Software Defined Radio (SDR)

While not really a topic important to new hams, Software Defined Radio (SDR) crops up often in amateur radio publications and advertising so we should at least introduce the idea here.

As its name suggests, SDR involves software working in radio equipment.  More than just being used for operator interface and general control, SDR software specifically replaces the functions of signal processing hardware employed by traditional radio circuits.


SDR greatly simplifies radio circuitry by replacing the functions of hardware oscillators, mixers, filters, modulators/demodulators, and detectors with software.  Since software is easily changed this also means that radio functionality may easily be improved or enhanced, or allow for new modes, protocols, and interfaces to other devices by reconfiguration or reprogramming.

SDR may be used on radio transmitters but the most common implementation is with receivers.  Most of the popular and available SDR products are receivers and most employ direct digital conversion techniques.


One of the more defining characteristics of SDR is the user interface (integrated or PC display) waterfall display and menu-driven controls interface.



There are various SDR interfaces out there, many (most?) are free applications.  These will typically have a waterfall display showing the entire receiver passband, band/frequency controls, filtering and other features (volume, AGC, noise, mode), and display controls/customization, along with recording and playback capability.

Current SDR use in amateur radio is typically for the HF bands; stand-alone modules or dongles running on PCs are commonly found and complete transceivers are quite popular although more expensive than traditional HF rigs (see references below).  As of this writing, the author is unaware of any widely-available VHF/UHF FM mobile or handheld Continue reading