two major types of deflection systems used to move
the electron beam around the face of the CRT.
Electromagnetic deflection systems use a series of
coils mounted on a yoke to generate a magnetic field.
The strength and polarity of the magnetic field cause
the beam to deflect. Electrostatic deflection systems
use four deflection plates mounted inside the CRT to
move the beam. A voltage is applied to each plate.
The polarity and strength of the voltage determine the
amount and direction the beam is moved.
CRT SCANNING CRT scanning moves the
electron beam around the face of the CRT to create
the display. The two methods of CRT scanning are
raster scanning and vector scanning.
RASTER SCANNING Raster scanning develops
the display by painting a series of lines across the
CRT. There are two types of raster scan: interlaced
scan and noninterlaced scan. Interlaced scan uses a
method of painting all the even lines of a frame from
top to bottom, then returning to the top of the CRT
and painting the odd frames. It is used in television
and low resolution digital monitors. Noninterlaced
scan paints each frame as a series of consecutive
horizontal lines and is used with most digital
monitors. Noninterlaced scan is used to increase the
resolution of the display.
VECTOR SCANNING Vector scan CRTs have
the ability to move the electron beam to any desired
point on the CRT at any time. They are used in
oscilloscopes and many radar display consoles. The
electron beam is moved to the desired location by
using an X/Y coordinate system that defines the exact
location of the beam.
COLOR CATHODE-RAY TUBES The color
CRT works in a very similar manner to the
monochrome CRT. The major difference is that the
color CRT has three electron beams that are
synchronized to strike dyed phosphor dots on the face
of the CRT. These dots are red, blue, and green, the
primary colors of light.
DISPLAYING RADAR SWEEP, VIDEO, AND
SYMBOLS The AN/UYA-4(V) data display group
uses vector scan CRTs in the plan position indicator
(PPI). The PPI is usually under the control of the
radar sweep logic and switches to symbol display
logic when a message is received from the computer.
RADAR SWEEP AND VIDEO Radar sweep
originates in the center of the CRT and travels
outward until the edge of the CRT or the end-of-
sweep signal is reached.
The radar azimuth is
developed by DC and DU pulse trains developed by a
piece of ancillary equipment. Video returns are
displayed as intensified sweep.
SYMBOL GENERATION Symbols are gener-
ated from data messages outputted by the computer.
Two methods of painting symbols are used in the
AN/UYA-4(V) system: the analog waveform method
and the digital stroke method. The analog waveform
method uses a separate piece of equipment called a
symbol generator. The symbol generator decodes the
computer messages and generates X, Y, and Z
waveforms to paint the proper symbo1. The X and Y
waveforms are applied to the CRT deflection plates,
while the Z waveform controls the unblinking of the
electron beam. The digital stroke method stores the
symbol in ROMs or PROMS as digital codes. The
digital stroke symbols are generated by each console
when the console is equipped with the console
internally generated and refreshed symbols (CIGARS)
modification or by a type of symbol generator.
DISPLAY SYSTEMS The Navy currently uses
two major display systems in the fleet: the Data
Display Group AN/UYA-4(V) and the Computer
Display Set AN/UYQ-21(V). Both systems are
designed to provide a real-time display of the tactical
picture using ships sensor data and tactical data from
the CDS computer.