rotate 0.07 λ more, counterclockwise, to complete the length. This puts us at the
0.346 1 0.07 5 0.416λ point, which is designated point Y in Fig. 13-37. We then draw
a line from Y to the prime center. The point at which this line intersects the SWR circle
is the actual antenna impedance. The normalized value is 0.72 1 j 0.33. Multiplying by
75 gives the actual value of the antenna impedance:
Z 5 75(0.72 1 j 0.33) 5 54 1 j 24.75 V
CHAPTER REVIEW
Online Activity
13-1 Coax Cable Variations
Objective: Examine several different types of coax cables.
Procedure:
1. Using standard Internet search techniques, look for information to answer the following questions. Search on
“coax manufacturers” or “types of coax” or similar terms.
3. Name the beneits of rigid coax.
4. What is the highest-frequency coax you can ind? What
is its attenuation at that frequency?
5. Name one common type of coax connector not listed in
this textbook.
Questions:
1. What is the most common coax characteristic impedance?
2. What is rigid coax, and where is it used?
Questions
1. Name the two basic types of transmission lines. Which
is the more widely used?
2. What is the name for a transmission line that has one of
its two conductors connected to ground?
3. Name a popular type of balanced line.
4. What is the name given to the distance that a signal
travels during one cycle?
5. Name a popular UHF connector used for coaxial cable.
6. What is the coaxial cable connector commonly used on
test equipment and in LANs?
7. What is the best coaxial cable connector for UHF and
microwave applications?
8. What type of coaxial connector is widely used for cable
TV and VCR connections?
9. Describe the equivalent circuit of a transmission line.
10. What determines the characteristic impedance of a
transmission line?
11. What is another name for characteristic impedance?
12. What is the importance of the velocity factor in determining cable lengths?
13. How does the cutoff frequency of a coaxial cable vary
with its length?
14. Describe the pattern of the current and voltage along a
properly matched transmission line.
15. Describe what happens if a transmission line is not terminated in its characteristic impedance.
16. What is the effect on transmitted power when load and
transmission line impedances are mismatched?
Transmission Lines
501
17. Under which two conditions will all incident power on
a line be relected?
18. What is the ratio of the relected voltage to the incident
voltage on a transmission line called?
19. What do you call a mismatched transmission line?
20. How does the length of a matched transmission line
affect the SWR?
21. Name two ways to implement a series resonant circuit
with a transmission line.
22. How do transmission lines that are less than λ/4 or
between λ/4 and λ/2 at the operating frequency act?
23. How many wavelengths does one complete revolution
around a Smith chart represent?
Problems
1. Compute the wavelength in meters at a frequency of
350 MHz. ◆
2. At what frequency does a line 3.5 in long represent
one-half wavelength?
3. A coaxial cable has a capacitance of 30 pF/ft and an
inductance of 78 nH/ft. What is the characteristic impedance? ◆
4. A coaxial cable has a capacitance of 17 pF/ft. The characteristic impedance is 75 V. What is the equivalent
inductance per foot?
5. What is the velocity factor of a coaxial cable with a
dielectric constant of 2.5? ◆
6. A manufacturer’s data sheet states that the velocity
factor for a speciic coaxial cable is 0.7. What is the
dielectric constant?
7. Determine the length in feet of a one-quarter wavelength coaxial cable with a velocity factor of 0.8 at a
frequency of 49 MHz. ◆
8. What is the time delay introduced by a coaxial cable with
the speciications given in Prob. 7 if the length is 65 ft?
9. What is the time delay of 120 ft of a coaxial cable with
a dielectric constant of 0.7? ◆
10. How much phase shift is introduced by a coaxial cable
15 ft long to a 10-MHz sine wave signal? The dielectric
constant is 2.9.
11. What is the attenuation of 350 ft of RG-11 U coaxial
cable at 100 MHz?
12. What is the approximate attenuation of 270 ft of type
9913 coaxial cable at 928 MHz?
13. A transmitter has an output power of 3 W that is fed to
an antenna through an RG-58A/U cable 20 ft long.
How much power reaches the antenna?
14. What should be the transmission line impedance for optimum transfer of power from a generator to a 52-V load?
15. A 52-V coaxial cable has a 36-V antenna load. What is
the SWR?
16. If the load and line impedances of the cable in Prob. 15
are matched, what is the SWR?
17. The maximum voltage along a transmission line is
170 V, and the minimum voltage is 80 V. Calculate the
SWR and the relection coeficient.
502
Chapter 13
18. The relection coeficient of a transmission line is 0.75.
What is the SWR?
19. What are the relection coeficient and SWR of an open
or shorted transmission line?
20. A transmission line has an SWR of 1.65. The power
applied to the line is 50 W. What is the amount of relected power?
21. A power meter inserted into a transmission line reads
1150 W of forward power and 50 W of relected power.
What is the SWR?
22. What must be the value of the load impedance on a
transmission line if the voltage variations along the line
go to zero at regular intervals?
23. At what frequency does an open-wire transmission line
6 in long act as a parallel resonant circuit? (The
dielectric is air.)
24. A coaxial cable has a velocity factor of 0.68. How
long is one-half wavelength of this cable at
133 MHz?
25. Calculate the impedance of a microstrip line whose
dimensions are h 5 0.05 in, w 5 0.125 in, and t 5
0.002 in. The dielectric constant is 4.5.
26. What is the length of one-quarter wavelength of the
microstrip in Prob. 25 at a frequency of 915 MHz?
27. Plot, in normalized form, the following impedances on
a Smith chart: Z1 5 80 1 j 25 and Z2 5 35 2 j 98, assuming a prime center value of 52 V.
28. Plot the load impedance 104 2 j58 on a coaxial line on
a Smith chart. Assume a characteristic impedance value
of 75 V. Then ind the SWR.
29. If the operating frequency is 230 MHz and the cable
length is 30 ft for Prob. 28, what is the impedance at the
generator if the velocity factor is 0.66? Use the Smith
chart and show all work.
30. What does the SWR circle on a Smith chart look like if
a 52-V load is connected to a 52-V coaxial cable?
◆ Answers to Selected Problems follow Chap. 22.