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Development of FFT based network analyzor with 500 kHz bandwidth

Hallgatói project
1996 - 1997

Local supervisor: Kollár István
Official project supervisor: BME MIT

The direct digital synthesis (DDS) has become realizable for practical applications by the increasing speed of digital logic circuits. A totally new generation of signal sources came to the market using DDS, these instruments have enhanced accuracy and services. Recently signal frequencies (of sine wave and others) as high as several hundred megahertz can be produced using this method, digitally. The most important applications are the communication and measurement that can benefit by this, however it is not often even in these areas yet.
As the price of digital signal processors (DSP) decreased, FFT based signal analyzers began to be widely used. Solutions using FFT had relatively large size and cost till now. DSP's can reduce cost and size and/or increase operating speed of instruments that need significant computing performance during signal processing. By combining the DDS and a DSP, a very advantageous network analyzer can be produced, because of its totally digital operation.
This diploma work describes the operation and the experiences of implementing a network analyzer based on this method. One important point of this development is the joining of the DDS to a sampling system. Implementation is more complex because of the undersampling resulted from the relatively high sampling frequency and high A/D converter prices. The main measuring functions are the transfer functions and various kinds of distortion measurements.

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