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In radio communication, a spurious emission is any component of a radiated radio frequency signal the complete suppression of which would not impair the integrity of the modulation type or the information being transmitted. [1] A radiated signal outside of a transmitter's assigned channel is an example of a spurious emission. [2] Spurious emissions can include harmonic emissions, intermodulation products and frequency conversion products. [3]
Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment. It is also the name given to the associated branch of electrical engineering.
In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference, noise, and jamming, to prevent detection, to limit power flux density, and to enable multiple-access communications.
Conformance testing — an element of conformity assessment, and also known as compliance testing, or type testing — is testing or other activities that determine whether a process, product, or service complies with the requirements of a specification, technical standard, contract, or regulation. Testing is often either logical testing or physical testing. The test procedures may involve other criteria from mathematical testing or chemical testing. Beyond simple conformance, other requirements for efficiency, interoperability or compliance may apply. Conformance testing may be undertaken by the producer of the product or service being assessed, by a user, or by an accredited independent organization, which can sometimes be the author of the standard being used. When testing is accompanied by certification, the products or services may then be advertised as being certified in compliance with the referred technical standard. Manufacturers and suppliers of products and services rely on such certification including listing on the certification body's website, to assure quality to the end user and that competing suppliers are on the same level.
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm ; at 30 Hz the corresponding wavelength is 10,000 km. Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a close, but slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a much higher frequency than the input signal does. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave, or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing. The term originated in radio communication, where the carrier wave creates the waves which carry the information (modulation) through the air from the transmitter to the receiver. The term is also used for an unmodulated emission in the absence of any modulating signal.
Medium frequency (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kilohertz (kHz) to 3 megahertz (MHz). Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the hectometer band as the wavelengths range from ten to one hectometer. Frequencies immediately below MF are denoted low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio broadcasting, navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.
In United States regulatory law, an unintentional radiator is any device that is designed to use radio frequency electrical signals within itself, or sends radio frequency signals over conducting cabling to other equipment, but is not intended to radiate radio frequency energy. An incidental radiator is a device that can generate radio frequency electrical energy even though it is not intentionally designed to do so. Unintentional and incidental radio frequency radiation can interfere with other electronic devices. In the United States, limits on radiated emissions from unintentional and incidental radiators are established by the Federal Communications Commission. Similar regulations have been promulgated by other governments. Reference is usually made in regulations to technical standards established by organizations such as ANSI, IEC and ITU.
A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the varying duration of the on and off periods of the signal, for example by Morse code in early radio. In early wireless telegraphy radio transmission, CW waves were also known as "undamped waves", to distinguish this method from damped wave signals produced by earlier spark gap type transmitters.
A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas—or omnidirectional antennas in general—when greater concentration of radiation in a certain direction is desired.
A variable frequency oscillator (VFO) in electronics is an oscillator whose frequency can be tuned over some range. It is a necessary component in any tunable radio transmitter or receiver that works by the superheterodyne principle, and controls the frequency to which the apparatus is tuned.
A tuned radio frequency receiver is a type of radio receiver that is composed of one or more tuned radio frequency (RF) amplifier stages followed by a detector (demodulator) circuit to extract the audio signal and usually an audio frequency amplifier. This type of receiver was popular in the 1920s. Early examples could be tedious to operate because when tuning in a station each stage had to be individually adjusted to the station's frequency, but later models had ganged tuning, the tuning mechanisms of all stages being linked together, and operated by just one control knob. By the mid 1930s, it was replaced by the superheterodyne receiver patented by Edwin Armstrong.
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data. Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras. EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.
The 80-meter or 3.5 MHz band is a band of radio frequencies allocated for amateur radio use, from 3.5 to 4.0 MHz in IARU Region 2, and generally 3.5 to 3.8 or 3.9 MHz in Regions 1 and 3 respectively. The upper portion of the band, which is usually used for phone (voice), is sometimes referred to as 75 meters. In Europe, 75m is a shortwave broadcast band, with a number of national radio services operating between 3.9 and 4.0 MHz.
In electronics, a local oscillator (LO) is an electronic oscillator used with a mixer to change the frequency of a signal. This frequency conversion process, also called heterodyning, produces the sum and difference frequencies from the frequency of the local oscillator and frequency of the input signal. Processing a signal at a fixed frequency gives a radio receiver improved performance. In many receivers, the function of local oscillator and mixer is combined in one stage called a "converter" - this reduces the space, cost, and power consumption by combining both functions into one active device.
A radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. Radio waves are electromagnetic waves with frequencies between about 30 Hz and 300 GHz. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves. Transmitters are necessary parts of all systems that use radio: radio and television broadcasting, cell phones, wireless networks, radar, two way radios like walkie talkies, radio navigation systems like GPS, remote entry systems, among numerous other uses.
The following outline is provided as an overview of and topical guide to radio:
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by another antenna connected to a radio receiver. Radio is very widely used in modern technology, in radio communication, radar, radio navigation, remote control, remote sensing, and other applications.
An RF module is a (usually) small electronic device used to transmit and/or receive radio signals between two devices. In an embedded system it is often desirable to communicate with another device wirelessly. This wireless communication may be accomplished through optical communication or through radio-frequency (RF) communication. For many applications, the medium of choice is RF since it does not require line of sight. RF communications incorporate a transmitter and a receiver. They are of various types and ranges. Some can transmit up to 500 feet. RF modules are typically fabricated using RF CMOS technology.
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