Software-Defined Radio (SDR)

Software-defined radio (or SDR) is a simple type of radio tuner, which relies on piggybacked software to tell the radio what to do, instead of built-in firmware and hardware components. Many modern consumer radios are now glorified SDR's, as they are far cheaper to manufacture than your typical digital scanner. This is also extremely useful for hobbyists and other people with too much time on their hands, who can spend forever working on the perfect custom radio setup by tweaking some applications on their computer.

The easiest way to get started with SDR, is with RTL-SDR, which is built off of the notoriously cheap and widely available Realtek RTL2832U. For under fifty dollars, you can get an RTL-SDR starter kit from RTL-SDR Blog or Nooelec, which works with any standard PC and even many phones, as long as you have the right software to make it work. With RTL-SDR you can only receive (no transmit) which is fine if you are using it as a scanner, though some high-end SDR models let you transmit as well.

Note: If you choose to go the RTL-SDR route, do so through Nooelec or RTL-SDR Blog. Because anyone can order a crate of these RTL2832U chips and haphazardly slap them in a case, there are many RTL-SDR knockoffs which are infamously unreliable. DO NOT try to cheap out on these already inexpensive chips by going to Aliexpress or eBay, as YOU WILL REGRET IT.