Six radios, and none of them expensive
Hardware for WaveShark
A €30 dongle does most of what this site describes. An Airspy buys more of the band at once and the HF+ the shortwave, a HackRF or a LimeSDR buys the wide protocols and a transmitter, a PLUTO transmits and receives at once, and a tuner on another machine puts the antenna where the signals are.
Any RTL2832U dongle, from about €30
RTL-SDR
The dongle that does the narrowband half of everything on this site: sensors, meters, aircraft, shipping, pagers, digital voice, radiosondes and weather satellites.
What it reaches →24 MHz to 1.8 GHz, 12 bit
Airspy R2 and Mini
The dongle’s range with four times the span and 12 bit samples, driven with no libairspy, on the desktop or in a browser.
What it reaches →HF+ and HF+ Discovery, shortwave to 260 MHz
Airspy HF+
Shortwave with no upconverter, and VHF to 260 MHz, on a receiver built for a crowded band. For FT8, DRM, weather fax, RTTY and Morse.
What it reaches →1 MHz to 6 GHz, transmit and receive
HackRF One
Wide enough for Wi-Fi, Bluetooth, drone Remote ID, television and 5.8 GHz video, and the cheapest way to get a transmitter into the same flow graph.
What it reaches →USB and Mini, full duplex, 12 bit
LimeSDR
Everything the HackRF reaches below 3.8 GHz, plus full duplex, 12 bit samples and a span wide enough for a whole satellite transponder.
What it reaches →Full duplex, on USB or the network
ADALM-PLUTO
A cheap full duplex transceiver, reached over USB or across the network, receiving and transmitting at once up to 4 MS/s.
What it reaches →IQStream, rtl_tcp, SpyServer and KiwiSDR
Remote tuners
A tuner on a machine at the mast, somebody else’s shared receiver, or several of them stitched into one wider span, opened as if it were plugged in here.
What it reaches →
The dividing line is bandwidth, not cleverness: one Wi-Fi channel is 20 MHz and a television multiplex is 8, where a dongle carries about 2.4. Everything narrower than that, which is most of the decoder list, runs on the cheapest receiver ever made.
Got a radio already?
Plug it in and press play. It opens on 433.92 MHz, where the devices it decodes are.
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