SDR -- And Why Its Future Looks Bright
A software-defined radio (SDR) is a radio implemented with reconfigurable software, which processes the raw samples of a digitized radio signal. This contrasts with conventional hardware radios, which employ RF circuits and digital signal processors to implement this processing. Because much of the functionality is implemented in software running on a PC and not hardware circuitry, then SDRs typically cost much less. A software-defined radio still requires some hardware, but this hardware is relegated to just receiving and transmitting radio signals. An SDR system consists of a low-cost receiver and a host computer running software that performs data acquisition and analysis, along with a graphical display.
PlutoSDR (ADALM Pluto)
Analog Devices' Active Learning Module (ADALM) PlutoSDR can acquire RF analog signals from 325 MHz to 3.8 GHz out of the box, and from 70 MHz to 6 GHz after applying a simple firmware update. Support for such a wide frequency range allows it to be used as a near real-time RF spectrum analyzer for a wide range of wireless applications. With amazing performance and at a cost between $150 to $200 USD then it's tough to ignore the value it brings to RF diagnostics -- especially since it covers UHF frequencies used by wireless pro audio and both 2.4x GHz and 5.x GHz Wi-Fi bands.
Here is a link that describes the steps for updating the PlutoSDR's firmware -- scroll down to the section entitled "Upgrade ADALM-Pluto Frequency Range".
Why Rational Waves?
An inherent feature that often goes unheralded is Rational Waves' ability to bring wide-band, fine resolution spectrum scans to devices that are otherwise limited by bandwidth or number of data points per scan. PlutoSDR devices are limited by small bandwidth (approx. 20 MHz). By "stitching together" many subscans the software can display wide band (up to 300 MHz) scans with fine resolution, allowing PlutoSDR receivers to be used as near, real-time RF spectrum analyzers. This is the primary value the software brings to the table. In addtion, Rational Waves supports a variety of different RF analyzers and displays data using several types of graphical charts, which help reveal patterns or events in the spectrum data that might otherwise go unnoticed.
Basic Specifications
A SDR receiver is defined by three basic specifications: bandwidth, resolution, and tuning range. Bandwidth is the instantaneous width of frequency content that the SDR receiver can receive. It can be thought of as the width of the SDR’s window into the RF spectrum. Resolution refers to the receiver's ability to distinguish between adjacent signals. If the resolution is too course then adjacent peaks may appear as one. And tuning range is the frequency range that the SDR receiver can tune to -- which is very specific to the receiver's hardware. For example, an AM radio can not receive FM signals and vice-versa.
For RF spectrum analysis, all three specification are important. If bandwidth is too narrow, then you can't scan a wide frequency range such as UHF or Wi-Fi. And if resolution is too course then you can't tell whether a peak is a single transmitter or two adjacent ones. And the tuning range must match with the frequency range you wish to monitor. The PlutoSDR has amazing performance and resolution that when combined with Rational Waves software provides an excellent diagnostic tool for troubleshooting a wide range of RF issues -- including wireless pro audio and both the 2.4x and 5.x GHz Wi-Fi bands.
Antennas
The most under-appreciated component of a wireless system is the antenna -- they are not all created equal. The frequency range supported by an antenna is *very* specific. If the frequency range of the antenna you are using does not match with your particular application then your project will fail. The two stock antennas the manufacturer includes with the PlutoSDR are essentially useless for wideband work. The good news is that antennas are relatively inexpenive -- only a few dollars -- so we recommend purchasing a few and testing which ones work best for your particular RF application.
Cost
PlutoSDR is available from a number of resellers around the world -- a Google search for "Buy PlutoSDR" will yield many results with prices generally ranging between $150 - $200 USD.