The Electromagnetic Spectrum
The electromagnetic spectrum is the range of frequencies of electromagnetic radiation that are arranged according to frequency and wavelength. The spectrum starts with radio waves at one end, recognised as having a low frequency and a long wavelength, through to gamma radiation at the opposite end, which has a high frequency and a short wavelength. Other examples of electromagnetic radiation include microwaves, visible radiation, infrared and x-rays.
Radio waves are utilised by antennas and are used to transmit data from one place to another. They range from Extremely Low Frequency (ELF) waves to Extremely High Frequency (EHF) waves as standardised by the International Telecommunications Union (ITU), which is a United Nations agency that deals with any issues regarding telecommunications technologies.
Very High Frequency (VHF) Radio Waves
The frequency at which a radio wave will cycle in a second is measured in hertz, and VHF radio waves have a frequency between 30 megahertz and 300 megahertz. VHF radio waves, often referred to as Frequency Modulated (FM) waves, are able to carry a higher amount of data information than lower frequency radio waves, and are not affected by static like longer wavelengths are. However, unlike longer wavelengths that can bend more readily around the curvature of the Earth, VHF signals have a wavelength of 1-10 metres and can only travel in a straight line.
As VHF radio waves travel in a similar fashion to visible light waves, the sending and receiving antennas require a clear line of sight for any transmission to be successful. By situating the sending and receiving antennas as high as possible to obtain a better range, the line of sight is maximised and therefore the transmission will be clearer and more efficient.
Due to VHF signals requiring a clear line of sight, geographical and manmade obstacles such as mountains and large structures can significantly affect the transmission of these radio waves. Although less affected by other electronic equipment than lower frequency radio waves, VHF signals can still be affected by atmospheric disturbances, which is why television signals are commonly interrupted during thunderstorms.
What Are VHF Radio Waves Used For?
The main use of VHF radio waves is for terrestrial television broadcasting and FM radio transmissions. Two way radio services, such as those used by taxi companies and also often employed for maritime and aviation purposes will utilise VHF signals. Public safety authorities such as local police and fire departments use VHF signals for effective emergency communication and data transmission.
Other uses of VHF radio waves include air traffic control, disaster prevention, marine communications and mobile communications whether for emergency, business, private or military use. Amateur radio operators, who use the exchange of data information via radio communication for the purposes of private recreation, often transmit on frequencies within the VHF band. Due to the clearer signals provided by VHF radio waves, this mode of communication becomes especially useful when landline communications are temporarily disrupted and the only way to broadcast an emergency signal is by using a radio system.