E9E Matching antennas to feed lines;
characteristics of open and
shorted feed lines: 1/8 wavelength; 1/4 wavelength; 3/8 wavelength;
1/2
wavelength; 1/4 wavelength matching transformers; feed lines: coax
versus open-wire; velocity factor; electrical length; transformation
characteristics of line terminated in impedance not equal to
characteristic impedance
E9E01
(B)
What
system matches a high-impedance transmission line to a lower impedance antenna
by connecting the line to the driven element in two places, spaced a fraction
of a wavelength each side of element center?
A. The gamma matching system
B. The delta matching system
C. The omega matching system
D. The stub matching system
E9E02
(A)
What
system matches an unbalanced feed line to an antenna by feeding the driven
element both at the center of the element and at a fraction of a wavelength to
one side of center?
A. The gamma matching system
B. The delta matching system
C. The omega matching system
D. The stub matching system
E9E03
(D)
What
impedance matching system uses a short perpendicular section of transmission
line connected to the feed line near the antenna?
A. The gamma matching system
B. The delta matching system
C. The omega matching system
D. The stub matching system
E9E04
(B)
What
should be the approximate capacitance of the resonating capacitor in a gamma
matching circuit on a 1/2-wavelength dipole antenna for the 20-meter wavelength
band?
A. 70 pF
B. 140 pF
C. 200 pF
D. 0.2 pF
E9E05
(A)
What
kind of impedance does a 1/4-wavelength transmission line present to a
generator when the line is shorted at the far end?
A. A very high impedance
B. A very low impedance
C. The same as the characteristic impedance of
the transmission line
D. The same as the generator output impedance
E9E06
(A)
What
kind of impedance does a 1/2-wavelength transmission line present to a
generator when the line is open at the far end?
A. A very high impedance
B. A very low impedance
C. The same as the characteristic impedance of
the line
D. The same as the output impedance of the
generator
E9E07
(D)
What is
the velocity factor of a transmission line?
A. The ratio of the characteristic impedance of
the line to the terminating impedance
B. The index of shielding for coaxial cable
C. The velocity of the wave on the transmission
line multiplied by the velocity of light in a vacuum
D. The velocity of the wave
on the transmission line divided by the velocity of light in a vacuum
E9E08
(C)
What
determines the velocity factor in a transmission line?
A. The termination impedance
B. The line length
C. Dielectrics in the line
D. The center conductor resistivity
E9E09
(D)
Why is
the physical length of a coaxial cable transmission line shorter than its
electrical length?
A. Skin effect is less pronounced in the
coaxial cable
B. The characteristic impedance is higher in
the parallel feed line
C. The surge impedance is higher in the
parallel feed line
D. RF energy moves slower
along the coaxial cable
E9E10
(B)
What is
the typical velocity factor for a coaxial cable with polyethylene dielectric?
A. 2.70
B. 0.66
C. 0.30
D. 0.10
E9E11
(C)
What
would be the physical length of a typical coaxial transmission line that is
electrically one-quarter wavelength long at 14.1 MHz? (Assume a velocity factor
of 0.66.)
A. 20 meters
B. 2.33 meters
C. 3.51 meters
D. 0.25 meters
E9E12
(C)
What is
the physical length of a parallel conductor feed line that is electrically
one-half wavelength long at 14.10 MHz? (Assume a velocity factor of 0.95.)
A. 15 meters
B. 20.2 meters
C. 10.1 meters
D. 70.8 meters
E9E13
(B)
What
parameter best describes the interactions at the load end of a mismatched
transmission line?
A. Characteristic impedance
B. Reflection coefficient
C. Velocity factor
D. Dielectric Constant
E9E14
(D)
Which
of the following measurements describes a mismatched transmission line?
A. An SWR less than 1:1
B. A reflection coefficient greater than 1
C. A dielectric constant greater than 1
D. An SWR greater than 1:1
E9E15
(A)
What
characteristic will 450-ohm ladder line have at 50 MHz, as compared to
0.195-inch-diameter coaxial cable (such as RG-58)?
A. Lower loss in dB/100 feet
B. Higher SWR
C. Smaller reflection coefficient
D. Lower velocity factor
E9E16 (B)
What would be the physical length of a typical coaxial
transmission line that is
electrically one-quarter wavelength long at 7.2 MHz?
(Assume a velocity factor
of 0.66.)
A. 10 meters
B. 6.9 meters
C. 24 meters
D. 50 meters
Table 9-1
Properties of open and shorted Feed-Line Sections
Length Termination Impedance
1/8 wavelength Shorted inductive
1/8 wavelength Open capacitive
1/4 wavelength Shorted very high impedance
1/4 wavelength Open very low impedance
1/2 wavelength Shorted very low impedance
1/2 wavelength Open very high impedance
E9E17 (C)
What kind of impedance does a 1/8-wavelength transmission
line present to a
generator when the line is shorted at the far end?
A. A capacitive
reactance
B. The same as
the characteristic impedance of the line
C. An inductive reactance
D. The same as
the input impedance to the final generator stage
E9E18 (C)
What kind of impedance does a 1/8-wavelength transmission
line present to a
generator when the line is open at the far end?
A. The same as
the characteristic impedance of the line
B. An inductive
reactance
C. A capacitive reactance
D. The same as
the input impedance of the final generator stage
E9E19 (B)
What kind of impedance does a 1/4-wavelength transmission
line present to a
generator when the line is open at the far end?
A. A very high
impedance
B. A very low impedance
C. The same as
the characteristic impedance of the line
D. The same as
the input impedance to the final generator stage
E9E20 (A)
What kind of impedance does a 1/4-wavelength transmission
line present to a
generator when the line is shorted at the far end?
A. A very high impedance
B. A very low
impedance
C. The same as
the characteristic impedance of the transmission line
D. The same as
the generator output impedance
E9E21 (B)
What kind of impedance does a 1/2-wavelength transmission
line present to a
generator when the line is shorted at the far end?
A. A very high
impedance
B. A very low impedance
C. The same as
the characteristic impedance of the line
D. The same as
the output impedance of the generator
E9E22 (A)
What kind of impedance does a 1/2-wavelength transmission
line present to a
generator when the line is open at the far end?
A. A very high impedance
B. A very low
impedance
C. The same as
the characteristic impedance of the line
D. The same as
the output impedance of the generator