SDR Soundcard Tester

Posted on Feb 7, 2014

The key to using a soundcard successfully in digital signal processing or digital radio applications lies principally in the characteristics of the soundcard itself. This applies in particular to SDR (software de ¬ ned radio) programs that turn your PC into a top-class AM/SSB/CW receiver, assuming your soundcard cooperates. If you want to experim

SDR Soundcard Tester
Click here to download the full size of the above Circuit.

ent with SDR and avoid a lot of frustration, it is worth checking ¬ rst whether the PC soundcard you plan to use is suitable. There are three essential elements to success: Many laptops have only a mono microphone input, sometimes also rather limited in bandwidth. In this case it may be possible to use an external USB soundcard. Most desktop PCs these days have an internal integrated soundcard, although some of these do not feature an anti-aliasing ¬ lter. Attempts to disable the integrated soundcard and replace it with a better one often meet with failure; again, an external USB soundcard is a possible solution. To avoid guesswork, the best way to proceed is to test the soundcard using this very small circuit. This will help to diagnose any problems and will help determine whether the card is suitable for use with an SDR program. Figure 1 shows a simple square-wave generator built around an NE555 timer IC. At the output is a 15 kHz signal rich in higher harmonics. Using this we can determine whether or not the soundcard can process the harmonics at 30 kHz, 45 kHz and so on. An anti-aliasing filter at the soundcard input should attenuate all signals above 24 kHz. The frequency of the test generator is, within limits, dependent on its supply voltage. Using an adjustable power supply, a frequency range from 10 kHz to 20 kHz can therefore be covered. There are two RC networks at the output of the test circuit, a high-pass...

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