NEETS Module 9 − Introduction to Wave− Generation and Wave−Shaping
Pages i,
1−1,
1−11,
1−21,
1−31,
1−41,
2−1,
2−11,
2−21,
2−31,
3−1,
3−11,
3−21,
3−31,
3−41,
3−51,
4−1,
4−11,
4−21,
4−31,
4−41,
4−51, Index
 
Matter, Energy,
and Direct Current 
 
Alternating Current and Transformers 
 
Circuit Protection, Control, and Measurement 
 
Electrical Conductors, Wiring Techniques,
and Schematic Reading 
 
Generators and Motors 
 
Electronic Emission, Tubes, and Power Supplies 
 
SolidState Devices and Power Supplies 
 
Amplifiers 
 
WaveGeneration and WaveShaping Circuits 
 
Wave Propagation, Transmission Lines, and
Antennas 
 
Microwave Principles 
 
Modulation Principles 
 
Introduction to Number Systems and Logic Circuits 
 
 Introduction to Microelectronics 
 
Principles of Synchros, Servos, and Gyros 
 
Introduction to Test Equipment 
 
RadioFrequency Communications Principles 
 
Radar Principles 
 
The Technician's Handbook, Master Glossary 
 
Test Methods and Practices 
 
Introduction to Digital Computers 
 
Magnetic Recording 
 
Introduction to Fiber Optics 
Note: Navy Electricity and Electronics Training
Series (NEETS) content is U.S. Navy property in the public domain. 
Q16. What is the filter called in which the low frequencies do not
produce a useful voltage?
Q17. What is the filter called that passes low frequencies but rejects
or attenuates high frequencies? Q18. How does a capacitor and an inductor
react to (a) low frequency and (b) high frequency?
Q19. What term is used to describe the frequency at which the filter
circuit changes from the point of rejecting the unwanted frequencies to the point
of passing the desired frequencies?
Q20. What type filter is used to allow a narrow band of frequencies
to pass through a circuit and attenuate all other frequencies above or below the
desired band?
Q21. What type filter is used to block the passage of current for
a narrow band of frequencies, while allowing current to flow at all frequencies
above or below this band?
MULTIsECTION FILTERS
All of the various types of filters we have discussed so far have had only one
section. In many cases, the use of such simple filter circuits does not provide
sufficiently sharp cutoff points. But by adding a capacitor, an inductor, or a resonant
circuit in series or in parallel (depending upon the type of filter action required),
the ideal effect is more nearly approached. When such additional units are added
to a filter circuit, the form of the resulting circuit will resemble the letter
T, or the Greek letter p (pi). They are, therefore, called T or ptype filters,
depending upon which symbol they resemble. Two or more T or ptype filters may
be connected together to produce a still sharper cutoff point.
Figure 123, (view A) (view B) and (view C), and figure 124, (view A) (view
B) and (view C) depict some of the common configurations of the T and ptype filters.
Further discussion about the theory of operation of these circuits is beyond the
intended scope of this module. If you are interested in learning more about filters,
a good source of information to study is the Electronics Installation and Maintenance
Handbook (EIMB), section 4 (Electronics Circuits), NAVSEA 0967LP0000120.
Figure 123A.  Formation of a Ttype filter.
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Figure 123B.  Formation of a Ttype filter.
Figure 123C.  Formation of a Ttype filter.
Figure 124A.  Formation of a ptype filter.
Figure 124B.  Formation of a ptype filter.
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Figure 124C.  Formation of a ptype filter.
Safety PRECautionS
When working with resonant circuits, or electrical circuits, you must be aware
of the potentially high voltages. Look at figure 125. With the series circuit at
resonance, the total impedance of the circuit is 5 ohms.
Figure 125.  Series RLC circuit at resonance.
Remember, the impedance of a seriesRLC circuit at resonance depends on the resistive
element. At resonance, the impedance (Z) equals the resistance (R). Resistance
is minimum and current is maximum. Therefore, the current at resonance is:
The voltage drops around the circuit with 2 amperes of current flow are:
E_{C} = I_{T} x X_{C}
E_{C} = 2 x 20
E_{C} = 40 volts AC
E_{L} = I_{T} x X_{L}
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E_{L} = 2 x 20
E_{L} = 40 volts AC
E_{R} = I_{T} x R
E_{R} = 2 x 5
E_{R} = 10 volts AC
You can see that there is a voltage gain across the reactive components at resonance.
If the frequency was such that X_{L} and X_{C} were equal
to 1000 ohms at the resonant frequency, the reactance voltage across the inductor
or capacitor would increase to 2000 volts AC with 10 volts AC applied. Be aware
that potentially high voltage can exist in seriesresonant circuits.
Summary
This chapter introduced you to the principles of tuned circuits. The following
is a summary of the major subjects of this chapter.
The EFFECT of Frequency on an INDUCTOR is such
that an increase in frequency will cause an increase in inductive reactance. Remember
that X_{L} = 2πfL; therefore, X_{L}
varies directly with frequency.
The EFFECT of Frequency on a Capacitor is such
that an increase in frequency will cause a decrease in capacitive reactance. Remember
that
therefore, the relationship between X_{C} and frequency is that
X_{C} varies inversely with frequency.
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RESULTANT REACTANCE X = (X_{L}  X_{C}) or X
= (X_{C}  X_{L}). X_{L} is usually plotted above
the reference line and X_{C} below the reference line. Inductance
and capacitance have opposite effects on the current in respect to the voltage in
AC circuits. Below resonance, X_{C} is larger than X_{L},
and the series circuit appears capacitive. Above resonance, X_{L} is larger
than X_{C}, and the series circuit appears inductive. At resonance, X_{L}
= X_{C}, and the total impedance of the circuit is resistive.
A RESONANT Circuit is often called a TANK Circuit.
It has the ability to take energy fed from a power source, store the energy alternately
in the inductor and capacitor, and produce an output which is a continuous AC wave.
The number of times this set of events occurs per second is called the resonant
frequency of the circuit. The actual frequency at which a tank circuit will oscillate
is determined by the formula:
IN a SeriesLC Circuit impedance is minimum and current is maximum.
Voltage is the variable, and voltage across the inductor and capacitor will be equal
but of opposite phases at resonance. Above resonance it acts inductively, and below
resonance it acts capacitively.
145
IN a PARALLELLC Circuit impedance is maximum and current is
minimum. Current is the variable and at resonance the two currents are 180 degrees
out of phase with each other. Above resonance the current acts capacitively, and
below resonance the current acts inductively.
146
The "Q" OR FIGURE of MERIT of a circuit is
the ratio of X_{L} to R. Since the capacitor has negligible losses, the
circuit Q becomes equivalent to the Q of the coil.
The Bandwidth of a circuit is the range of frequencies between
the halfpower points. The limiting frequencies are those at either side of resonance
at which the curve falls to .707 of the maximum value. If circuit Q is low, you
will have a wide bandpass. If circuit Q is high, you will have a narrow bandpass.
147
A FILTER Circuit consists of a combination of capacitors, inductors,
and resistors connected so that the filter will either permit or prevent passage
of a certain band of frequencies.
a LowPASS FILTER passes low frequencies and attenuates high
frequencies.
148
A HighPASS FILTER passes high frequencies and attenuates low
frequencies.
A Bandpass FILTER will permit a certain band of frequencies
to be passed.
149
A BandREJECT FILTER will reject a certain band of frequencies
and pass all others.
A Safety PRECaution concerning series resonance: Very high reactive
voltage can appear across L and C. Care must be taken against possible shock hazard.
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Answers to Questions Q1. Through Q21.
A1.
a. X_{L} varies directly with frequency.
X_{L} = 2πfL
b. X_{C} varies inversely with frequency.
c. Frequency has no affect on resistance.
A2. Resultant reactance.
A3.
A4. Decreases.
A5. Impedance low Current high.
A6. Nonresonant (circuit is either above or below resonance).
A7. Inductor magnetic field.
A8. Capacitor.
A9. Natural frequency or resonant frequency (f_{r}).
A10. Maximum impedance, minimum current.
A11. At the resonant frequency.
A12.
A13. Bandwidth of the circuit.
A14. a filter.
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A15.
a. Lowpass.
b. Highpass
c. Bandpass.
d. Bandreject.
A16. Highpass filter, lowfrequency discriminator, or lowfrequency
attenuator.
A17. Lowpass filter, highfrequency discriminator or highfrequency
attenuator.
A18. At lowfrequency, a capacitor acts as an open and an inductor
acts as a short. At highfrequency, a capacitor acts as a short and an inductor
acts as an open.
A19. Frequency cutoff (f_{co}).
A20. Bandpass.
A21. Bandreject.
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