ECET 303 Communications I Fall Introduction to the Course

Transcription

1 ECET 303 Communications I Fall 2016 Introduction to the Course Text Book: Electronic Communications Systems, 5th Edition, by Wayne Tomashi, published by Pearson. Dr. Hadi Alasti, Assistant Professor and Paul I-Hai Lin, Professor of Electrical and Computer P.E. States of Indiana & California Dept. of Computer, Electrical and Information Technology Indiana University Purdue University Fort Wayne Prof. Paul Lin & Dr. Hadi Alasti 1 ECET 303 Communications I Review of the previous session Logarithm review decibel (db) and Bel dbm and db Class Practice Assignment db, dbm (due next Monday) Next Topics of Discussion Prof. Paul Lin & Dr. Hadi Alasti 2 1

2 Review In the first session of the course after reviewing the course learning objectives, assessment parts, and the class rules; Communication Electronics history was reviewed chronologically. We also became familiar with some of the well-known scientist and technologists whose their contributions impressed the evolution of communications systems in our world. Prof. Paul Lin & Dr. Hadi Alasti 3 Review of Logarithm From your algebra courses you remember that, based on definition: If A = B C then C = Log B (A) and vise versa As an example 10 3 =1000 then Log 10 (1000) = 3. The number B is the base of logarithm and the number Aisitsargument. Prof. Paul Lin & Dr. Hadi Alasti 4 2

3 Review of Logarithm Logarithm base The base of the logarithm can be: 10 Base 10 is used in many applications in engineering and science e = (Neper number) Logarithm with base e, or so-called natural logarithm is also very frequently used in engineering and science. 2 Base 2 is normally used in digital communications, computer science and engineering and mathematics. Prof. Paul Lin & Dr. Hadi Alasti 5 Review of Logarithm Properties of Logarithm Argument of a logarithm must be a non-zero, positive number. Logarithm of a number is smaller in value than that number. Property #1: Log B (X * Y) = Log B (X) + Log B (Y) Property #2: Log B (X/Y) = Log B (X) - Log B (Y) Property #3: Log B (X n ) = n Log B (X) Prof. Paul Lin & Dr. Hadi Alasti 6 3

4 Logarithmic measurement - 1 There are several examples of logarithmic measurement of physical quantities. Example 1: The magnitude of earthquakes intensity, which is measured in the unit of Richter scale, measures the intensity of the earthquakes relative to a reference intensity that can be measured using seismograph. A 6 Richter earthquake is 10 times stronger than a 5 Richter earthquake and 100 times stronger than a 4 Richter earthquake. Prof. Paul Lin & Dr. Hadi Alasti 7 Logarithmic measurement - 2 Example 2: The acoustic loudness of the sound or Sound Pressure Level (SPL) is measured in logarithmic scale relative to the hearing threshold of a normal human-being. The unit of measurement of SPL is in db. 0 db is the strength of the threshold level sound. The upper limit of the hearing of a normal humanbeing is around 120 db. Prof. Paul Lin & Dr. Hadi Alasti 8 4

5 Measuring Sound Pressure Level (SPL) and Loudness decibel (db) and Bel DeciBel (abbreviated db) is a logarithmic unit that can be used to measure ratios of virtually anything. By definition, the db value of a quantity such as A, is: A db = 10 Log 10 (A) Bell is a smaller logarithmic unit. By definition, the value of a quantity such as A, in Bell is: A Bel = Log 10 (A) Bel and db are a relative unit, and as you remember from the last two examples, there must be a reference level. Prof. Paul Lin & Dr. Hadi Alasti 10 5

6 decibel (db) - 1 db is a common unit in calculation and measurement of power gain and loss in electrical systems. The absolute power gain of an system with Pin, input power and Pout, output power is defined: Power gain in db is simply calculated from: Prof. Paul Lin & Dr. Hadi Alasti 11 decibel (db) - 2 Example 3: 10 mw power in launched into a power amplifier. The output power measured at the output load is 200 mw. Calculate the power gain of this amplifier in db. Solution: First, we calculate the absolute power gain: = Then, let us plug the above value in the following formula to calculate the power gain db db Prof. Paul Lin & Dr. Hadi Alasti 12 6

7 decibel (db) - 3 Similar to power gain, the power loss of a passive system is calculated from: < 1 Where to calculate the total power loss we use the following formula: 10 loss is a negative number in db db is used in calculation of link budgets in communications. Prof. Paul Lin & Dr. Hadi Alasti 13 Decibel concept in technology 7

8 dbm Engineers and technicians use an assumed reference power level to express the other power values in dbx units. dbm is the unit of power relative to one mw power level. Accordingly, dbm is defined a: 10 1 Example 4: Convert 200 mw power to dbm. Solution: Prof. Paul Lin & Dr. Hadi Alasti 15 Class practice (5-10 minutes) Now, for today s class practice, lets work as a group with one partner and try to solve the problems of the examples 1-1, 1-3, 1-4 and 1-5. Ask your professor, if you see any ambiguities. Prof. Paul Lin & Dr. Hadi Alasti 16 8

9 Assignment Challenge problem Due: Discussion in class on Monday Challenge yourself and try to explain the solution of the example 1-2, page 6. What are the differences in the formula in comparison to when you wanted to calculate power gain in db? Prof. Paul Lin & Dr. Hadi Alasti 17 Next session s topic On the next session, we will : continue working on db and dbm. Explain the basic concept of modulation and demodulation in communication systems. Become familiar with spectrum Prof. Paul Lin & Dr. Hadi Alasti 18 9