Page:Electronics Technician - Volume 7 - Antennas and Wave Propagation - NAVEDTRA 14092.pdf/107

 1-23. For ionospheric reflection to occur, the ionized layer must not be thicker than. how many wavelengths of the transmitted frequency?
 * One
 * Two
 * 1) Three
 * 2) Four

1-24. The ability of radio waves to turn sharp corners and bend around obstacles is known as
 * 1) reflection
 * 2) refraction
 * 3) diffraction
 * 4) waveshaping

1-25. Which of the following definitions best describes a shadow zone?
 * 1) The area of complete coverage at vlf frequencies
 * 2) The area within the diameter of an obstruction
 * 3) The area ranging the height of the obstruction
 * 4) The area on the opposite side of the obstruction, in line-of-site from the transmitter to the receiver

1-26. What type of fading occurs for the longest amount of time?
 * 1) Phase shift
 * 2) Absorption
 * 3) Multipath
 * 4) Diffraction

1-27. Which of the following are examples of multipath radio wave transmissions?
 * 1) Groundwaves
 * 2) Ionospheric refractions
 * 3) Reflection from the earth's surface
 * 4) All of the above

1-28. Fading on the majority of the ionospheric circuits is a result of what particular type fading?


 * 1) Selective
 * 2) Absorption
 * 3) Multipath
 * 4) Weather

IN ANSWERING QUESTIONS 1-29 AND 1-30, SELECT FROM THE FOLLOWING LIST THE DEFINITION OF THE INDICATED TERM.

A. Two or more receiving antennas spaced apart to produce a usable signal

B. Two or more receiving antennas of varying heights located together

C. The use of two separate transmitters and receivers on different frequencies transmitting the same information

D. The use of two separate transmitters and receivers on the same frequency transmitting the same information

1-29. Space diversity.
 * A
 * B
 * C
 * D

1-30. Frequency diversity.
 * A
 * B
 * C
 * D

1-31. A. wide band of frequencies is transmitted and selective fading occurs. Which of the following statements best describes the effect of the fading on the signal?
 * 1) It affects various frequencies
 * 2) It can cause changes in phase and amplitude
 * 3) It can cause severe distortion and limit total signal strength
 * 4) All of the above

Which ionospheric layer is most dense during the winter? 3
 * E
 * D
 * F2
 * F1