Development and evaluation of a programmable radio frequency signal

Abstract

Most commercially available signal generators make use of a phase-locked loop in combination with analogue frequency synthesis to generate the desired frequency range. Advances in the development of components being used in digital frequency synthesis have made the use of direct digital synthesis (DDS) a viable option in radio frequency (RF) signal generation. The project consists of designing the interfacing between a DDS unit and a microcontroller to provide a versatile frequency generator in the lower high frequency (HF) spectrum. The research was aimed at testing the following hypothesis: A programmable Radio Frequency signal generator can be developed, using a DDS-based system with a microcontroller providing the required intelligence. A continuously variable frequency range in 1 Hz steps over a spectrum of 0- 10 MHz can be achieved. The following features were included in the design of the signal generator: • Setting the generator to a specific frequency; • Displaying the frequency and prompts from the microcontroller on a liquid crystal display; • Interfacing with a keypad; • Interfacing with a personal computer for remote RS232 operation; • Interfacing with a rotary optical encoder for up-and-down frequency control; • Sweeping of a range of frequencies; • Setting the step size of frequency increments; • Frequency shift keying (FSK) capability. The above features allowed ample demonstration of the software control over the associated hardware and enabled easy evaluation of the product. To evaluate the product, it was decided to concentrate on the following measurable aspects of a typical radio frequency (RF) signal generator: • The accuracy of the output frequency; • Evaluating the frequency range limits of the generator; • Making a spectral analysis of the output signal. During the execution of the project, insight was gained with respect to the following: • DDS theory; • DDS hardware interfacing; • C-programming as well as using the versatile DSSOOO microcontroller; • The importance of sound design principles in a hybrid digital and analogue radio frequency project. • Setting the step size of frequency increments; • Frequency shift keying (FSK) capability. The above features allowed ample demonstration of the software control over the associated hardware and enabled easy evaluation of the product. To evaluate the product, it was decided to concentrate on the following measurable aspects of a typical radio frequency (RF) signal generator: • The accuracy of the output frequency; • Evaluating the frequency range limits of the generator; • Making a spectral analysis of the output signal. During the execution of the project, insight was gained with respect to the following: • DDS theory; • DDS hardware interfacing; • C-programming as well as using the versatile DSSOOO microcontroller; • The importance of sound design principles in a hybrid digital and analogue radio frequency project.