This thesis is concerned with two main lines of work which have followed parallel and complementary paths. The first one consists in using the technique of subharmonic sampling to investigate the frequency stabi lity of microwave oscillators using a convenient low frequency replica. The second line has been concerned with a detailed study of the Allan variance and the dependence of this variance on the operation of digital frequency counters, with special emphasis on the effects of 'dead-time'. This has led to the concept of an 'extended' variance over a time window NT obtained by averaging elementary estimates over a window T. After Chapter 1 which contains an overview of the basic concepts of frequency stability and summarises current measurement systems, Chapter 2 discusses in detail the operation of digital frequency counters and related mathematical modelling of the operation. As indicated above the chapter concludes with an original method of obtaining an extrapolated measurement of the two pair Allan variance. Chapter 3 extends the sampling theory to the down-conversion of a microwave signal using trapezoidal pulses with the objective of generating a low frequency replica. Recovery of the sampled signal, optimisation techniques and noise limitations are discussed in detail. Based on these considerations Chapter 4 explains the experimental equipment developed; it allows a microwave signal of up to 3 GHz to be translated down into the range 5 MHz to 7.5 MHz using a sampling gate driven by a variable width pulse generator coherent with a highly stable 5 MHz clock. Chapter 5 discusses the data acquisition and processing together with the calibration and checks of the experimental apparatus. Verification of the operation showed good agreement with the theoretical calculations and with an alternative mixing technique. The thesis concludes with Chapter 6 where after a detailed overview of the research work suggestions are given for further work.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:304204 |
| Date | January 1984 |
| Creators | Faulkner, N. D. |
| Publisher | University of Portsmouth |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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