His AirSpy Mini SDR was connected to a home-brew quadrifilar helical (QFH) “eggbeater” antenna on his roof. What’s nice about this antenna is that it’s fixed rather than tracking ...

and finally into an AirSpy SDR. GNURadio was used to build the spectrometer needed to determine the galactic rotation curve, or the speed of rotation of the Milky Way galaxy relative to distance ...