Thesis (M.Sc.)--University of Adelaide, 1953. / Typewr. copy.

Thesis (M.S.)--University of Wisconsin--Madison, 1947. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 189-194).

The various stages in the design and construction of a frequency standard for use in microwave spectroscopy is described. Procedures are laid down for the use of the instrument. The standard is of the variable frequency type which gives it several advantages over the fixed frequency machines. It is capable of providing complete coverage at microwave frequencies and is capable of determining the microwave harmonic generated without recourse to a wave-meter. Furthermore it can conveniently be used in conjunction with a calibrated communications receiver to measure frequency separations to a high degree of accuracy. A stable 200 kc crystal controlled oscillator is used as the base frequency. This frequency is multiplied by harmonic generators to 4800 kc and supplied to the oscillator grids of a balanced mixer. The variable 125 to 250 kc output from a BC221 signal generator is supplied to the signal grids of this same mixer. The mixer output is tuned with a band pass circuit passing 4925 to 5050 kc and consequently the two input frequencies are summed. The balanced mixer serves to eliminate several troublesome frequency components. The mixer signal is multiplied successively to 25 mc, 75 mc and 200 mc. An output from one of these VHF stages is chosen and impressed upon a 1N26 silicon crystal rectifier. This rectifier acts as a harmonic generator producing frequency markers in the microwave region. Since both the 200 kc oscillator and BC221 signals have a high degree of stability and can conveniently be calibrated relative to standard frequency broadcasts from the U.S. Bureau of Standards, these microwave frequency markers are known to a high degree of accuracy. This microwave standard signal is fed into the spectrometer waveguide and picked up by a crystal mixer. The spectrometer klystron signal is also detected by this crystal and consequently beats are produced equal to the difference between the standard harmonics and the klystron frequencies. This beat note is supplied to a tuned amplifier whose, output is applied to the Y plates of the spectrometer oscillograph. The time base of the latter is supplied by the sawtooth wave which sweeps the klystron frequency. When the beat note frequency is equal to the frequency to which the amplifier is tuned a marker pip will occur on the screen. Since the frequency of the standard signal and the tuning of the amplifier are known the frequency of the klystron at this point of the time base can be determined. By tuning the variable frequency oscillator, the pip can be moved across the horizontal axis until it is coincident with a spectrum line. Consequently the frequency of this line can be measured with an accuracy of 1 part in 10⁶. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (M.S. in Telecommunication Systems Management)--Naval Postgraduate School, March 1990. / Thesis Advisor(s): Davidson, Kenneth L. Second Reader: Tulloch, A. W. "March 1990." Description based on signature page as viewed on August 26, 2009. DTIC Descriptor(s): Atmospheric Refraction, Very High Frequency, Ultrahigh Frequency, Communication And Radio Systems, Tools, Parameters, Wind, Forecasting, Accuracy, Theses, Electromagnetic Radiation, Pressure, Radiosondes, Refraction, Pacific Ocean, Climatology, Troposphere, Humidity, Gradients, Shores, East(Direction), Computer Printouts, Television Display Systems, Weather, Guided Missiles, Synoptic Meteorology, Test And Evaluation, Data Bases. DTIC Identifier(s): IREPS (Integrated Refractive Effect Prediction System). Author(s) subject terms: Communications, IREPS, refraction. Includes bibliographical references (p. 70-71). Also available online.

Thesis (PhD)--University of South Australia, 1996

Thesis (Ph.D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 124-129)

Thesis (M.Eng.Sc.)--School of Electrical & Electronic Engineering , 2005.

A range of shortwave frequencies will be returned to earth by the ionosphere such that long-distance shortwave communication is accomplished. Because of ionospheric variations, operation parameters are not the same in different time duration. We must select optimized parameters with the aim of utilizing the ionosphere effectively for shortwave radio communications. Shortwave propagation prediction programs can provide such information. Empirical models are often used to represent the variations of the electron density with height in the ionosphere, since radio propagations are concerned with electron density. We develop a graphical user interface based on VOACAP that is one of the most widely used prediction programs. We also improve the electron density model in VOACAP. A gradient discontinuity occurs in the original parabolic ionospheric model. We incorporate an electron density model that does not contain any gradient discontinuities. In this model the electron density profile is composed of three segments: (1) a cosine F2 layer; (2) an E-F layer comprising a secant function, and optional cosine function to provide an F1 ledge (3) a parabolic E layer. Compared with experimental data, our modified model results in more accurate predictions.

No description available.

Thesis (PhD) -- University of South Australia, 1998.