I came up with this idea after seeing Farhan Ashar’s spectrum analyzer design which uses some of the same bits and pieces I used in the Simple Scalar Network Analyzer. Farhan’s is a classic heterodyne SA design – the addition of mixers and filters in front of the power detector makes the analyzer frequency selective, vs the Simple Scalar Network Analyzer which is not. Both tools are quite useful to the RF hobbyist.
PyDSA takes a different approach – high speed direct digital sampling. This method is used in some inexpensive but quite powerful analyzers from Tektronix, Signal Hound and other companies. The bandwidth of such a device is limited by the sampling speed which according to Nyquist’s criteria must be at least twice the frequency we wish to analyze. To be useful for amateur radio work we would like to have a bandwidth of 100 MHz or more which means sampling at at least 200 MHz. Unfortunately, a 200 MHz sampler is not an easy thing to build at home…
Details at rheslip’s Open Emitter blog.