Aviation Electronics Technician 1 - Historic Naval Ships Association

Band-Rejection FiltersA band-rejection (band-stop) filter is used toreject or block a band of frequencies from beingpassed. This filter allows all frequencies above andbelow this band to be passed with little or noattenuation.The band-stop filter circuit consists of inductiveand capacitive networks combined and connected toform a definite frequency response characteristic.The band-stop filter is designed to attenuate a specificfrequency band and to permit the passage of allfrequencies not within this specific band. Thefrequency range over which attenuation or poortransmission of signals occurs is called the“attenuation band.” The frequency range over whichthe passage of signals readily occurs is called the“bandpass.” The lowest frequency at which theattenuation of a signal starts to increase rapidly isknown as the lower cutoff frequency. The highestfrequency at which the attenuation of a signal starts toincrease rapidly is known as the upper cutofffrequency. The basic configurations into which theband-reject filter elements can be arranged orassembled are known as the L- or half-section, theT-section, and the Pi-section configurations. Theseconfigurations are shown in figure 10-14. For a morein-depth discussion on the various filters discussed inthis chapter, you should refer to NAVSHIPS0967-000-0120, (EIMB), section 4.becomes a high impedance. The impedance of such aresonant lead becomes greater without limit as the dcresistance becomes lower. Multiple bonding usingthe same length of bonding jumper increases theimpedance at the resonant frequency, but also tends tosharpen the high-impedance area around the resonantfrequency. This sharpening is done by the rapid fallof impedance on each side of resonance.PURPOSES OF BONDINGBonding must be designed and executed to obtainthe following results:l Protect the aircraft and personnel from hazardsassociated with lightning discharges. Provide power-current and fault-current returnpathsl Provide sufficient homogeneity and stability ofconductivity for RF currents affecting transmissionand reception. Prevent development of ac potentials onconducting frames, enclosures, cables of electricaland electronic equipment, and on conducting objectsadjacent to unshielded transmitting antenna lead-insBONDINGLearning Objective: Identify purposes andtechniques of bonding.Aircraft electrical bonding is defined as theprocess of obtaining the necessary electricalconductivity between all the metallic component partsof the aircraft. Bonding successfully brings all itemsof empennage and internal conduction objects toessentially the same dc voltage level appearing on thebasic structure of the fuselage. However, bonding forradio frequencies is not quite so simple. Only directbonding between affected components canaccomplish the desired results at all frequencies.Only when direct bonding is impossible oroperationally impracticable should bonding jumpersbe used. Regardless of its dc resistance, any length ofconductor has inductive reactance that increasesdirectly with frequency. At a frequency for which thelength of a bond is a quarter wavelength, the bondFigure 10-14.-Examples of band-reject filter circuits10-14