Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
Radar is a system that uses radio waves to determine the distance (ranging), direction, and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain.
In wireless communications, fading refers to the variation of signal attenuation over variables like time, geographical position, and radio frequency. Fading is often modeled as a random process. In wireless systems, fading may either be due to multipath propagation, referred to as multipath-induced fading, weather, or shadowing from obstacles affecting the wave propagation, sometimes referred to as shadow fading.
MISTRAM was a high-resolution tracking system used by the United States Air Force to provide highly detailed trajectory analysis of rocket launches.
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters. Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.
A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it.
Very High Frequency Omnidirectional Range Station (VOR) is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons. It uses frequencies in the very high frequency (VHF) band from 108.00 to 117.95 MHz. Developed in the United States beginning in 1937 and deployed by 1946, VOR became the standard air navigational system in the world, used by both commercial and general aviation, until supplanted by satellite navigation systems such as GPS in the early 21st century. As such, VOR stations are being gradually decommissioned. In 2000 there were about 3,000 VOR stations operating around the world, including 1,033 in the US, but by 2013 the number in the US had been reduced to 967. The United States is decommissioning approximately half of its VOR stations and other legacy navigation aids as part of a move to performance-based navigation, while still retaining a "Minimum Operational Network" of VOR stations as a backup to GPS. In 2015, the UK planned to reduce the number of stations from 44 to 19 by 2020.
In aviation, distance measuring equipment (DME) is a radio navigation technology that measures the slant range (distance) between an aircraft and a ground station by timing the propagation delay of radio signals in the frequency band between 960 and 1215 megahertz (MHz). Line-of-visibility between the aircraft and ground station is required. An interrogator (airborne) initiates an exchange by transmitting a pulse pair, on an assigned 'channel', to the transponder ground station. The channel assignment specifies the carrier frequency and the spacing between the pulses. After a known delay, the transponder replies by transmitting a pulse pair on a frequency that is offset from the interrogation frequency by 63 MHz and having specified separation.
A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics.
Continuous-wave radar is a type of radar system where a known stable frequency continuous wave radio energy is transmitted and then received from any reflecting objects. Individual objects can be detected using the Doppler effect, which causes the received signal to have a different frequency from the transmitted signal, allowing it to be detected by filtering out the transmitted frequency.
An amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Many repeaters are located on hilltops or on tall buildings as the higher location increases their coverage area, sometimes referred to as the radio horizon, or "footprint". Amateur radio repeaters are similar in concept to those used by public safety entities, businesses, government, military, and more. Amateur radio repeaters may even use commercially packaged repeater systems that have been adjusted to operate within amateur radio frequency bands, but more often amateur repeaters are assembled from receivers, transmitters, controllers, power supplies, antennas, and other components, from various sources.
The UDOP multistatic radar and multiradar system (MSRS) utilizes Doppler radar for missile tracking and trajectory measurement. A target is illuminated at 450 MHz. Five receiving stations, located along the baselines with the lengths from 40 to 120 km, receive signals from the target's transponder at 900 MHz. These five stations yield slant-range rate. To compute the range or position, an initial position is required from some other tracking system. The random error is 6 cm (2.4 in), but total error includes the systematic error of 2.7 m (8.9 ft) plus the initial error. UDOP had relatively low cost compared with other high-accuracy systems. In the US, MSRS has found important application in the precision measurement of missile trajectories at the Air Force Eastern Test Range, which extends from the Florida mainland to the Indian Ocean. These MSRSs include the AZUSA, the MISTRAM, and the UDOP. All systems employ a cooperative beacon transponder on the observed target and a ground-based transmitting station with several receiving stations at separate, precisely located sites.
The AN/FPS-16 is a highly accurate ground-based monopulse single object tracking radar (SOTR), used extensively by the NASA crewed space program, the U.S. Air Force and the U.S. Army. The accuracy of Radar Set AN/FPS-16 is such that the position data obtained from point-source targets has azimuth and elevation angular errors of less than 0.1 milliradian and range errors of less than 5 yards (5 m) with a signal-to-noise ratio of 20 decibels or greater.
Radar engineering is the design of technical aspects pertaining to the components of a radar and their ability to detect the return energy from moving scatterers — determining an object's position or obstruction in the environment. This includes field of view in terms of solid angle and maximum unambiguous range and velocity, as well as angular, range and velocity resolution. Radar sensors are classified by application, architecture, radar mode, platform, and propagation window.
A communications satellite's transponder is the series of interconnected units that form a communications channel between the receiving and the transmitting antennas. It is mainly used in satellite communication to transfer the received signals.
Radio is the technology of 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. They are received by another antenna connected to a radio receiver. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.
A radio science subsystem (RSS) is a subsystem placed on board a spacecraft for radio science purposes.
The Unified S-band (USB) system is a tracking and communication system developed for the Apollo program by NASA and the Jet Propulsion Laboratory (JPL). It operated in the S band portion of the microwave spectrum, unifying voice communications, television, telemetry, command, tracking and ranging into a single system to save size and weight and simplify operations. The USB ground network was managed by the Goddard Space Flight Center (GSFC). Commercial contractors included Collins Radio, Blaw-Knox, Motorola and Energy Systems.
Explorer 29, also called GEOS 1 or GEOS A, acronym to Geodetic Earth Orbiting Satellite, was a NASA satellite launched as part of the Explorer program, being the first of the two satellites GEOS. Explorer 29 was launched on 6 November 1965 from Cape Canaveral, Florida, with a Thor-Delta E launch vehicle.
Explorer 36 was a NASA satellite launched as part of the Explorer program, being the second of the two satellites GEOS. Explorer 36 was launched on 11 January 1968 from Vandenberg Air Force Base, with Thor-Delta E1 launch vehicle.
