SDR

The SDR software stack, at least according to PothosWare (authors of SoapySDR)

Software-defined radio moves the majority of radio processing into software, facilitating relatively inexpensive wide-band hardware interfaces to the electromagnetic spectrum, especially those frequencies below 3GHz. Pairing advanced SDRs with software-defined antennas yields dynamically optimal cognitive radio. Perhaps most famously, DVB-T television tuners built around the RTL2832U chip, and available in USB form factor for less than $30 (particularly the Rafael Micro R820T2), can reliably provide 2MHz of RX bandwidth anywhere from ~30MHz to ~2GHz (still lower frequencies are supported via direct sampling). For $500, powerful units capable of tremendous bandwidth and range (as well as transmission capabilities) are available, and from there it's not that great a leap to building your own stingray--if the cops have 'em, so should you, doyouknowhatiamsayin?

On the more ballin' end of things, a tricked-out Per Vices Cyan will run you $290k before shipping.

Hardware

Device	Tuner	BW (MHz)	Samples (Msps)	ADC	Tune (MHz)	Xmit?	FPGA?	Bus	MSRP
RTL-SDRv3	R820TR2	2.4 sustained 3.2 peak		8	25--1750	No	No	USB2A	$20
NooElec NESDR SMArt	R820TR2	2.4 sustained 3.2 peak	225--300kHz .9--2.56MHz	8	25--1750	No	No	USB2A	$20
NooElec NESDR SMArt XTR	E4000	2.4		8	65--1100 1200--2300	No	No	USB2A	$35
SDRPlay RSP2		10		12	DC--2000	No	No	USB2B	$170
SDRPlay RSP1A	MSI001	6		14	DC--2000	No	No	USB2B	$100
HackRF One	RFFC5072	20	2--20	8	1--6000	Half	No	USB2Aµ	$300
Mirics MSi3101	MSi001
AirSpy R2	R820TR2	10	2.5--10	12	24--1800	No	No	USB2Aµ	$170
AirSpy Mini	R820TR2	12	6	12	24--1750	No	No	USB2Aµ	$100
AirSpy HF+		0.768		16	DC--31 60--260	No	No	USB2Aµ	$150
bladeRF 2.0µ xA4	AD9361	56	61.44	12	47--6000	2x	Cyclone V	USB3B	$480
bladeRF x40	LMS6002D	28	40	12	300--3800	1x	Cyclone IV	USB3B	$420
Ettus B210 USRP	AD9361	56	61.44	12	70--6000	2x	Spartan 6 XC6SLX150	USB3B	$1100
Ettus B200 USRP	AD9361	56	61.44	12	70--6000	1x	Spartan 6 XC6SLX75	USB3B	$675
Per Vices Noctar		250	125	12 / 16	DC--4000	1x	Cyclone IV EP4CGX22C	4xPCIe	$2500

Software

The Linux SDR software ecosystem is robust, but complex. There are multiple middleware layers available, providing generic access to various hardware devices; many user-exposed applications support both middlewares, sometimes in addition to their own native hardware support. As a result, there can be multiple ways to specify a given piece of hardware in a particular tool.

Kernel

At the lowest level live the various driver libraries for SDR hardware. It is atypical for SDR hardware to require (or provide) a Linux kernel driver; most appear to be implemented wholly in userspace atop raw USB devices (exceptions include the Mirics MSi2500 and the Ettus USRP). Indeed, the primary interaction most users will have with their kernel might be removing (and possibly blacklisting) the dvb_usb_rtl28xxu DVB driver autoloaded for the RTL-SDRv3 USB dongle. This driver prevents the RTL from being used with rtl_sdr, the userspace RTLSDR libraries. To blacklist it, create an entry ending in .conf in /etc/modprobe:

dank@vespula:~$ cat /etc/modprobe.d/blacklist-rtl8xxxu.conf 
blacklist dvb_usb_rtl28xxu
dank@vespula:~$ 

note that users of initramfs might need to rebuild or modify their initramfs to include this file. Adding a blacklist entry does not remove a loaded module; for that, use rmmod dvb_usb_rtl28xxu.

Userspace drivers

As noted above, most of these drivers work on raw USB devices. You'll need set up appropriate udev rules to give users permission.

Family	Software	Source	Tools
RTL2832U	rtl-sdr from OsmoCom	https://github.com/osmocom/rtl-sdr.git	rtl_test, rtl_sdr, rtl_power, rtl_tcp, rtl_fm, rtl_eeprom, rtl_adsb
HackRF	libHackRF from Great Scott	https://github.com/mossmann/hackrf.git	hackrf_cpldjtag, hackrf_debug, hackrf_info, hackrf_spiflash, hackrf_sweep
BladeRF	libbladerf from Nuand	https://github.com/Nuand/bladeRF	bladeRF-cli, bladeRF-fsk, bladeRF-install-firmware
Airspy	AirSpy One from AirSpy	https://github.com/airspy/airspyone_host.git	airspy_gpio, airspy_gpiodir, airspy_info, airspy_lib_version, airspy_r820t, airspy_rx, airspy_si5351c, airspy_spiflash
Ettus	UHD from Ettus	https://github.com/EttusResearch/uhd.git	uhd_cal_rx_iq_balance, uhd_find_devices, uhd_siggen, uhd_cal_tx_dc_offset, uhd_image_loader, uhd_siggen_gui, uhd_cal_tx_iq_balance, uhd_images_downloader, uhd_usrp_probe, uhd_config_info, uhd_rx_cfile