IFF — identification, friend or foe

Originated in WWII for just mat purpose — a way for our radars to identify friend

aircraft from enemy aircraft by assigning a unique identifier code to friend aircraft tran­sponders.

The system is considered a secondary radar system since it operates completely dif­ferently and independently of the primary radar system that tracks aircraft skin returns only, although the same CRT display is frequently used for both.

The system was initially intended to distinguish between enemy and friend but has evolved such that the term «IFF» commonly refers to all modes of operation, including civil and foreign aircraft use.

There are four major modes of operation currently in use by military aircraft plus one submode. Mode 1 is a nonsecure low cost method used by ships to track aircraft and other ships. Mode 2 is used by aircraft to make carrier controlled approaches to ships during inclement weather. Mode 3 is the standard system also used by commercial aircraft to relay their position to ground controllers throughout the world for air traffic control (АТС). Mode 4 is secure encrypted IFF (the only true method of determining friend or foe) Mode «C» is the altitude encoder.

The non-secure codes are manually set by the pilot but assigned by the air traffic controller.

A cross-band beacon is used, which simply means that the interrogation pulses are at one frequency and the reply pulses are at a different frequency. 1030 MHz and 1090 MHz is a popular frequency pair used in the U.S.

The secondary radar transmits a series of selectable coded pulses. The aircraft tran­sponder receives and decodes the interrogation pulses. If the interrogation code is cor­rect, the aircraft transponder transmits a different series of coded pulses as a reply.

The advantage of the transponder is that the coded pulses «squawked» (передавать сигналы ответчика) by the aircraft transponders after being interrogated might typi­cally be transmitted at a 10 watt ERP (effective radiated power), which is much stronger than the microwatt skin return to the primary radar. Input power levels may be on the order of several hundred watts.

The transponder antenna is low gain (с малым усилением) so that it can receive and reply to a radar from any direction.

An adjunct to the IFF beacon is the altitude encoding transponder known as mode С — all commercial and military aircraft have them, but a fair percentage of general aviation light aircraft do not because of cost. The number of transponder installations rises around many large metropolitan areas where they are required for safety (easier identification of aircraft radar tracks).

Air traffic control primary radars are similar to the two dimensional search radar (working in azimuth and range only) and cannot measure altitude.

Радиолокационная станция (РЛС), (радиолокатор, радар), устройство для на­блюдения за различными объектами (целями) методами радиолокации. Основные узлы РЛС — передающее и приёмное устройства, расположенные в одном пунк­те (т. е. совмещенная РЛС) или в пунктах, удалённых друг от друга на некоторое (обычно значительное) расстояние (двух — и многопозиционные РЛС); в РЛС, применяемых для пассивной радиолокации, передатчик отсутствует. Антенна мо­жет быть общей для передатчика и приёмника (у совмещенной РЛС) или могут применяться раздельные антенны (у многопозиционных РЛС). Важная составная часть приёмного устройства РЛС (после собственно приёмника) — световой ин­дикатор на электроннолучевой трубке (ЭЛТ), а в современных (середины 70-х гг.) РЛС наряду с индикатором — ЦВМ, автоматизирующая многие операции по об­работке принятых сигналов. Основные характеристики РЛС: точность измерений, разрешающая способность, предельные значения ряда параметров (максимальная и минимальная дальность действия, сектор и время обзора и др.), помехоустойчи­вость. К основным характеристикам относят также мобильность РЛС, её массу, габариты, мощность электрогаггания, срок службы, количество обслуживающего персонала и многие др. эксплуатационные параметры.

Основные типы РЛС. РЛС различают прежде всего по конкретным задачам, выполняемым ими автономно или в комплексе средств, с которыми они взаимо­действуют, например: РЛС систем управления воздушным движением, РЛС обна­ружения или наведения зенитных управляемых ракет систем ПВО, РЛС для поис­ка космических летательных аппаратов (КЛА) и сближения с ними, самолётные РЛС кругового или бокового обзора и т.д. Специфика решения отдельных задач и их широкий спектр привели к большому разнообразию типов РЛС. Например, для повышения точности стрельбы по самолётам в головках зенитных снарядов устанавливают миниатюрные РЛС, измеряющие расстояние от снаряда до объек­та и приводящие в действие (на определённом расстоянии) взрыватель снаряда; для своевременного предупреждения самолёта о приближении со стороны его «хвоста» др. самолёта на нём устанавливают РЛС «защиты хвоста», автоматичес­ки вырабатывающую предупредительный сигнал.

В зависимости от места установки РЛС различают наземные, морские, са­молётные, спутниковые РЛС и т.д. РЛС подразделяют также по техническим ха­рактеристикам: по несущей частоте (рабочему диапазону длин волн) — на РЛС метрового, дециметрового (ДМ), сантиметрового (СМ), миллиметрового (ММ) и др. диапазонов; по методам и режимам работы — на РЛС импульсные и с не­прерывным излучением, когерентные и с некогерентным режимом работы и т.д.; по параметрам важнейших узлов РЛС — передатчика, приёмника, антенны и сис­темы обработки принятых сигналов, а также по др. техническим и тактическим параметрам РЛС.

 

 

LESSON # 4

RADAR GUN

 

To understand how radar detectors work, you first have to know what they're de­tecting. The-concept of measuring vehicle speed with radar is very simple. A basic speed gun is just a radio transmitter and receiver combined into one unit A radio transmitter is a device that oscillates an electrical current so the voltage goes up and down at a certain frequency. This electricity generates electromagnetic energy, and when the current is oscillated, the energy travels through the air as an electromagnetic wave. A transmitter also has an amplifier that increases the intensity of the electromagnetic energy and an antenna that broadcasts it into the air.

A radio receiver is just the reverse of the transmitter. It picks up electromagnetic waves with an antenna and converts them back into an electrical current At its heart, this is all radio is — the transmission of electromagnetic waves through space.

Radar is the use of radio waves to detect and monitor various objects. The simplest junction of radar is to tell you how far away an object is. To do this, the radar device emits a concentrated radio wave and listens for any echo. If there is an object in the path of the radio wave, it will reflect some of the electromagnetic energy, and the radio wave will bounce back to the radar device. Radio waves move through the air at a constant speed (the speed of light), so the radar device can calculate how far away the object is based on how long it takes the radio signal to return.

Radar can also be used to measure the speed of an object, due to a phenomenon called Doppler shift. Like sound waves, radio waves have a certain frequency, the num­ber of oscillations per unit of time. When the radar gun and the car are both standing still, the echo will have the same wave frequency as the original signal. Bach part of the signal is reflected when it reaches the car, mirroring the original signal exactly.

But when the car is moving, each part of the radio signal is reflected at a different point in space, which changes the wave pattern. When the car is moving away from the radar gun, the second segment of the signal has to travel a greater distance to reach the car than the first segment of the signal. As you can see in the diagram below, this has the effect of «stretching out» the wave, or lowering its frequency. If the car is moving toward the radar gun, the second segment of the wave travels a shorter distance than the first segment before being reflected. As a result, the peaks and valleys of the wave get squeezed together The frequency increases.

Based on how much the frequency changes, a radar gun can calculate how quickly a car is moving toward it or away from it. If the radar gun is used inside a moving police car, its own movement must also be factored in. For example, if the police car is going 50 miles per hour and the gun detects that the target is moving away at 20 miles per hour, the target must be driving at 70 miles per hour. If the radar gun determines that the target is not moving toward or away from the police car, than the target is driving at exactly 50 miles per hour.

 

Radar (speed) gun — радиолокационный измеритель скорости

Radar detector— радарный детектор, антирадар

 

Translate the following text:

Radar system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, the principle of radar is not confined to any particular frequency range. There are some radar units that operate on frequencies well below 100 megahertz (megacycles) and others that operate in the infrared range and above. The term radar, an acronym for radio detection and ranging, is also used to denote the ap­paratus for implementing the technique.

 

Principles of Radar

Radar involves the transmission of pulses of electromagnetic waves by means of a directional antenna; some of the pulses are reflected by objects that intercept them. The reflections are picked up by a receiver, processed electronically, and converted into visible form by means of a cathode-ray tube. The range of the object is determined by measuring the time it takes for the radar signal to reach the object and return. The object's location with respect to the radar unit is determined from the direction in which the pulse was received. In most radar units the beam of pulses is continuously rotated at a constant speed, or it is scanned (swung back and forth) over a sector, also at a constant rate. The velocity of the object is measured by applying the Doppler principle: if the object is approaching the radar unit, the frequency of the returned signal is greater than the frequency of the transmitted signal; if the object is receding from the radar unit, the returned frequency is less; and if the object is not moving relative to the radar unit, the return signal will have the same frequency as the transmitted signal.

Applications of Radar

The information secured by radar includes the position and velocity of the object with respect to the radar unit. In some advanced systems the shape of the object may also be determined. Commercial airliners are equipped with radar devices that warn of obstacles in or approaching their path and give accurate altitude readings. Planes can land in fog at airports equipped with radar-assisted ground-controlled approach (GCA) systems, in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot. A ground-based radar system for guiding and landing aircraft by remote control was developed in 1960.

Radar is also used to measure distances and map geographical areas (shoran) and to navigate and fix positions at sea. Meteorologists use radar to monitor precipitation; it has become the primary tool for short-term weather forecasting and is also used to watch for severe weather such as thunderstorms and tornados. Radar can be used to study the planets and the solar ionosphere and to trace solar flares and other moving particles in outer space.

Various radar tracking and surveillance systems are used for scientific study and for defense. For the defense of North America the U. S. government developed (c. 1959—63) a radar network known as the Ballistic Missile Early Warning System (BMEWS), with radar installations in Thule, Greenland; Clear, Alaska; and Yorkshire, England. A radar system known as Space Detention and Tracking System (SPADATS), operated collab­oratively by the Canada and the U. S., is used to track earth-orbiting artificial satellites.

 

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