FCC Exam Question: 8-17B5

Pulse RADARs require precise timing for their operation. Which type circuit below might best be used to provide these accurate timing pulses?

A. Single-swing blocking oscillator.
B. AFC controlled sinewave oscillator.
C. Non-symmetrical astable multivibrator.
D. Triggered flip-flop type multivibrator.
Correct Answer: A

Explanation: A single-swing blocking oscillator is uniquely suited for providing precise timing pulses in Pulse RADARs. It is a type of monostable multivibrator designed to produce a single, very high-power, short-duration pulse when triggered. This characteristic is vital for RADAR, as it generates the individual, precisely timed transmit pulse and defines the short, accurate timing intervals required for range measurement and synchronization. Its rapid recovery allows for precise control of the pulse repetition frequency. An AFC controlled sinewave oscillator generates continuous waves, not the discrete, high-power pulses needed for radar transmission. A non-symmetrical astable multivibrator produces a continuous, free-running train of pulses, lacking the precise triggered control and the single-pulse nature required for each radar transmission event. While a triggered flip-flop type multivibrator (like a monostable) can generate a single pulse, blocking oscillators are specifically designed for the high-power, very narrow, and fast-rising pulses necessary to drive radar modulators, ensuring accurate timing for range determination.

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Includes Elements 1, 3, 6, 7R, 8, and 9.