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Frequency Chart

Examples

• 10 Hz, cyclic rate of a typical automobile engine at idle (equivalent to 600 rpm)
• 50 Hz or 60 Hz (50 Hz for European AC, Tokyo AC or 60 Hz for American AC, Osaka AC), electromagnetic — standard AC mains power
• 20 Hz to ~16 kHz, acoustic — normal range of adult human hearing (most children and some animals perceive sounds outside this range)
• 100 Hz, cyclic rate of a typical automobile engine at redline (equivalent to 6000 rpm)
• 261.626 Hz, acoustic — the musical note middle C
• 440 Hz, acoustic — concert pitch (A above middle C), used for tuning musical instruments
• 530 kHz to 1.710 MHz, electromagnetic — AM radio broadcasts
• 740 kHz, transitions — the clock speed of the world's first commercial microprocessor, the Intel 4004 (1971)
• 1 MHz to 8 MHz, transitions — clock speeds of early home/personal computers (mid-1970s to mid-1980s)
• 42 MHz to 260 MHz, electromagnetic — VHF terrestrial TV broadcast channels
• 88 MHz to 108 MHz, electromagnetic — FM radio broadcasts
• 1420 MHz, the frequency of the hyperfine transition of hydrogen, the most common element in the universe.
• 3.73 GHz, transitions — clock speed of the Pentium 4 "Prescott" microprocessor (2005)
• 428 THz to 750 THz, electromagnetic — visible light, from red to violet
• 30 PHz, electromagnetic — x-rays

Lower frequencies

• Once per minute (one rpm): about 16.667 mHz
• Hourly: about 277.8 µHz
• Daily: about 11.57 µHz
• Weekly: about 1.653 µHz
• Monthly (on average): about 380.5 nHz
• Yearly: about 31.71 nHz
• Once per decade: about 3.171 nHz
• Once per generation: about 1 nHz
• Once per century: about 317.1 pHz
• Once per millennium: about 31.71 pHz

Hertz

The hertz (symbol: Hz) is the SI unit of frequency. It is named in honour of the German physicist Heinrich Rudolf Hertz who made important scientific contributions to electromagnetism.

One Hertz is defined as one cycle per second.

1 Hz = 1 s−¹

Multiple	Name	Symbol	Multiple	Name	Symbol
10^0	hertz	Hz
10^1	decahertz	daHz	10^–1	decihertz	dHz
10^2	hectohertz	hHz	10^–2	centihertz	cHz
10^3	kilohertz	kHz	10^–3	millihertz	mHz
10^6	megahertz	MHz	10^–6	microhertz	µHz
10^9	gigahertz	GHz	10^–9	nanohertz	nHz
10^12	terahertz	THz	10^–12	picohertz	pHz
10^15	petahertz	PHz	10^–15	femtohertz	fHz
10^18	exahertz	EHz	10^–18	attohertz	aHz
10^21	zettahertz	ZHz	10^–21	zeptohertz	zHz
10^24	yottahertz	YHz	10^–24	yoctohertz	yHz

One hertz simply means "one per second" (1 / s); 100 Hz means "one hundred per second", and so on. The unit may be applied to any periodic event – for example, a clock might be said to tick at 1 Hz, or a human heart might be said to beat at 1.2 Hz. Frequency of random events, such as radioactive decays, is expressed in becquerels.

The name hertz was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, replacing the previous name for the unit, cycles per second (cps), along with its related multiples, primarily kilocycles (kc) and megacycles (mc). Hertz largely replaced cycles in common use by 1970.

Radio frequency spectrum

Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. Such frequencies account for the following parts of the spectrum shown in the table below.

Band name	Abbr	ITU band	Frequency Wavelength	Example uses
			< 3 Hz > 100,000 km
Extremely low frequency	ELF	1	3–30 Hz 100,000 km – 10,000 km
Super low frequency	SLF	2	30–300 Hz 10,000 km – 1000 km
Ultra low frequency	ULF	3	300–3000 Hz 1000 km – 100 km
Very low frequency	VLF	4	3–30 kHz 100 km – 10 km	Military communication
Low frequency	LF	5	30–300 kHz 10 km – 1 km	Navigation, time signals, AM longwave broadcasting
Medium frequency	MF	6	300–3000 kHz 1 km – 100 m	AM broadcasts
High frequency	HF	7	3–30 MHz 100 m – 10 m	Shortwave broadcasts and amateur radio
Very high frequency	VHF	8	30–300 MHz 10 m – 1 m	FM and television broadcasts
Ultra high frequency	UHF	9	300–3000 MHz 1 m – 100 mm	television broadcasts, wireless LAN
Super high frequency	SHF	10	3–30 GHz 100 mm – 10 mm	microwave devices, mobile phones
Extremely high frequency	EHF	11	30–300 GHz 10 mm – 1 mm
			Above 300 GHz < 1 mm

Note:

Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

The ELF, SLF, ULF, and VLF bands overlap the AF (audio frequency) spectrum, which is approximately 20–20,000 Hz. However, sounds are transmitted by atmospheric compression and expansion, and not by electromagnetic energy.

Radio waves:

EHF = Extremely high frequency (Microwaves)

SHF = Super high frequency (Microwaves)

UHF = Ultrahigh frequency

VHF = Very high frequency

HF/SW = High frequency (ShortWave)

MF/MW = Medium frequency (MediumWave)

LF = Low frequency

VLF = Very low frequency

ULF/VF = Voice frequency

VF = Voice frequency

ELF = Extremely low frequency

EHF = Extremely high frequency (Microwaves)

Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light. This band has a wavelength of one to ten millimetres, giving it the name millimeter band.

Radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength.

This band is commonly used in radio astronomy.

In the USA, the band 38.6 - 40.0 GHz is used for licensed high-speed microwave data links, and the 60 GHz band can be used for unlicensed short range (1.7 km) data links with data throughputs up to 2.5 Gbit/s (gigabits per second).

SHF = Super high frequency (Microwaves)

Microwaves are electromagnetic waves with wavelengths longer than those of infrared light, but shorter than those of radio waves.

Microwaves have wavelengths approximately in the range of 30 cm (frequency = 1 GHz) to 1 mm (300 GHz). However, the boundaries between far infrared light, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The existence of electromagnetic waves, of which microwaves are part of the higher frequency spectrum, was predicted by James Clerk Maxwell in 1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building apparatus to produce radio waves.

The microwave range include ultra-high frequency (UHF) (0.3-3 GHz), super high frequency (SHF) (3-30 GHz), and extremely high frequency (EHF) (30-300 GHz) signals.

Note: above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

Ultra high frequency (UHF)

Ultra high frequency (UHF) designates a range (band) of electromagnetic waves whose frequency is between 300 MHz (Wavelength 1 meter) and 3.0 GHz (Wavelength 10 centimetres) . Waves whose frequency is above the UHF band fall into the microwave or higher bands, while lower frequency signals fall into the VHF or lower bands. See electromagnetic spectrum for a full listing of frequency bands.

UHF and VHF are the most common frequency bands for television. Modern mobile phones also transmit and receive within the UHF spectrum, and UHF is widely used for two-way radio communication (usually using narrowband frequency modulation, but digital services are on the rise) by both public service agencies and the general public. Though television broadcasting is common on UHF, there has traditionally been very little radio broadcasting in this band until fairly recently; see digital audio broadcasting for details.

Very high frequency (VHF)

Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). Frequencies immediately below VHF is HF, and the next higher frequencies are known as Ultra high frequency (UHF).

Common uses for VHF are FM radio broadcast at 88-108 MHz and television broadcast (together with UHF). VHF is also commonly used for terrestrial navigation systems (VOR in particular) and aircraft communications.

VHF frequencies' propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and don't interfere with transmissions thousands of kilometres away). VHF is also less affected by atmospheric noise and interference from electrical equipment than low frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less bothered by buildings and other less substantial objects than higher frequencies.

Two unusual propagation conditions can allow much farther range than normal. The first, tropospheric ducting, can occur in front of and parallel to an advancing cold weather front, especially if there is a marked difference in humidities between the cold and warm air masses. A duct can form approximately 150 miles (240 km.) in advance of the cold front, much like a ventilation duct in a building, and VHF radio frequencies can travel along inside the duct, bending or refracting, for hundreds of miles. For example, a 50-watt Amateur FM transmitter at 146 MHz can talk from Chicago, Illinois, to Joplin, Missouri, directly, and to Austin, Texas, through a repeater. The second type, much more rare, is called Sporadic-E, referring to the E-layer of the ionosphere. A sunspot eruption can pelt the Earth's upper atmosphere with charged particles, which may allow the formation of an ionized "patch" dense enough to reflect back VHF frequencies the same way HF frequencies are usually reflected (skywave). For example, TV channel 2 (54-60 MHz) from Midland, Texas was seen in Chicagoland, pushing out Chicago's own TV channel 2. These patches may last for seconds, or extend into hours. FM stations from Miami, Florida; New Orleans, Louisiana; Houston, Texas and even Mexico were heard for hours in central Illinois during one such event.

It was also easier to construct efficient transmitters, receivers, and antennas for it in the earlier days of radio, as compared to UHF. In most countries, the VHF spectrum is used for broadcast audio and television, as well as commercial two-way radios (such as those operated by taxis and police), marine two-way audio communications, and aircraft radios.

The large technically and commercially valuable slice of the VHF spectrum taken up by television transmission has attracted the attention of many companies and governments recently, with the development of more efficient digital television broadcasting standards. In some countries much of this spectrum will likely become available (probably for sale) in the next decade or so (currently scheduled for 2008 in the United States).

High frequency (HF)

High frequency (HF) radio frequencies are between 3 and 30 MHz. This range is often called shortwave.

Since the ionosphere often reflects HF radio waves quite well, this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:

Sunlight/darkness at site of transmission and reception

Transmitter/receiver proximity to terminator

Season

Sunspot cycle

Solar activity

Polar aurora

Maximum usable frequency

Lowest usable frequency

Frequency of operation within the HF range

The high frequency band is very popular with amateur radio operators, who can take advantage of direct, long-distance (often inter-continental) communications and the "thrill factor" resulting from making contacts in variable conditions. International shortwave broadcasting utilizes this set of frequencies, as well as a seemingly declining number of "utility" users (marine, aviation, military, and diplomatic interests), who have, in recent years, been swayed over to less volatile means of communication (for example, via satellites), but may maintain HF stations after switch-over for back-up purposes. CB radios operate in the higher portion of the range (around 27 MHz), as do some studio-to-transmitter (STL) radio links. Some modes of communication, such as continuous wave morse code transmissions (especially by amateur radio operators) and single sideband voice transmissions are more common in the HF range than on other frequencies, because of their bandwidth-conserving nature, but broadband modes, such as TV transmissions, are generally prohibited by HF's relatively small chunk of electromagnetic spectrum space.

Noise, especially man-made interference from electronic devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over "broadband over power lines" (BPL) Internet access, which is believed to have an almost destructive effect on HF communications. This is due to the frequencies on which BPL operates (typically corresponding with the HF band) and the tendency for the BPL "signal" to leak from power lines. Some BPL providers have installed "notch filters" to block out certain portions of the spectrum (namely the amateur radio bands), but a great amount of controversy over the deployment of this access method remains.

Medium Frequency-MF/MW

Medium Frequency-MF-Mediumwave radio transmissions (sometimes called Medium frequency or MF) are those between the frequencies of 300 kHz and 3000 kHz. In most of the world, mediumwave serves as the most common band for broadcasting. The standard AM broadcast band is 525 kHz to 1715 kHz in North America, but remains only up to 1615 kHz elsewhere.

Mediumwave signals have the property of following the curvature of the earth (the groundwave) at all times, and also reflecting off the ionosphere at night (skywave). This makes this frequency band ideal for both local and continent-wide service, depending on the time of day. For example, during the day a radio receiver in the state of Maryland is able to receive reliable but weak signals from high-power stations WFAN, 660 kHz, and WOR, 710 kHz, 400 km away in New York City, due to groundwave propagation. The effectiveness of groundwave signals largely depends on ground conductivity-higher conductivity results in better propagation. At night, the same receiver picks up signals as far away as Mexico City and Chicago reliably. Many stations are required to shut down or reduce power at night in order to make way for clear channel stations that can then be received over a wider range.

In the Americas, mediumwave stations are separated by 10 kHz and have two sidebands of ±5 kHz. In the rest of the world, the separation is 9 kHz, with sidebands of ±4.5 kHz. Both provide adequate audio quality for voice, but are insufficient for high-fidelity broadcasting, which is common on the VHF FM bands. In the US the maximum transmitter power is restricted to 50 kilowatts, while in Europe there are medium wave stations with transmitter power up to 2.5 megawatts.

Stereo transmission is possible and offered by some stations in the U.S., Australia, South Africa, and France. However, there are multiple standards for AM stereo with C-QUAM being the legal one in the United States, and receivers that actually implement the technologies are relatively rare but not uncommon. Failed systems include Kahn Powerside and others.

In September 2002, the United States Federal Communications Commission approved the iBiquity in-band on-channel (IBOC) system of digital audio broadcasting, which is meant to improve the audio quality of signals. The Digital Radio Mondiale (DRM) IBOC system has been approved by the ITU for use outside the Americas.

Low Frequency or LF

Low Frequency or LF (sometimes called longwave) refers to Radio Frequencies (RF) in the range of 30-300 kHz. In Europe, part of the LF spectrum is used for AM broadcast service. In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. Time signal stations MSF, DCF77, JJY and WWVB are found in this band.

In the USA, the portion between 160 and 190 kHz can be used for experimental purposes and is sometimes called the "Lost Band". Unlicensed operation by the public is permitted south of 60 degrees north latitude, except where interference would occur to 10 licensed location service stations located along the coasts. Regulations for use include a power output of no more than 1 watt, and an antenna/ground-lead length of no more than 15 meters, and a field strength of no more than 4.9 microvolts/meter. Also, emissions outside of the 160-190 kHz band must be attenuated by at least 20 dB below the level of the unmodulated carrier. Amateur Radio operators experiment in this band.

The UK's 73-kHz band is a 2.8 kHz sliver of spectrum, from 71.6 to 74.4 kHz and has been available to Amateur Radio operators since April 1996. They must apply for a Notice of Variation to use the band on a noninterference basis with a maximum output power of 1 W ERP (effective radiated power). A 1-watt transmission of very slow Morse Code between G3AQC (in the UK) and W1TAG (in the USA) spanned the Atlantic Ocean for 3275 miles on November 21-22, 2001.

A 136 kHz allocation (135.7 to 137.8 kHz) band is available to French Radio Amateurs with a maximum ERP of 1 W. The new ruling includes French territories such as Guadeloupe, French Guyana, Martinique and Saint Pierre et Miquelon. Canada and the UK also allow licensed Radio Amateurs to use this allocation with special permits.

Very low frequency or VLF

Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals are used, such as for radionavigation. Because VLF waves can penetrate water only to a depth of roughly 10 to 40 metres (30 to 130 feet), depending on the frequency and the salinity of the water, they are used to communicate with submarines near the surface. (ELF is used for fully submerged vessels.)

This frequency range is used nowadays for the transmission of instructions to submerged submarines (for example with the transmitter DHO38), since radio waves can penetrate some dozen of meters in sea water in this frequency band. They are also used for radio navigation (alpha) and for the transmission of time signals (beta). Early in the history of radio engineering within the band starting from 20 kHz attempts were made to use radiotelephone using amplitude and single-sideband modulation, but the result was unsatisfactory, because of the small available bandwidth. The frequency range under 30 kHz also is used for time signals and radio navigation beacons. The very long wave transmitters, SAQ in Grimeton and Varberg in Sweden can be visited by public at certain times, such as on Alexanderson Day. As a rule very long wave transmitters work in the frequency range between 10kHz and 30kHz. There are also stations, which work in the frequency range under 10 kHz. This frequency range is subject to no control on the part of the international communications organization (International Telecommunication Union) and may be used in some states license-free.

In the USA, the time signal station WWVL began transmitting a 500 W signal on 20 kHz in August 1963. It used Frequency Shift Keying (FSK) to send data, shifting between 20 kHz and 26 kHz. The WWVL service was discontinued in July 1972.

Many natural radio emissions, such as whistlers, can be also heard in this band.

Ultra Low Frequency (ULF)

Ultra Low Frequency (ULF) is the frequency range between 300 hertz and 3000 hertz.

This band is used for communications in mines, as it can penetrate the earth.

A voice frequency (VF)

A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech.

In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, allowing a sample rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN.

The term voice frequency can also be used to refer to the band of the electromagnetic spectrum between 300 and 3000 Hz.

The voiced speech of a typical adult male with have a fundamental frequency of from 85 to 155 Hz, and that of a typical adult female from 165 to 255 Hz. Thus, the fundamental frequency of most speech falls below the bottom of the "voice frequency" band as defined above. However, enough of the harmonic series will be present for the missing fundamental to create the impression of hearing the fundamental tone.

Super Low Frequency (SLF)

Super Low Frequency (SLF) is the frequency range between 30 hertz and 300 hertz. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz).

The radio services Saguine (USA) on 76 hertz and ZEVS (Russia) on 82 hertz operate in this range, which is often incorrectly called Extremely Low Frequency (ELF). They both provide communication services for submarines at depth. There are rumors that there is to be a comparable transmitter in Berlin Tempelhof, named teddybaer, but confirmation is lacking.

PCs with integrated sound cards are increasingly being used instead of radio receivers for this frequency range, because of their much smaller size and lower cost. Signals received by the sound card with a coil or a wire antenna are analysed by a software Fast Fourier Transform algorithm and converted into audible sound.

Extremely low frequency (ELF)

Extremely low frequency (ELF) is the band of radio frequencies from 3 to 300 Hz.

ELF was used by the US Navy to communicate with submerged submarines. Because of the electrical conductivity of salt water, submarines are shielded from most electromagnetic communications. Signals in the ELF frequency range, however, can penetrate much more deeply. The low transmission rate of most ELF communications limits their use as communications channels; generally an ELF signal serves to request that a submarine surface and initiate some other form of contact. For details see: communication with submarines.

One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. In order to transmit internationally using ELF frequencies, an extremely large antenna is required. The US maintained two sites, in the Chequamegon National Forest, Wisconsin and the Escanaba State Forest , Michigan, until dismantling them beginning in late September 2004. Both sites used long power lines as antennae, in multiple strands ranging from 14 to 28 miles (22.5 to 45 kilometers) long. Considerable amounts of electrical power are generated and emitted by ELF.

There have been some concerns over the possible ecological impact of ELF signals. In 1984 a federal judge halted construction requiring more environmental and health studies. This judgement was overruled by a federal appeals court on the basis that the US Navy claimed to have spent over 25 million dollars studying the effects of the electromagnetic fields with results indicating that they were similar to the effect produced by standard power distribution lines. The judgement was not accepted by everyone and during the time ELF was in use Wisconsin politicians such as Herb Kohl, Russ Feingold and Dave Obey called for its closure.

Transmitters in the 20 Hz range are also found in pigs, used in the maintenance of pipelines. The transmitted signal is often used to track the pig when it becomes stuck in the pipeline.

Some amateur radio aficionados record ELF (or even lower) signals from very large homemade antennas, and play them back at higher speeds in order to catch the Earth's natural fluctuations in its electromagnetic field. Increasing the speed of the magnetic tape increases the pitch, so that it is brought into the audio frequency range.

Microwave frequency bands Designation Frequency range

L band 1 to 2 GHz

S band 2 to 4 GHz

C band 4 to 8 GHz

X band 8 to 12 GHz

Ku band 12 to 18 GHz

K band 18 to 26 GHz

Ka band 26 to 40 GHz

Q band 30 to 50 GHz

U band 40 to 60 GHz

V band 50 to 75 GHz

E band 60 to 90 GHz

W band 75 to 110 GHz

F band 90 to 140 GHz

D band 110 to 170 GHz

A brief summary of some UHF frequency usage:

300-420 MHz: government use, including meteorology

420-450 MHz: radiolocation and Amateur "70 cm" band

450-470 MHz: UHF business band, GMRS, and FRS 2-way "walkie-talkies"

470-512 MHz: TV channels 14-20, public safety

512-698 MHz: TV channels 21-51

698-806 MHz: TV channels 52-69 (to be auctioned for other uses once conversion to digital TV has been accomplished)

806-824 MHz: pocket pagers and Nextel SMR band

824-849 MHz: Cellular phones, A & B franchises, mobile phone

849-869 MHz: public safety 2-way (fire, police, ambulance)

869-894 MHz: cellular phones, A & B franchises, base station

902-928 MHz: ISM band: cordless phones and stereo, RFID, datalinks, Amateur radio 33cm band

928-960 MHz: mixed Studio-Transmitter Links, mobile 2-way, other

1240-1300 MHz: Amateur radio

1850-1910 MHz: PCS mobile phone-note below

1930-1990 MHz: PCS base stations-note below

note: order is A, D, B, E, F, C blocks. A, B, C = 15 MHz; D, E, F = 5 MHz

2310-2360 MHz: Satellite radio (Sirius and XM)

2390-2450 MHz: Amateur radio, shared with below:

2400-2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN

around 2450 MHz: Microwave oven

The general services in the VHF band are:

30-46 MHz: Licensed 2-way land mobile communication

30-88 MHz: Military VHF-FM, including SINCGARS

43-50 MHz: Cordless telephones, "49 MHz" FM walkie-talkies, and mixed 2-way mobile communication

50-54 MHz: Amateur radio "6-meter" band

54-72 MHz: TV channels 2, 3, and 4

72-76 MHz: Remote Control devices

76-88 MHz: TV channels 5 and 6

88-108 MHz: FM radio broadcasting (88-92 non-commercial, 92-108 commercial)

108-118 MHz: Air navigation beacons VOR

118-132 MHz: Airband for Air Traffic Control, AM, 121.5 MHz is emergency frequency

132-144 MHz: Auxiliary civil services, satellite, space research, and other miscellaneous services

144-148 MHz: Amateur band 2 Meters

148-174 MHz: "VHF Business Band," the new unlicensed Multi-Use Radio Service (MURS), and other 2-way land mobile, FM

156-174 MHz VHF Marine Radio; narrow band FM, 156.8 MHz (Channel 16) is the maritime emergency and contact frequency

162.40-162.55: NOAA Weather Stations, FM

174-216 MHz: TV channels 7 through 13, and professional wireless microphones (low power, certain exact frequencies only)

216-222 MHz: mixed services

222-225 MHz: Amateur "1-1/4-meter" band

above 225 MHz: Federal services, notably military aircraft radio (225-400 MHz) AM, including HAVE QUICK, dGPS RTCM-104

Longwave radio frequencies are those below 500 kHz, which correspond to wavelengths longer than 600 meters. They have the property of following the curvature of the earth, making them ideal for continuous, continental communications. Unlike shortwave radio, longwave signals do not reflect or refract using the ionosphere, so there are fewer phase-caused fadeouts. Instead, the D-layer of the ionosphere and the surface of the earth serve as a waveguide directing the signal.

The earliest radio transmitters, including the Alexanderson alternator, were all longwave transmitters.

Audio Frequency -AF

An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies audible to humans. The variable whose frequency is being measured can be any physical property capable of oscillating in this frequency range, such as electric current, sound pressure in air, or mechanical vibration.