A finite natural resource with a wide range of uses
The radio spectrum is a finite national resource. It is the backbone for a wide range of activities in sectors including;
- public security,
- emergency services,
- research and development,
- scientific services and
- hobbies/leisure uses.
Such radio services play an important role in the communications infrastructure of a modern economy.
Transcending national borders
Radio waves do not stop at national boundaries, yet we expect to use the radio spectrum without suffering interference. Interference free use is possible due to international agreements on the use of the radio spectrum. National administrations implement these agreements in their day-to-day management of the spectrum.
Different properties at different frequencies
Different uses make use of different radio frequencies due to the properties of the radio waves operating at those frequencies. Hence we use low frequencies for large area transmissions (LW and MW radio, shipping and aircraft radio beacons)
We use higher frequencies (VHF-FM radio, private business two-way radio) for local transmissions.
The lower frequencies penetrate walls better than higher frequencies, but require very large aerials for effective transmission. Higher frequencies do not penetrate walls as easily, but require smaller aerials for effective transmission.
Different bandwidths for different uses
The broadcast radio and two-way business radio cases only carry one voice/sound stream in a transmission. These do not take up too much spectrum. Services such as TV signals require a larger bandwidth, that is they require more spectrum per stream. That means that we must transmit TV signals at higher frequencies.
The more data we want to fit onto a radio signal the larger its bandwidth and the more spectrum it needs. Newer digital mobile phone systems combine many voice and data streams from different users into a single transmitter signal. As a result they also operate at higher frequencies.
The varying demands of large data bandwidth, penetration into buildings and small aerials all have to be balanced in the choice of radio frequency for a given use.
Decisions on frequencies and uses
Manufacturers, operators and governments must make decisions on the most appropriate frequencies to use for different requirements. They must make these decisions globally applicable in order to achieve economies of scale in manufacture. Governments make these global decisions under the auspices of the International Telecommunications Union at World Radiocommunications Conferences.
Some decisions remain at national level and European level. National spectrum policy sets out the desired results of national level decisions.
Microwaves and dishes
Satellite and Radio link systems use frequencies offering high bandwidth but which do not penetrate well. These systems use dish type aerials, which are sometimes very large. The signals can travel large distances once they have clear vision (line of sight) between the transmitting and receiving dishes. Many satellite signals travel from satellites in orbit about 36000km from earth. These geostationary satellites appear to be in the same place in the sky all the time.
Short waves; a special frequency range
Short waves are a specific range of frequencies exhibiting properties which are unusual and run contrary to the general rule. Before the invention of satellites, broadcasters used Short Waves (SW) to transmit radio programmes to locations in other continents. Though there are still some SW broadcasts, they are not the main focus of the sector these days. Defence, maritime and aviation sectors and amateur radio (Ham Radio) enthusiasts still use SW spectrum. Licensed radio amateurs use various radio frequencies for self-education and training in both hobby and humanitarian/civil society assistance contexts. Further information is available from the Irish Radio Transmitters Society. The Commission for Communications Regulations (ComReg) issues licences to Radio Amateurs.
Terminology used over time
In the early days of radio, people associated the frequency with its wavelength. Over the years the general public have known different frequency bands by various names. These have sometimes changed with time. The wavelength and frequency are inversely proportional. Nowadays it is more common to refer to a frequency or frequency band.
Engineers now call Long Wave (LW) (for example 1500 meters) by the name Low Frequency (LF), at around 200kHz. Equally they now call Medium Wave (MW) (for example 300 meters) Medium Frequency (MF) at around 1000kHz. On broadcast radio receivers these bands, though mainly MW, may both be labeled "AM". Radio amateurs collectively refer to the Short Wave bands from 80 meters to 10 meters as High Frequency (HF) bands. When broadcast radio services around 100MHz first appeared people bought radios which could receive the Very High frequency (VHF) band. However these days you will see radios which can receive FM. Nobody has ever referred to these frequencies as the 3 meter band!
Consumers "tuned" to channels A to J when initial TV services began. Channels A-J were on the VHF bands (near 55 MHz or 200MHz). This started the trend of not quoting a frequency or wavelength. Later TV services used the Ultra High Frequency (UHF) bands around 500-800 MHz. That is wavelengths of about 50cm broadly speaking. The UHF TV services were often more commonly referred to by "channel numbers" between 21 and 69. Nowadays mobile phone services occupy the frequencies above 800MHz (channels numbers 61-69). Most European countries have committed to give over the frequencies above 700MHz (channel numbers 49-60) to supplement the bands for mobile phone services before 2021. This has been called the digital dividend.
Modern equipment does not need the user to select a service by frequency
Consumers generally do not need to know the frequencies used for digital TV services. The user does not to "tune in" each service each time they wish to change TV or radio service. This is because modern equipment such as Saorview TV receivers and other digital broadcasting service receivers do this automatically. They will often offer a general scan to memory.