Aviation Electronics Technician 1 - Historic Naval Ships Association

ias circuit, horizontal and vertical deflection coils,and CRT. Symbols are drawn at the rate of 50 times asecond on the CRT. The rapidly moving electronbeam is generated by the bright-up pulse from thesignal data processor. The bright-up pulse isamplified by the bright-up amplifier, and then appliedto the CRT grid. The CRT, which is normally biasedinto cutoff, is turned on, and an electron beam isemitted. The electron beam strikes the CRT face at aposition determined by the amount of current flowingin the horizontal and vertical deflection coils. Theamount of light (symbol brightness) emitted from theCRT is controlled by the cathode bias circuit. Acontrol voltage from the control panel is applied to thecathode bias circuit, which serves as a referencevoltage for the autobrilliance sensor and the CRTcathode. The voltage output from the autobrilliancesensor is amplified by the autobrilliance amplifier.The output is applied to the cathode bias circuit,which changes the amount of bias (brightness) on theCRT. Thus, an optimum CRT contrast is constantlymaintained under varying ambient light.DEFLECTION MODULE.— The deflectionmodule contains the X and Y deflection amplifiers, Xand Y low amplifiers, X and Y comparators, and oneOR gate. The type and location of each symbol on thecombiner is determined by X and Y analog voltagesapplied to the deflection circuits. As the need for asymbol arises, the busy signal from the HUD issampled by the symbol generator. The busy signal isgenerated any time current is flowing in eitherdeflection coil. Comparators, connected across eachcoil, are used to detect when the deflection coilcurrent is equal to zero. As the current in eitherdeflection coil reaches zero, the output from thecomparator, connected across the coil, goes low.When both comparator outputs are low, the OR gateoutput goes low, and the busy signal is removed fromthe symbol generator input. At the same instant, thesymbol generator applies a precise analog voltage tothe X and Y deflection amplifiers. The output fromthe deflection amplifiers causes current to flow in thedeflection coils. The current amplitude isprecalculated to drive the CRT electron beam to thestart point of the symbol to be drawn. A bright-uppulse is then applied to the bright-up amplifier in thevideo module. At the same instant, the deflectionvoltage is modulated at a predetermined rate andamplitude by the symbol generator. The modulationis detected by the deflection amplifiers and applied toeach deflection coil. A specific part (or all) of asymbol is then drawn on the CRT face in a preciselocation. The bright-up pulse continues long enoughto draw the prescribed line or circle that makes up thesymbol. When the bright-up pulse is removed, theCRT is driven into cutoff until the next bright-uppulse is applied. This process is repeated until allsymbols have been displayed on the CRT.BITE FunctionsBoth the signal data processor and the heads-updisplay unit contain built-in test equipment (BITE).SIGNAL DATA PROCESSOR.— The built-intest equipment contained in the signal data processorconsists of a clock pulse monitor, data test equipment,raw data test equipment, six low-voltage comparators,a signal data processor fail indicator, and a thermaloverload sensor.HEADS-UP DISPLAY UNIT.— The built-in testequipment contained in the HUD unit consists of ahigh-voltage comparator, seven low-voltagecomparators, a bright-up parity circuit, a HUD failindicator, and a thermal overload sensor.SYMBOLOGYThe symbols that are used with the various modesof operation in the F-14 are listed and described infigure 5-9. These symbols give the pilot importantinformation, such as aircraft attitude, heading,altitude, angle-of-attack, and ground track duringflight. Attack information, such as closure rate, rangeto target, maximum range for weapon launch,minimum range for weapon launch, and boresightreference, is available during air-to-air andair-to-ground operations. Ordnance information,such as number of rounds remaining, the type ofweapon selected, and the number of weapons readyfor launch, is also available.DECLUTTERThe system used in the F-14 (AVA-12) has afeature known as declutter. It is used to removepreselected, unwanted symbols from the displayduring certain modes of operation. This feature isespecially important during an air-to-air situation.When the pilot is trying to locate and engage anenemy target, the declutter feature will clear theunnecessary symbols from his/her view.5-10