From the beginning, one of the biggest challenges to radio designers has been the limitations of bandwidth. Early on, our radio forefathers thought that frequencies above a few hundred kHz were of no value because of detector limitations. Pioneers like Branly, Fessenden, Marconi, and many others struggled with this, until Armstrong and Levy perfected heterodyning, opening higher frequencies of spectrum by down-converting to lower frequencies that detectors could adequately process with technology of the day. While higher frequencies were opened by the super-heterodyning process, the bandwidth was still relatively limited.
Until recent years, processing more than a few 10s of MHz has been a challenge and often limited to expensive solutions that often employed massively paralleled radio technology. It has long been desirable to simplify this and employ a method to simultaneously process as much bandwidth as possible. This capability has slowly evolved over the last few decades, as semiconductor processes and monolithic analog-to-digital converter (ADC) architectures have matured. From modest beginnings in the early ’90s until today, the direct RF sampling capability of ADCs has increased from about 20 MHz of Nyquist bandwidth, to over 5 GHz with products like the AD9213.
With the introduction of the AD9213 and the large instantaneous bandwidth it supports, many new options are opened, not just for instrument-grade receivers, but also for direct RF sampling radios, SIGINT, and radar.