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
The Question Pool
[edit | edit source]Question 1
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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
[edit | edit source]- 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.