Technician pool, section T7C

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Subelement T7

PRACTICAL CIRCUITS

Section T7C

Antenna and transmission line measurements and troubleshooting: measuring SWR, effects of high SWR, causes of feed line failures; Basic coaxial cable characteristics; Use of dummy loads when testing

T7C01

What is the primary purpose of a dummy load?

Correct Answer
A.
To prevent transmitting signals over the air when making tests
B.
To prevent over-modulation of a transmitter
C.
To improve the efficiency of an antenna
D.
To improve the signal-to-noise ratio of a receiver

T7C01

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T7C02

Which of the following is used to determine if an antenna is resonant at the desired operating frequency?

A.
A VTVM
Correct Answer
B.
An antenna analyzer
C.
A Q meter
D.
A frequency counter

T7C02

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T7C03

What does a typical RF dummy load consist of?

A.
A low-voltage power supply and an AC relay
Correct Answer
B.
A 50-ohm non-inductive resistor mounted on a heat sink
C.
A low-voltage power supply and a DC relay
D.
A 50-ohm inductive reactance mounted in a shielded enclosure

T7C03

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T7C04

What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?

A.
50:50
B.
Zero
Correct Answer
C.
1:1
D.
Full Scale

T7C04

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T7C05

Why do most solid-state transmitters reduce output power as SWR increases beyond a certain level?

Correct Answer
A.
To protect the RF output amplifier transistors
B.
To comply with FCC rules on spectral purity
C.
Because power supplies cannot supply enough current at high SWR
D.
To lower the SWR on the transmission line

T7C05

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T7C06

What does an SWR reading of 4:1 indicate?

A.
Loss of -4 dB
B.
Good impedance match
C.
Gain of +4 dB
Correct Answer
D.
Impedance mismatch

T7C06

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T7C07

What happens to power lost in a feed line?

A.
It increases the SWR
B.
It is radiated as harmonics
Correct Answer
C.
It is converted into heat
D.
It distorts the signal

T7C07

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T7C08

Which instrument can be used to determine SWR?

A.
Voltmeter
B.
Ohmmeter
C.
Iambic pentameter
Correct Answer
D.
Directional wattmeter

T7C08

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T7C09

Which of the following causes failure of coaxial cables?

Correct Answer
A.
Moisture contamination
B.
Solder flux contamination
C.
Rapid fluctuation in transmitter output power
D.
Operation at 100% duty cycle for an extended period

T7C09

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T7C10

Why should the outer jacket of coaxial cable be resistant to ultraviolet light?

A.
Ultraviolet light can increase the resistance of the conductors
B.
Ultraviolet light can increase losses in the cable’s jacket
C.
Ultraviolet and RF signals can mix, causing interference
Correct Answer
D.
Ultraviolet light can damage the jacket and allow water to enter the cable

T7C10

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T7C11

What is an advantage of foam-dielectric versus solid-dielectric coaxial cable?

A.
It is more resistant to moisture contamination
B.
It has higher voltage breakdown
Correct Answer
C.
It has less loss per foot
D.
It has a better impedance match to 50 ohms

T7C11

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