Garmin GMA 1347D-00 Installation Manual

Page 2-6 GMA 1347D Installation ManualRevision C 190-00303-212.7 Installation Approval Considerations for Pressurized AircraftAntenna and cable installations on pressurized cabin aircraft require FAA approved installation designand engineering substantiation data whenever such installations incorporate alteration (penetration) of thecabin pressure vessel by connector holes and/or mounting arrangements.For needed engineering support pertaining to the design and approval of such pressurized aircraft antennainstallations, it is recommended that the installer proceed according to any of the following listedalternatives:1. Obtain approved antenna installation design data from the aircraft manufacturer.2. Obtain an FAA approved Supplemental Type Certificate (STC) pertaining to and valid for thesubject antenna installation.3. Contact the FAA Aircraft Certification Office in the appropriate Region and request identificationof FAA Designated Engineering Representatives (DERs) who are authorized to prepare andapprove the required antenna installation engineering data.4. Obtain FAA Advisory Circular AC-183C and select (and contact) a DER from the roster ofindividuals identified thereunder.5. Contact an aviation industry organization such as the Aircraft Electronics Association and requesttheir assistance.2.8 Electrical NoiseBecause the audio panel is a point in the aircraft where signals from many pieces of equipment arebrought together, take care to minimize effects from coupled interference and ground loops.Coupled interference can sneak into audio system interconnecting cables when they are routed near largeAC electric fields, AC voltage sources and pulse equipment (strobes, spark plugs, magnetos, EL displays,CRTs, etc). Interference can also couple into audio system interconnecting cables by magnetic inductionwhen they are routed near large AC current-carrying conductors or switched DC equipment (heaters,solenoids, fans, autopilot servos, etc).Ground loops are created when there is more than one path in which return currents flow or when signalreturns share the same path as large currents from other equipment. These large currents createdifferences in ground potential between the various equipment operating in the aircraft. These differencesin potential can produce an additive effect on audio panel input signals.The audio panel may “see” the desired input signal plus an unwanted component injected by grounddifferentials, a common cause of alternator-related noise. This is the main reason why all audio jacksshould be isolated from ground. Terminating audio shields just at one end eliminates another potentialground loop injection point.Single-point grounding cannot be overstressed for the various avionics producing and processing audiosignals. Single-point, in this context, means that the various pieces of equipment share a single commonground connection back to the airframe. Good aircraft electrical/charging system ground bonding is alsoimportant.The wiring diagrams and accompanying notes in this manual should be followed closely to minimizenoise effects.