TABLE OF CONTENTS Radios must detect signals of widely varying magnitude in the presence of interferers. A radio is required to minimize excess noise while tolerating large input signals (both wanted and interfering signals) without excessive distortion. Transmit distortion must be minimized to avoid spurious radiation outside the intended channel and band. Radios must provide good frequency selectivity and tunability and adapt to a huge range of input power.
Modern digital radios combine frequency conversion with analog-to-digital conversions. There are three popular architectures: superhet, NZIF, and direct conversion, each with its own advantages and pitfalls. Each analog component has certain key performance parameters. Amplifiers are characterized by gain, distortion, and noise. Mixers add isolation to distortion and noise. Synthesizers must deliver low phase noise and good frequency stability. Filters require narrow bandwidths, low insertion loss, and good rejection of unwanted signals. Switches need good insertion loss, fast actuation, and sufficient isolation. Radio boards are a mixture of discrete and integrated analog and digital components. The final radio chain is a compromise between gain, noise, distortion, DC power consumption, and cost of component acquisition and radio manufacture.
