In addition to Amateur Radio, I enjoy listening to all sorts of radio signals in the low, medium and high frequency spectrum, from 100 kHz to 30 MHz. And I enjoy using and playing with new technologies, including computer-controlled and software defined radios.
The two main types are :
Conventional superheterodyne radios controlled by software, with either a minimal or no front panel human interface. Signal detection/demodulation is done in hardware/firmware, with "software defined" techniques generally applied only on the last IF. Examples:
Software Defined Radios (SDR). All signal detection/demodulation is done in software. Examples I have used include:
AFEDRI SDR-Net (Ethernet capable, network SDR clients support Windows, Linux, MacOS)
RFSpace Cloud-IQ (network SDR clients support Windows, Linux, MacOS)
SDRPlay, 12/14-bitSDRs, 100 kHz - 380 MHz, 430 MHz - 2 GHz, with support for Windows, Linux, MacOS, Rasberry Pi, and Android
Software Radio Laboratory LLC QS1R (My favorite, receives 7 bands at once, and supports Windows, Linux, and Mac)
KiwiSDR network accessible SDR with web browser interface.
The TV-tuner and "system on a chip" radio revolution
Shortly after the year 2000, a number of specialty chips were developed to support new digital television standards, DVB-T (Europe, Africa, Asia) and ATSC (North America, South America and South Korea). Eventually radio, hardware, and software hobbyists figured out how to repurpose these chips for use as general purpose SDR communications receivers. These chipsets have enabled the production of very inexpensive, yet capable, radios.
One of the earliest and most popular series of such SDRs are the many variants of RTL-SDR. These are based on a variety of chips such as RTL2832U ,Elonics E4000, Rafael Micro R820T/R860/R828D, FitiPower FC0012/FC0012, and the FCI FC2580. Many RTL-SDRs are implemented in the USB-dongle form factor, similar to a USB memory stick. The basic chips have 8-bit analog-to-digital converters, which does limit their dynamic range. More detail about RTL-SDR can be found at RTL-SDR.COM.
Another popular digital Radio/TV chipset from Mirics Semiconductor, the MSi001 tuner chip and the MSi2500 USB interface/ADC chip, are used in the SDRPlay series, the FUNCube Dongle Pro+ and many Chinese "MSI-SDR" or "RSP1" clones.
More recently, the Silicon Laboratories/Skyworks Solutions Si47xx and the NXP TEF6686/TEF6688 radio chipsets, have become very popular. These radios use an ESP-32 microprocessor to control the display and user interface, and do not require an external computer for normal operation. The Si47xx-based receivers can cover 0.1 to 30 MHz with both AM and SSB/CW modes, and the commercial FM bands. The TEF chipsets provide similar frequency coverage, but only AM and FM demodulation, no SSB/CW. There are many variants of the Si4732-based ATS-25 the ATS mini, the Si4734-based ATS-20 and TEF6686 radios.
While computer controlled and SDRs can be much smaller and lighter than conventional or boatanchor radios, many require the use of a separate computer (desktop, laptop, tablet, phone) to control them. My favorite radios support open application programming interfaces and/or front ends that support multiple operating systems. With the Qt framework, there's really no excuse for single-operating system SDR front ends.