With some insight from Gert Baars, you can build an instrument that integrates both a sweep frequency generator and a spectrum analyzer. Let’s take a look at the design.

System Overview

In the sweep frequency generator mode, also known as a 'wobbulator,' the device measures the frequency response of various components or circuits up to 450 MHz. In spectrum analyzer mode, it evaluates the outputs of circuits, equipment, and antennas, providing a comprehensive analysis of their frequency characteristics. This combination allows for versatile testing and analysis in RF applications.
 
sweep generator block diagram
Block diagram of the sweep frequency generator/spectrum analyzer.
The measurement system consists of two parts: a hardware module in a separate enclosure with all the signal inputs and outputs and software that runs on a PC. The measurements are displayed in graphic form on the PC monitor, and the user can configure all the variables and options as desired via the keyboard.

Refer to the schematic in the article, which will be free to download for the two weeks after the publication of this news item. As you will see, the DDS IC occupies a central position.
 
RF sweep generator article Elektor
Click to access the article.
“The original intention was to simply make a sweep frequency generator (SFG) for frequencies extending as far as the UHF (70 cms) band, Baars explains. “However, the idea of adding a spectrum Analyzer function arose quite quickly. This is only natural, since an SFG already includes a large number of the elements necessary for a spectrum Analyzer, such as a DDS (direct digital synthesizer) IC, a logarithmic detector, and a microcontroller with an A/D converter and UART. The main additional elements that are necessary are a mixer and some IF filters. Of course, the software must also be able to make use of both functions.

RF Sweep Frequency Generator/Spectrum Analyzer Article

Baar’s article, “RF Sweep Frequency Generator/Spectrum Analyzer,” was published in Elektor October 2008. The article is freely available to everyone in the community for at least the two weeks after the publication of this news item. Enjoy!
Editor's Note: This article was originally published in a previous edition of our magazine. Please note that some of the products (e.g., PCBs) and links may no longer be available. However, we believe the educational content remains valuable and hope it inspires you to embark on new and exciting projects.
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