By I. Funa
Radio frequency spectrum is a natural and limited resource. Radio waves are a mean to transfer information from one point to another without using any media. One of the most important properties of any waves is their wavelength or frequency. Radio frequency determines the position in Radio frequency spectrum and hence all the properties of radio wave propagation and potential use.
Because radio waves travel across country borders and may interfere with other radio waves there are many rules, frequency plans and procedures that define how to use radio frequency spectrum to avoid interferences. Because different frequencies have different properties there are some general harmonized frequency bands that define main purpose of the band and basic technical parameters of transmitters using these frequencies. The so called allocations are accepted on international levels and provide basic rules for frequency usage. Each allocation is then further refined and countries may have special agreements on how to use specific frequencies.
One of the most popular services using radio frequencies is terrestrial or satellite broadcasting. Radio and television are a well know and established way to send picture and sound with radio waves. Because we usually want large coverage areas with few transmitters we are using high power transmitters on high transmitting sites. Large coverage areas also mean coverage across the border.
This is a very important fact because in the same area there can be only one transmitter that can operate on a particular frequency without causing interference. Of course, there are special cases like digital broadcasting and single frequency networks where nearby transmitters operate on the same frequency without causing interference, but for analog broadcasting careful frequency planning is a must.
For broadcasting frequency bands there are many special regional agreements that very precisely define particular frequencies allocated to each country, procedures to be used to modify the plan and also many rules that have to be respected to avoid interference.
When we would like to listen to a particular radio we need to know the frequency on which this radio broadcasts. A frequency is like a street address where each house has its own number. For television the same applies. However, for practical reasons we usually do not operate with frequencies directly but we use channels where each channels number represents one (central) frequency with some channel bandwidth.
In general, most consumers are not aware of all the technical details that regulate frequency usage and are used to provide many wireless services. They only expect good music, quality movies and mobile phones that work anywhere.
One of a very practical uses of radio frequency spectrum is credit card processing at remote or outdoor places. Until recently salespeople, delivery or catering services had to use a manual credit card imprinter or wait until they returned to the office to enter the sale. With latest wireless credit card readers it is possible to process credit cards in real time at any place.