Communication Systems : Practice Questions and Answers

The correct answer is B: Secondary.

An information source is anything that might inform a person about something by providing knowledge. Information sources may be observations, people, speeches, documents, pictures, organizations, etc.

Types of Information Sources:

• Primary Sources: Contain first-hand information — the author's own account of a specific topic or event they participated in. Examples: scholarly research articles, diaries.
• Secondary Sources: Compiled from or referring to primary sources. The original information has been modified, selected, or reorganized to serve a definite purpose for a group of users. Examples: manuals, tables, handbooks, newspapers, dictionaries.
• Tertiary Sources: Summarize or synthesize research from secondary sources. Examples: textbooks, reference books. Usually not credited to a particular author.

Since a local newspaper is a secondary source, collecting weather information from it is an example of a Secondary type of source.

The correct answer is D.

Concept:

The modulation index in AM is always kept less than 1 to avoid distortion or clipping of the message signal. When m > 1, the carrier undergoes a phase reversal of 180° and the envelope of the modulated signal no longer contains the actual message signal, resulting in a distorted output from the envelope detector.

Explanation:

• When m > 1, the amplitude of the message signal exceeds the amplitude of the carrier signal.
• This causes over-modulation, leading to envelope distortion where the envelope detector cannot faithfully recover the original message.
• Additionally, m > 1 results in overlapping of both sidebands, causing loss of information.
• Therefore, option D is the correct answer.