Radio Receiver Design
This reference focuses on understanding and designing radio receivers and systems, presenting the characteristics of individual receiver components and their interaction in cascade.
TABLE OF CONTENTS Radio Receiver Design
Chapter 2: Filters
Still a man hears what he wants to hear and disregards the rest.
-Simon and Garfunkel, The Boxer
2.1 Introduction
In the frequency domain, we differentiate between wanted and unwanted signals. A filter removes the unwanted signals while retaining (and not distorting) the signals we want. Thus, relevant questions that will be addressed in this chapter include:
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How many unwanted signals can we tolerate? A filter will not remove the unwanted spectra entirely; it will attenuate them by some finite amount. How much attenuation do we actually need?
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How much insertion loss can we tolerate in the filtering process? As a desired filter removes the unwanted signals, its insertion loss will also attenuate the signals we want to preserve.
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How does the filter alter the wanted signal? The filter may change the magnitude of the wanted signal unevenly over its bandwidth or it may produce more subtle changes by altering the signal's phase.
2.2 Linear Systems Review
Calling a system linear has several specific implications.
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If we excite a linear system at a particular frequency, we will observe only that frequency in the system. We may observe phase and amplitude changes, but we will not find any frequencies present in the system that were not intentionally included.
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The transfer function of the system does not depend upon the magnitude of the input signal. If the system performance varies with signal level, the system is not linear.
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Superposition works. We can excite a system with a signal S 1
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