A personal FM transmitter is a low-power FM

radio transmitter In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna with the purpose of signal transmissio ...

that broadcasts a signal from a portable audio device (such as an MP3 player or a smartphone) to a standard FM radio. Most of these transmitters plug into the device's

headphone jack A phone connector is a family of cylindrically-shaped electrical connectors primarily for analog audio signals. Invented in the late 19th century for tele''phone'' switchboards, the phone connector remains in use for interfacing wired a ...

and then broadcast the signal over an

FM broadcast band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union ( ...

frequency, so that it can be picked up by any nearby radio. Some FM transmitters have Bluetooth capabilities for use with smartphones. This allows portable audio devices to make use of the louder or better sound quality of a home

audio system Sound recording and reproduction is the electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording te ...

car stereo Vehicle audio is equipment installed in a car or other vehicle to provide in-car entertainment and information for the occupants. Such systems are popularly known as car stereos. Until the 1950s, it consisted of a simple AM radio. Additions sin ...

without requiring a wired connection. They are often used in cars but may also be in fixed locations such as broadcasting from a computer

sound card A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio ...

throughout a building. Being low-powered, most transmitters typically have a short range of , depending on the quality of the receiver, obstructions and elevation. Typically they broadcast on any FM

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

from 87.5 to 108.0

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

in most of the world, 76.0 - 95.0 MHz for Japan, 65.0 - 74.2 MHz for Russia, and 88.1 to 107.9 MHz in the US and Canada.

Uses

Personal FM transmitters are commonly used as a workaround for playing portable audio devices on car radios that don't have an Auxiliary "AUX" input jack or Bluetooth audio connectivity. They are also used to broadcast a stationary audio source, like a computer or a television, around a home. They can also be used for

low-power broadcasting Low-power broadcasting is broadcasting by a broadcast station at a low transmitter power output to a smaller service area than "full power" stations within the same region. It is often distinguished from "micropower broadcasting" (more common ...

and

pirate radio Pirate radio is a radio station that broadcasts without a valid license, whether an invalid license or no license at all. In some cases, radio stations are considered legal where the signal is transmitted, but illegal where the signals are rec ...

but only to a very limited audience in near proximity. They can also be used as a "talking sign" in real estate sales or similar. Devices can be operated by connecting to the audio source or to a proprietary port of a specific device it is made for. In addition, certain devices such as hands-free car kits, navigation tools such as the TomTom GO, mobile phones like some

Nokia Nseries The Nokia Nseries was a high-end lineup of feature phones, smartphones, and tablets marketed by Nokia Corporation from 2005 to 2011. The Nseries devices commonly supported multiple high-speed wireless technologies at the time, such as 3G, or W ...

models, and MP3 players may have FM transmitters built-in, however this has become uncommon.

Legality

The legality and maximum permitted power levels or field strengths of these devices varies by country. In 2006 these devices became legal in most countries in the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...

. In the UK Statutory Instrument IR2030/26/2 2011/0401/UK (from December 2011) permits unlicensed use of devices that can be shown to radiate less than 50 nanowatts (-43dBm), on a 0.2 MHz raster in the range 87.5–108 MHz.

Industry Canada Innovation, Science and Economic Development Canada (ISED; ; )''Innovation, Science and Economic Development Canada'' is the applied title under the Federal Identity Program; the legal title is Department of Industry (). is a department of the G ...

permits transmitters that have an output lower than 100 μV/m at (approximately 1 microwatt output). However, an exception is made for "personal radiocommunication transmitters providing short range transmissions to nearby FM receivers (e.g. FM transmitters integrated in MP3 players) ... without a license." In the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, Part 15 of the

U.S. Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, internet, wi-fi, satellite, and cable across the United States. The FCC maintains ju ...

rules specifies that no license is needed if range of the transmitter does not exceed , although the Part 15 rules specify that the field strength should not exceed 250 μV/m (48db) at 3 meters, which is less than the service contour for commercial stations (60db), necessary for the satisfactory reception of FM stereo. In

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

, no license is needed for devices with a

signal strength In telecommunications, particularly in radio frequency engineering, signal strength is the transmitter power output as received by a reference antenna at a distance from the transmitting antenna. High-powered transmissions, such as those used i ...

of less than 500 μV/m at 3 meters.

References

External links

''Frequently Asked Questions on Low-Power FM Broadcasting from Industry Canada''
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Micro-Broadcasting: ''Getting The Most Out Of Part 15 Radio'' originally published by ''Monitoring Times'', Sept. 2011

''Understanding the FCC Regulations for Low-Power, Non-Licensed Transmitters'' at the FCC. (USA)
IPod accessories Consumer electronics Digital audio players Wireless transmitters Radio hobbies Repurposing

Uses

Legality

See also

References

External links