broadcast television stations. As demand has surged, the spectrum has grown increasingly congested over recent decades. This pressure has driven a wave of innovation: trunked radio systems, spread spectrum techniques, ultra-wideband technology, frequency reuse, dynamic spectrum management, frequency pooling, and cognitive radio all emerged as strategies to extract more utility from the same fixed bandwidth. The spectrum itself cannot be expanded; only its efficiency can improve.

Physical Constraints at the Extremes

Two fundamental physical limits define the usable range of radio communication. At the low-frequency end, antenna size becomes the primary obstacle. The structure needed to radiate power efficiently grows in proportion to wavelength, meaning lower frequencies demand ever-larger installations. Below roughly 10 kHz, where wavelengths stretch to 30 km, elevated wire antennas kilometers long are necessary, making practical deployment rare. Below about 30 kHz, even audio modulation becomes impractical, restricting transmission to very slow data rates. The absolute low-frequency extreme is embodied in ELF submarine communication systems, which employ ground dipole antennas 20 to 60 km long, megawatt-level transmitter power, and achieve only about 1 bit per minute—roughly five minutes per character. At the high-frequency end, atmospheric absorption is the limiting factor. Above 30 GHz, gases in the atmosphere absorb increasing amounts of signal power, reducing useful range to about 1 km. In the terahertz band above 300 GHz, ozone, water vapor, and carbon dioxide render the atmosphere essentially opaque, attenuating signals to zero within just a few meters.

Band Planning and the ITU's Organizational Framework

To prevent interference and ensure efficient sharing, the radio spectrum is organized into discrete bands—contiguous frequency sections where channels are reserved for similar purposes such as broadcasting, mobile radio, or navigation. For each band, the ITU publishes a band plan that specifies how the spectrum is to be used and shared. These plans define the frequency range, channel numbering schemes, center frequencies and channel spacing, bandwidth or deviation limits, spectral masks for extraneous signal attenuation, permissible modulation types, allowed content such as audio, video, analog, or digital signals, and licensing procedures. The ITU divides the entire radio spectrum into 12 bands, each beginning at a wavelength that is a power of ten in meters. Local regulatory agencies like the US Federal Communications Commission enforce these allocations domestically, while voluntary best practices among operators provide an additional layer of interference avoidance. Together, this layered governance structure transforms a chaotic electromagnetic environment into an orderly, usable resource.

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