Gqrx

gqrx "is an open source software defined radio receiver (SDR) powered by the GNU Radio and the Qt graphical toolkit." It supports multiple SDR hardware devices, including (but not limited to) the RTL-SDR, HackRF, and Airspy. A complete list of supported hardware can be found at https://gqrx.dk/supported-hardware.

Notable features include AM, SSB, CW, and (wide) FM demodulation, spectrum plots and waterfalls, and the ability to record and stream audio output. A more complete list of features can be found on the gqrx website: https://gqrx.dk/

Kernel
If using an RTL-SDR, you will need to configure your kernel to blacklist the rtl2832 module, as the normal DVB-T driver is not compatible for its use as an SDR. More information regarding this can be found on the RTL-SDR wiki page.

USE flags
USE flags for gqrx itself are as follows:

It is important to specify the correct USE flags for the net-wireless/gr-osmosdr dependency, or else gqrx will not find your SDR device:

For example, if one has an RTL-SDR, the following can be used:

Files

 * - User configuration file for the configured SDR device.

The above file will be created on first launch when selecting the SDR device and associated options. If the supplied config results in an error, gqrx will detect this and let the user re-specify their config on the next launch.

Invocation
Start gqrx's graphical interface as follows: Additional options can be seen with -h/--help:

Troubleshooting
SDR device not listed

If the SDR device you are trying to use is not listed, then it is possible that net-wireless/gr-osmosdr was not compiled with the correct USE flag(s). Launch gqrx from the command line and look for the following line:For reference, a build of gr-osmosdr with support for most SDR devices will look like this:Check the USE flags that are set for the net-wireless/gr-osmosdr package to ensure the correct one(s) are set for your devices.

External resources

 * The gqrx homepage