2.9 KiB
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
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T7C01 (A) What is the primary purpose of a dummy load? #card
- 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
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T7C02 (B) Which of the following is used to determine if an antenna is resonant at the desired operating frequency? #card
- A. A VTVM
- B. An antenna analyzer
- C. A Q meter
- D. A frequency counter
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T7C03 (B) What does a dummy load consist of? #card
- A. A high-gain amplifier and a TR switch
- B. A non-inductive resistor mounted on a heat sink
- C. A low-voltage power supply and a DC relay
- D. A 50-ohm reactance used to terminate a transmission line
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T7C04 (C) What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line? #card
- A. 50:50
- B. Zero
- C. 1:1
- D. Full Scale
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T7C05 (A) Why do most solid-state transmitters reduce output power as SWR increases beyond a certain level? #card
- A. To protect the 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
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T7C06 (D) What does an SWR reading of 4:1 indicate? #card
- A. Loss of -4 dB
- B. Good impedance match
- C. Gain of +4 dB
- D. Impedance mismatch
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T7C07 (C) What happens to power lost in a feed line? #card
- A. It increases the SWR
- B. It is radiated as harmonics
- C. It is converted into heat
- D. It distorts the signal
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T7C08 (D) Which instrument can be used to determine SWR?
- A. Voltmeter
- B. Ohmmeter
- C. Iambic pentameter
- D. Directional wattmeter
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T7C09 (A) Which of the following causes failure of coaxial cables? #card
- A. Moisture contamination
- B. Solder flux contamination
- C. Rapid fluctuation in transmitter output power
- D. Operation at 100% duty cycle for an extended period
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T7C10 (D) Why should the outer jacket of coaxial cable be resistant to ultraviolet light? #card
- 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, causing interference
- D. Ultraviolet light can damage the jacket and allow water to enter the cable
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T7C11 (C) What is a disadvantage of air core coaxial cable when compared to foam or solid dielectric types? #card
- A. It has more loss per foot
- B. It cannot be used for VHF or UHF antennas
- C. It requires special techniques to prevent moisture in the cable
- D. It cannot be used at below freezing temperatures