RTL-SDR | Smart Ham Radio

What is Software Defined Radio?

Radio components such as modulators, demodulators and tuners are traditionally implemented in hardware components. The advent of modern computing and analogue to digital converters allows most of these traditionally hardware based components to be implemented into software instead. Hence, the term software defined radio. This enables easy signal processing and thus cheap wide band scanner radios to be produced. Software-defined radio (SDR) is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system. While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which used to be only theoretically possible. This enables easy signal processing and thus cheap wide band scanner radios to be produced

What is RTL-SDR?

RTL-SDR is a very cheap ~$25 USB dongle that can be used as a computer based radio scanner for receiving live radio signals in your area (no internet required). Depending on the particular model it could receive frequencies from 500 kHz up to 1.75 GHz. Most software for the RTL-SDR is also community developed, and provided free of charge.

The origins of RTL-SDR stem from mass produced DVB-T TV tuner dongles that were based on the RTL2832U chipset. With the combined efforts of Antti Palosaari, Eric Fry and Osmocom (in particular Steve Markgraf) it was found that the raw I/Q data on the RTL2832U chipset could be accessed directly, which allowed the DVB-T TV tuner to be converted into a wideband software defined radio via a custom software driver developed by Steve Markgraf. If you’ve ever enjoyed the RTL-SDR project please consider donating to Osmocom via Open Collective.

Over the years since its discovery RTL-SDR has become extremely popular and has democratized access to the radio spectrum. Now anyone including hobbyists on a budget can access the radio spectrum. It’s worth noting that this sort of scanner capability would have cost hundreds or even thousands of dollars just a few years ago. The RTL-SDR is also sometimes referred to as RTL2832U, DVB-T SDR, DVB-T dongle, RTL dongle, or the “cheap software defined radio”.

There are now many other software defined radios better than the RTL-SDR, but they all come at a higher price. Currently we think that the Airspy ($169) and SDRPlay ($99) SDR’s are the best low cost RX only SDR’s. There is also the HackRF ($300USD) which can both transmit and receive.

What is RTL?

In digital circuit design, register-transfer level (RTL) is a design abstraction which models a synchronous digital circuit in terms of the flow of digital signals (data) between hardware registers, and the logical operations performed on those signals.

Register-transfer-level abstraction is used in hardware description languages (HDLs) like Verilog and VHDL to create high-level representations of a circuit, from which lower-level representations and ultimately actual wiring can be derived. Design at the RTL level is typical practice in modern digital design.[1]

Unlike in software compiler design when register-transfer level intermediate representation is the lowest level, RTL level is the usual input that circuit designers operate on and there are many more levels than it. In fact, in circuit synthesis, an intermediate language between the input register transfer level representation and the target netlist is sometimes used. Unlike in netlist, constructs such as cells, functions, and multi-bit registers are available.[2] Examples include FIRRTL and RTLIL.