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(2080, 'History The first usable radio direction finder was created in 1907 by italian engineers Ettore Bellini and Alessandro Tosi In 1939 it was replaced by the more efficient Adcock antenna Operation World War II US Navy high frequency radio direction finder Radio Direction Finding works by comparing the signal strength of a directional antenna pointing in different directions At first this system was used by land and marine based radio operators using a simple rotatable loop antenna linked to a degree indicator This system was later adopted for both ships and aircraft and was widely used in the 1930s and 1940s On pre World War II aircraft RDF antennas are easy to identify as the circular loops mounted above or below the fuselage Later loop antenna designs were enclosed in a aerodynamic teardrop shaped fairing In ships and small boats RDF receivers first employed large metal loop antennae similar to aircraft but usually mounted atop a portable battery powered receiver In use the RDF operator would first tune the receiver to the correct frequency then manually turn the loop either listening or watching an S meter to determine the direction of the null the direction at which a given signal is weakest of a long wave LW or medium wave AM broadcast beacon or station listening for the null is easier than listening for a peak signal and normally produces a more accurate result This null was symmetrical and thus identified both the correct degree heading marked on the radio s compass rose as well as its 180 degree opposite While this information provided a baseline from the station to the ship or aircraft the navigator still needed to know beforehand if he was to the east or west of the station in order to avoid plotting a course 180 degrees in the wrong direction By taking bearings to two or more broadcast stations and plotting the intersecting bearings the navigator could locate the relative position of his ship or aircraft Later RDF sets were equipped with rotatable ferrite loopstick antennae which made the sets more portable and less bulky Some were later partially automated by means of a motorized antenna ADF A key breakthrough was the introduction of a secondary vertical whip or sense antenna that substantiated the correct bearing and allowed the navigator to avoid plotting a bearings 180 degrees opposite the actual heading After World War II there many small and large firms making direction finding equipment for mariners including Apelco Aqua Guide Bendix Gladding and its marine division Pearce Simpson Ray Jefferson Raytheon and Sperry In aircraft equipment Bendix and Sperry Rand were two of the larger manufacturers of RDF radios and navigation instruments Usage in Maritime and Aircraft Navigation Radio transmitters for air and sea navigation are known as beacons and are the radio equivalent to a lighthouse The transmitter sends a Morse Code transmission on a Long wave 150 400 Khz or Medium wave AM 520 1720 Khz frequency incorporating the station s identifier that is used to confirm the station and its operational status Since these radio signals are broadcast in all directions omnidirectional during the day the signal itself does not include direction information and these beacons are therefore referred to as non directional beacons or NDBs As the commercial medium wave AM broadcast band lies within the frequency capability of most RDF units these stations and their transmitters can also be used for navigational fixes While these commercial radio stations can be useful due to their high power and location near major cities there may be several miles between the location of the station and its transmitter which can reduce the accuracy of the fix when approaching the broadcast city A second factor is that some AM radio stations are omnidirectional during the day and switch to a reduced power directional signal at night RDF was once the primary form of aircraft and marine navigation Strings of beacons formed airways from airport to airport while marine NDBs provided navigational assistance to small watercraft approaching a landfall In the 1950s the aviation NDBs were augmented by the VOR system in which the direction to the beacon can be extracted from the signal itself hence the distinction with non directional beacons Use of marine NDBs was largerly supplanted in North America by the development of LORAN in the 1970s Today many NDBs have been decommissioned in favor of faster and far more accurate GPS navigational systems However the low cost of ADF and RDF systems and the continued existence of AM broadcast stations as well as navigational beacons in countries outside North America has allowed these devices to continue to function primarily for use in small boats as an adjunct or backup to GPS Automatic Direction Finder ADF A typical aircraft ADF indicator An Automatic Direction Finder ADF is a marine or aircraft radio navigation instrument which 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 operating in the LW band between 190 535 160 kHz Like RDF units most ADF receivers can also receive medium wave AM broadcast stations though as mentioned these are less reliable for navigational purposes The operator tunes the ADF receiver to the correct frequency and verifies the identity of the beacon by listening to the Morse code 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 compass rose 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 home directly towards the beacon or may also use the magnetic compass and calculate the direction from the beacon the radial at which their aircraft is located 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 Like the RDF a sense antenna verified the correct direction from its 180 degree opposite More modern aviation ADFs contain a small array of fixed aerials and use electronic sensors to deduce the direction using the strength and phase of the signals from each aerial The electronic sensors listen for the trough 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 the aircraft s attitude or heading Such 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 Typical NDB services ranges Class of NDB Transmission Power Effective Range Locator below 25 watts 15 NM MH below 50 watts 25 NM H 50 to 1 999 watts 50 NM HH 2 000 watts 75 NM Station passage 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 directly behind This indicates station passage 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 altitude a few moments at low levels to several minutes at high altitude Homing The ADF may be used to home 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 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 Tracking The ADF may also be used to track a desired course using a 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 using the ADF adjusts the correction as required A direct track will yield the shortest distance and time to the ADF location RMI A Radio Magnetic Indicator 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 Most RMI incorporate two direction needles Often one needle generally the thin single barred needle is connected to an ADF and the other thicker and or double barred is connected to a VOR Using multiple indicators a navigator can accurately fix the position of their aircraft without requiring station passage There is great variation between models and the operator must take care that their selection displays information from the appropriate ADF and VOR See also Amateur radio direction finding Cardioid Battle of the Beams radio navigation VOR DME Radio direction finding Traffic analysis Huff Duff Wullenweber Real time locating Notes FAA 2003 Pilot s Handbook of Aeronautical Knowledge US Dept of Transportation 160 Civil Aviation Safety Authority http www casa gov au pilots download NDB pdf Operational Notes on Non Directional Beacons NDB and Associated Automatic Direction Finding ADF PDF http www casa gov au pilots download NDB pdf Retrieved August1 2008 160 Bob Tait 2008 CPL Navigation Bob Tait s Aviation Theory School 160 References Boffa P D Sistemi per la radionavigazione ed Siderea 1985 V Piazzi Sistemi radioelettrici di navigazione vol V A A R Trebbi Strumenti e navigazione ed Aviabooks F Francescotti Avionica ed Aviolibri Alessandro Tosi Il radiogoniometro Bellini Tosi alla esposizione di storia della scienza in Firenze Taranto A Dragone amp C 1929 Alessandro Tosi L enciclopedia italiana e radiosistema a radiogoniometro Pisa 160 Pacini Mariotti 1932 Alessandro Tosi Contributo della marina all avvento del radiogoniometro Roma E Pinci 1929 Apparati R T di bordo e radiogoniometro Ministero dell Aeronautica Ispettorato Scuole Roma 1937 Impiego pratico del radiogoniometro d F M 3 sulle navi mercantili Ministero delle Poste e delle telecomunicazioni Roma Ist Poligr Dello Stato 1950 Musella Francesco Il radiogoniometro ed il radiofaro nella navigazione Roma Ist Poligr Dello Stato 1934 Radiogoniometro Marconi per uso di bordo tipo 11 F Roma tip Radio 1926 Catalogo illustrato per radiogoniometro p 57 n campale Siemens S A Ministero della guerra Direzione superiore del servizio studi ed esperimenti del Genio Milano Tip L Toffaloni 1942 Istruzioni per l uso dell alimentatore Tf 109 per radiogoniometro e ricevitore a cura della Siemens Ministero dell aeronautica Ufficio centrale delle telecomunicazioni e dell assistenza del volo Milano 1941 Catalogo illustrato per impianto radiogoniometro E 393 N 160 Siemens S n Ministero della guerra Direzione superiore del servizio studi ed esperimenti del genio Milano tip L Toffaloni 1942 21 Il radiogoniometro Marconi per stazioni terrestri 160 tipo 12 A Roma Ufficio Marconi 1923 Tosi A Il radiosistema Bellini Tosi a radiogoniometro 160 l ultima fase Taranto Arti Grafiche Dragone 1930 23 Radiogoniometro Marconi per aeromobili 160 tipo 14 160 codice Airder Roma Ufficio Marconi e Genova Officine radiotelegrafiche Marconi 1923 Il radiogoniometro e la radiotelegrafia direttiva Ufficio Marconi Roma Tip Unione Ed 1920 Radiogoniometro Marconi per uso di bordo 160 Descrizione funzionamento manutenzione impiego nella condotta della navigazione Genova 160 Tip Radio 1923 Radiogoniometro Marconi r 160 G M 3 Istruzioni per l uso e la manutenzione del segnale d allarme automatico senza regolaggio tipo s F R Roma 160 Ist Profess G Marconi 1950 Radiogoniometro Marconi r 160 G M 3 Istruzioni per l uso e la manutenzione del segnale d allarme automatico senza regolaggio tipo s F R Roma Ist Professionale di Radiotelegrafia G Marconi 1949 Radiogoniometro indicatore di rotta tipo P 63 N 160 descrizione ed istruzioni per l uso Ministero dell aeronautica Divisione generale delle costruzioni e degli approvvigionamenti Milano Toffaloni 1941 Impiego pratico del radiogoniometro D F M 3 sulle navi mercantili Ministero delle Comunicazioni Direzione generale delle poste e dei telegrafi Roma Ist Poligr Stato 1932 Vincenzo Nastro Gabriella Messina Navigazione radiogoniometrica in Navigazione aerea Milano Hoepli 2002 pp 160 213262 ISBN 88 203 2942 5 External links Flash based Radio Magnetic Indicator RMI simulator Wikimedia Commons has media related to RDF receivers Categories Avionics Radio navigation Italian inventionsHidden categories Articles lacking in text citations from February 2010 All articles lacking in text citations')
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