The aim of my thesis is to present a method for developing a personal computer controlled radio spectrum monitoring system operating in the shortwave (1 – 30 MHz) frequency range. My work is divided into two main parts. In the first part I create a method for designing broadband shortwave loop antennas. Then I use this technique for designing and building an antenna suitable for shortwave spectrum monitoring purposes. In the second part I discuss the steps of creating a computer controlled spectrum measurement system based on discrete Fourier transform (DFT).
In unit 1.1 I summarize the characteristics of small loop antennas, then I define their equivalent circuit and their design parameters. I work out a method for adjusting these parameters using a set of curves. I check the reliability of the equivalent circuit by simulation and measurement. Finally I use the developed design method to create a broadband loop antenna for the spectrum measurement system.
In unit 1.2 I design the antenna amplifier. I first define the amplifier design parameters. This is followed by describing the amlifier circuit and calculating the value of its components. I analyze the performance of the device by simulation and measurement. I piece the amplifier and the loop antenna together and make measurements with the assembled active antenna.
In unit 2.1 I discuss the basic theory of spectrum estimation using DFT. I also include program code examples.
Based on the theory described in unit 2.1 I develop a computer-controlled spectrum measurement application using a highspeed digitizer card in unit 2.2. I demonstrate its performance by measurement.
Finally I describe a possible realization of a laptop-controlled shortwave spectrum measurement system using sound card data acquisition.