SDR Utilities

I’ve been experimenting with an SDR dongle to see how it can be used as a 1.5GHz scalar network analyser, as a time domain reflectometer, and to estimate digital signal edge speeds. While doing that I’ve developed several general-purpose command-line utilities which capture and post-process power spectrums. These utilities are distributed with a MIT licence, and the code is at the bottom of this note.

  • rtlscan: scans, measures and displays a raw scalar power spectrum, and saves the power spectrum in a CSV file
  • rtlplot: displays one or more raw power spectrums
  • rtldiff: displays one or more calibrated power spectrums, i.e. the difference between multiple raw spectrums and a single reference or calibration spectrum
  • rtltdr: displays the impulse response implicit in a calibrated power spectrum

The graphs can have linear or logarithmic frequency axis, can be zoomed, panned and printed, and have text annotations added. The interaction with the SDR dongle is via Kyle Keen’s rtl_power program, so its capabilities and limitations are reflected in these utilities.

As is traditional, these are an unfinished work; I already know of the next change I would make, but I have not verified that it would be an improvement. Nonetheless, the utilities are usable.

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Measuring RF Filters with a Homebrew 1.5GHz Scalar Network Analyser Costing £32/$48

I already have useful low/medium frequency signal sources, spectrum analysers and oscilloscopes. Now I want to inexpensively measure RF filters and transmission line imperfections. This is possible for only £32/$48, as illustrated by the measured response of 300MHz and 460MHz high-pass filters and an open-stub transmission line filter:

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