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Consumer Electronics by S. P. Bali

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MEGAPHONES

Portable electronic megaphones, Fig. 26.19 are used by construction workers, law-enforcement officials, boat navigators and so on. The unit comprises a reentrant horn speaker with a microphone mounted on the back.

A 5-transistor class-B amplifier is typically employed to step-up the microphone signal. The unit is powered with a 9 volt battery and has a maximum output of 8 watts with a sound range of 600 yards. A volume control is provided and a built in siren signal source is available in the unit shown in Fig. 26.19. Yet another design is shown in Fig. 26.20. This is a 20 watt unit and provides more than twice as much as the portable unit. A switch is provided to change the circuit configuration into a sensitive directional listening ...

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