Radio Receiver Architectures

The radio receiver is designed to receive radio signals. How it does that job depends on the receiver architecture. Radio receivers are at the heart of nearly all communications activities. This chapter covers receiver architecture, the different types of radio receivers on the market and also discusses the basic problem of radio reception: separating signals from noise. A receiver must perform two basic functions—it must respond to, detect, and demodulate desired signals; and it must not respond to, detect, or be adversely affected by undesired signals. If it fails in either of these two functions, then the design performs poorly. Crystal video receivers grew out of primordial crystal sets, but sometimes they are used in microwave bands, even today. Modern crystal video receivers use silicon or gallium-arsenide microwave diodes and a wideband video amplifier. The tuned radio frequency (TRF) radio receiver uses an L-C resonant circuit in the front end, followed by one or more radio frequency amplifiers ahead of a detector stage. The purpose of a superheterodyne receiver is to convert the incoming RF frequency to a single frequency where most of the signal processing takes place. A superheterodyne receiver works by frequency converting (heterodyning—the super part is 1920s vintage advertising hype) the RF signal. This occurs by nonlinearly mixing the incoming RF signal with a local oscillator (LO) signal.