TC 9-64 _________________________________________________________________________
27. What are the two main sources of electromagnetic interference (EMI) with which radio waves
must compete?
28. Thunderstorms, snowstorms, cosmic sources, and the sun are a few examples of EMI sources.
What type of EMI comes from these sources?
29. Motors, switches, voltage regulators, and generators are a few examples of EMI sources.
What type of EMI comes from these sources?
30. What are three ways of controlling the amount of transmitter-generated EMI?
31. What are three ways of controlling radiated EMI during transmission?
32. What are the two general types of variations in the ionosphere?
33. What is the main difference between these two types of variations?
34. What are the four main classes of regular variation that affect the extent of ionization in the
ionosphere?
35. What are the three more common types of irregular variations in the ionosphere?
36. What do the letters MUF, LUF, and FOT stand for?
37. When is MUF at its highest and why?
38. What happens to the radio wave if the LUF is too low?
39. What are some disadvantages of operating transmitters at or near the LUF?
40. What are some disadvantages of operating a transmitter at or near the MUF?
41. What is FOT?
42. How do raindrops affect radio waves?
43. How does fog affect radio waves at frequencies above 2 gigahertz?
44. How is the term "temperature inversion" used when referring to radio waves?
45. How does temperature inversion affect radio transmission?
46. In what layer of the atmosphere does virtually all weather phenomena occur?
47. Which radio frequency bands use the tropospheric scattering principle for propagation of
radio waves?
48. Where is the tropospheric region that contributes most strongly to tropospheric scatter
propagation?
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