No description available.

Thesis (M.S.)--Ohio University, March, 1993. / Title from PDF t.p.

M.Ing. / The aim of this project is to research the feasibility of an all-fibre laser distance measurement device that utilises a figure-eight fibre laser (F8L), in the nonlinear amplifying loop mirror (NALM) configuration, as a light source and implements pulse compression to improve the accuracy and signal-to-noise ratio of the system. A figure-eight fibre laser in the NALM configuration for use in a laser distance measurement device is described. The theory of fibre lasers is discussed, including mode-locking and Qswitching, and the characteristics of a NALM loop are analysed. By varying the length of the NALM loop from 500 m to 2000 m or inserting highly nonlinear dispersion shifted fibre, a variety of pulses in the picosecond to nanosecond range can be produced. The lengths of the pulses depend on the length of the NALM loop, the pump power and the setting of the polarisation controllers. The figure-eight fibre laser is pumped with a 980 nm laser diode up to 550 mA, which corresponds to 320 mW. Distance measurements are done with short unmodulated and long modulated pulses. Distance measurement with short unmodulated pulses is discussed only briefly and tested with a simple experiment. The focus of this project is distance measurement with long modulated pulses. A low autocorrelated binary sequence is modulated onto one of the long pulses produced by the figure-eight fibre laser by an electro-optic amplitude modulator. The long pulse gives the proposed system a good signal-to-noise ratio (SNR), while the modulation improves the accuracy. A Barker code of length 13 is proposed as modulation code because of its good autocorrelation properties. The Barker code will improve the accuracy 13-fold, with a corresponding increase in SNR. An electro-optic amplitude modulator is used to implement the modulation. The modulated long pulse is then sent to a target. After reflection, the signal is detected and cross-correlated to obtain the time-of-flight for the pulse. The code generation and cross-correlation are implemented with an FPGA via VHDL programming. The distance to a target can be calculated by knowing the time-of-flight and the speed of light in the propagation medium. In this project the resolution, single-shot precision, accuracy, linearity, repeatability and maximum unambiguous distance of the proposed all-fibre laser distance measurement device are examined.

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This report summarizes the design of a DME (Distance Measuring Equipment) simulator to be used in the testing of an Area Navigation System. The purpose of the simulator is to generate a signal representing an aircraft's distance from a ground station. This information is in the form of two pulses whose separation represents that elapsed transmission time for an aircraft to receive a reply from the ground station to an interrogation by the aircraft. The pulse spacing must be selectable as fixed distances for static tests and as distance changing at a constant rate to simulate flying to or from the station for dynamic testing. Thumbwheel switches are used to input fixed distances and up/down counters provide inbound and outbound range rates. The rate clock is derived from a crystal oscillator whose output is divided down by a programmable, modulo-n, divider to the desired rate/frequency. This input distance information, available in parallel binary coded decimal format, is then converted to the required pulse pair spacing. This is accomplished with presettable down counters clocked by another crystal oscillator whose frequency represents two-way propagation time for radio waves.

This report summarizes the design of a digital frequency synthesizer for airborne distance measuring equipment. It is the purpose of the frequency synthesizer to provide a stable frequency source for the local oscillator of the airborne receiver and for the power amplifiers in the transmitter chain. The synthesizer is required to furnish a frequency ranging from 260.250 mHz to 287.50 mHz in channel steps of 250 kHz at a power level of +7.0 dBm. the stability of the frequency must be greater than .005% over the temperature range of from minus 45 degrees centigrade to plus 55 degrees centigrade, requiring a crystal controlled source. Digital techniques are employed using two crystal controlled oscillators to synthesize all required channel frequencies. Linear circuits using standard configurations are employed for the oscillators, buffers, and mixers. Primary attention is paid to optimizing the transient characteristics of the synthesizer which employ programmable digital counters to change the division ratio in a phase locked loop. Decoding is provided to interface the modulus of the counters with the aircraft cockpit controls.

Three systematic instrumental errors exist in electronic distance measuring instruments (EDMI): 1) scale error, 2) constant offset error, and 3) cyclic error. The potential magnitude of these errors requires that each EDMI should be calibrated for all three errors. The calibration constants of EDMI may be monitored on an arbitrary base line; however, a calibrated base line is required to perform an accurate EDMI calibration for constant offset and scale errors. Calibration of cyclic error requires monumentation not normally found on a calibration base line. Cyclic error can be measured on a short base line in the laboratory. The surveyors in the State of Virginia would benefit from a statewide network of calibrated base lines. A network covering the state would provide convenient access for the state's surveyors. A unified network of base lines would give the states surveyors a standard of comparison for their EDMI. This standard of comparison would be nationwide if Virginia would choose the National Geodetic Survey (NGS) to calibrate the base lines in its network. Base line calibration by NGS would require that the state abide by NGS specifications for establishing its base line network. / M.S.

Thesis (M.S.)--Ohio University, June, 2001. / Title from PDF t.p.