ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / During the program researching on airborne telemetering transmitter of a certain remote telemetry system, small size and a variety of voltage on board are design difficulties. Due to the above important factors, the performance of power supply makes a big affect to the parameters of BPSK modulated signal, especially the EVM (Error Vector Magnitude). The author analyzes the cause of power supply noise and puts forward some suggestions to damp the noise. With these methods, the EVM of modulated signal is improved. Finally, we can conclude the related principles about the suppression of power supply noise.

The development of a novel type of resonant sound absorber is described, designed specifically for the absorption of sound at low frequencies and at high intensities. A review of previous work on resonant sound absorbers shows that existing theoretical models for describing the phenomena are incomplete and that there remains a need for further extensions to the relevant models to cater for non-linear effects which become particularly important at high intensities. It is also shown that there are limitations to the current methods for testing absorbers which make them less suitable at low frequency and when the signals are nonharmonic. In the present work a theoretical model of a Helmholtz type of absorption resonator working in the nonlinear regime is developed using nonlinear hydrodynamic equations for viscous incompressible fluids. The model is able to predict the input impedance, the resonant frequency and the absorption coefficient of the device under nonlinear conditions. The model is also used to account for "difference frequency" generation, the reflection of signals of any shape from the surface, and the isolation characteristics of this type of absorber when a porous layer is fixed to the back of the resonant cavity. A new method for the development of acoustic characteristic~ of resonant sound absorbers is described, which was developed as part of the present work and which overcomes the limitations of existing methods. Measurements carried out using this and other techniques show that the acoustic characteristics of the absorber described are very close to those predicted from the model. A new type of packless absorber (one without fibrous material) based on the above theoretical model is described. Such an absorber has been constructed and tested in a reverberant sound field and is shown to provide effective sound absorbtion under conditions typical of a working industrial environment.

An inadequate level of noise attenuation provided by a building element is frequently the result of a lack of completeness in the construction. This often invisible fault acts as a noise source in a room, so in order to undertake remedial work the source position must be found. Recently, near field noise intensity measurement has been the popular method for noise source location in buildings. This method of using intensity studies requires a grid of readings to be taken. An alternative method, the one used in this work, employs a different strategy. Here, the source location is identified by direction scanning of time delays at a number of microphones arranged in a regular three-dimensional array. A novel arrangement of seven microphones, in the shape of a wheel-brace, is used to measure the differences in time taken for the sound waves to travel from a source to the various microphones. The magnitudes of these time differences are combined and converted into the coordinates of the source, relative to an origin which is placed at the centre of the wheel-brace array. The mathematics for this conversion is derived and the errors in the experimental arrangement discussed. The use of this airay for the identification of faults in built structures is explored. A significant contribution is made to the knowledge of noise source location in buildings, since the microphone array is used to demonstrate the location of a noise source irrespective of the direction of the incoming noise. The use of computerised data collection is described for a budget system, where time was cheap, but equipment expensive. The accuracy of the technique would be improved considerably if state-of-the-art electronics were used to measure the lime differences. The feasibility, advantages and potential performance of a modem system, that could be assembled today, is described and discussed.

Noise in electronic circuits can sometimes cause problems. It is especially problematic in for example high sensitive sensors and high end audio and video equipment. In audio and video equipment the noise will make its way into the sound and picture reducing the overall quality. Sensors that are constructed to sense extremely small changes can only pick up changes larger than the noise floor of the circuit. By lowering the noise, sensors can achieve higher accuracy.  This thesis presents an ultra low noise solution of the biasing circuitry to the bolometer used in one of FLIR Systems high end cameras. The bolometer uses different adjustable direct current voltage sources and is extremely sensitive to noise. The purpose is to improve the picture quality and the thermal measurement resolution. A prototype circuit was constructed and in the end of the thesis a final circuit with successful result will be presented.

International Telemetering Conference Proceedings / October 29-November 02, 1990 / Riviera Hotel and Convention Center, Las Vegas, Nevada / An innovative digital approach to analog noise synthesis is described. This method can be used to test bit synchronizers and other communications equipment over a wide range of data rates. A generator has been built which has a constant RMS output voltage and a well-defined, closely Gaussian amplitude distribution. Its frequency spectrum is flat within 0.3 dB from dc to an upper limit which can be varied from 1 Hz to over 100 MHz. Both simulation and practical measurement have confirmed that this generator can verify the performance of bit synchronizers with respect to the standard error rate curve.

No description available.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / Current IRIG standards provide guidelines for system phase noise and several manufactures provide receivers and transmitters that perform within this standard. However, legacy receivers and transmitters that do not meet the current IRIG standards are sometimes still used during a mission. This paper will address how phase noise outside of the current IRIG standard affects the performance of an FM data link when using a trellis demodulator, as well as the performance of an SOQPSK data link in a high phase noise environment. Bit error rate performance and test results at several different rates with various phase noise masks are presented in this paper.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

The aim of this project is two-fold: 1) to investigate developmental differences in intelligibility gains from visual cues in speech perception-in-noise, and 2) to examine how different types of maskers modulate visual enhancement across age groups. A secondary aim of this project is to investigate whether or not bilingualism differentially modulates audiovisual integration during speech in noise tasks. To that end, both child and adult, monolingual and bilingual participants completed speech perception in noise tasks through three within-subject variables: (1) masker type: pink noise or two-talker babble, (2) modality: audio-only (AO) and audiovisual (AV), and (3) Signal-to-noise ratio (SNR): 0 dB, -4 dB, -8 dB, -12 dB, and -16 dB. The findings revealed that, although both children and adults benefited from visual cues in speech-in-noise tasks, adults showed greater benefit at lower SNRs. Moreover, although child monolingual and bilingual participants performed comparably across all conditions, monolingual adults outperformed simultaneous bilingual adult participants. These results may indicate that the divergent use of visual cues in speech perception between bilingual and monolingual speakers occurs later in development. / text

Active noise control, an alternative to conventional passive control, duplicates an existing noise field in antiphase so that when the noise and its antidote are added together the result is silence. This dissertation describes work aimed at implementing active control techniques on various noise problems. As each one was successfully completed confidence grew that the technique is on the verge of becoming a potential reality. The first project demonstrated the cancellation of the discrete frequency sound produced by a pair of large Electricity board transformers; the noise in a nearby office was reduced by some 20 decibels. Initial attempts at broadband cancellation demonstrated the necessity for an adaptable form of filtering. Digital techniques were developed to optimally control one-dimensional sound waves in an air-conditioning duct: some 20 decibels than three octaves of random sound. Their application to a practical problem at the Royal Signals and Radar Establishment, Malvern demonstrated their simplicity and. flexibility: it took only a day to design, and construct a device that stopped the low-frequency sound produced by a Diesel generator from entering an anechoic chamber. Further development has led to. control algorithms for a broadband adaptive controller. Its rapid convergence was demonstrated in an experiment which stopped the sound of a wind tunnel fan from disturbing sensitive measurements of turbulence in the test section. The control of three-dimensional sound presents many practical problems. One possible approach to these problems was presented by Olson in 1953 who described a device for cancelling local noise fields in order to produce a quiet zone in a noisy environment. We built an optimal form of that device and demonstrated some of its potential but its direct incorporation as one of many in an array was shown to result in an unstable system. Slight modification of that system has lead to the design of a stable array that effectively reflects sound. An investigation was carried out for Rolls-Royce into the possibility of using such an array to stop the broadband, lowfrequency sound, produced by two RB211 engine test-beds, from disturbing people in a large office 250 Metres away. The scale of the. solution was beyond the scope of a PhD. project. Finally a combination of all the techniques developed have been used to assess the possible performance of an active control system in a Fleet Street press room. The predictions are likely to be tested in a demonstration which is currently being planned. This research has helped reveal the major problems inhibiting the application of active noise control methods. Most of these have been overcome so that it should now be possible for the solutions outlined in this thesis to be applied relatively easily to design reliable and effective noise control systems.