Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The thesis deals with the extraction of weak radio frequency signals buried in noise by the technique of multichannel spectral analysis based on radio frequency lock-in detection. The technique and the developed instrument find extensive use in the fields of radio astronomy, remote sensing, and spectroscopy.;Radio frequency spectral resolution over a reception range of 0 - 512 MHz was achieved with a multichannel spectrum analyzer consisting of a radio-frequency pre-processor and a set of 64 parallel lock-in receivers. The reception range is divided uniformly into 64 evenly spaced channels of 8 MHz bandwidth. System control was facilitated through a user programmable microcomputer which performs data acquisition, data preprocessing, graphic display, and tape storage.;The technique for resolving weak radio frequency signals has been improved by the application of the concepts of parallel processing, modularity, and symmetry.;The concepts of parallel processing as applied to RF processing of weak signals were successfully employed in the multichannel spectrum analyzer. The resulting system is characterized by reduced hardware complexity, low-noise electronic circuitry, and improved reliability. The concepts of modularity and symmetry proved advantageous in reducing design and hardware development time.;The channel receiver is a novel design based on the principles of superheterodyne reception incorporating improved detection stages. A dual square-law detection scheme for thermal compensation significantly reduced the problem of thermal drift. The gated synchronous detector scheme eliminated contaminating noise that was asynchronous with the chopping signal and also chopper transition noise.;The minimum detectable power across all channels was measured to be -138 dBm (+OR-)1 dB. In addition, across all channels, a noise figure of 3.05 (+OR-) 0.3 dB and a receiver noise temperature of 306 (+OR-) 43 K was measured. Through software control, the system can perform auto-calibration, address any combination of receivers, perform preprocessing of data for graphical display, and perform digital integration for extended periods of time.



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