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Sierra Academy of Aeronautics IR GroundLesson 3ADF Nondirectional Radio Beacons(NDBs)n nNDBs transmit in the low/medium frequency range between 190 to 535 kHzn nNDBs are not limited to line of sightn nNDB signals travel both as ground waves that penetrate obstacles and as sky waves that are refracted by the ionosphereNondirectional Radio Beacons(NDBs)n nGround waves&Sky wavesGround waves&Sky wavesNDBs are grouped into 4 classesNDB aircraft componentsn n2 antennas:Sense 2 antennas:Sense and Loopand Loopn nAutomatic direction Automatic direction Finder(ADF)uses Finder(ADF)uses both antennas to both antennas to determine relative determine relative position to NDBposition to NDBNDB aircraft components cont.n nLoop AntennaThe loop antenna senses direction of the station The loop antenna senses direction of the station but cannot determine whether the station is but cannot determine whether the station is behind or ahead,or to the left or right.behind or ahead,or to the left or right.n nIt breaks down all possibilities to 2.It breaks down all possibilities to 2.360 or 180360 or 180270 or 90270 or 90020 or 200020 or 200n nSense AntennaThe sense antenna solves the ambiguityThe sense antenna solves the ambiguityNDB aircraft components cont.n nThe ADF receiver may have several function switchesThe ADF receiver may have several function switches ADF:Operates as automatic direction finder using ADF:Operates as automatic direction finder using both antennas(normal mode)both antennas(normal mode)REC/ANT:Receiver provides maximum sensitivity to REC/ANT:Receiver provides maximum sensitivity to radio signals for improved audio and radio signals for improved audio and identifying capabilities identifying capabilities BFO:Beat Frequency Oscillator for positive navigating BFO:Beat Frequency Oscillator for positive navigating outside the US outside the US Test:Offsets bearing pointer to verify free movement Test:Offsets bearing pointer to verify free movement (Needle should return)(Needle should return)NDB aircraft components cont.n nTypical older SIU ADF Typical older SIU ADF Indicator&ReceiverIndicator&ReceiverNDB ground componentsn nOne variation of an NDB ground antennaADF Limitationsn nMountainous Terrainn nPrecipitation Staticn nThunderstormsn nTwilight Effect n nShoreline EffectADF Limitations cont.n nMountainous terrainThe signal can be The signal can be reflected by irregular reflected by irregular terrainterrainADF Limitations cont.n nPrecipitation StaticPrecipitation Static When flying in rain,snow or clouds a buildup of When flying in rain,snow or clouds a buildup of static electricity occurs on the aircraft.If buildup static electricity occurs on the aircraft.If buildup becomes significant enough,the ADF needle becomes significant enough,the ADF needle wanders aimlessly.wanders aimlessly.n nThunderstormsThunderstorms Lightning radiates radio waves in the L/MF band Lightning radiates radio waves in the L/MF band and causes the ADF indicator to momentarily and causes the ADF indicator to momentarily point towards the area of electrical discharge.point towards the area of electrical discharge.ADF Limitations cont.n nTwilight effectTwilight effect Height of the ionosphere Height of the ionosphere changes around sunset changes around sunset and sunrise.This can and sunrise.This can cause erratic ADF cause erratic ADF indications.indications.n nShoreline EffectShoreline Effect The NDB signal can be The NDB signal can be bent in areas where it bent in areas where it crosses the shoreline.crosses the shoreline.For Your Informationn nHow can you tell if you are receiving erroneous bearing information?Must be continuously monitored for Must be continuously monitored for identification and reliable signal.identification and reliable signal.n nHow can you tell when station passage occurs?As you pass the station the needle will swing As you pass the station the needle will swing from 0 to 180 on the indicatorfrom 0 to 180 on the indicatorADF cont.n nThere are 2 types of ADF indicatorsThere are 2 types of ADF indicators Fixed Card Fixed Card Moveable Card Moveable CardADF terminologyn nBearingThe horizontal direction The horizontal direction TOTO or or FROMFROM any point any point which is measured clockwise through 360 deg.which is measured clockwise through 360 deg.from magnetic northfrom magnetic northn nRelative Bearing(RB)The number of degrees between the nose of The number of degrees between the nose of the aircraft and the station.the aircraft and the station.n nMagnetic BearingCourse to or from the stationCourse to or from the station“Course To”or“Bearing From”“Course To”or“Bearing From”ADF terminology(Bearings)n nThe formulaThe formulaMagnetic Magnetic HeadingHeading+Relative Relative BearingBearing=Magnetic Magnetic BearingBearingMH+RB=MBADF terminology(Bearings)ADF doing the mathn nWhat is the mag.bearing to the station?What is the mag.bearing to the station?MH=010MH=010 RB=60RB=60 MH010+RB +060 MB070ADF doing the mathn nWhat is the mag.bearing What is the mag.bearing toto the station?the station?MH=210 MH=210 RB=300 RB=300MHMH+RBRB=MBMB210210+300300=510510510510-360360=150150ADF doing the mathn nWhat is the mag.bearing FROM the station?MHMH+RBRB=MBMB330330+110110=440440-360-360MBMBToTo=080080+180+180MBMBFromFrom=260260The easier way in flightn nTranspose the Transpose the ADF needle ADF needle onto the DGonto the DGADF Orientationn nWhat is your bearing to the station?What is your bearing to the station?n nWhere are you in relation to the station?Where are you in relation to the station?ADF Orientationn nWhat is your bearing to the station?What is your bearing to the station?n nWhere are you in relation to the station?Where are you in relation to the station?More ADF OrientationMore ADF OrientationADF Homingn nHoming-Keeping the needle pointed on ZeroHoming-Keeping the needle pointed on ZeroNDB NDB Tracking/BracketingTracking/BracketingNDB Interceptsn nOn an NDB intercept you are on course when the ADF needle deflection equals the angle of interceptn nNeedle deflection is in reference to nose when going TO the stationn nNeedle deflection is in reference to tail when going From the stationRadio Magnetic Indicator(RMI)n nCombines the heading indicator(DG)with one or two bearing pointersn nSlaved to remote flux valven nUsed mainly for supporting navigation/orientationn nUseful for DME ARCSRMI cont.cont.RMI OrientationRMI Orientation
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