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79-531: The Black Sea Region is a coastal strip of land 20–60 kilometres (12–37 mi) wide that runs along the coasts of Romania, Bulgaria, and a broader coastal strip in northern Turkey and Georgia. The coastline has rocky bays and sea cliffs, but is dominated by long stretches of low sand dunes and beaches sloping into the Black Sea. The sea has a moderating effect on the climate, so temperatures do not fall much below 0 °C (32 °F) in winter, and are not as high in

158-539: A directional antenna , one could determine the direction to the broadcasting antenna. A second measurement using another station was then taken. Using triangulation , the two directions can be plotted on a map where their intersection reveals the location of the navigator. Commercial AM radio stations can be used for this task due to their long range and high power, but strings of low-power radio beacons were also set up specifically for this task, especially near airports and harbours. Early RDF systems normally used

237-403: A loop antenna , a small loop of metal wire that is mounted so it can be rotated around a vertical axis. At most angles the loop has a fairly flat reception pattern, but when it is aligned perpendicular to the station the signal received on one side of the loop cancels the signal in the other, producing a sharp drop in reception known as the "null". By rotating the loop and looking for the angle of

316-413: A 30 Hz AM reference signal, and a 1020 Hz 'marker' signal for station identification. Conversion from this audio signal into a usable navigation aid is done by a navigation converter, which takes the reference signal and compares the phasing with the variable signal. The phase difference in degrees is provided to navigational displays. Station identification is by listening to the audio directly, as

395-450: A computer. Satellite navigation systems send several signals that are used to decode the satellite's position, distance between the user satellite, and the user's precise time. One signal encodes the satellite's ephemeris data, which is used to accurately calculate the satellite's location at any time. Space weather and other effects causes the orbit to change over time so the ephemeris has to be updated periodically. Other signals send out

474-511: A different frequency to determine if the aircraft is pointed in the "right direction." Some aircraft will usually employ two VOR receiver systems, one in VOR-only mode to determine "right place" and another in ILS mode in conjunction with a glideslope receiver to determine "right direction." }The combination of both allows for a precision approach in foul weather. Beam systems broadcast narrow signals in

553-439: A few dozen satellites to provide worldwide coverage . As a result of these advantages, satellite navigation has led to almost all previous systems falling from use . LORAN, Omega, Decca, Consol and many other systems disappeared during the 1990s and 2000s . The only other systems still in use are aviation aids, which are also being turned off for long-range navigation while new differential GPS systems are being deployed to provide

632-404: A fix. Gee was accurate to about 165 yards (150 m) at short ranges, and up to a mile (1.6 km) at longer ranges over Germany. Gee remained in use long after World War II, and equipped RAF aircraft as late as the 1960s (approx freq was by then 68 MHz). With Gee entering operation in 1942, similar US efforts were seen to be superfluous. They turned their development efforts towards

711-540: A fortified nucleus against the oncoming barbarian tribes and was one of the 15 cities in the province of Scythia. In 513, a battle ensued between Kaliakra and the Byzantine emperor Anastasius I. The settlement and fortress developed in the following centuries, but according to some researchers in the 7th century a decline occurred because the Slavs and Proto-Bulgarians showed no interest in settling this place. In 10th century sources,

790-719: A major storm along with his whole fleet. Kaliakra Glacier on Livingston Island in the South Shetland Islands , Antarctica is named after Kaliakra. Radio navigation Radio navigation or radionavigation is the application of radio waves to determine a position of an object on the Earth , either the vessel or an obstruction. Like radiolocation , it is a type of radiodetermination . The basic principles are measurements from/to electric beacons , especially Combinations of these measurement principles also are important—e.g., many radars measure range and azimuth of

869-474: A much longer-ranged system based on the same principles, using much lower frequencies that allowed coverage across the Atlantic Ocean . The result was LORAN , for "LOng-range Aid to Navigation". The downside to the long-wavelength approach was that accuracy was greatly reduced compared to the high-frequency Gee. LORAN was widely used during convoy operations in the late war period. Another British system from

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948-411: A short pulse of a powerful radio signal, which is sent into space through broadcast antennas. When the signal reflects off a target, some of that signal is reflected back in the direction of the station, where it is received. The received signal is a tiny fraction of the broadcast power, and has to be powerfully amplified in order to be used. The same signals are also sent over local electrical wiring to

1027-469: A target. These systems used some form of directional radio antenna to determine the location of a broadcast station on the ground. Conventional navigation techniques are then used to take a radio fix . These were introduced prior to World War I, and remain in use today. The first system of radio navigation was the Radio Direction Finder , or RDF. By tuning in a radio station and then using

1106-428: A time. This was addressed in the later Gee-H system by placing the transponder on the ground and broadcaster in the aircraft. The signals were then examined on existing Gee display units in the aircraft (see below). Gee-H did not offer the accuracy of Oboe, but could be used by as many as 90 aircraft at once. This basic concept has formed the basis of most distance measuring navigation systems to this day. The key to

1185-401: A transponder, or "beacon" in this role, with high accuracy. The British put this concept to use in their Rebecca/Eureka system, where battery-powered "Eureka" transponders were triggered by airborne "Rebecca" radios and then displayed on ASV Mk. II radar sets. Eureka's were provided to French resistance fighters, who used them to call in supply drops with high accuracy. The US quickly adopted

1264-454: Is 190–1750 kHz, but the same system can be used with any common AM-band commercial station. VHF omnidirectional range , or VOR, is an implementation of the reverse-RDF system, but one that is more accurate and able to be completely automated. The VOR station transmits two audio signals on a VHF carrier – one is Morse code at 1020 Hz to identify the station, the other is a continuous 9960 Hz audio modulated at 30 Hz, with

1343-520: Is a cape in the Southern Dobruja region of the northern Bulgarian Black Sea Coast , which ends with a long and narrow headland 12 kilometres (7 mi) east of Kavarna , 60 kilometres (37 mi) northeast of Varna and 65 kilometres (40 mi) southwest of Mangalia . The coast is steep with vertical cliffs reaching 70 metres (230 ft) down to the sea. Kaliakra is a nature reserve, where dolphins and cormorants can be observed. It sits on

1422-449: Is almost always used in conjunction with VOR, and is normally co-located at a VOR station. This combination allows a single VOR/DME station to provide both angle and distance, and thereby provide a single-station fix. DME is also used as the distance-measuring basis for the military TACAN system, and their DME signals can be used by civilian receivers. Hyperbolic navigation systems are a modified form of transponder systems which eliminate

1501-521: Is based on the same principles (see below). A great advance in the RDF technique was introduced in the form of phase comparisons of a signal as measured on two or more small antennas, or a single highly directional solenoid . These receivers were smaller, more accurate, and simpler to operate. Combined with the introduction of the transistor and integrated circuit , RDF systems were so reduced in size and complexity that they once again became quite common during

1580-533: Is of Byzantine Greek origin. It is a combination of "καλός" ("beautiful") and "άκρα" ("headland" or "edge" or "extremity") and is traditionally translated as "Beautiful Headland". Kaliakra was the site of the naval Battle of Cape Kaliakra on 11 August 1791, part of the Russo-Turkish War (1787–1792) . The first modern lighthouse on Kaliakra was built in 1866 by the Compagnie des Phares de l’Empire Ottoman;

1659-440: Is sent. Amplified signals from the receiver are then sent to the Y input, where any received reflection causes the beam to move upward on the display. This causes a series of "blips" to appear along the horizontal axis, indicating reflected signals. By measuring the distance from the start of the sweep to the blip, which corresponds to the time between broadcast and reception, the distance to the object can be determined. Soon after

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1738-482: Is the best known of the wetlands. In Bulgaria and Romania the region is threatened by development of agriculture, industry, urbanization and tourism. The Black Sea itself, a very deep inland sea, is poor in oxygen and supports very little marine life in the deeper regions. However, it had a productive fishery until the 1960s, when stocks crashed in part because of over-fishing and in part from pollution and invasion by exotic species. The first list of Natura 2000 sites in

1817-580: The Black Sea rather than face the prospect of being captured by the Ottomans . An obelisk dedicated to this legend is placed at the entrance to the cape, called The Gate of the 40 Maidens . Another legend tells the story of Saint Nicholas , the patron of seamen, who was running away from the Ottomans when God made the earth under him longer and longer so he could escape, and the cape was formed this way. The saint

1896-480: The Via Pontica , a major bird migration route from Africa into Eastern and Northern Europe. Many rare and migrant birds can be seen here in spring and autumn and, like much of this coastline, is home to several rare breeding birds (e.g. pied wheatear and a local race of European shag ). The rest of the reserve also has unusual breeding birds; saker falcon , lesser grey shrike and a host of others. It also features

1975-479: The "A" or "N" tone would become louder and the pilot knew to make a correction. The beams were typically aligned with other stations to produce a set of airways , allowing an aircraft to travel from airport to airport by following a selected set of stations. Effective course accuracy was about three degrees, which near the station provided sufficient safety margins for instrument approaches down to low minimums. At its peak deployment, there were over 400 LFR stations in

2054-597: The "καλός" – beautiful / good and "τσέρκι" – a hoop, given the three walls of the Kaliakra fortress. The Bulgarian Navy of the First World War included a mine-clearing boat named "Kalatserka". The heyday of Kaliakra was in the second half of the 14th century when it was the capital of the principality (despotate) of Carvun under the Bulgarian rulers Balik and Dobrotitsa. The despotate covered the northeastern Bulgarian lands, and

2133-495: The 0-degree referenced to magnetic north. This signal is rotated mechanically or electrically at 30 Hz, which appears as a 30 Hz AM signal added to the previous two signals, the phasing of which is dependent on the position of the aircraft relative to the VOR station. The VOR signal is a single RF carrier that is demodulated into a composite audio signal composed of a 9960 Hz reference signal frequency modulated at 30 Hz,

2212-533: The 1930s provided a way to directly determine the distance to an object even at long distances. Navigation systems based on these concepts soon appeared, and remained in widespread use until recently. Today they are used primarily for aviation, although GPS has largely supplanted this role. Early radar systems, like the UK's Chain Home , consisted of large transmitters and separate receivers. The transmitter periodically sends out

2291-568: The 1960s, and were known by the new name, automatic direction finder , or ADF. This also led to a revival in the operation of simple radio beacons for use with these RDF systems, now referred to as non-directional beacons (NDB). As the LF/MF signals used by NDBs can follow the curvature of earth, NDB has a much greater range than VOR which travels only in line of sight . NDB can be categorized as long range or short range depending on their power. The frequency band allotted to non-directional beacons

2370-412: The 4th century, a third fortification with 10 m walls, 2.90 m thick, was erected even farther from the end of the peninsula. During the archeological excavations made in the 20th century, the remains of ancient and early Christian necropolises were discovered on Kaliakra. In the 5-6th century, according to Hierocele, the fortress (now known as Accra Castellium or simply Accra-cape) gained the importance of

2449-427: The 9960 Hz and 30 Hz signals are filtered out of the aircraft internal communication system, leaving only the 1020 Hz Morse-code station identification. The system may be used with a compatible glideslope and marker beacon receiver, making the aircraft ILS-capable (Instrument Landing System)}. Once the aircraft's approach is accurate (the aircraft is in the "right place"), the VOR receiver will be used on

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2528-499: The US. The remaining widely used beam systems are glide path and the localizer of the instrument landing system (ILS). ILS uses a localizer to provide horizontal position and glide path to provide vertical positioning. ILS can provide enough accuracy and redundancy to allow automated landings. For more information see also: Positions can be determined with any two measures of angle or distance. The introduction of radar in

2607-496: The area is variously listed as Tetrasida, Tetrasiada, Tetrisias, Trisa, Tirisa, or Tirista. The earliest dated Western European map that mentions the modern name Kaliakra is that of the Italian Petrus Vesconta, from 1318. In other Italian maps and 14th-century writings, the peninsula is also described as Capo Calacria or Calacria. The German armored bearer Hans Schiltberger describes the peninsula as Kalacerca, derived from

2686-522: The beam systems before it, civilian use of LORAN-C was short-lived when GPS technology drove it from the market. Similar hyperbolic systems included the US global-wide VLF / Omega Navigation System , and the similar Alpha deployed by the USSR. These systems determined pulse timing not by comparison of two signals, but by comparison of a single signal with a local atomic clock . The expensive-to-maintain Omega system

2765-456: The beams, and were thus less flexible in use. The rapid miniaturization of electronics during and after World War II made systems like VOR practical, and most beam systems rapidly disappeared. In the post-World War I era, the Lorenz company of Germany developed a means of projecting two narrow radio signals with a slight overlap in the center. By broadcasting different audio signals in the two beams,

2844-502: The bomber crew over voice channels, and indicated when to drop the bombs. The British introduced similar systems, notably the Oboe system. This used two stations in England that operated on different frequencies and allowed the aircraft to be triangulated in space. To ease pilot workload only one of these was used for navigation – prior to the mission a circle was drawn over the target from one of

2923-411: The circuitry for driving this display was quite small, Decca systems normally used three such displays, allowing quick and accurate reading of multiple fixes. Decca found its greatest use post-war on ships, and remained in use into the 1990s. Almost immediately after the introduction of LORAN, in 1952 work started on a greatly improved version. LORAN-C (the original retroactively became LORAN-A) combined

3002-651: The fan-like beams of the Lorenz signal, for instance. As the distance between the broadcaster and receiver grows, the area covered by the fan increases, decreasing the accuracy of location within it. In comparison, transponder-based systems measure the timing between two signals, and the accuracy of that measure is largely a function of the equipment and nothing else. This allows these systems to remain accurate over very long range. The latest transponder systems (mode S) can also provide position information, possibly derived from GNSS , allowing for even more precise positioning of targets. The first distance-based navigation system

3081-559: The first of the native rulers to begin building a navy. Dobrotica's galleys participated in successful combat operations in the Black Sea. In 1393 - 1394 the Carvun principality became one of the last Bulgarian possessions to fall under Ottoman rule. In 1402, the Vlach voivode Mircea Stari took over the lands around Kaliakra, but later that year the area was again occupied by the Ottoman troops. In 1444,

3160-432: The front line to direct the aircraft to points in front of them, directing fire on the enemy. Beacons were widely used for temporary or mobile navigation as well, as the transponder systems were generally small and low-powered, able to be man portable or mounted on a Jeep . In the post-war era, a general navigation system using transponder-based systems was deployed as the distance measuring equipment (DME) system. DME

3239-429: The installation more difficult. During the era between World War I and World War II , a number of systems were introduced that placed the rotating antenna on the ground. As the antenna rotated through a fixed position, typically due north, the antenna was keyed with the morse code signal of the station's identification letters so the receiver could ensure they were listening to the right station. Then they waited for

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3318-408: The introduction of radar, the radio transponder appeared. Transponders are a combination of receiver and transmitter whose operation is automated – upon reception of a particular signal, normally a pulse on a particular frequency, the transponder sends out a pulse in response, typically delayed by some very short time. Transponders were initially used as the basis for early IFF systems; aircraft with

3397-669: The knights of the Polish and Hungarian King Vladislav III Varnenczyk were stopped near Cape Kaliakra in their campaign against the Ottoman Empire. In the old Turkish lawmen, Kaliakra is mentioned as a port with a Kilagra or Celigra Burun customs. On July 31, 1791, the largest naval battle in the Black Sea began off the coast of Kaliakra during the Russo-Turkish War of 1787–1792. The Russian squadron, led by Admiral Fyodor Ushakov, repeatedly defeated Hussein Pasha's superior Turkish armada, and helped end

3476-473: The late 1970s, LORAN-C units were the size of a stereo amplifier and were commonly found on almost all commercial ships as well as some larger aircraft. By the 1980s, this had been further reduced to the size of a conventional radio, and it became common even on pleasure boats and personal aircraft. It was the most popular navigation system in use through the 1980s and 90s, and its popularity led to many older systems being shut down, like Gee and Decca. However, like

3555-423: The navigator to determine a line of position on his chart of all the positions at that distance from both stations. More typically, the signal from one station would be received earlier than the other. The difference in timing between the two signals would reveal them to be along a curve of possible locations. By making similar measurements with other stations, additional lines of position can be produced, leading to

3634-421: The need for an airborne transponder. The name refers to the fact that they do not produce a single distance or angle, but instead indicate a location along any number of hyperbolic lines in space. Two such measurements produces a fix. As these systems are almost always used with a specific navigational chart with the hyperbolic lines plotted on it, they generally reveal the receiver's location directly, eliminating

3713-403: The need for manual triangulation. As these charts were digitized, they became the first true location-indication navigational systems, outputting the location of the receiver as latitude and longitude. Hyperbolic systems were introduced during World War II and remained the main long-range advanced navigation systems until GPS replaced them in the 1990s. The first hyperbolic system to be developed

3792-429: The null, the relative bearing of the station can be determined. Loop antennas can be seen on most pre-1950s aircraft and ships. The main problem with RDF is that it required a special antenna on the vehicle, which may not be easy to mount on smaller vehicles or single-crew aircraft. A smaller problem is that the accuracy of the system is based to a degree on the size of the antenna, but larger antennas would likewise make

3871-406: The operator's station, which is equipped with an oscilloscope . Electronics attached to the oscilloscope provides a signal that increases in voltage over a short period of time, a few microseconds. When sent to the X input of the oscilloscope, this causes a horizontal line to be displayed on the scope. This "sweep" is triggered by a signal tapped off the broadcaster, so the sweep begins when the pulse

3950-450: The present one, a 10-metre (33 ft) cylindrical stone masonry tower with lantern and gallery, was erected in 1901, with focal plane height of 68 metres (223 ft) and a white flash (every 5 seconds); it also has a radio navigation emitter and a foghorn . Near Kaliakra, there is a large mediumwave broadcasting facility , which never went into service as planned. As of 2009, several wind power facilities are under development in

4029-408: The proper transponder would appear on the display as part of the normal radar operation, but then the signal from the transponder would cause a second blip to appear a short time later. Single blips were enemies, double blips friendly. Transponder-based distance-distance navigation systems have a significant advantage in terms of positional accuracy. Any radio signal spreads out over distance, forming

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4108-427: The receiver could position themselves very accurately down the centreline by listening to the signal in their headphones. The system was accurate to less than a degree in some forms. Originally known as "Ultrakurzwellen-Landefunkfeuer" (LFF), or simply "Leitstrahl" (guiding beam), little money was available to develop a network of stations. The first widespread radio navigation network, using Low and Medium Frequencies,

4187-436: The receiver within a wide area. Finer accuracy was then provided by measuring the phase difference of the signals, overlaying that second measure on the first. By 1962, high-power LORAN-C was in place in at least 15 countries. LORAN-C was fairly complex to use, requiring a room of equipment to pull out the different signals. However, with the introduction of integrated circuits , this was quickly reduced further and further. By

4266-734: The region was adopted in December 2008. This included 40 Sites of Community Importance under the Habitats Directive and 27 Special Protection Areas under the Birds Directive for the part of the Black Sea biogeographical region in the European Union. Some sites meet both criteria, so the total was less than 67. About half the land area was covered by the sites. As of 12 December 2017 there were 45 Sites of Community Importance . These were: Kaliakra Kaliakra ( Bulgarian : Калиакра )

4345-410: The remnants of the fortified walls, water-main, baths and residence of Despot Dobrotitsa in the short-lived Despotate of Dobruja 's medieval capital. The Bolata Cove with a small sheltered beach lies just north at the mouth of a picturesque canyon, also part of the nature reserve. The following names have been used for the headland and the fortress throughout their history: The name "Kaliakra"

4424-408: The same era was Decca Navigator. This differed from Gee primarily in that the signals were not pulses delayed in time, but continuous signals delayed in phase. By comparing the phase of the two signals, the time difference information as Gee was returned. However, this was far easier to display; the system could output the phase angle to a pointer on a dial removing any need for visual interpretation. As

4503-570: The signal to either peak or disappear as the antenna briefly pointed in their direction. By timing the delay between the morse signal and the peak/null, then dividing by the known rotational rate of the station, the bearing of the station could be calculated. The first such system was the German Telefunken Kompass Sender , which began operations in 1907 and was used operationally by the Zeppelin fleet until 1918. An improved version

4582-472: The sky, and navigation is accomplished by keeping the aircraft centred in the beam. A number of stations are used to create an airway , with the navigator tuning in different stations along the direction of travel. These systems were common in the era when electronics were large and expensive, as they placed minimum requirements on the receivers – they were simply voice radio sets tuned to the selected frequencies. However, they did not provide navigation outside of

4661-454: The stations, and the aircraft was directed to fly along this circle on instructions from the ground operator. The second station was used, as in Y-Gerät, to time the bomb drop. Unlike Y-Gerät, Oboe was deliberately built to offer very high accuracy, as good as 35 m, much better than even the best optical bombsights . One problem with Oboe was that it allowed only one aircraft to be guided at

4740-441: The summer as in area further inland. The Kaliakra cliffs in the north of Bulgaria are rich in flora, including many species in common with the neighboring Steppic and Mediterranean Regions. The western Black Sea Region is the Via Pontica , Europe's second largest bird migration route. The migrating birds use the coastal lakes, marshes and lagoons behind the shoreline, and some spend the winter in these wetlands. The Danube Delta

4819-509: The system for paratroop operations, dropping the Eureka with pathfinder forces or partisans, and then homing in on those signals to mark the drop zones. The beacon system was widely used in the post-war era for blind bombing systems. Of particular note were systems used by the US Marines that allowed the signal to be delayed in such a way to offset the drop point. These systems allowed the troops at

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4898-408: The system was generically known simply as a "Lorenz beam". Lorenz was an early predecessor to the modern Instrument Landing System . In the immediate pre-World War II era the same concept was also developed as a blind-bombing system. This used very large antennas to provide the required accuracy at long distances (over England), and very powerful transmitters. Two such beams were used, crossing over

4977-555: The target to triangulate it. Bombers would enter one of the beams and use it for guidance until they heard the second one in a second radio receiver, using that signal to time the dropping of their bombs. The system was highly accurate, and the ' Battle of the Beams ' broke out when United Kingdom intelligence services attempted, and then succeeded, in rendering the system useless through electronic warfare . The low-frequency radio range (LFR, also "Four Course Radio Range" among other names)

5056-475: The techniques of pulse timing in Gee with the phase comparison of Decca. The resulting system (operating in the low frequency (LF) radio spectrum from 90 to 110 kHz) that was both long-ranged (for 60 kW stations, up to 3400 miles) and accurate. To do this, LORAN-C sent a pulsed signal, but modulated the pulses with an AM signal within it. Gross positioning was determined using the same methods as Gee, locating

5135-549: The time as measured by the satellite's onboard atomic clock . By measuring signal times of arrival (TOAs) from at least four satellites, the user's receiver can re-build an accurate clock signal of its own and allows hyperbolic navigation to be carried out. Satellite navigation systems offer better accuracy than any land-based system, are available at almost all locations on the Earth, can be implemented (receiver-side) at modest cost and complexity, with modern electronics, and require only

5214-412: The transponder concept is that it can be used with existing radar systems. The ASV radar introduced by RAF Coastal Command was designed to track down submarines and ships by displaying the signal from two antennas side by side and allowing the operator to compare their relative strength. Adding a ground-based transponder immediately turned the same display into a system able to guide the aircraft towards

5293-508: The vicinity. The area now has three championship golf courses designed by the legendary golfers Gary Player and Ian Woosnam . The earliest naval settlement dates back to the 4th century BC, when the area was inhabited by the Thracian tribe of Tiris and who gave the area its original name of Tirisis. The ancient geographer Strabo , describing Kaliakra, stated that the capital of King Lisimachus, one of Alexander's generals and ruler of Thrace ,

5372-481: The war. A plaque with a bas-relief of the Russian Admiral was erected on the headland's tip. On August 10, 2006, the 215th anniversary of this victory, a monument to him was erected. The monument is a figure in full height and is located on a hill, where it is visible from the sea. Probably the most popular legend about the place is one about 40 Bulgarian girls, who preferred to tie their hair together and jump into

5451-471: Was "keyed" with the Morse code signal "A", dit-dah, and the second pattern "N", dah-dit. This created two opposed "A" quadrants and two opposed "N" quadrants around the station. The borders between these quadrants created four course legs or "beams" and if the pilot flew down these lines, the "A" and "N" signal merged into a steady "on course" tone and the pilot was "on the beam". If the pilot deviated to either side

5530-490: Was detached from the central government. Dobrotica is also called Dobrudzha, which is the Turkish pronunciation of its name. Written records speak of a powerful, medieval town where the ruler cut his own coins and turned the fortress into a church center. Today there are remains of the fortress walls on the tip of the headlands; some of the water supply, baths and the residence of the prince are still preserved. Kaliakra's despots were

5609-451: Was eventually captured and a chapel was built in 1993, symbolizing his grave. A dervish monastery is also said to have existed on the same place during Ottoman rule , which is thought to have preserved the relics of Muslim Bektashi saint Sarı Saltık . A third legend is about Lysimachus , a successor of Alexander the Great , who seized the royal treasure and escaped to Kaliakra, dying in

5688-444: Was identical to Gee-H in concept, but used new electronics to automatically measure the time delay and display it as a number, rather than having the operator time the signals manually on an oscilloscope. This led to the possibility that DME interrogation pulses from different aircraft might be confused, but this was solved by having each aircraft send out a different series of pulses which the ground-based transponder repeated back. DME

5767-572: Was instead led by the US (see LFF, below). Development was restarted in Germany in the 1930s as a short-range system deployed at airports as a blind landing aid. Although there was some interest in deploying a medium-range system like the US LFF, deployment had not yet started when the beam system was combined with the Orfordness timing concepts to produce the highly accurate Sonne system. In all of these roles,

5846-505: Was introduced by the UK as the Orfordness Beacon in 1929 and used until the mid-1930s. A number of improved versions followed, replacing the mechanical motion of the antennas with phasing techniques that produced the same output pattern with no moving parts. One of the longest lasting examples was Sonne , which went into operation just before World War II and was used operationally under the name Consol until 1991. The modern VOR system

5925-508: Was located here. According to rumor, he hid in the caves near the peninsula his innumerable treasure, reputedly captured on the campaigns against Persia. In the Hellenistic era, a second fortress wall was built inland, and in Roman times the Thracian fortress was expanded. In the years 341–342, round towers were completed, and there was already a city built up around the fortress. In the second half of

6004-444: Was shut down in 1997 as the US military migrated to using GPS . Alpha is still in use. Since the 1960s, navigation has increasingly moved to satellite navigation systems . These are essentially hyperbolic systems whose transmitters are in orbits. That the satellites move with respect to the receiver requires that the calculation of the positions of the satellites must be taken into account, which can only be handled effectively with

6083-513: Was the British Gee system, developed during World War II . Gee used a series of transmitters sending out precisely timed signals, with the signals leaving the stations at fixed delays. An aircraft using Gee, RAF Bomber Command 's heavy bombers , examined the time of arrival on an oscilloscope at the navigator's station. If the signal from two stations arrived at the same time, the aircraft must be an equal distance from both transmitters, allowing

6162-469: Was the German Y-Gerät blind-bombing system. This used a Lorenz beam for horizontal positioning, and a transponder for ranging. A ground-based system periodically sent out pulses which the airborne transponder returned. By measuring the total round-trip time on a radar's oscilloscope, the aircraft's range could be accurately determined even at very long ranges. An operator then relayed this information to

6241-440: Was the main navigation system used by aircraft for instrument flying in the 1930s and 1940s in the U.S. and other countries, until the advent of the VOR in the late 1940s. It was used for both en route navigation as well as instrument approaches . The ground stations consisted of a set of four antennas that projected two overlapping directional figure-eight signal patterns at a 90-degree angle to each other. One of these patterns

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