1-1
CHAPTER 1
TUNED CIRCUITS
LEARNING OBJECTIVES
Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a
preview of the information you are expected to learn in the chapter. The comprehensive check questions
are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met
the objectives and have learned the information. The learning objectives are listed below.
Upon completion of this chapter, you will be able to:
1. State the applications of a resonant circuit.
2. Identify the conditions that exist in a resonant circuit.
3. State and apply the formula for resonant frequency of an a.c. circuit.
4. State the effect of changes in inductance (L) and capacitance (C) on resonant frequency (fr).
5. Identify the characteristics peculiar to a series resonant circuit.
6. Identify the characteristics peculiar to a parallel resonant circuit.
7. State and apply the formula for Q.
8. State what is meant by the bandwidth of a resonant circuit and compute the bandwidth for a given
circuit.
9. Identify the four general types of filters.
10. Identify how the series- and parallel-resonant circuit can be used as a bandpass or a band-reject
filter.
INTRODUCTION TO TUNED CIRCUITS
When your radio or television set is turned on, many events take place within the "receiver" before
you hear the sound or see the picture being sent by the transmitting station.
Many different signals reach the antenna of a radio receiver at the same time. To select a station, the
listener adjusts the tuning dial on the radio receiver until the desired station is heard. Within the radio or
TV receiver, the actual "selecting" of the desired signal and the rejecting of the unwanted signals are
accomplished by what is called a TUNED CIRCUIT. A tuned circuit consists of a coil and a capacitor
connected in series or parallel. Later in this chapter you will see the application and advantages of both
series- and parallel-tuned circuits. Whenever the characteristics of inductance and capacitance are found
in a tuned circuit, the phenomenon as RESONANCE takes place.
You learned earlier in the Navy Electricity and Electronics Training Series, Module 2, chapter 4, that
inductive reactance (XL) and capacitive reactance (XC) have opposite effects on circuit impedance (Z).
