I was working on a project for a biologist friend of mine, that involved tracking RF tag implants on wildlife, using an SDR DVB-T dongle. He wanted a portable solution to be placed near the sprainting places of Otters(Lutra lutra), the main subject of the study, where they regularly come to deposit scent marks.
An RF tag is implanted on the animal which sends pulses on a frequency unique for each tag, this way we're able to tell them apart, this is what a cheap RF tag looks like, this one has a frequency of 148.354Mhz
The osmocom project provides a user space driver for the dongle, I started with pyrtlsdr, a Python binding for librtlsdr, and pylab for signal processing of the samples collected by the SDR, to compute and plot the PSD, that last spike corresponds to the signal of the RF tag above:
Finally, I ported everything to an olinuxino ARM-based board running Linux, a script runs on boot and logs the detected frequencies to file on SD card for later processing, the board still hasn't been tested in the field yet, I'm still working out some issues with the power management.