Question

Answer all of the question

name Test 2 vic Data Comm. & Networking Where calculations are required, show solutions in two significant digits. 1) What characteristics of an analog signal are changed to represent the digital signal in QAM? (4 points) 2) Constellation diagrams are used in practice to monitor problems on a received signal such as excessive noise or timing problems. The constellation shown here represents what specific modulation type? (4 points) 3) When a communication channel is disturbed to the point the dots of the constellation blur and cross-over (eliminating the clean border region around each), data errors result. What parameter change can be implemented to eliminate (or at least significantly reduce) errors while still using the same (disturbed) communication channel? (5 points) 4) What is the key benefit of FM which resulted in its high popularity vs. AM for broadcast radio (4 points)? 5) Explain the purpose of a guard-band. (4 points) Milwaukee Area Technical College ELCTEC-150 Page 1

Answer 1

1. Quadrature amplitude modulation (QAM) changes both phase and amplitude of the analog signal.

2. The given constellation represents Quadrature amplitude modulation (QAM) type.

3. Carrier frequency and band width change can be implemented to eliminate errors while using disturbed channel.

4. Improved noise to signal ratio is the key benifit of using FM. Carrier modulation and alteration in FM and AM varies.. Slight changes in amplitude doesn't affect carrier in FM

5. A guard band is a narrow frequency range that separates two ranges of wider frequency. It provides channel separation in order to avoid mutual interference. Guard bands are commonly used in FDM but are also used in any data transmission method that relies on frequencies. A guard band may also be necessary between different systems, such as GSM and DECT, to avoid interference from one system into the other system.