Questions - Transmission Lines 

Question file 26


  1. Any length of transmission line may be made to appear as an infinitely long line by:  STUDY NOTES 
    1. shorting the line at the end
    2. leaving the line open at the end                                       QUESTIONS WITHOUT ANSWERS 
    3. terminating the line in its characteristic impedance
    4. increasing the standing wave ratio above unity
    ========= Answer is c =========
  2. The characteristic impedance of a transmission line is determined by the:
    1. length of the line
    2. load placed on the line
    3. physical dimensions and relative positions of the conductors
    4. frequency at which the line is operated
    ========= Answer is c =========
  3. The characteristic impedance of a 20 metre length of transmission line is 52 ohm. If 10 metres is cut off, the impedance will be:
    1. 13 ohm
    2. 26 ohm
    3. 39 ohm
    4. 52 ohm
    ========= Answer is d =========
  4. The following feeder is the best match to the base of a quarter wave ground plane antenna:
    1. 300 ohm balanced feedline
    2. 50 ohm coaxial cable
    3. 75 ohm balanced feedline
    4. 300 ohm coaxial cable
    ========= Answer is b =========
  5. The designed output impedance of the antenna socket of most modern transmitters is nominally:
    1. 25 ohm
    2. 50 ohm
    3. 75 ohm
    4. 100 ohm
    ========= Answer is b =========
  6. To obtain efficient transfer of power from a transmitter to an antenna, it is important that there is a:
    1. high load impedance
    2. low load impedance
    3. correct impedance match between transmitter and antenna
    4. high standing wave ratio
    ========= Answer is c =========
  7. A coaxial feedline is constructed from:
    1. a single conductor
    2. two parallel conductors separated by spacers
    3. braid and insulation around a central conductor
    4. braid and insulation twisted together
    ========= Answer is c =========
  8. An RF transmission line should be matched at the transmitter end to:
    1. prevent frequency drift
    2. overcome fading of the transmitted signal
    3. ensure that the radiated signal has the intended polarisation
    4. transfer maximum power to the antenna
    ========= Answer is d =========
  9. A damaged antenna or feedline attached to the output of a transmitter will present an incorrect load resulting in:
    1. the driver stage not delivering power to the final
    2. the output tuned circuit breaking down
    3. excessive heat being produced in the transmitter output stage
    4. loss of modulation in the transmitted signal
    ========= Answer is c =========
  10. A result of mismatch between the power amplifier of a transmitter and the antenna is:
    1. reduced antenna radiation
    2. radiation of key clicks
    3. lower modulation percentage
    4. smaller DC current drain
    ========= Answer is a =========
  11. Losses occurring on a transmission line between a transmitter and antenna result in:
    1. less RF power being radiated
    2. a SWR of 1:1
    3. reflections occurring in the line
    4. improved transfer of RF energy to the antenna
    ========= Answer is a =========
  12. If the characteristic impedance of a feedline does not match the antenna input impedance then:
    1. standing waves are produced in the feedline
    2. heat is produced at the junction
    3. the SWR drops to 1:1
    4. the antenna will not radiate any signal
    ========= Answer is a =========
  13. A result of standing waves on a non-resonant transmission line is:
    1. maximum transfer of energy to the antenna from the transmitter
    2. perfect impedance match between transmitter and feedline
    3. reduced transfer of RF energy to the antenna
    4. lack of radiation from the transmission line
    ========= Answer is c =========
  14. A quarter-wave length of 50-ohm coaxial line is shorted at one end. The impedance seen at the other end of the line is:
    1. zero
    2. 5 ohm
    3. 150 ohm
    4. infinite
    ========= Answer is d =========
  15. A switching system to use a single antenna for a separate transmitter and receiver should also:
    1. disable the unit not being used
    2. disconnect the antenna tuner
    3. ground the antenna on receive
    4. switch between power supplies
    ========= Answer is a =========
  16. An instrument to check whether RF power in the transmission line is transferred to the antenna is:
    1. a standing wave ratio meter
    2. an antenna tuner
    3. a dummy load
    4. a keying monitor
    ========= Answer is a =========
  17. This type of transmission line will exhibit the lowest loss:
    1. twisted flex
    2. coaxial cable
    3. open-wire feeder
    4. mains cable
    ========= Answer is c =========
  18. The velocity factor of a coaxial cable with solid polythene dielectric is about:
    1. 0.66
    2. 0.1
    3. 0.8
    4. 1.0
    ========= Answer is a =========
  19. This commonly available antenna feedline can be buried directly in the ground for some distance without adverse effects:
    1. 75 ohm twinlead
    2. 300 ohm twinlead
    3. 600 ohm open-wire
    4. coaxial cable
    ========= Answer is d =========
  20. If an antenna feedline must pass near grounded metal objects, the following type should be used:
    1. 75 ohm twinlead
    2. 300 ohm twinlead
    3. 600 ohm open-wire
    4. coaxial cable
    ========= Answer is d =========