Aviation Electronics Technician 1 - Historic Naval Ships Association

CHAPTER 10ELECTROSTATIC DISCHARGE PROGRAMThe electrical noise generated in a radio or radarreceiver is often confused with electrical noisegenerated external to the receiver and coupled into thereceiver. The internally generated noise is the resultof circuit deficiencies in the receiver itself, and can beeliminated by replacing the defective component orreplacing the entire receiver. Electrical noiseproduced external to the receiver enters the receiverby various means. The noise causes interference inthe receiver, as well as poor reception.In early naval aircraft, electrical noise interferencewas not a major problem because there werefewer external sources of electrical noise. Receiversensitivities were low, and the aircraft controlcomponents were manually operated. In today’saircraft, however, there are considerably moresources of externally generated electrical noise. Theaircraft now contains numerous receivers with highersensitivities, and the aircraft controls are operated byvarious electrical and/or mechanical devices. Thesedevices include control surface drive motors, fuel andhydraulic boost pumps, ac inverters, and cabinpressurization systems. In addition, pulsed electronictransmitters, such as TACAN, radar, and IFF, can besources of electrical noise interference. Listening toelectrical noise interference in the output of a radioreceiver can cause nervous fatigue in aircrewpersonnel. Electrical noise may also reduce theperformance (sensitivity) of the receiver. For thesereasons, electrical noise should be kept at the lowestpossible level.The overall objective of this chapter is to assistyou in recognizing various types of electrical/electronic noise, their effects on radio and radarreceivers, and what the electrostatic dischargeprogram means to you as the work center supervisor.This chapter also provides you with information forkeeping electrical noise interference as low aspossible in electronic equipment aboard navalaircraft.TYPES AND EFFECTS OF RECEIVERNOISE INTERFERENCELearning Objective: Recognize the types andeffects of radio noise, including natural andman-made interference.The types of electrical noise interference thatenter aircraft receivers are broadly categorized asnatural interference and man-made interference.NATURAL INTERFERENCERadio interference caused by natural electricalnoise is separated into three types: atmosphericstatic, precipitation static, and cosmic noise. Eachtype is discussed below.Atmospheric StaticAtmospheric static is a result of the electricalbreakdown between masses (clouds) of oppositelycharged particles in the atmosphere. An extremelylarge electrical breakdown between two clouds orbetween the clouds and ground is called “lightning.”Atmospheric static is completely random in nature,both as to rate of recurrence and as to intensity ofindividual discharges. Atmospheric static producesirregular popping and crackling in audio outputs and“grass” on visual output devices. Its effects rangefrom minor annoyance to complete loss of receiverusefulness. Atmospheric interference is seldom of acrippling intensity at frequencies from 2 MHz to 30MHz, but it can be annoying. Above 30 MHz, thenoise intensity decreases to a very low level. Atfrequencies below 2 MHz, natural static is theprincipal limiting factor on usable receiver sensitivity.The intensity of atmospheric static varies withlocation, season, weather, time of day, and thefrequency to which the receiver is tuned. It is mostintense at the lower latitudes, during the summerseason, during weather squalls, and at the lower radiofrequencies. Many schemes have been devised tominimize the effects of atmospheric static. However,the best technique is to avoid those frequenciesassociated with intense static, if possible.10-1