In order to have a better understanding of the radio frequency spectrum, we need to know what radio bands are. Radio stations use different frequencies of radio waves for delivering the radio signals. The radio waves can easily travel through the air and therefore easily reach to cover long distances. The conventional range of frequencies is from 30 MHz up to 3000 MHz. This range is known as shortwave, VHF, UHF, and SHF respectively.
Radio bands are determined by the wavelength of the signals transmitted. The wavelength determines the frequencies that can be used for transmission. 1 kHz signals have a wavelength of approximately 5.3 km. VLF signals are characterized by wavelengths in excess of 10 km, resulting in a lot of attenuation in the atmosphere. Due to this reason, it is used for the transmission of signals underwater only. The radio spectrum bands include;
1. Extremely low frequency
The frequency band of 3Hz to 3 kHz is referred to as Extremely low frequency or ELF.
The ELF has an extremely low frequency. It comprises the frequency starting from 3Hz to 3 kHz. It is highly vulnerable to disturbance and can easily get distorted by atmospheric changes. Scientists use this frequency band in seismic studies. ELF waves are used in communication systems to transmit voice and data. In such systems, data is encoded in the form of messages that have an extremely small bandwidth. ELF waves do not reflect from the ground and hence cannot be used for broadcasting. This is due to the high attenuation that takes place while these waves pass through the earth
2. Very low frequency
Very low frequency ( VLF ) is the ITU designation for radio frequencies (RF) in the range of 3 kilohertz (kHz) to 30 kHz and corresponding wavelengths from 100 to 10 kilometers (km), with corresponding wavelengths of 1000 to one kilometer, respectively. The band is also known as the myriametre band or myriametre wave as the wavelengths range from one to ten myriametres (a myriameter being 10 kilometers). Due to its favorable medium, in Europe and in areas where ground conductivity is high, the VLF band is used for long-distance radio transmission, especially trans-oceanic communication and broadcasting, but also ground-based military communication systems and deep-space communications.
Although frequencies immediately below VLF are mainly used for microwave radio relay transmission, carrier current transmission, and pulse modulation like single-sideband modulation for long-distance telegraphy.
3. Low frequency
Low frequency, or LF, is a range of electromagnetic frequencies from 30 to 300 kilohertz. This band is characterized by a wavelength between 0.3 and 3 meters. Because of their wavelengths, these frequencies can diffract around large obstacles, making them suitable for long-distance communications, in contrast with higher frequency communication links that cannot bend around barriers.
Because of their low frequency, 30–300 kHz waves can reflect from ionospheric layers that would be too thin to reflect higher frequency radio waves. Low frequencies can also travel long distances by ground wave.
Reflection takes place due to the refractive index gradient caused by an electric field in the atmosphere. The ground reflection allows waves to be reflected at great distances (sometimes around the globe) if there are no obstructions or tropospheric scatter in the signal path
4. Medium frequency
Medium frequency operates in the range of 300 kHz and 3 MHz. The designs of its receivers, transmitters, and antenna are less complex than other high frequencies. It has been used in AM radio transmission, navigation systems for aircraft and ships, coastal guards, emergency distress signals, etc.
5. High frequency
High frequency operates in the range of 3 MHz to 30 Mhz. It is suitable for long-distance communication. It is used by the aviation industry, whether broadcasting stations, amateur radio operators, near field communication, and government systems.
6. Very high frequency
Very high frequency or VHF/UHF mobile radio operates in the range of 30 MHz to 300 MHz. It is used in analog TV broadcasting, FM radio broadcasting at 88 MHz to 108MHz, air traffic controllers and airline pilots communicating at 118 MHz to 137 MHz, submarines, and medical equipment.
7. Ultra high frequency
Ultra-high frequency operates in the range of 300 MHz to 3 GHz. It is used in GPS navigation systems, satellites, WI-FI, LTE mobile transmission, Bluetooth, etc.
8. Super high frequency
Super high frequency ranges from 3 GHz to 30 GHz. It is used in satellite systems, WI-FI, microwave oven, and mobile networks.
9. Extremely high frequency
Extremely high frequency ranges between 30 GHz and 300 GHz. It is used in advanced communication systems such as radio astronomy and weather analysis.