• Home
  • Textbooks
  • Electronic Communications: A Systems Approach
  • COMMUNICATIONS CIRCUITS

Electronic Communications: A Systems Approach

Jeffrey S. Beasley

Chapter 4

COMMUNICATIONS CIRCUITS - all with Video Answers

Educators

Chapter Questions

Problem 1

Draw schematics for Hartley and Colpitts oscillators. Briefly explain their operation and differences.

Check back soon!

Problem 2

Describe the reason that a Clapp oscillator has better frequency stability than the Hartley or Colpitts oscillators.

Check back soon!
02:03

Problem 3

List the major advantages of crystal oscillators over the $L C$ varieties. Draw a schematic for a Pierce oscillator.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
01:28

Problem 4

The crystal oscillator time base for a digital wristwatch yields an accuracy of $\pm 15 \mathrm{~s} / \mathrm{month}$. Express this accuracy in parts per million (ppm). ( $\pm 5.787 \mathrm{ppm}$ )

Averell Hause
Averell Hause
Carnegie Mellon University
00:58

Problem 5

Explain the makeup of a practical inductor and capacitor. Include the quality and dissipation in your discussion.

Keshav Singh
Keshav Singh
Numerade Educator
02:49

Problem 6

Define resonance and describe its use.

DD
David Dick
Numerade Educator
04:56

Problem 7

Calculate an inductor's $Q$ at $100 \mathrm{MHz}$. It has an inductance of $6 \mathrm{mH}$ and a series resistance of $1.2 \mathrm{k}$. Determine its dissipation. $\left(3.14 \times 10,0.318 \times 10^{-3}\right)$

Donald Albin
Donald Albin
Numerade Educator
04:48

Problem 8

Calculate a capacitor's $Q$ at $100 \mathrm{MHz}$ given $0.001 \mu \mathrm{F}$ and a leakage resistance of $0.7 \mathrm{M} \Omega$. Calculate $D$ for the same capacitor. $\left(4.39 \times 10^5, 2.27 \times 10^{-6}\right)$

Sikandar Baig
Sikandar Baig
Numerade Educator
02:32

Problem 9

The inductor and capacitor for Problems 7 and 8 are put in series. Calculate the impedance at $100 \mathrm{MHz}$. Calculate the frequency of resonance $\left(f_r\right)$ and the impedance at that frequency. (3.77 M $\Omega, 65 \mathrm{kHz}, 1200 \Omega$ )

Ryan Hood
Ryan Hood
Numerade Educator

Problem 10

Calculate the output voltage for the circuit shown in Figure $4-16$ at $6 \mathrm{kHz}$ and $4 \mathrm{kHz}$. Graph these results together with those of Example 4-2 versus frequency. Use the circuit values given in Example 4-2.

Check back soon!
02:03

Problem 11

Sketch the $e_{\text {oul }} / e_{\text {in }}$ versus frequency characteristic for an $L C$ bandpass filter. Show $f_{\mathrm{ic}}$ and fic on the sketch and explain how they are defined. On this sketch, show the bandwidth (BW) of the filter and explain how it is defined.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator

Problem 12

Define the quality factor $(Q)$ of an $L C$ bandpass filter. Explain how it relates to the "selectivity" of the filter. Describe the major limiting value on the $Q$ of a filter.

Check back soon!

Problem 13

An FM radio receiver uses an $L C$ bandpass filter with $f_r=10.7 \mathrm{MHz}$ and requires a $\mathrm{BW}$ of $200 \mathrm{kHz}$. Calculate the $Q$ for this filter. (53.5)

Check back soon!
01:07

Problem 14

The circuit described in Problem 13 is shown in Figure 4-18. If $C=0.1 \mathrm{nF}\left(0.1 \times 10^{-9} \mathrm{~F}\right)$, calculate the required inductor value and the value of $R .(2.21 \mu \mathrm{H}, 2.78 \Omega)$

Raj Bala
Raj Bala
Numerade Educator
01:13

Problem 15

A parallel $L C$ tank circuit has a $Q$ of 60 and coil winding resistance of $5 \Omega$. Determine the circuit's impedance at resonance. $(18 \mathrm{k} \Omega)$

Narayan Hari
Narayan Hari
Numerade Educator
01:29

Problem 16

A parallel $L C$ tank circuit has $L=27 \mathrm{mH}, C=0.68 \mu \mathrm{F}$, and a coil winding resistance of $4 \Omega$. Calculate $f_n Q, Z_{\max }$, the BW, $f_{\mathrm{lc}}$ and $f_{\mathrm{hc}}(1175 \mathrm{~Hz}, 49.8,9.93 \mathrm{k} \Omega, 23.6 \mathrm{~Hz}, 1163 \mathrm{~Hz}, 1187 \mathrm{~Hz})$

Nolan Smyth
Nolan Smyth
Numerade Educator
01:11

Problem 17

Explain the significance of the $k$ and $m$ in constant- $k$ and $m$-derived filters.

Nicole Smina
Nicole Smina
Numerade Educator
View

Problem 18

Describe the criteria used in choosing either an $R C$ or $L C$ filter.

Lainey Roebuck
Lainey Roebuck
Numerade Educator

Problem 19

Explain the importance of keeping lead lengths to a minimum in RF circuits.

Check back soon!
01:02

Problem 20

Describe a pole.

Narayan Hari
Narayan Hari
Numerade Educator

Problem 21

Explain why Butterworth and Chebyshev filters are called constant- $k$ filters.

Check back soon!

Problem 22

Draw the approximate equivalent circuit of a quartz crystal.

Check back soon!

Problem 23

What are the undesired effects of the crystal holder capacitance in a crystal filter, and how are they overcome?

Check back soon!

Problem 24

What crystalline substance is widely used in crystal oscillators (and filters)?

Check back soon!
07:13

Problem 25

Using your library or some other source, provide a schematic for a four-element crystal lattice filter and explain its operation.

Nadia Lara
Nadia Lara
Numerade Educator

Problem 26

What are the principal advantages of crystal control over tuned circuit oscillators (or filters)?

Check back soon!
01:00

Problem 27

Explain the operation of a ceramic filter. What is the significance of a filter's shape factor?

Zulfiqar Ali
Zulfiqar Ali
Numerade Educator

Problem 28

Define shape factor. Explain its use.

Check back soon!

Problem 29

A bandpass filter has a 3-dB ripple amplitude. Explain this specification.

Check back soon!
02:03

Problem 30

Explain the operation and use of mechanical filters.

AM
Andrew Macphail
Numerade Educator

Problem 31

Why are SAW filters not often used in SSB equipment?

Check back soon!

Problem 32

What are the typical inputs and outputs for a balanced modulator?

Check back soon!

Problem 33

Briefly describe the operation of a balanced ring modulator.

Check back soon!

Problem 34

Explain the advantages of using an IC for the four diodes in a balanced ring modulator as compared with four discrete diodes.

Check back soon!

Problem 35

Referring to the specifications for the AD630 LIC balanced modulator in Figure 4-28, determine the channel separation at $10 \mathrm{kHz}$, explain how a gain of +1 and +2 are provided.

Check back soon!

Problem 36

Explain how to generate an SSBSC signal from the balanced modulator.

Check back soon!

Problem 37

Draw a block diagram of a phase-locked loop (PLL) and briefly explain its operation.

Check back soon!

Problem 38

List the three possible states of operation for a PLL and explain each one.

Check back soon!

Problem 39

A PLL's VCO free-runs at $7 \mathrm{MHz}$. The VCO does not change frequency until the input is within $20 \mathrm{kHz}$ of $7 \mathrm{MHz}$. After that condition, the VCO follows the input to $\pm 150 \mathrm{kHz}$ of $7 \mathrm{MHz}$ before the VCO starts to free-run again. Determine the PLL's lock and capture ranges. $(300 \mathrm{kHz}, 40 \mathrm{kHz}$ )

Check back soon!

Problem 40

Explain the operation of a basic frequency synthesizer as illustrated in Figure 4-32. Calculate $f_0$ if $f_R=1 \mathrm{MHz}$ and $N=61$. $(61 \mathrm{MHz})$

Check back soon!

Problem 41

Discuss the relative merits of the synthesizers shown in Figures 4-34(a), (b), and (c) as compared to the one in Figure 4-32.

Check back soon!

Problem 42

Describe the operation of the synthesizer divider in Figure 4-35. What basic problem does it overcome with respect to the varieties shown in Figures 4-32 and 4-34?

Check back soon!

Problem 43

Calculate the output frequency of a synthesizer using the divider technique shown in Figure 4-35 when the reference frequency is $1 \mathrm{MHz}, A=26, M=28$, and $N=4 .(138 \mathrm{MHz})$

Check back soon!

Problem 44

Briefly explain DDS operation based on the block diagram shown in Figure 4-36.

Check back soon!

Problem 45

A DDS system has $f_{C K K} M A x=60 \mathrm{MHz}$ and a 28 -bit phase accumulator. Calculate its approximate maximum output frequency and frequency resolution when operated at $f_{\text {CLK MAX- }}$ $(24 \mathrm{MHz}, 0.223 \mathrm{~Hz}$ )

Check back soon!