Hyperbolic Navigation

Hyperbolic navigation A class of navigational system based on the difference in timing between the reception of two signals, without reference to a common clock. Timing reveals the difference in distance from receiver to the two stations. plotting all potential locations for measured delay produce a series of hyperbolic lines in a chart Taking two measurements and finding their intersection reveals receiver’s location Any other form of navigational information can be used to eliminate ambiguity and determine a fix.

Hyperbolic navigation earliest known use was during World War I as acoustic location system for locating enemy artillery Based on radio techniques: GEE by Royal Air Force for use by RAF Bomber Command Decca Navigator System in 1944 by the Royal Navy LORAN by the US Navy for long- range navigation at sea

Hyperbolic navigation Timing-based navigation baseline T R “secondary” 300km, exactly 1ms apart at light speed T “master” Two ground-based radio stations Both equipped with identical transmitter One of the station is equipped with a radio receiver, called “secondary” When the receiver hears the signal from the other station referred to as the “master” The master can broadcast any series of pulses, with the secondary hearing these and generating the same series after 1ms delay.

Hyperbolic navigation Absolute vs. Differential timing Time it took to reach the receiver- basis of modern electronics 1930s: crystal oscillator- drifts 1 to 2 seconds in a month 1960s: commercial atomic clocks Difference between two signals 1935 and 1938: Chain Home by UK – radar didplay s based on oscilloscopes, producing a “blip” when return signal sent into the scope display The signals from secondary arrive they would cause a blip on the display in the same fashion as a target on a radar, and the exact delay between the master and secondary can be easily determined.

Hyperbolic navigation If the receiver is located on the midpoint of the baseline the two signals will be received at exactly the same time, so delay between them will be zero. Receiver cannot determine exact location, only that it lies perpendicular to the baseline By plotting a chart, producing a measured delay they form a hyperbolic curve centred on the baseline The operator can determine which of these lines they lie on by measuring the delay and looking at the charts Consists of nothing more than a conventional radio receiver hooked to an oscilloscope

Gee System

GEE System Development October 2937, R. J. Dippy : system that would measure difference in time arrival 1938, Dr R. V. Jones: suggested use of pulse transmitters but without success 1940, R. J. Dippy : for a master station with three slave for navigation December 1942, R. J. Dippy : awarded the British Patent 581602 for his invention Trinity – the three transmitter used to ascertain position “Goon” – mask of the name GEE “grid” – the meaning of GEE, the electronic grid latitude and longitude derived from the combination of three signals received by the aircraft

GEE System Signal Characteristics transmission of short (6 microseconds) pulses at frequencies around 30Mhz(later extended up to 80Mhz) Slaves operate on the same frequency as their master On baseline extension behind the slaves the difference would be zero and the pulses would overlap. Sample of the GEE lattice

GEE System Signal Characteristics master (A) always appeared at the start of both traces of a twin trace presentation. The B slave after the master on the top trace, the C slave after the master on the lower trace, and the D slave appeared on both traces but was a double pulse. The correct A pulse for starting the time base was selected by arranging the A transmitter to transmit twice as fast as the others but making every other pulse a double one. The final appearance of the time base was as in the figure.

A GEE Mk II rceiver/indicator with cabling GEE System GEE Equipment A GEE Mk II rceiver/indicator with cabling

Gee station components GEE System GEE Equipment Gee station components

Gee set installation in a Lancaster bomber mockup GEE System GEE Equipment Gee set installation in a Lancaster bomber mockup

Close up of Gee Indictor GEE System GEE Equipment Close up of Gee Indictor

GEE System GEE CHAINS Become the standard in the US eight Air Force as well as in RAF Radiated power output around 330kW and operated in four frequency bands between 20 and 85 MHz. Approximately limited to 150 miles at ground level and 450 miles for high flying aircraft 1954 – a new receiver was designed 1970- the last GEE chain being taken out of service GEE coverage in UK in August 1948