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 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.