What Are Radio Waves?

1. What is a Wave?

A "wave" is a term used to describe a periodic disturbance in time that has repeating peaks and valleys and can move from one location to another.

For example, a wave in water is a disturbance in the water level, a sound wave is a disturbance in the air density, and a radio wave is a disturbance in the electric and magnetic fields. Water waves or sound can only propagate in matter, while radio waves do not require a medium to propagate.

2. Essence and Basic Nature of Radio Waves

Oscillating electric and magnetic fields produce electromagnetic (EM) radiation.
Radio waves are part of the wider EM Spectrum. Radio waves, like all EM waves, travel at the speed of light.

3. Wavelength, frequencies
Radio waves have two important properties: wavelength and frequency. The distance between two consecutive wave crests is represented by wavelength, whereas frequency is the number of wave cycles that pass a given point in one second.
4. Spectrum
The wavelengths range from less than a millimeter to over 100,000 kilometers (10^-3 - 10⁸ meter); frequencies 3 Hz - 300 GHz.

Radio waves are classified into bands based on their frequency and wavelength.

Band name	abbr.	ITU band	Frequency	Wavelength	Bands Allocated to Amateurs
Extremely low frequency	ELF	1	3 - 30 Hz	10,000-100,000 km	none
Super low frequency	SLF	2	30 - 300 Hz	1,000 - 10,000 km	none
Ultra low frequency	ULF	3	300 Hz - 3 kHz	100 - 1000 km	none
Very low frequency	VLF	4	3 - 30 kHz	10 - 100 km	none
Low frequency Longwave (LW)*	LF	5	30 - 300 kHz	1 - 10 km	**2200 m
Medium frequency Medium-wave (MW)*	MF	6	300 - 3000 kHz	100 - 1000 m	**630, 160 m
High frequency Short-wave (SW)*	HF	7	3 - 30 MHz	10 - 100 m	80, 60, 40, 30, 20, 17, 15, 12, 10 m
Very high frequency	VHF	8	30 - 300 MHz	1 - 10 m	**6, 4, 2 m
Ultra high frequency	UHF	9	300 - 3000 MHz	10 - 100 cm	**70, 23, 13 cm
Super high frequency	SHF	10	3 - 30 GHz	1 - 10 cm	**5, 3, 1.2 cm
Extremely high frequency	EHF	11	30 - 300 GHz	1 - 10 mm	**6, 4, 1 mm

^*Historical term used in the first half of the 20th century.

^**Amateur radio frequency allocations vary around the world. Several bands are common for amateurs worldwide, usually in the HF part of the spectrum. Other bands are national or regional allocations only due to differing allocations for other services, especially in the LF, MF, VHF, and UHF parts of the radio spectrum.

5. History of Human Knowledge

The discovery and understanding of radio waves have a rich history. In the late 19th century, James Clerk Maxwell's equations provided the theoretical foundation for EM waves. It was Heinrich Hertz who first demonstrated the existence of radio waves in the laboratory in the 1880s. Hertz's experiments showed that electric sparks could produce and detect radio waves, marking a significant breakthrough.

However, it was Guglielmo Marconi who made practical use of radio waves for wireless communication in the early 20th century. His work led to the development of the first radio transmitters and receivers, paving the way for modern wireless communication systems.

6. Natural Sources

Since the Big Bang Radio waves have been produced by various natural sources. One of the most prominent natural sources of radio waves is celestial objects, including stars, planets, and galaxies. Radio telescopes are specialized instruments designed to observe these cosmic radio emissions, allowing scientists to study the universe's hidden secrets. Earth's atmosphere also emits radio waves through processes like lightning strikes, which generate radio signals known as sferics (sometimes also spelled "spheric"). These natural radio emissions can be harnessed for meteorological and atmospheric studies.

7. Uses / Applications

Radio waves have an extensive range of practical applications in our daily lives. Some key uses include:

1. Wireless Communication: Radio waves are the foundation of wireless communication systems, including radio and television broadcasting, cell phones, Wi-Fi, and Bluetooth. They enable the transmission of voice, data, and video over long distances.
2. Radar: Radio waves are used in radar systems for navigation, weather monitoring, and military applications. Radar technology relies on the principle of emitting radio waves and detecting their reflections to determine the position and speed of objects.
3. Satellite Communication: Satellites in orbit around the Earth use radio waves to transmit signals for television broadcasting, internet connectivity, weather monitoring, and global positioning systems (GPS).
4. Radio Astronomy: Radio telescopes detect and study radio waves from celestial objects, allowing astronomers to explore the universe and gain insights into phenomena such as quasars, pulsars, and cosmic microwave background radiation.
5. Medical Imaging: Magnetic resonance imaging (MRI) uses radio waves to create detailed images of the human body's internal structures, aiding in medical diagnoses.
6. Remote Sensing: Satellites equipped with radio wave sensors monitor Earth's environment, providing crucial data for weather forecasting, environmental monitoring, and disaster management.

In conclusion, radio waves are a fundamental part of the EM spectrum with unique properties that make them indispensable for a wide range of human endeavors, from communication to scientific exploration and beyond. Their discovery and application have revolutionized how we connect, communicate, and explore the universe, making them an essential part of our daily lives and scientific endeavors.

References:
1. Radio wave ^Wikipedia
2. What are radio waves? ^NASA
3. Radio Waves ^UCAR
4. What are radio waves? ^{Northwestern.edu}
5. Electromagnetic radiation ^Wikipedia
6. Electromagnetic spectrum ^Wikipedia
7. Radio spectrum ^Wikipedia
8. Tour of the Electromagnetic Spectrum ^NASA