LORAN-A N.S.Balaji(110051101021) Dhada peer mohammed(110051101026) Balachander(110051101020) Badhri narayanan(110051101019)

HISTORY: Precision radio navigation system with an accuracy of at least 1000 feet at a range of 200 miles. 'Project 3 (or C)' by the Microwave Committee. Loran-A operated in the 1850 to 1950 kHz band, used pulse-time difference as its operating principle and generally speaking had a day/night range of about 800 to 1600 nm. The first Loran-A pair was on the air permanently by June 1942 (Montauk Point, NY, and Fenwick Is, Del.), and by October there were additional stations alongthe Canadian east coast.

HISTORY: Loran stations varied somewhat in size, depending on their locations. They have averaged about fifteen men. Pacific that Loran made its greatest direct contribution to winning the war. One major difference in the way Loran-A operated compared with Gee was that its transmitters operated in pairs rather than as chains.

APN-4

USCG Loran-A station in the SW Pacific

Loran-A chart Loran stations also had Unit designators. LORAN program was a secret during WWII. Dope 1/2/3 were code names for the stations in Greenland during the Cold War. It holds true for the stations that were established to support the Korean War.

EARLY EQUIPMENT Because of vacuum tube size and power requirements, LORAN only saw shipboard use initially because the equipmentwas too large for aircraft. By 1943 an airborne LORAN, the APN-4, was small enough to be used on large bombers and patrol aircraft. The APN-4 consisted of two units each about 1 ft. x 2 ft by 2.5 ft. APN-9 came into use at an amazing weight reduction. It only weighed 40 pounds.

AN/APN-9 Loran 'A' set

SIGNAL CHARACTERISTICS Each transmission pulse lasted about 40 microseconds . This interval, called the Pulse Repetition Interval (P.R.I.) varied for each station and lasted between 29,000 and 40,000 μs. These pulses provided precise index marks for use in time measurements. The transmissions of corresponding master and slave pulses were separated by a fixed time interval which consisted of the time for a signal to travel from the master to the slave, plus one-half the P.R.I., plus an additional small time called the 'coding delay.

Loran chart showing the location of a master and two slave stations Loran chart showing the location of a master and two slave stations. Also shown are station identifiers and time differences on the curves.

PRINCIPLES OF OPERATION The system required at least three transmitting stations for each 'chain', and the observer used a special Loran receiver. A chain consisted of one master and two slave stations. Differences in the arrival time of pulses from a pair of stations was measured and displayed on the face of a cathode ray tube. The readings were then transposed to a Loran lattice chart and position could be plotted.

PRINCIPLES OF OPERATION Loran-A signals were pulsed and not continuous transmissions, tremendous peak power levels could be achieved by a relatively small transmitter. The maximum reliable range for Loran-A was 700 miles by day and 1,400 miles at night.

Coast Guard Loran 'A' Station at Cape Sarichef, Alaska

The model DAS-2 was a popular Loran-A receiver.

DAS-3 receiver/ indicator

CFE 46216 (Receiver section) of DAS3 radio navigation system

IDENTIFICATION OF LORAN-A PAIRS Loran-A stations did not transmit call signs. Two distinguishing characteristics: Radio frequency channel. Pulse repetition rate. STATION IDENTIFICATION SYMBOLS Channel. basic pulse repetition rate. specific pulse repetition rate.

THE END OF LORAN-A The accuracy of Loran-A varied according to location, time of day, weather and relative geometry of transmitting stations. Aside from some testing by the USCG, the follow-on system Loran-B, never made it as a commercial system of navigation due to technical problems. The Chinese chains began with a '1' and the Japanese chains with a '2'. The ground wave ranged from 650 to 900 nautical miles and the sky wave up to 1250 to 1500 nautical miles.

Chains Rate LORAN-A Chain 1L1 Chengshan Jiao / Shanggulin chain 1L0 Chengshan Jiao / Zhuanghe chain 1L4 Sheyanghe / Chengshan Jiao chain 2S3 Niigata / Matsumae chain 2S4 Niigata / Miho Wan chain 2S5 Tsushima / Miho Wan chain

REFERENCE: USCG web page: http://www.uscg.mil/lantarea/bjc/aton.htm Loran A History Site http://www.loran-history.info/loran-A.htm 15) Frank Statham <fstatham(at)telus.net> Public Works Canada http://www.pwgsc.gc.ca/db/text/archives/2002/summer2002/article009-e.html USCG web page: http://www.uscg.mil/lantarea/bjc/aton.htm 

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