Radar viewer
A radar viewer (also popularly referred to as a radar screen ) is a screen display of analog echo signals from radars or data or symbols digitized therefrom. It is intended to display a graphic representation of the position of the radar targets in real time that is as easy to grasp as possible and as true to scale as possible . If possible, additional information such as the identifier or the identification of the target is also displayed.
There are different versions of display devices, the names of which have historically originated and were mostly taken from the English-speaking area:
A-scope
The A-Scope has a one-dimensional display and only shows the distance of the echoes, usually only for one direction. It is the oldest form of the vision device. With the first radar devices, they only wanted to prove the presence and distance of objects. Thus an A-scope was completely sufficient. At the moment of sending, the electron beam starts from the left side and moves to the right at a constant speed. When the receiver receives an echo, the electron beam is deflected upwards. Due to the reflections on the ground, there is a lot of noise in the close range, which is best seen on the A-Scope. The simplest form of the A-scope would be an oscilloscope , which is connected to the video output of the radar receiver.
The name “A-scope” (or sometimes “A-picture”) is derived from the type of modulation of the display: here the amplitude-modulated deflection.
B-scope
The B-scope (and all following types of display devices) use brightness modulation for display. From the English name Brightness Brightness is the name B-scope deduced. The brightness modulation enabled the surface of the screen to display two-dimensional coordinates. In a B-scope in which is the abscissa of the azimuth angle (azimuth) and plotted in the ordinate the distance. The information as to whether a target is present (and if so: where) was represented by a brightly lit spot. This form of vision device is preferred for fire control radar devices .
The azimuth values can usually be shifted using handwheels (the entire antenna is then rotated in the new direction). The center of the screen is usually the main receiving direction of the antenna. The lateral angle range is covered by an electromechanical or electronic beam swiveling.
C-scope
The C-scope shows the directions of elevation angle on the ordinate and side angle on the abscissa . It is a particularly suitable representation for aiming and was therefore used in fighter planes. However, no distance could be displayed, which is why a J-scope was usually used in addition to the C-scope.
E-scope
The E-Scope was used as a height viewing device in old analog radar devices. It indicated the distance on the abscissa and the elevation angle on the ordinate . The target height could mostly be determined with the help of a nomogram on the viewing device.
J-scope
The J-scope is an outdated display device for displaying distances in historical radar devices, for example in the FuG 212 ( "Lichtenstein" device ), the radar device in the German night fighter Bf 110 G-4 . It is an A-scope with a circular deflection. Due to the circular arrangement of the deflection beam, the diameter of the cathode ray tube was used about three times better than with the A-scope. This brought an improvement in the range resolution and accuracy.
RHI-scope
The RHI-Scope ( R reasonable H eight- I ndicator) has a two-dimensional view and shows the level and the distance of the planes for a direction. In the past it was often used together with an A-scope on the approach controller. The RHI-Scope is basically an A-Scope that moves synchronously with the joint of the antenna , which means it can move up and down like this. The echoes are shown here as differences in brightness, not as a deflection, as with the A-Scope.
PPI scope
The PPI-Scope ( P LAN P osition- I ndicator) has a two-dimensional view and shows the distance and direction for all echoes. It is the classic form of the viewing device. With a deliberately long afterglow period on the screen, you can also see the last positions of the target (the so-called “afterglow trail”, formed by the slowly fading light spots of the same portable target, received during the previous antenna revolutions). In practice, the sweep (the line of the current position of the antenna) is set so dark that the user can no longer see it because it only has a disruptive effect due to the long persistence. The sweep visualization practically corresponds to an A-scope, which rotates around the center and, like the B-scope, shows the echoes as bright points.
With a few exceptions, the top of the PPI scope is always north. However, if the radar is vehicle or aircraft-related (navigation radar), a distinction is also made between head-up (vehicle longitudinal axis or front is up) and north-up (north direction is up; compass data must be included in the display for this) ) or a course-up display in which a selectable azimuth value (usually the target course of the vehicle) is at the top and thus, if necessary, a path deviation from the specified course is made visible. Furthermore, navigation radar systems often offer the so-called true-motion display, in which the origin of the sweep moves along the vehicle path on the screen.
An ( analog ) PPI scope was originally always a cathode ray tube (CRT), around which a rotating ring is placed on which a deflection coil sits. The position of the antenna and the position of the coil are synchronized so that the electron beam is radially deflected from the center of the screen synchronously with the transmission pulse and is brightly controlled while a radar echo is received. The distance and direction marks are generated by the same electron beam, whose brightness is modulated for this purpose. Usually the markings are not quite as bright as the echoes, the luminous intensity of which corresponds to the strength of the received signal.
At the time the radar was invented in World War II, the German name for such a viewing device was “Sternschreiber”. There was also an optical solution, the so-called "Seeburg table" in which instead of the cathode ray tube a bright, sharp point of light was controlled from below on a glass table covered with a general staff card.
In the case of pixel-oriented or digital displays currently in use , specific display properties of a classic PPI scope (based on CRT) are simulated using computer algorithms - for example, the display of the sweep, the adjustable brightness of displayed distance rings and direction vectors and the particularly long one or more rotations The afterglow behavior of the phosphor layer used in conventional radar picture tubes persists in the radar antenna. The latter, in particular, is intended to make it easier for the radar operator to visually differentiate between stationary and moving targets relative to one's own vehicle (or position).
Beta scan scope
The Beta Scan Scope displays the information determined by a precision approach radar in two separate "images" based on right-angled coordinates. The upper picture is a side view with the imaginary line of the landing approach up to the touchdown point on the runway as a reference line. This upper picture shows the data obtained by the antenna for height scanning. It is therefore also called an elevation image.
Correspondingly, the top view of the imaginary extension of the center line of the runway, the touchdown point and the distance marks is shown in the picture below. This picture below shows the data captured by the horizontal sector scan antenna. It is therefore also referred to as an azimuth image.
Raster scan scope
The synthetic display (or raster scan scope ) is a representation of the radar information in the style of a television screen. This form of data display is completely artificial and is the only display that not only contains distance and direction, but also additional information such as the altitude of the flight destination, geographic information and virtually any other desired information. Depending on the version, it can also be switched to pure RHI or A-Scope. Due to the synthetic representation, only a small area can be zoomed out without any problems or data from other radar devices can be switched on, with which an area of any size can be shown on a display. With a weather radar you can show the level of cloud cover in color, and thus distinguish a thunderstorm from a light rain area. Synthetic displays are usually generated by a computer, which can then make this data available to other computers via a LAN or WAN . For example, some data from the German armed forces are also made available to German air traffic control .
Due to its flexibility, the synthetic display will replace the remaining PPI and RHI scopes in the future. The A-Scope will continue to exist for some time as an aid for the technician.