3c251 Volume 4
3C251 Volume 4. UREs only.
- 1.What led to the development of very high frequency (VHF) and ultra high frequency (UHF) radio systems during World War II?
- A.
The longer distances involved in communications with forces of Europe
- B.
The need for more reliable high-capacity communications
- C.
The development of line of sight (LOS) communications
- D.
The need for more resistance to nuclear blast
- 2.The two primary types of radio waves are
- A.
Direct and surface
- B.
Sky and surface
- C.
Ground and sky
- D.
Direct and sky
- 3.What condition causes the downward bending of a radio wave as it grazes the top of an obstruction such as a mountain peak?
- A.
Reflection
- B.
Refraction
- C.
Diffraction
- D.
Diffusion
- 4.During periods of maximum sunspot activity, what is the density level and altitude effect of the F layer?
- A.
Less dense and at a lower altitude
- B.
More dense and at a lower altitude
- C.
Less dense and at a higher altitude
- D.
More dense and at a higher altitude
- 5.What type of frequency is the highest frequency that returns to earth when it is transmitted vertically under given ionospheric conditions?
- A.
Frequency of optimum traffic
- B.
Maximum usable frequency
- C.
Most usable frequency
- D.
Critical frequency
- 6.A satellite system that requires numerous satellites in randomly spaced orbits to provide acceptable coverage is
- A.
An active system
- B.
A passive system
- C.
A synchronous system
- D.
A low-altitude system
- 7.What is a major disadvantage of a geostationary satellite?
- A.
It can't amplify signals
- B.
It orbits the earth in a figure eight pattern
- C.
The transmitted frequency is below 10-gigahertz (GHz)
- D.
The two-way propagation delay is about 0.6 seconds
- 8.Above what frequency does the propagation loss because of oxygen and water absorption become very serious in satellite communication?
- A.
10 gigahertz (GHz)
- B.
8 GHz
- C.
6 GHz
- D.
4 GHz
- 9.The reduction in amplitude of a radio signal as it travels away from the source through a propagation medium that's free of obstructing, scattering, or reflecting effects is called
- A.
Faraday effect
- B.
Doppler effect
- C.
Free space attenuation
- D.
None of the above
- 10.The Doppler effect, inherent to satellite communications, is caused by
- A.
Transmit frequency drift
- B.
Transmit frequency drift off phase-lock ground receivers
- C.
The satellite's motion in space relative to ground stations
- D.
Rotation of the polarization of radio waves
- 11.Which satellite communications subsystem consist of a satellite antenna array and a transponder?
- A.
Earth
- B.
Space
- C.
Orbital
- D.
Control
- 12.What satellite device receives, amplifies, and retransmits signals from earth to terminals?
- A.
Station keeper
- B.
Satellite amplifier
- C.
Satellite transponder
- D.
Regenerative repeater
- 13.At a minimum, a typical link involves
- A.
An active satellite and one earth terminal
- B.
An active satellite and two earth terminal
- C.
Two active satellite and one earth terminal
- D.
Two active satellite and two earth terminal
- 14.Maintaining optimum performance of a satellite's transponder is a function of
- A.
Satellite control
- B.
Station keeping
- C.
Satellite ground track
- D.
Communications control
- 15.What type of multiple-access service used in satellite communications provides each earth terminal exclusive use of the satellite transponder for a specified time interval?
- A.
Spread spectrum multiple access (SSMA)
- B.
Frequency division multiple access (FDMA)
- C.
Demand assignment multiple access (DAMA)
- D.
Time division multiple access (TDMA)
- 16.Two system control problems with time division multiple access are in the area of network timing and
- A.
Power
- B.
Frequency
- C.
Synchronization
- D.
Transponder complexity
- 17.What satellite access system lets several users occupy the same frequency spectrum in the transponder simultaneously?
- A.
Frequency division multiple access (FDMA)
- B.
Time division multiple access (TDMA)
- C.
Spread spectrum multiple access (SSMA)
- D.
Band spreading multiple access
- 18.Which organization is responsible for the design, acquisition, and single systems management of the Defense Switched Network?
- A.
Defense Logistics Agency
- B.
Communications Squadron
- C.
Air Force Communications Agency
- D.
Defense Information Systems Agency (DISA)
- 19.How is survivability provided in the Defense Switched Network (DSN)?
- A.
End offices are multiple-homed
- B.
End offices do not interoperate with allied networks
- C.
The DSN offers precedence access thresholding (PAT)
- D.
The DSN offers single multilevel precedence and preemption (MLPP)
- 20.How is responsiveness provided in the Defense Switched Network (DSN)?
- A.
End offices are multiple-homed
- B.
End offices do not interoperate with allied networks
- C.
The DSN offers precedence access thresholding (PAT)
- D.
The DSN offers single multilevel precedence and preemption (MLPP)
- 21.What type of Defense Switched Network (DSN) precedence call cannot be preempted?
- A.
Flash
- B.
Priority
- C.
Intermediate
- D.
Flash Override
- 22.What type of precedence is assigned to Defense Switched Network (DSN) calls pertaining to situations that gravely affect the security of national and allied forces?
- A.
Flash
- B.
Priority
- C.
Intermediate
- D.
Flash Override
- 23.Which encryption device makes end-to-end encryption available to any user of the Defense Switched Network (DSN)?
- A.
KG-84
- B.
KG-94
- C.
KIV-7
- D.
Secure telephone unit-III (STU-III)
- 24.What is the primary difference in the Defense Switched Network (DSN) subsystems?
- A.
Access line protocol functions
- B.
Network management functions
- C.
Internal call processing features and functions
- D.
Administrative, operations and maintenance functions
- 25.Why should high-priority users not be terminated on a remote switching unit (RSU)?
- A.
A Secure telephone unit-III (STU-III) cannot make calls through a RSU
- B.
Precedence calling is not available with a RSU
- C.
RSU can become saturated and deny all service
- D.
RSU can become isolated from the parent switch
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