SDR

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 $140k before shipping.

Hardware

Device	Tuner	BW (MHz)	Samples (Msps)	ADC	Tune (MHz)	Xmit?	FPGA?
RTL-SDRv3	R820TR2	2.4 sustained 3.2 peak		8	25--1750	No	No
NooElec NESDR SMArt	R820TR2	2.4 sustained 3.2 peak	225--300kHz .9--2.56MHz	8	25--1750	No	No
NooElec NESDR SMArt XTR	E4000	2.4		8	65--1100 1200--2300	No	No
HackRF One	RFFC5072	20	2--20	8	1--6000	Half	No
AirSpy R2	R820TR2	10	2.5--10	12	24--1800	No	No
BladeRF 2.0 micro	AD9361	56	61.44	12	47--6000	2x	Cyclone V
BladeRF x40/x115	LMS6002D	28	40	12	300--3800	1x	Cyclone IV
Ettus B210 USRP	AD9361	56	61.44	12	70--6000	2x	Spartan 6 XC6SLX150
Ettus B200 USRP	AD9361	56	61.44	12	70--6000	1x	Spartan 6 XC6SLX150
Per Vices Noctar		250	125	12 / 16	DC--4000	1x	Cyclone IV