Radio_frequency

Special properties of RF electrical signals

Electrical currents that oscillate at RF have special properties not shared by direct current signals. One such property is the ease with which they can ionize air to create a conductive path through air. This property is exploited by 'high frequency' units used in electric arc welding. Another special property is an electromagnetic force that drives the RF current to the surface of conductors, known as the skin effect. Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor. The degree of effect of these properties depends on the frequency of the signals.

Frequencies

Name	Symbol	Frequency	Wavelength	Applications
Extremely low frequency	ELF	a 3–30 Hz	k 10,000–100,000 km	Directly audible when converted to sound, communication with submarines
Super low frequency	SLF	b 30–300 Hz	j 1,000–10,000 km	Directly audible when converted to sound, AC power grids (50–60 Hz)
Ultra low frequency	ULF	c 300–3000 Hz	i 100–1,000 km	Directly audible when converted to sound, communication with mines
Very low frequency	VLF	d 3–30 kHz	h 10–100 km	Directly audible when converted to sound (below ca. 20 kHz; or ultrasound otherwise)
Low frequency	LF	e 30–300 kHz	g 1–10 km	AM broadcasting, navigational beacons, lowFER
Medium frequency	MF	f 300–3000 kHz	f 100–1000 m	Navigational beacons, AM broadcasting, maritime and aviation communication
High frequency	HF	g 3–30 MHz	e 10–100 m	Shortwave, amateur radio, citizens' band radio
Very high frequency	VHF	h 30–300 MHz	d 1–10 m	FM broadcasting, amateur radio, broadcast television, aviation, GPR
Ultra high frequency	UHF	i 300–3000 MHz	c 10–100 cm	Broadcast television, amateur radio, mobile telephones, cordless telephones, wireless networking, remote keyless entry for automobiles, microwave ovens, GPR
Super high frequency	SHF	j 3–30 GHz	b 1–10 cm	Wireless networking, satellite links, microwave links, satellite television, door openers
Extremely high frequency	EHF	k 30–300 GHz	a 1–10 mm	Microwave data links, radio astronomy, remote sensing, advanced weapons systems, advanced security scanning

Name

Symbol

Frequency

Wavelength

Applications

Extremely low frequency

ELF

3–30 Hz

10,000–100,000 km

Directly audible when converted to sound, communication with submarines

Super low frequency

SLF