Digital Receiver Handbook Basics of Software Radio

Digital Receiver Handbook: Basics of Software Radio
®
Digital Receiver Handbook:
Basics of Software Radio
Sixth Edition
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by
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Copyright © 1998, 2001, 2003, 2006 Pentek Inc.All rights reserved.Contents of this publication may not be reproduced in any form without written permission.Specifications are subject to change without notice.Pentek, GateFlow, ReadyFow and VIM are registered trademarks of Pentek, Inc.
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Preface
Digital receivers have revolutionized electronic systems for avariety of applications including communications, data acquisition and signal processing.
This handbook shows how digital receivers, the fundamental building block for software radio,can replace conventional analog receiver designs, offering significant benefits in performance, density and cost.
In order to fully appreciate the benefits of digital receivers, a conventional analog receiversystem will be compared to its digital receiver counterpart, highlighting similarities and differences.
The inner workings of the digital receiver will be explored with an in-depth description of the internalstructure and the devices used. Finally, some actual receiver system implementations and availableoff-the-shelf board level digital receiver products for embedded systems will be described.
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Figure 1 Figure 2
The conventional heterodyne radio receiver, as seen The mixer performs an analog multiplication of thein Figure 1, has been in use for nearly a century. Let's two inputs and generates a difference frequency signal.review the structure of the analog receiver so comparisonto the digital receiver becomes apparent. The frequency of the local oscillator is set so thatthe difference between the local oscillator frequency andFirst the RF signal from the antenna is amplified, desired input signal (the radio station you want totypically with a tuned RF stage, that amplifies a region receive) equals the IF.of the frequency band of interest. For example, if you wanted to receive an FM This amplified RF signal is then fed into a mixer station at 100.7 MHz and the IF is 10.7 MHz, you wouldstage. The other input to the mixer comes from the local tune the local oscillator to:oscillator whose frequency is controlled by the tuningknob on the radio. 100.7 - 10.7 = 90 MHz
The mixer translates the desired input signal to the This is called "downconversion" or "translation"IF (Intermediate Frequency). See Figure 2. because a signal at a high frequency is shifted down to alower frequency by the mixer.The IF stage is a bandpass amplifier that only letsone signal or radio station through. Common center The IF stage acts as a narrowband filter which onlyfrequencies for IF stages are 455 kHz and 10.7 MHz passes a "slice" of the translated RF input. The band-for commercial AM and FM broadcasts. width of the IF stage is equal to the bandwidth of thesignal (or the "radio station") that you are trying toThe demodulator recover... [download for more]