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The Basic – Sound, Electrical Signal,

The Basic – Sound, Electrical Signal, . Dr. Farid Farahmand CET 533. Sound. What is Sound? Periodic variation in air pressure Travels through media with different speed – air, metal, wood, etc. Sound waves Pressure waves that vibrate molecules in a medium

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The Basic – Sound, Electrical Signal,

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  1. The Basic – Sound, Electrical Signal, Dr. Farid Farahmand CET 533

  2. Sound • What is Sound? • Periodic variation in air pressure • Travels through media with different speed – air, metal, wood, etc. • Sound waves • Pressure waves that vibrate molecules in a medium • Similar to throwing a stone in water • Human Voice • Vibrations created in vocal cords traveling out of the mouth and changing (disturbing) the air around us http://www.grc.nasa.gov/WWW/K-12/airplane/sndwave.html

  3. Telecommunications Basics • Telecommunications is about sending data and voice • Telephony and data communication • The sound/data must be converted into electrical signals • Sound waves are characteristics by their physical properties • Frequency and wavelength • Power or strength • Amplitude or volume (loudness) • Communication circuits convert sound into electrical waves • Electrical waves are characterized by • Voltage • Current • Power • Impedance • Frequency and wavelength

  4. Sound Properties • Frequency • Number of cycles (events) over a time unit • Cycles per second (Hz) - FIGURE • Wavelength • Describes the length of the waveform • Amplitude • Determines the loudness (height of the signal) • Describes the loudness or softness • Higher volume  traveling longer (more power) • Hence: Distance µ Volume µ Power

  5. Sound Properties • Audibility • Frequency range that is sensible to human ear 20-20K Hz • Human speech: 300-4KHz • That is why the sampling rate for human speech is 8KHz! • Size of the eardrum determines the frequency sensibility • Dogs are more sensible to hear higher frequencies; they have small ear drums • Telephones tend to hear sounds with low frequencies • Teenagers are more sensitive to high pitch noises! One way to disperse them! • Telephone systems are designed for human speech • Filtering any frequencies beyond 300-4KHz • You can not listen to a Mozart’s concert too well! Assuming you are in space, would a very loud explosion hurt your ears drums? ANSWER http://www.school-for-champions.com/science/sound.htm

  6. The Speed of Sound speed of sound (m/s) = 331.5 + 0.60 T(°C) The motion relationship "distance = velocity x time" is the key to the basic wave relationship. With the wavelength as distance, this relationship becomes l=vT. Then using f=1/T gives the standard wave relationship http://library.thinkquest.org/11924/swchar.html http://library.thinkquest.org/19537/Physics4.html

  7. Communication Systems • Basic components • Converter (sound to electrical & electrical to sound) • TX and RX • Medium (air, copper, water, etc.) – typically a conductor - FIGURE • Speed of the electrical signals through a conductor is faster than air • Faster due to shock wave effect of electrons (similar to domino effect)

  8. Basics of Electrical Signals • Four basic properties • Current, Voltage, Power, and Impedance • Voltage: The force causing flow of electrons down the conductor (or medium) – (V) • Current is the flow of electrons (I) • More flow when there is less resistance in the medium • Can be direct or alternating (DC or AC) • Power defines as P=V.I AC Voltage: http://micro.magnet.fsu.edu/electromag/java/generator/ac.html

  9. Basics of Electrical Signals • A little more about AC Voltage • Generators typically generate AC voltage • A moving wire through magnetic field – FIGURE • It converts mechanical energy to electrical energy • AC voltage has amplitude and frequency • In US the amplitude from an outlet is 120 RMS with f=60 Hz FIGURE • RMS = 0.707 x ½ (Vpeak-to-peak) • The Vpeak-to-peak in US is +170 to -170  340 V • Hence: 0.707 x ½ (340) = 120 V RMS!! http://www.walter-fendt.de/ph11e/mfwire.htm http://micro.magnet.fsu.edu/electromag/java/compass/index.html

  10. Basics of Electrical Signals • Impedance • Measured in Ohm or W • Composed of Resistance, Inductive Reactance, Capacitive Reactance • Resistance is the force impeding the flow of electrons • All conductors have some resistance • Effects both AC and DC signals • V = I.R

  11. Basics of Electrical Signals • Inductive Reactance (XL) • Only impacts AC signals (alternating flow through Tip and Ring in telephone cables) • Defined as XL = 2fp.L • L is called the inductance and measured in Henry • Inductance depends on the wire gauge and the material • Example: f=100, L=0.01H, XL=0.63 Ohm • Note: Higher frequency results in higher Inductive Reactance

  12. Basics of Electrical Signals • Capacitive Reactance (XC) • Only impacts AC signals (capacitance effect between the Tip and Ring wires) • Defined as XC = 1/(2fp.C) • C is called the capacitance and measured in Farad • Capacitance is proportional to the wire length • Example: f=1000, C=0.083F, XC=1917 Ohm • Note: Higher frequency results lower XC

  13. Basics of Electrical Signals • Remember: f  Very High, then XL0 and XC¥ • We can couple the capacitance and inductance effects to cancel them! • If XL = XC; What is the frequency? • This is called the resonant frequency • In this case we call the circuit Tuned • Example: f=10KHz, C=253.3 nF, L=1mH • XL=62.83 Ohm • XC=62.83 Ohm • The resonant frequency = 10KHz

  14. Power in Telecommunication Systems • Often we are interested in comparing power levels • Input power vs. output power in an amplifier • Ratio between good signal and bad signal (noise) • Loss of signal on a wire • Power in telecom systems is defines as 1 mW of electricity flowing through one ohm of resistance • P = VxI = RxI2  Double the current what happens? • We use dBm to express signal power in telecommunications • Converting Power in mW to dBm: • Example: If Power is 10mW -> Power is 10 dBm

  15. Power in Telecommunication Systems • We are also interested to see what happened to the power level • The unit to compare is decibel (dB) • Gain = P2/P1 = Power_out / Power_in If P1=2W and the gain is 3dB, find P1!

  16. Power in Telecommunication Systems • Remember: • Example 1: if P2=2mW and P1 = 1mW  3dB • Example 2: if P2=1KW and P1=10W 20dB • What if dB is given and you must find P2/P1? • P2/P1 = Antilog(dB/10) = 10 dB/10 . • Example 3: if dB is +10 what is P2/P1? • P2/P1 = Antilog(+10/10) = 10 +10/10 = 10

  17. Power Analysis (FIGURE)

  18. Organizations • Who deals with telecommunication issues? • Who can use what spectrum • Signal formats and technology • Connectivity, addressing, etc. • FCC (Federal Communication Commission) – Controls all communication at federal levels. • Standard Organizations • International Telecommunication Union (ITU) – UN-based • Has several branches: ITU-T (telecommunication), ITU-R (radio) • CCITT world organized standards organization for telecommunications • American National Standards Institute (ANSI) • ANSI X.3T9.5 Focusing on US telecommunications – similar to ITU • International Standard Organization (ISO) – Liaison between ANSI and ITU

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