Decca Navigation System Pdf
Proc is a modified version hereof. But the improvement of electronics through this period was so rapid that it was only a few years before Loran-C units of similar size and cost were available. This volume was known to the British armed forces as Admiralty B. This consists of a high stability, crystal-controlled, oscillator which is set up, before departure, to be in phase with the transmissions of the master station at that end of the route.
The groundwave remained fairly sharp, but could be received only at shorter distances and was primarily used during the day. When plotted on a chart, the collection of possible locations for any given time difference forms a hyperbolic curve. To do this a master and slave pair of stations is located at each end of the route in such a way that the route perpendicularly bisects the line joining the slave to the master of each pair. In order to maintain secrecy, frequencies were changed at irregular intervals.
The goal was to perfectly align the two traces. Unlike their system, Gee had largely completed development and was proceeding to production. Automated receivers became available in the s, but the same improved electronics also opened the possibility of new systems with higher accuracy.
This was due largely to the large numbers of surplus Loran-A units released from the Navy as ships and aircraft replaced their sets with Loran-C. The Navy had also been experimenting with a similar concept during this period, but using a different method to extract the timing. It was phase comparison at this common frequency that resulted in the hyperbolic lines of position. This guaranteed predictable annual income. At nighttime, accuracy was guaranteed out to be nm by the British Admiralty.
Early Decca receivers were fitted with three rotating Decometers that indicated the phase difference for each pattern. Previous page Top of page Next page. This was due largely to two important factors. The sets of hyperbolae due to each pair of stations make a pattern such as is shown in Fig. To get complete information it is necessary that the phase comparator be of such a kind that it integrates the total phase change.
Two chains in Vietnam were used during the Vietnam War for helicopter navigation, with limited success. For a production system, the team began working with a system using a circular J-scope display for improved accuracy. An experimental chain was installed with coverage of central London and receivers placed in London buses and other vehicles to demonstrate an early vehicle location and tracking system. This system shared the middle tower, which broadcast on both frequencies.
This reduced fuel load allowed the bombload to be increased. You could be comparing the first waveform from one station to the first from another, but the second waveform looks identical. Merging Decca's radar assets with their own, Racal began selling off the other portions of the company, including avionics and Decca Navigator.
This made it much easier to implement the receivers using s electronics, eliminating the need for a cathode ray tube. Stations were identified with a simple code, with a number indicating the frequency band, a letter for the pulse repetition frequency, and a number for the station within the chain.
This was not the first such system, but O'Brien apparently developed his version without knowledge of the others, and made several advancements in the art that would prove useful. In the late s an experimental Decca chain was set up in the United States, in the New York area, to be used for navigating the Vertol helicopters of New York Airways. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft, but found its main use on the ships and aircraft operating in the Pacific theatre.
As there were three secondaries there were three patterns, termed Red, Green and Purple. When the patents on the original technology lapsed in the early s, new receivers were quickly built by a number of companies.
Coast Guard Dickinson, William T. In this way, assuming the point of departure was known, a more or less distinct location could be identified.
Dippy also instituted a number of simple changes that would prove extremely useful in practice. It was used for specialised applications such as precision measurements involved with oil-drilling and by the Royal Navy for detailed mapping and surveying of coasts and harbours. The swept areas were marked with buoys in preparation for the Normandy Landings.
DECCA Navigation System
Schwarz, was chief engineer of the Decca Record company in England. After the initial ship tests, Decca conducted tests in cars, analisis estructural pdf driving in the Kingston By-Pass area to verify receiver accuracy.
Different frequencies are used for the master-slave pair at either end of the route. In the car installation, it was found possible to navigate within an individual traffic lane. The patterns were drawn on nautical charts as a set of hyperbolic lines in the appropriate colour. This is actually quite easy to do in electronics, and can be displayed directly using a simple mechanical pointer. After take-off comparison of the phase of the master station's transmission with that of the crystal-controlled oscillator gives a direct measure of the distance travelled.
At that point, measurement starts. The Hi-Fix equipment was leased for a period with temporary chains established to provide coverage of the area required, Hi-Fix was commercialised by Racal Survey in the early s. The area between two adjacent lines of zero phase difference is known as a lane and phase comparisons carried out at the receiving point will merely show the position within a lane. Since the pattern depended on the atmospherics between the transmitter and receiver, the received pattern was different for the two stations.
Decca navigation system
Further, as military ships and aircraft moved from Loran-A to Loran-C, the older receivers were made surplus. This article needs additional citations for verification.
During this period he had the idea of position fixing by means of phase comparison of continuous wave transmissions. By the early s such units were relatively common, although they remained relatively expensive compared to devices like a radio direction finder. When they said they did not, the land was quickly secured. In the air a somewhat similar process is followed. Popular in Manufacturing And Engineering.
Decca continued to propose that Dectra be used for the long-range role. Navigational Aids Decca Major system characteristics. The purpose of this chain was to provide accurate air navigation for the corridor between Western Germany and Berlin in the event that a mass evacuation of allied personnel may be required.
The intersections of the two sets of curves normally results in two possible locations. Measurement times on the order of three to five minutes were typical, requiring the navigator to take into account the motion of the vehicle during this time.
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