Radio altimeter

Radio altimeters are different in execution:

• as an independent station (mobile or stationary);
• as part of the electronic equipment of aircraft;
• three - coordinate radar simultaneously plays the role of an altimeter.

According to the type of radio emission used and the method of its processing, airborne altimeters are divided into two groups:

• frequency modulated (FM) radio altimeters have a measurement range of up to several hundred meters (usually up to 1,500 m) and are used mainly when the aircraft approaches;
• pulse height modulation (IM) altimeters are designed to measure higher altitudes and are used primarily in military aviation , in space , for aerial photography and for other special purposes.

Onboard

The principle of operation of a radio altimeter is based on determining the propagation time of a radio signal from a transmitting antenna to a reflective surface and vice versa, to a receiving antenna (the basic principle of radar ). The height and delay time of the signal are related by the formula:

where h is the height; t is the delay time; c is the speed of propagation of radio waves (equal to the speed of light ).

The method for determining signal delay depends on its type:

• when using pulse signals, by the usual methods of pulse technology (using analog circuits or digital counters), the time interval between the pulses of the transmitter and receiver is measured;
• with frequency modulation of the radio signal by sawtooth or triangular pulses, the resulting signal is a high-frequency oscillations, with an instantaneous frequency, piecewise linearly changing in time, that is, the delayed signal in the instantaneous frequency is slightly different from the original. When the emitted and received signals are mixed , beats are formed with a frequency equal to the difference in instantaneous frequencies, since the law of change in instantaneous frequency in time is linear, the difference frequency is proportional to the delay. The beat frequency is measured by a frequency meter (analog in old models or digital in new), after which the measurement information is displayed on the indicating device in the form of a distance to the ground.

Ground

The radar determines the distance to the aircraft , the speed and direction of its movement. The altimeter control device calculates the angular velocity of the aircraft relative to the station and begins to rotate the altimeter antenna at the appropriate speed. At the same time, the antenna goes up and down, scanning the space with a narrow beam. Thus, the aircraft elevation angle is calculated. The simplest transformations can determine the height above the ground.

Three-coordinate radars for the same purpose use a large number of rays emitted by several transmitting antennas. This method of finding altitude is less accurate, but after the initial processing, along with the coordinates of the aircraft, its altitude is also given.

The world's first radio altimeter was developed by Bell Laboratories (USA) and demonstrated in New York on October 9, 1938 .

In the USSR, the first mass-produced radio altimeters (RV-2, RV-10 and RV-17) were developed in 1947-1954 . From 1962 to 1965, the TsKB-17 of the Ministry of Aviation Industry developed a high-altitude radio altimeter, which on February 3, 1966, for the first time in the history of astronautics, provided a soft landing of the Luna-9 spacecraft on the lunar surface.

Airborne Altimeters

Mobile radio altimeters

• PRV-9
• PRV-10
• PRV-11
• PRV-13
• PRV-16
• PRV-17

Books

• Lobanov M. M. Development of Soviet radar technology . - M .: Military Publishing, 1982.
• Pestryakov V.V., Kuzenkov V.D. Radio engineering systems. Textbook for high schools . - M.: “Radio and Communications”, 1985.
• Cherdyntsev V.A. Radio engineering systems. Study guide . - Mn .: "Higher school", 1988.
• Silyakov V. A., Gorbatsky V. V., Krasyuk V. N. Detection of reflected signals in search systems for radio altimeters with linear frequency modulation // “Sensors and Systems”. - 2003 . - No. 2.
• Bakulev P.A. Radar systems. Textbook for high schools - M .: "Radio Engineering", 2004.

Regulatory and technical documentation

• GOST 17589-72. Aircraft and helicopter altimeters for altitudes up to 1500 m. Main parameters and technical requirements.
• GOST 28154-89. Low altitude radio altimeters with digital external communications. General technical requirements.
• GOST R 50860-96. Airplanes and helicopters. Antenna-feeder communication devices, navigation, landing and ATC. General technical requirements, parameters, measurement methods.
• Aviation radio communications. International Standards and Recommendations (International Civil Aviation Organization, 1972).
• TO GU1.301.034. Radio altimeters RV-3, RV-3M. Technical Description (1968).
• And GU1.301.034. Radio altimeters RV-3, RV-3M. Operating Instructions (1968).

• Radio range finder
• Radar
• Radio navigation
• Air navigation

• Radio altimeters RV-3, RV-3M
• Issues of Accuracy and Uncertainty in Satellite Altimeria
• To the theory of the World Cup of Altimeter (inaccessible link)
• Funk- und Funkmessausrüstung