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microwave radar

November 18, 2011

transmitter to receive programme signals – “…Microwave radiation has lower frequencies and longer wavelengths than visible light. Microwaves with certain wavelengths are absorbed by water molecules and can be used for cooking. Water in the food absorbs the microwave radiation, which causes the water to heat up and cook the food. The water in living cells can also absorb microwave radiation. As a result, they can be killed or damaged by the heat released…Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range. Certain microwave radiation wavelengths pass through the Earth’s atmosphere and can be used to transmit information to and from satellites in orbit. Radio waves have lower frequencies and longer wavelengths than microwaves. They are used to transmit television and radio programmes. Television uses higher frequencies than radio…A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. For low frequency radio waves diffraction can allow them to be received behind hills, although repeater stations are often used to improve the quality of the signals. The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the Ionosphere. This means that they can reach receivers that are not in the line of sight because of the curvature of the Earth’s surface…” (The electromagnetic spectrum)

pulse initiates the ionization – “Radio frequency energy in radar is transmitted in short pulses with time durations that may vary from 1 to 50 microseconds or more. A special modulator is needed to produce this impulse of high voltage. The hydrogen thyratron modulator is the most common radar modulator. It employs a pulse-forming network that is charged up slowly to a high value of voltage. The network is discharged rapidly through a pulse transformer by the thyratron keyer tube to develop an output pulse, The shape and duration of the pulse are determined by the electrical characteristics of the pulse-forming network and of the pulse transformer…As circuit for storing energy the thyratron modulator uses essentially a short section of artificial transmission line which is known as the pulse- forming network (PFN). Via the charging path this PFN is charged on the double voltage of the high voltage power supply with help of the magnetic field of the charging impedance. Simultaneously this charging impedance limits the charging current. The charging diode prevents that the PFN discharge himself about the intrinsic resistance of the power supply again. The function of thyratron is to act as an electronic switch which requires a positive trigger of only 150 volts. The thyratron requires a sharp leading edge for a trigger pulse and depends on a sudden drop in anode voltage (controlled by the pulse- forming network) to terminate the pulse and cut off the tube. The R-C Combination acts as a DC- shield and protect the grid of the thyratron. This trigger pulse initiates the ionization of the complete thyratron by the charging voltage. This ionization allows conduction from the charged pulse-forming network through pulse transformer. The output pulse is then applied to an oscillating device, such as a magnetron…” (Radar Modulator)

electronic pulses from radar – “…Radar is an electronic system that detects and tracks distant objects like aircraft and ships. Radar transmits radio waves (at 300,000 km/sec.), and precisely monitors the electronic echo reflected by objects in the area of the transmission. Aircraft and ships also use electronic pulses from radar to track nearby landmasses when darkness or poor weather make visual navigation difficult or impossible. RCAF radar veterans of the Second World War formed the Canadian Radar History Project to collect and record information about their accomplishments and experiences. This exhibition provides a sampling of the important research these veterans – now in their 70’s and 80’s- have done to ensure that their story will survive for future generations.” (Canadian Radar History)

Radar is an object-detection system which uses electromagnetic waves—specifically radio waves—to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish, or antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave’s energy to a dish or antenna which is usually located at the same site as the transmitter. Practical radar was developed in secrecy during World War II by Britain and other nations. The term RADAR was coined in 1940 by the U.S. Navy as an acronym for radio detection and ranging. The term radar has since entered the English and other languages as the common noun radar, losing all capitalization. In the United Kingdom, the technology was initially called RDF (range and direction finding), using the same initials used for radio direction finding to conceal its ranging capability. The modern uses of radar are highly diverse, including air traffic control, radar astronomy, air-defense systems, antimissile systems; nautical radars to locate landmarks and other ships; aircraft anticollision systems; ocean-surveillance systems, outer-space surveillance and rendezvous systems; meteorological precipitation monitoring; altimetry and flight-control systems; guided-missile target-locating systems; and ground-penetrating radar for geological observations. High tech radar systems are associated with digital signal processing and are capable of extracting objects from very high noise levels. Other systems similar to radar have been used in other parts of the electromagnetic spectrum. One example is “lidar”, which uses visible light from lasers rather than radio waves (Wikepedia).

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