Faculty of Engineering Electrical Engineering Department Communication Engineering I Lab (EELE 3170) Eng. Adam M. Hammad

Faculty of Engineering Electrical Engineering Department Communication Engineering I Lab (EELE 3170) Eng. Adam M. Hammad

EXPERIMENT #2 UNDERSTANDING TELEPHONE BASICS

Telephone components: 1. Handset containing a transmitter and receiver. 2. Switch hook. 3. Dialer (either rotary or touch-tone) 4. Ringer.

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Typical telephone does the following: Requests service from the network. Performs dialing functions. Performs a notification function (it rings) Provides answer and disconnect supervision. Converts outgoing speech to electrical signals, and vice versa.

Understanding Telephony Signaling: For a telephone call to be completed, several forms of signaling must occur: Access signaling Station loop signaling Address signaling

Access signaling Determines when a line is off hook or on hook. When the handset is on its cradle, the phone is on hook. When a telephone is on hook, the two wires do not touch, so the circuit (loop) is open and no current flows. When the handset is out of its cradle, it goes off hook. And the wires touch, closing the loop, allowing current to flow through the two conductors that connect the phone to the network, sending an "off-hook" signal to the switch. To place a call, the phone must be off hook. To receive a call it must be on hook

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Station loop signaling When initiating a call, the telephone is placed off-hook. The connected network switch senses the off-hook condition (current flow) and provides an audible Ready signal known as 'Dial Tone'. Tones used in telephone system are: Dial tone : consist of a summation of two low distortion sine waves. Precise dial tone consists of 350 and 440Hz. Busy tone: Precise busy signal consists of 480 and 620 Hz. Call waiting: 440 Hz.

Address signaling The caller can request connection to another telephone by transmitting the address (telephone number) of the requested telephone to the network. This is known as address signaling. Telephones generally use two basic types of address signaling: Pulse dialing (rotary dialing) Tone dialing

Pulse dial (rotary dialing) Rotary dial phones represent the digit being dialed by momentarily stopping the current flow when the user turns the circular dial. For example, the circuit is broken three times, which creates three pulses in the current, to dial the digit "3.", and for zero, the line is "disconnected" ten times.

Tone dial DTMF or dual tone multi-frequency. Used by pushbutton telephones. Touch-tone telephone dialing is example of using Fourier analysis. Telephone signaling is based on encoding keypad digits using two sinusoids of different frequencies, hence the name DTMF. Each digit is represented by a low frequency and a high frequency sinusoids.

Dual-Tone Multi-Frequency (DTMF) Wl is the low frequency of the sine wave. Wh is the high frequency of the sine wave. A & B are amplitude of the signals φ is the initial phase shift.

Tone Generator

Tone Decoder

Generation of 1 Button Tone Low Freq. = 697 Hz High Freq. = 1210 Hz So, This tone is 1.

Read files using MATLAB

Finding Frequency of A Given Tone Low Freq. = 769 Hz High Freq. = 1336 Hz So, This tone is 5.

Finding Frequency of Unknown Tone s Numbers

Continued.. Divide signal into interval Low Freq. = 699 Hz High Freq. = 1329 Hz So, This tone is 2.

Experiment 1 1. Read the following files using MATLAB. (dial_tone.wav, busy.wav). 2. Use the command 'sound' to listen the tones. 3. Find the Fourier Transform for each signal. 4. Plot each signal with its magnitude spectrum in one figure. 5. From the plot, determine the frequencies for dial tone signal and for busy tone.

Experiment 2 1. Use Matlab to generate the 12 DTMF signals of telephone keypad, and plot these signals clearly. 2. Find Fourier Transform for the 12 DTMF signals, and plot the magnitude spectrum for each signal. (From the plot, notice the frequency components for each signal).

Experiment 3 1. Using Matlab, read the files x1.wav and x2.wav 2. Use the command 'sound' to listen to the tones. 3. Find the fourier transform for each signal. 4. Plot each signal with its magnitude spectrum in one figure. 5. From the plot, determine the button in telephone keypad that generated x1.wav and x2.wav.

Experiment 4 1. Using Matlab, read the file dtmf.wav. 2. Use the command 'sound' to listen to the tone. 3. Find the Fourier transform of the signal. 4. Plot the signal with its magnitude spectrum in one figure. 5. From the plot: Determine how many digits does this signal act? Can you determine the dialed number from the plot? If yes, explain how you can determine the dialed number.