Radio frequency

Radio frequency, often shortened to RF, refers to how fast an electric current or voltage changes. It also describes magnetic, electric, or electromagnetic fields that move up and down within a certain range of frequencies. This range is usually from about 20 kilohertz (kHz) to 300 gigahertz (GHz).

At these frequencies, energy from a changing current can travel through space as radio waves. This makes radio frequency very important for many technologies we use every day, especially for radio and communication systems. Because different sources may define the exact limits slightly differently, the range of what counts as radio frequency can vary.

Radio frequency is a key part of how we send and receive information without wires. Whether it's listening to the radio, using a mobile phone, or connecting to the internet through Wi-Fi, radio frequency helps make these technologies possible.

Electric current

Electric currents that move back and forth at radio frequencies (RF currents) act differently from the electricity in our homes. One big difference is that RF currents can travel through the air as electromagnetic waves or radio waves. This is how radios work.

RF currents also have special behaviors. They flow mostly along the outside of wires, not through them. They can pass through materials that usually stop electricity. But they can be stopped by coils of wire. When RF currents travel through cables, they sometimes bounce back and create patterns called standing waves.

Frequency bands

Main article: Radio spectrum

The range of frequencies for radio waves is split into different groups, each with a special name decided by the International Telecommunication Union (ITU).

Frequencies of 1 GHz and higher are usually called microwave, and those of 30 GHz and higher are known as millimeter wave. There are more specific names for these bands set by standards from the IEEE and also by EU/NATO designations.

Frequency range	Wavelength range	ITU designation		IEEE bands
		Full name	Abbreviation
Below 3 Hz	>10⁵ km			—N/a
3–30 Hz	10⁵–10⁴ km	Extremely low frequency	ELF	—N/a
30–300 Hz	10⁴–10³ km	Super low frequency	SLF	—N/a
300–3000 Hz	10³–100 km	Ultra low frequency	ULF	—N/a
3–30 kHz	100–10 km	Very low frequency	VLF	—N/a
30–300 kHz	10–1 km	Low frequency	LF	—N/a
300 kHz – 3 MHz	1 km – 100 m	Medium frequency	MF	—N/a
3–30 MHz	100–10 m	High frequency	HF	HF
30–300 MHz	10–1 m	Very high frequency	VHF	VHF
300 MHz – 3 GHz	1 m – 100 mm	Ultra high frequency	UHF	UHF, L, S
3–30 GHz	100–10 mm	Super high frequency	SHF	S, C, X, Ku, K, Ka
30–300 GHz	10–1 mm	Extremely high frequency	EHF	Ka, V, W, mm
300 GHz – 3 THz	1 mm – 0.1 mm	Tremendously high frequency	THF	—N/a

Applications

See also: Applications of radio and Radio spectrum § Applications

Radio has many useful purposes. It helps us listen to music and news, talk to people far away, send and receive information, find objects with radar, get medical help, and control things from a distance. These are just a few ways radio makes our lives easier and better.

Measurement

Test tools for radio frequencies can be simple at low frequencies, but they become more special for high frequencies.

Radio-frequency signal generators are used in testing and setup. They give out controlled signals across many frequency ranges. Besides tools you can buy, some companies and engineering groups share guides on how to build and use RF generators and high-frequency power systems.

Mechanical oscillations

While RF usually talks about electrical vibrations, there are also mechanical RF systems. You can find these in things like mechanical filters and RF MEMS.