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aircraft is in a banked attitude, as the needle dips down in the direction of the turn. This is the result of the loop itself banking with the aircraft and therefore being at a different angle to the beacon. For ease of visualisation, it can be useful to consider a 90° banked turn, with the wings vertical. The bearing of the beacon as seen from the ADF aerial will now be unrelated to the direction of the aircraft to the beacon.
31:
278:) is an alternate ADF display providing more information than a standard ADF. While the ADF shows relative angle of the transmitter with respect to the aircraft, an RMI display incorporates a compass card, actuated by the aircraft's compass system, and permits the operator to read the magnetic bearing to or from the transmitting station, without resorting to arithmetic.
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in on a station. Homing is flying the aircraft on the heading required to keep the needle pointing directly to the 0° (straight ahead) position. To home into a station, tune the station, identify the Morse code signal, then turn the aircraft to bring the ADF azimuth needle to the 0° position. Turn to
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Dip error is sometimes wrongly confused with quadrantal error, which is the result of radio waves being bounced and reradiated by the airframe. Quadrantal error does not affect signals from straight ahead or behind, nor on the wingtips. The further from these cardinal points and the closer to the
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that occurs when the antenna is at right angles to the signal, and provide the heading to the station using a direction indicator. In flight, the ADF's RMI or direction indicator will always point to the broadcast station regardless of aircraft heading. Dip error is introduced, however, when the
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Unlike the RDF, the ADF operates without direct intervention, and continuously displays the direction of the tuned beacon. Initially, all ADF receivers, both marine and aircraft versions, contained a rotating loop or ferrite loopstick aerial driven by a motor which was controlled by the receiver.
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a desired course using an ADF and allowing for winds aloft, winds which may blow the aircraft off-course. Good pilotage technique has the pilot calculate a correction angle that exactly balances the expected crosswind. As the flight progresses, the pilot monitors the direction to or from the NDB
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and provides an accurate position fix for the navigator. Less accurate station passage, passing slightly to one side or another, is shown by slower (but still rapid) swinging of the needle. The time interval from the first indications of station proximity to positive station passage varies with
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As an aircraft nears an NDB station, the ADF becomes increasingly sensitive, small lateral deviations result in large deflections of the needle which sometimes shows erratic left/right oscillations. Ideally, as the aircraft overflies the beacon, the needle swings rapidly from directly ahead to
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The ADF indicators are a kind of navigational display consisting of a dial and a needle that rotates around the dial and points to the beacon. This needle suggests the "to" bearing of the beacon, and to fly the "from" bearing, 180° needs to be added or subtracted from the reading.
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There are two types of ADF indicators: the "fixed azimuth dial" type with 0° always represents the aircraft nose, and 180° always represents the aircraft tail; and the type with rotating dials that can be rotated to align the azimuth with the aircraft heading.
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keep the ADF heading indicator pointing directly ahead. Homing is regarded as poor piloting technique because the aircraft may be blown significantly or dangerously off-course by a cross-wind, and will have to fly further and for longer than the direct track.
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signal transmitted by the NDB. On marine ADF receivers, the motorized ferrite-bar antenna atop the unit (or remotely mounted on the masthead) would rotate and lock when reaching the null of the desired station. A centerline on the antenna unit moving atop a
285:. Some models allow the operator to select which needle is connected to each navigation radio. There is great variation between models, and the operator must take care that their selection displays information from the appropriate ADF and VOR.
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ADF receivers can be used to determine current position, track inbound and outbound flight path, and intercept a desired bearing. These procedures are also used to execute holding patterns and non-precision instrument approaches.
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An ADF indicator with a fixed azimuth dial. The airplane is flying a 40° magnetic heading, while the station is 310° relative to the plane (called "relative bearing"). The magnetic bearing to the station in this case is
105:
quadrantal points (i.e. 45°, 135°, 225° and 315° from the nose) the greater the effect, but quadrantal error is normally much less than dip error, which is always present when the aircraft is banked.
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indicated in degrees the bearing of the station. On aviation ADFs, the unit automatically moves a compass-like pointer (RMI) to show the direction of the beacon. The pilot may use this pointer to
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instrument that automatically and continuously displays the relative bearing from the ship or aircraft to a suitable radio station. ADF receivers are normally tuned to aviation or marine NDBs (
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Most RMI's incorporate two direction needles. Often one needle (the thicker, double-barred needle) is connected to an ADF and the other (generally thin or single-barred) is connected to a
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A teardrop-shaped housing that encases LP-21 rotatable loop antenna attached to the underside of
Douglas DC-3 "Flagship Knoxville". The loop antenna is used for automatic radio compass.
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Non-directional beacons in North
America are classified by power output: "low" power rating is less than 50 watts; "medium" from 50 W to 2,000 W; and "high" at more than 2,000 W.
296:. The HSI, along with the VOR system, has largely replaced use of the RMI, however the HSI's much higher cost keeps the older combination of an RMI and an
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65:) units, most ADF receivers can also receive medium wave (AM) broadcast stations, though these are less reliable for navigational purposes.
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More modern aviation ADFs contain a small array of fixed aerials and use electronic sensors to deduce the direction using the strength and
292:. The Heading Indicator can be combined with information from navigation radios (primarily VOR/ILS) in a similar way, to create the
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using the ADF, adjusts the correction as required. A direct track will yield the shortest distance and time to the ADF location.
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This instrument display can replace a magnetic compass display in the instrument panel, but not necessarily the gyroscopic
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The operator tunes the ADF receiver to the correct frequency and verifies the identity of the beacon by listening to the
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directly towards the beacon, or may also use the magnetic compass and calculate the direction from the beacon (the
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418:"Operational Notes on Non-Directional Beacons (NDB) and Associated Automatic Direction Finding (ADF)"
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Like the RDF, a sense antenna verified the correct direction from its 180-degree opposite.
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altitude — a few moments at low levels to several minutes at high altitude.
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of the signals from each aerial. The electronic sensors listen for the
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61:) operating in the LW band between 190 – 535 kHz. Like RDF (
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130:
528:. Archerfield, Queensland: Bob Tait's Aviation Theory School.
319:
AN 01-40NC-2 Handbook
Erection and Maintenance Instructions
343:"Flagship Knoxville — an American Airlines Douglas DC-3"
113:
Typical service ranges of non-directional beacons (NDBs)
451:
475:. ALLSTAR Network. May 4, 2008. Archived from
27:Marine or aircraft radio-navigation instrument
8:
457:. Tehran: Civil Aviation Technology College.
449:Latifiyan, Pouya (2022). "NDB in Aviation".
136:Effective range, nautical miles (
506:Pilot's Handbook of Aeronautical Knowledge
374:Pilot's Handbook of Aeronautical Knowledge
423:. Government of Australia. Archived from
416:Civil Aviation Safety Authority (2005).
364:Federal Aviation Administration (2008).
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38:For broader coverage of this topic, see
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85:) at which their aircraft is located.
300:attractive to cost-conscious pilots.
7:
469:"ADF (Automatic Direction Finder)"
126:of NDB, by power rating
25:
322:. U.S. Air Force. 15 October 1944
223:directly behind. This indicates
511:Federal Aviation Administration
380:. US Dept. of Transportation.
341:May, Joseph (8 January 2013).
294:Horizontal Situation Indicator
258:Radio magnetic indicator (RMI)
1:
513:. 2023-07-17. pp. 29–30.
473:Navigation Systems – Level 3
249:The ADF may also be used to
509:(FAA-H-8083-25C ed.).
129:Transmission power output,
600:
503:"Chapter 16: Navigation".
53:) is a marine or aircraft
47:automatic direction finder
37:
366:"Chapter 15: Navigation"
272:radio magnetic indicator
18:Radio magnetic indicator
236:The ADF may be used to
40:Radio direction-finding
345:. Hearst Seattle Media
298:Omni Bearing Indicator
267:
201:
63:Radio Direction Finder
59:Non-Directional Beacon
35:
265:
198:
33:
574:Aircraft instruments
559:American inventions
479:on 28 December 2010
569:Italian inventions
524:Tait, Bob (2008).
268:
202:
36:
584:Navigational aids
387:978-1-56027-783-5
290:Heading Indicator
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16:(Redirected from
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564:Radio navigation
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55:radio-navigation
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266:An aircraft RMI
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225:station passage
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145:Locator beacon
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579:Air navigation
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526:CPL Navigation
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430:on 30 May 2009
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481:. Retrieved
477:the original
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399:. Retrieved
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75:compass rose
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434:11 February
548:Categories
483:17 October
304:References
133: (W)
70:Morse code
534:224434684
170:50–2,000
554:Avionics
349:3 August
326:4 August
245:Tracking
181:2,000+
167:Medium
532:
384:
232:Homing
213:Stages
98:trough
83:radial
428:(PDF)
421:(PDF)
395:(PDF)
378:(PDF)
369:(PDF)
251:track
200:350°.
178:High
159:0–50
148:0–25
131:watts
124:Class
94:phase
530:OCLC
485:2010
436:2011
403:2015
382:ISBN
351:2014
328:2014
238:home
156:Low
79:home
283:VOR
276:RMI
184:75
173:50
162:25
151:15
138:nmi
51:ADF
45:An
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270:A
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274:(
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