For an electromagnetic wave to carry information, its properties such as frequency, amplitude and phase, need to be systematically modulated. To communicate information, the modulated wave will then have to be transmitted, detected and finally transformed into other signals such as sound. This whole process is generally called radio communication. The frequencies used for radio are just a small portion of the whole electromagnetic spectrum.
1. Understand how radio frequencies are used.
The whole spectrum of radio frequencies ranges from 3 Hz to 300 GHz. However, not all of this is used for regular or commercial communication. Those that range from 3 to 30 Hz are called extremely low frequencies (ELF) and are used by submarines. On the other end are the extremely high frequencies (EHF) ranging from 30 to 300 GHz. EHF is used more for microwave communication and astronomy.
The frequencies we're more familiar with are those in the middle. AM radio broadcasting is at the low frequency (LF) range of 30 to 300 kHz and regular television uses ultra high frequencies (UHF), which are at 300 to 3000 MHz. Satellite television and wireless networks use super high frequencies (SHF) and these range from 3 to 30 GHz.
2. Know how radio frequencies are divided and assigned.
Besides these general categories of radio frequencies, divisions into more specific frequency ranges are applied. A radio frequency band is a set of frequencies that have been set aside for a particular communication purpose or assigned for use by a particular group. The frequency band is then further divided into channels which may be a single frequency, a pair, or a group of frequencies. The Marine VHF radio frequency band, for example, has a range of 156 to 174 MHz; it is used by most seafaring crafts, as well as harbors and marinas. Channel 16 in this band is 156.8 MHz, and this is used for making distress calls. Frequency allocation is obviously necessary to avoid interference and confusion. Radio frequency bands are standardized, set and agreed upon by international organizations such as the International Telecommunication Union and the European Telecommunications Standards Institute.
For a radio frequency band to be established, it has to have a bandplan. This defines how a particular frequency will be used, how it will be divided into channels, how wide each channel should be (bandwidth) and what content is to be communicated on those channels. Channel assignation usually involves a numbering scheme. Bandplans also lay down protocols for transmission and device compatibility. They further include procedures for licensing.
4. Here are some of the more common radio frequency bands:
FM radio broadcast: 88 - 108 MHz
Citizen's band (CB radio): 26.965 -27.405 MHz
Regular television channels (in the Americas): 174 - 216 MHz
Airband (used for air traffic control): 108 -137 MHz
Radio frequency bands are primarily identified by their frequency ranges, as these are allocated for specific uses by particular groups. To be able to know which is which, one would need to be familiar with the assignations set by various international organizations that manage the field of radio communications.