Amateur radio hobbyists Frank Schmaling (DL2ALF), Wolf-Henning Rech (DF9IC) and Alexander Kurpiers (DL8AAU) have uploaded a pdf document containing slides which show how they made a cheap noise figure indicator using an E4000 RTL-SDR dongle. A noise figure indicator can be used to check the noise figure of various components used in RF applications.

The hardware of the device consists of an RTL-SDR, a MGZ 30889 preamp, a noise source, a 28V boost converter to power the noise source and a serial to USB converter to control the noise source. They also created their own custom software in C# to go along with the hardware.

Their results showed that this setup was comparable to a professional noise figure test set.