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 8: Support Circuit Design
Most of today s support circuits are so useful that a modern transmitter or receiver could not satisfactorily function without them. Support circuits include electronic switches, attenuators, frequency multipliers, automatic gain control, the power supply, for example. Other circuits can only be called bells and whistles. They are not essential for proper systems operation and are only present for added operator convenience; these circuits will not be discussed.
8.1 Frequency Multipliers
8.1.1 Introduction
Because sinusoidal crystal oscillators can rarely be designed to operate reliably at frequencies above 200 MHz, even on a crystal s overtone, frequency multipliers, or sometimes SAW oscillators, must be employed for this purpose. The frequency doublers and triplers used in FM transmitters to increase a signal s frequency, as well as in microwave local oscillator stages, are either a basic tuned-output nonlinear (Class B or C) amplifier or a diode multiplier circuit. These multipliers are not only able to increase an FM or CW signal s frequency, but also any FM deviation present. This is required in an FM transmitter system, as a carrier oscillator s frequency and its deviation may need to be multiplied by 30 or more times. For instance, a modulated RF carrier that began at 6 MHz, with an FM deviation of 150 Hz, could be altered, if fed through a 30 chain of multipliers, into an output frequency of 180 MHz, with an FM deviation of 4500 Hz.
Because of their nonlinear nature, common Class C amplifiers (Fig. 8.1) work quite well as frequency multipliers,...
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