Radio receiver technology

Information, articles, and tutorials about all the essentials of radio receivers from basic principles, specifications and circuits to overall radio receiver concepts including the superheterodyne receiver, SDR, and cognitive radio for radio communications.

Radio receivers are obviously a very important part of wireless and radio communications technology. Their performance is critical to many applications. The basic radio receiver concepts including the superhet or superheterodyne receiver and other topologies such as the direct conversion receiver are of great interest. Elements such as selectivity, sensitivity including signal to noise ratio, SINAD, and noise figure, dynamic range, and many more are of great importance to any radio receiver. So too are some of the circuits and techniques employed. Mixers, demodulators and frequency synthesizers along with techniques such as digital signal processing, DSP, software defined radio, SDR are a few examples.

Radio receivers are used in a very wide variety of radio communications applications ranging from two way radio communications as well as general fixed and mobile radio communications and satellite communications. In addition to this radio receivers are sued in cellular telecommunications as well as applications such as Wi-Fi, WiMAX, and many other standards. As such radio receivers represent an important technology in radio communications.

Radio receiver types

Principle of the superhet. Virtually all receivers today use the superhet or superheterodyne principle. Find out how the superhet, or superheterodyne receiver works.
Introduction to the superhet or superheterodyne radio receiver

Radio receiver specifications

There are many specifications and facilities related to radio receivers and hence to radio communications systems. Sensitivity, noise figure, SINAD, overload and dynamic range, selectivity, filter shape factor and many more are all important:
Selectivity - filter specifications and shape factor
Image response and IF breakthrough
Sensitivity - signal to noise, SINAD and noise figure
      Signal to noise ratio
      SINAD
      Noise figure
      The noise floor of a radio receiver
Cross modulation, intermodulation distortion and intercept point
Dynamic range
FM reception - squelch, quieting and capture ratio

Phase locked loops, PLLs

Phase locked loops, PLLs are widely used in radio circuits as the basis of many frequency synthesizers and for FM demodulators amongst other radio communications applications.
The phase locked loop the basis of many synthesizers and Fm demodulators
        - Phase detector
        - Voltage controlled oscillator, VCO
        - Low phase noise oscillator
        - Loop filter

Frequency Synthesizers

Frequency synthesizers are widely used in radio receivers. Upon their performance depends many of the parameters of the whole receiver. Particularly important is the phase noise performance as this can limit the performance of a complete radio communications system.
Basic operation of an indirect (PLL) frequency synthesizer
Phase noise and reciprocal mixing
The basics of direct digital synthesis
Graphical method for designing frequency synthesizers to meet a phase noise specification

Demodulators and demodulation

Filters

Within a radio receiver the filter is one of the most critical items as it provides the selectivity for the set.
Radio receiver filter options - a summary of the options available including LC, crystal, mechnical and ceramic filters.
Quartz crystal band pass filters
Mechanical filters
Surface acoustic wave, SAW, filter

Digital Signal Processing, DSP

Digital signal processing, DSP, is becoming more widely used now that sufficiently powerful processors are available for relatively low cost, making DSP cards an attractive proposition for many radio receiver applications.
Basics of Digital Signal Processing, DSP
The trade-off between FPGAs and DSP processors for DSP hardware

Software defined radio (SDR)

With software taking over more of the function of a radio, the software defined radio is the ultimate and provides many advantages in many circumstances.
An overview of the software defined radio
Cognitive Radio - a technology beyond the software defined radio