Complete Wireless Design
If you want to climb the learning curve with grace, and start designing what you need immediately, this easy-to-understand guide will help you design an entire radio system from the ground up.
TABLE OF CONTENTS Complete Wireless Design
Chapter 9: Communications System Design
Without a solid understanding of the complete communications system all the way from the transmitter s modulator input to the receiver s demodulator output including everything in between and how the selection of various components, circuits, and specifications can make or break an entire system, any wireless design will surely fail. The interrelationships of the transmitter, the receiver, the antenna, the air-interface link, the type of digital or analog modulation, adjacent channel and cochannel considerations, etc., are critical to a dependable link for a high data rate at the required BER for digital radio, or with the expected voice quality for analog radio.
9.1 Receivers
9.1.1 Introduction
The most difficult-to-design element in any communications system is the receiver. A receiver must have a low noise figure (at VHF and above), low group delay variations and IMD, high dynamic range, stable AGC, appropriate RF and IF gain, good frequency stability, satisfactory gain flatness across multiple channels, low phase noise, negligible in-band spurs, sufficient selectivity, suitable BER and sometimes the most critical specification of all be within certain cost constraints.
An important concern of any superheterodyne receiver is the image frequency, in that any signal received within this image band will be amplified by the receiver s IF stages and then be unavoidably transferred on to the demodulator to be output as interference. This image frequency can be eliminated only at the front end of a receiver, before down-conversion, by a filter that blocks the interfering frequency: the image filter. When the local oscillator is higher in...
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