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?	MSRP
RTL-SDRv3	R820TR2	2.4 sustained 3.2 peak		8	25--1750	No	No	$20
NooElec NESDR SMArt	R820TR2	2.4 sustained 3.2 peak	225--300kHz .9--2.56MHz	8	25--1750	No	No	$20
NooElec NESDR SMArt XTR	E4000	2.4		8	65--1100 1200--2300	No	No	$35
SDRPlay RSP2		10		12	DC--2000	No	No	$170
SDRPlay RSP1A	MSI001	6		14	DC--2000	No	No	$100
HackRF One	RFFC5072	20	2--20	8	1--6000	Half	No	$300
AirSpy R2	R820TR2	10	2.5--10	12	24--1800	No	No	$170
AirSpy Mini	R820TR2	12	6	12	24--1750	No	No	$100
AirSpy HF+		0.768		16	DC--31 60--260	No	No	$150
BladeRF 2.0 micro	AD9361	56	61.44	12	47--6000	2x	Cyclone V	$480
BladeRF x40/x115	LMS6002D	28	40	12	300--3800	1x	Cyclone IV	$420
Ettus B210 USRP	AD9361	56	61.44	12	70--6000	2x	Spartan 6 XC6SLX150	$1100
Ettus B200 USRP	AD9361	56	61.44	12	70--6000	1x	Spartan 6 XC6SLX150	$675
Per Vices Noctar		250	125	12 / 16	DC--4000	1x	Cyclone IV	$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. 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.

Hardware-specific packages

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