Radio frequency in the context of Cable TV

Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. The abbreviations AC and DC are often used to mean simply alternating and direct, respectively, as when they modify current or voltage.

The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa (the full period is called a cycle). "Alternating current" most commonly refers to power distribution, but a wide range of other applications are technically alternating current although it is less common to describe them by that term. In many applications, like guitar amplifiers, different waveforms are used, such as triangular waves or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission.

A mobile phone or cell phone is a portable wireless telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones (landline phones). This radio frequency link connects to the switching systems of a mobile phone operator, providing access to the public switched telephone network (PSTN). Modern mobile telephony relies on a cellular network architecture, which is why mobile phones are often referred to as 'cell phones' in North America.

Beyond traditional voice communication, digital mobile phones have evolved to support a wide range of additional services. These include text messaging, multimedia messaging, email, and internet access (via LTE, 5G NR or Wi-Fi), as well as short-range wireless technologies like Bluetooth, infrared, and ultra-wideband (UWB).

Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broadcast television, in which the television signal is transmitted over-the-air by radio waves and received by a television antenna, or satellite television, in which the television signal is transmitted over-the-air by radio waves from a communications satellite and received by a satellite dish on the roof. FM radio programming, high-speed Internet, telephone services, and similar non-television services may also be provided through these cables. Analog television was standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operation.

A cable channel (sometimes known as a cable network) is a television network available via cable television. Many of the same channels are distributed through satellite television. Alternative terms include non-broadcast channel or programming service, the latter being mainly used in legal contexts. The abbreviation CATV is used in the US for cable television and originally stood for community antenna television, from cable television's origins in 1948; in areas where over-the-air TV reception was limited by distance from transmitters or mountainous terrain, large community antennas were constructed, and cable was run from them to individual homes.

In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves (electromagnetic waves of radio frequency) and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The receiver uses electronic filters to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier to increase the power of the signal for further processing, and finally recovers the desired information through demodulation.

Radio receivers are essential components of all systems based on radio technology. The information produced by the receiver may be in the form of sound, video (television), or digital data. A radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar type of radio receiver for most people is a broadcast radio receiver, which reproduces sound transmitted by radio broadcasting stations, historically the first mass-market radio application. A broadcast receiver is commonly called a "radio". However radio receivers are very widely used in other areas of modern technology, in televisions, cell phones, wireless modems, radio clocks and other components of communications, remote control, and wireless networking systems.

In radio reception, radio noise (commonly referred to as radio static) is unwanted random radio frequency electrical signals, fluctuating voltages, always present in a radio receiver in addition to the desired radio signal.

Radio noise is a combination of natural electromagnetic atmospheric noise ("spherics", static) created by electrical processes in the atmosphere like lightning; human-made radio frequency interference (RFI) from other electrical devices picked up by the receiver's antenna; and thermal noise present in the receiver input circuits, mostly caused by the random thermal motion of molecules inside resistors.

A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum, just as optical telescopes are used to make observations in the visible portion of the spectrum in traditional optical astronomy. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.

Since astronomical radio sources such as planets, stars, nebulas and galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio telescopes are typically large parabolic ("dish") antennas similar to those employed in tracking and communicating with satellites and space probes. They may be used individually or linked together electronically in an array. Radio observatories are preferentially located far from major centers of population to avoid electromagnetic interference (EMI) from radio, television, radar, motor vehicles, and other man-made electronic devices.

Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy.

Photon energy can be expressed using any energy unit. Among the units commonly used to denote photon energy are the electronvolt (eV) and the joule (as well as its multiples, such as the microjoule). As one joule equals 6.24×10 eV, the larger units may be more useful in denoting the energy of photons with higher frequency and higher energy, such as gamma rays, as opposed to lower energy photons as in the optical and radio frequency regions of the electromagnetic spectrum.

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 transmission to a radio receiver. 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 component parts of all electronic devices that communicate by radio, such as radio (audio) and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, ships, spacecraft, radar sets and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not usually called transmitters, even though they often have similar circuits.

Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes and horn antennas, so they are used for point-to-point communication and data links and for radar. This frequency range is used for most radar transmitters, wireless LANs, satellite communication, microwave radio relay links, satellite phones (S band), and numerous short range terrestrial data links. They are also used for heating in industrial microwave heating, medical diathermy, microwave hyperthermy to treat cancer, and to cook food in microwave ovens.

Frequencies in the SHF range are often referred to by their IEEE radar band designations: S, C, X, K_u, K, or K_a band, or by similar NATO or EU designations.

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic field. This re-orientation occurs with absorption of electromagnetic radiation in the radio frequency region from roughly 4 to 900 MHz, which depends on the isotopic nature of the nucleus and increases proportionally to the strength of the external magnetic field. Notably, the resonance frequency of each NMR-active nucleus depends on its chemical environment. As a result, NMR spectra provide information about individual functional groups present in the sample, as well as about connections between nearby nuclei in the same molecule. As the NMR spectra are unique or highly characteristic to individual compounds and functional groups, NMR spectroscopy is one of the most important methods to identify molecular structures, particularly of organic compounds.

The principle of NMR usually involves three sequential steps:

Dielectric heating, also known as electronic heating, radio frequency heating, and high-frequency heating, is the process in which a radio frequency (RF) alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is caused by molecular dipole rotation within the dielectric.

In navigation, a radio beacon or radiobeacon is a kind of beacon, a device that marks a fixed location and allows direction-finding equipment to find relative bearing. It is a fixed-position radio transmitter which radiates radio waves which are received by navigation instruments on ships, aircraft or vehicles.

The beacon transmits a continuous or periodic radio signal on a specified radio frequency containing limited information (for example, its identification or location). Occasionally, the beacon's transmission includes other information, such as telemetric or meteorological data.

A television channel, or TV channel, is a terrestrial frequency or allocated number over which a television station or television network is distributed. For example, in North America, channel 2 refers to the terrestrial or cable band of 54 to 60 MHz, with carrier frequencies of 55.25 MHz for NTSC analog video (VSB) and 59.75 MHz for analog audio (FM), or 55.31 MHz for digital ATSC (8VSB). Channels may be shared by many different television stations or cable-distributed channels depending on the location and service provider.

Depending on the multinational bandplan for a given region, analog television channels are typically 6, 7, or 8 MHz in bandwidth, and therefore television channel frequencies vary as well. Channel numbering is also different. Digital terrestrial television channels are the same as their analog predecessors for legacy reasons, however through multiplexing, each physical radio frequency (RF) channel can carry several digital subchannels. On satellites, each transponder normally carries one channel, however multiple small, independent channels can be on one transponder, with some loss of bandwidth due to the need for guard bands between unrelated transmissions. ISDB, used in Japan and Brazil, has a similar segmented mode.

Wafer fabrication is a procedure composed of many repeated sequential processes to produce complete electrical or photonic circuits on semiconductor wafers in a semiconductor device fabrication process. Examples include production of radio frequency (RF) amplifiers, LEDs, optical computer components, and microprocessors for computers. Wafer fabrication is used to build components with the necessary electrical structures.

The main process begins with integrated circuit design, where electrical engineers designing the circuit and defining its functions, and specifying the signals, inputs/outputs and voltages needed. These electrical circuit specifications are entered into electrical circuit design software, such as SPICE, and then imported into circuit layout programs, which are similar to ones used for computer aided design. This is necessary for the layers to be defined for photomask production. The resolution of the circuits increases rapidly with each step in design, as the scale of the circuits at the start of the design process is already being measured in fractions of micrometers. Each step thus increases circuit density for a given area.

Electronic tagging is a form of surveillance that uses an electronic device affixed to a person to monitor their location or physiological state. It is a specific application of asset tracking technology where the "asset" being monitored is a person.

In some jurisdictions, an electronic tag fitted above the ankle is used for individuals as part of their bail or probation conditions. It is also used in healthcare settings and in immigration contexts. Electronic tagging can be used in combination with a GPS tracking unit for wide-area monitoring, but for short-range monitoring of a person, radio frequency technology is often used.