FCC Technician Class Exam Study Guide - 2014-2018/Subelement T7 Group C

Antenna measurements and troubleshooting: measuring SWR; dummy loads; coaxial cables; feed line failure modes

Question 1

 * What is the primary purpose of a dummy load?
 * A. To prevent the radiation of signals when making tests
 * B. To prevent over-modulation of your transmitter
 * C. To improve the radiation from your antenna
 * D. To improve the signal to noise ratio of your receiver

The correct answer is A.

Question 2

 * Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency?
 * A. A VTVM
 * B. An antenna analyzer
 * C. A Q meter
 * D. A frequency counter

The correct answer is B.

Question 3

 * What, in general terms, is standing wave ratio (SWR)?
 * A. A measure of how well a load is matched to a transmission line
 * B. The ratio of high to low impedance in a feed line
 * C. The transmitter efficiency ratio
 * D. An indication of the quality of your station's ground connection

The correct answer is A.

Question 4

 * What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?
 * A. 2 to 1
 * B. 1 to 3
 * C. 1 to 1
 * D. 10 to 1

The correct answer is C.

Question 5

 * What is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power?
 * A. 2 to 1
 * B. 1 to 2
 * C. 6 to 1
 * D. 10 to 1

The correct answer is A.

Question 6

 * What does an SWR reading of 4 to 1 indicate?
 * A. Loss of -4dB
 * B. Good impedance match
 * C. Gain of +4dB
 * D. Impedance mismatch

The correct answer is D.

Question 7

 * What happens to power lost in a feed line?
 * A. It increases the SWR
 * B. It comes back into your transmitter and could cause damage
 * C. It is converted into heat
 * D. It can cause distortion of your signal

The correct answer is C.

Question 8

 * What instrument other than an SWR meter could you use to determine if a feed line and antenna are properly matched?
 * A. Voltmeter
 * B. Ohmmeter
 * C. Iambic pentameter
 * D. Directional wattmeter

The correct answer is D.

Question 9

 * Which of the following is the most common cause for failure of coaxial cables?
 * A. Moisture contamination
 * B. Gamma rays
 * C. The velocity factor exceeds 1.0
 * D. Overloading

The correct answer is A.

Question 10

 * Why should the outer jacket of coaxial cable be resistant to ultraviolet light?
 * A. Ultraviolet resistant jackets prevent harmonic radiation
 * B. Ultraviolet light can increase losses in the cable's jacket
 * C. Ultraviolet and RF signals can mix together, causing interference
 * D. Ultraviolet light can damage the jacket and allow water to enter the cable

The correct answer is D.

Question 11

 * What is a disadvantage of air core coaxial cable when compared to foam or solid dielectric types?
 * A. It has more loss per foot
 * B. It cannot be used for VHF or UHF antennas
 * C. It requires special techniques to prevent water absorption
 * D. It cannot be used at below freezing temperatures

The correct answer is C.

Question 12

 * Which of the following is a common use of coaxial cable?
 * A. Carrying dc power from a vehicle battery to a mobile radio
 * B. Carrying RF signals between a radio and antenna
 * C. Securing masts, tubing, and other cylindrical objects on towers
 * D. Connecting data signals from a TNC to a computer

The correct answer is B.

Question 13

 * What does a dummy load consist of?
 * A. A high-gain amplifier and a TR switch
 * B. A non-inductive resistor and a heat sink
 * C. A low voltage power supply and a DC relay
 * D. A 50 ohm reactance used to terminate a transmission line

The correct answer is B.