Rtl-sdr

Introduction
RTL-SDR is a driver that enables the use of a Realtek RTL2832-series based DVB-T tuner as a cheap (<$25 USD) Software Defined Radio.

Kernel
RTL-SDR is incompatible with the rtl2832 driver kernel module. If this module has been built it must be blacklisted:

If the rtl2832 driver was built into the kernel it must either be built as a module and blaclksted (if DVB functionality is desired), or not selected.

Userspace
Install the RTL-SDR driver:

Create the sdr group to allow non-root users to access the device:

Add any users that need to access the SDR device to the sdr group:

Use lsusb to confirm the product and vendor IDs of the device:

Add a udev rule to create the device :

Reload udev rules:

Plug in the device and ensure that is created by udev.

Test the device using rtl_test.

Software
Install an application such as CubicSDR to gain a graphical view of the radio spectrum and easily capture FM (etc).

The utility (installed as part of net-wireless/rtl-sdr) can be used to scan the spectrum available to the rtl2832 device (~64 - 1700MHz) for a period of time and output the results to a csv file. This can be converted into a waterfall graph that can be analysed to find interesting signals to investigate.

The example command below will scan from 13MHz to 1750MHz in bins of 200kHz, with a scan interval of 10 seconds for four hours:

This can be converted to a waterfall using the script available here.