Com Lab Manual

communication System Lab Aim: Study of delta modulation /demodulation system Objective: (a) To understand the working principle of delta modulation and demodulation. (b) Study of slope overload distortion and methods those are used for minimising it. Requirement: Trainer Kit ST2105 CRO Introduction: Delta modulation is a system of digital modulation developed after pulse code modulation. In this system, at each sampling time, say the kth sampling time, the difference between the sample value at sampling time K and the sample value at (the previous sampling time (k-1) is encoded into just a single bit), thus the O/P from the modulator is a series of zeros and ones. Working of delta modulator: The analog signal, which is to be encoded into a digital data, is applied to the positive input of the voltage comparator, which compares it with the signal applied to its negative input from the integrator O/P. The comparator’s O/P is logic “High” or “Low” depending on whether the input signal at the terminal is lower or greater than the negative terminal input signal. The comparator’s O/P is then lathed into a flip-flop, which is clocked by the transmitter clock. This binary data stream is transmitted to receiver and is also fed to the unipolar to bipolar converter block. This block convert logic “0” to voltage level of +4V and logic “1” to voltage level –4V Bipolar O/P is applied to the integrator, whose O/P is rising linear ramp signal when -4V is applied to it and falling linear ramp signal when +4V is applied to it. The integrator O/P is then connected to the negative terminal of voltage comparator. Delta demodulation consists of flip-flop, a unipolar to bipolar converter followed by an integrator and LPF. Procedure: 1. Connect the mains supply 2. Connect the board as shown in diagram 1. 3. Select clock frequency selector block switches A & B are in A=0 & B=0 position. 4. The integrator 1 block’s switches are in following positions: a. Gain control switch in left-hand position b. Switch A & B are in A=0 & B=0 positions. 5. The integrator 2 block switches are in following positions: a. Gain control switch in right hand position b. Switch A & B are in A=0 & B=0 positions. 6. First connect the “+” input of the delta modulator’s VOLTAGE COMPARATOR to 0V and monitor on an oscilloscope O/P of integrator 1 (t.p.17) 7. Adjust the transmitter’s LEVEL CHANGER preset until the O/P of integrator (t.p.17) is triangle wave cantered around 0 volts. The peak –to-peak amplitude of the triangle wave at the integrator’s O/P should be 0.5V(approx) this amplitude is known as the integrator STEP size. The O/P from the transmitter BISTABLE circuit (t.p.14) will now be stream of alternate ‘1’ and ‘0’s this is also the O/P of delta modulator itself. 8. Examine the signal at the O/P of the INTEGRATOR 2 (t.p.47) at the Receiver. This should be triangle wave, with step size equal to that of integrator 1, and ideally centred around 0 volt. otherwise remove it by adjusting the receiver’s LEVEL ADJUST preset. The receiver’s LPF leave a DC level at the filter’s O/P (t.p.51). 9. Now disconnect the voltage comparator’s “+” input from OV and reconnect it to the 250Hz O/P from the FUNCTION GENERATOR block; i.e 250Hz sine-wave. 10. Display the data of the transmitter’s BISTABLE (t.p.14) together with the analog input at t.p.9 and note that the 250Hz sine wave has effectively been encoded into a stream of data bits. 11. Now display the O/P of INTEGRATOR 2 (t.p.47) together with the O/P of the receiver’s LPF block (t.p.51), note that some ripple still remains at the filter’s O/P. This ripple is due to “quantisation noise” at the integrator’s O/P, which is caused by relatively large integrator step size. 12. This step size can be reduced by increasing the rate at which the system is clocked that is (the sampling frequency) since this reduces the sampling period and hence the time available between samples for the integrators to charges up and down. 13. Now increases the system clock frequency to 64KHz, by putting the switches in the A=0, B=1 position in CLOCK FREQUENCY SELECTOR block. 14. Now examine the ripple at the LPF’s O/P (t.p.51) note that this is now less than it was before. 15. By changing the system Clock frequency to first 128KHz (A=1, B=0) and then to 256KHz (A=1, B=1 position) note the improvement in the LPF’s O/P signal (t.p.51). Once again, it may be necessary to adjust slightly the transmitter’s LEVEL ADJUST preset in order to obtain a stable oscilloscope trace. 16. Now disconnect the comparator’s ‘+’ input from 250Hz sine wave O/P and reconnect it to the 500Hz, 1KHz and 2KHz O/P in turn. Note that as the frequency of the analog signal increases so the LPF’s O/P becomes more distorted and reduced in amplitude. 17. Now when the comparator’s + input is 2KHz sine wave then examine the O/P of INTEGRATOR 2 (t.p.47) which is no longer an approximation to the analog i/p signal but is instead somewhat triangular in shape. Since the analog signal is now changing so quickly that the integrators O/P can’t ramp fast enough to “Catch Up” with it and the result is known as “ Slope overloading” 18. Although the system clock frequency (i.e. the sampling freq.) determine how often the integrator’s o/p direction (up or down) can change, it does not affect how quickly the integrator’s o/p can ramp up and down. 19. Slope over loading can be avoided by a. Reducing the frequency of the analog input signal since there was no problem with the 250Hz analog i/p b. Reducing the amplitude of the i/p signal. This can be shown by slowly tuning the 2KHz preset anticlockwise. c. By increasing the gain of the integrators, so that they can ramp up and down faster. To illustrate this, first return to 2KHz preset to its fully clock wise (max amplitude) position, so that slope overloading can once again be seen on the scope. d. At both integrator blocks there are integrator gain switch A&B: now change the position A&B switches from A=0, B=0 to A=0, B=1, to double the gain of the two integrators, note that a slope overloading still occurs and continue to A=1, B=1 slope overloading can be eliminated. Result: Precautions (if any): Communication System Lab Aim: To generate an AM signal measuring its depth of modulation and demodulate it. Objective: (a) Study of AM modulation. (b) Measurement of depth of modulation. Equipment Required: Trainer kit for AM modulation, function generator, CRO. Theory: Amplitude modulation is a process in which the amplitude of carrier is varied in accordance with the modulating signal. m= Procedure: 1. Switch on the experiment kit. 2. Connect the carrier signal generator to the terminals where carrier is written (1&2) 3. Connect the CRO on output terminals of modulator. 4. Connect the function generator oscillator to the modulating signal terminals i.e. between 3 & 4. 5. Trace the waveshapes, which are amplitude modulated wave. 6. Note the Vmax and Vmin of modulated wave. 7. Calculate the percentage modulation. 8 Observe the waveform on the CRO and compare it with the input waveform. 9 Trace the waveshapes, which is modulating signal. 10 Disconnect the CRO and AF oscillator from the circuit. 11 Connect the AF oscillator to CRO and trace the wave shape. V max − v min × 100% V max = V min AF in Regulated Power Supply Amplitude Modulator AM Signal Carrier Generation Amplitude Demodulator Modulating Signal Modulated Signal R C Demodulated O/P Result: Precautions (If any): Questions: 1. Indicate the false statement. Modulation is used to a. Amplify lower frequency signals b. Allow the use of practicable antennas c. Increase the rate of transmission d. Reduce the bandwidth of transmission. 2. Draw the diode detector circuit and explain its action. 3. For an AM signal, modulated to a depth of 100% by a sinusoidal, the total power is a. Same as that of the carrier b. Twice as large as that of the carrier c. 50% more than that of the carrier. 4. What are the limitations of amplitude modulation? 5. The modulation index of AM wave is changed from 0 to 1, the transmission power is a. Unchanged b. Doubled c. Increased by 50%. 6. Amplitude modulated signals are detected by a. a synchronous detector b. an envelope detector c. a ring demodulator. 7. Vestigial sideband transmission is used in a. TV Transmission b. RT System c. Mobile telephony 8. What do you understand by coherent and non-coherent detection of signals? 9. The O/P of a diode detector contains a. Modulating signal or b. dc voltage or c. Both (a) and (b). 10. What is the necessity of modulation in radio communication systems? 11. Explain the following terms as related to AM a. Depth of modulation b. Synchronous detection c. Diagonal clipping in demodulator. this is being amplitude modulated by the output from audio oscillator. whose band is so chosen as to pass only upper side band and reject lower side band. Generate a DSB AM signal Generate a DSB-SC signal by removing the carrier component from the DSB AM signal To understand each and every block used in AM transmission and receptation Equipments Required: Trainer Kit ST-2201 and ST-2202. which contains only two side bands. which is selected. Which is achieved by feeding the DSBSC signal to the input of ceramic band pass filter. 1MHz Crystal Oscillator: This crystal generate 1MHz frequency which is used as carrier for the two balanced modulators& band pass filter circuits. which will be transmitted via a cable or through antenna. than it feeds back inverted variable carrier. 455 KHz Oscillators: The circuit comprises of a coil and a transistor 2N3904 generates as frequency lightly less than 455khz and is used a carrier signal for a balanced modulator. fed to audio amplifier balanced modulator & balanced modulator & band pass filter circuit. (2) (3) (4) (5) (6) . which then generates an output. The output is an amplified signal. Ceramic Band pass Filter: It is used to generate a SSB signal from the DSBSC signal obtained from the balanced modulator. which generates sine wave output whose frequency can be adjusted from 300 Hz to 3.4 KHz by varying the frequency pot..Communication System Lab Aim: Study of AM Transmitter and Receiver. Theory: (1) The AM transmission Block consists of following functional blocks. This frequency will be used as our modulating signal. Balanced Modulator: It generates two sidebands viz. upper sideband & lower side band with carrier. 2. Audio Oscillator: This block comprises of monolithic function generator IC 8038. Output Amplifier: The input to this section may be a DSB or SSB signal depending on the position of mode switch. 3. Objective: 1. As the information signal increases in amplitude. the carrier wave is also made to increases in amplitude. Information Signal Modulator AM Waveform Carrier Wave Output Amplifier: This amplifier is used to increase the strength of the signal before being passed to the antenna for transmission. Likewise.AMPLITUDE MODULATION (AM): The information signal should control the amplitude of the carrier wave. as the information signal decreases. Vmax – Vmin Percentage modulation = ---------------------.X 100% Vmax +Vmin Main parts of the transmitter shown below. then the carrier amplitude decreases. . Information Signal Audio Oscillator Modulator Output Amplifier Carrier Generator The Modulator: In this circuit the amplitude of the carrier is increased and decreased in sympathy with the incoming information signal. the RF amplifier frequency. From RF amplifier Mixer To IF amplifier From local oscillator Intermediate Frequency Amplifier (IF Amplifiers): It consists of two stages of amplification and provides the main signal amplification and selectivity.DSB Receiver The EM Wave from the transmitting antenna will travel to the receiving antenna carrying the information with it. however its output frequency is adjustable. The Diode Detector: The function of the diode detector is to extract the audio signal from the signal at the output of the IF Amplifiers. The Radio Frequency (RF) Amplifier: The first stage of amplification. or tracks. (ii) A ‘sum’ frequency equal to local oscillator frequency +RF signal frequency. It performs this task in a very similar way to a half wave rectifier converting an AC input to a DC output. Mixer: It performs a similar function to the modulator in transmitter. then the incoming RF signals. The Local Oscillator: An Oscillator producing a sinusoidal output similar to the carrier wave oscillator in the transmitter. The Receiving Antenna: It operates in the reverse mode to the transmitter antenna. by a fixed amount. which amplify the incoming signal above the level of the internally generated noise and also to start the process of selecting the wanted station and rejecting the unwanted ones. which is higher. The electromagnetic wave strikes the antenna and generates a small voltage in it. It is always maintained at a frequency. (iii) A component at the local oscillator frequency. Diode Input C R Output . It combines the signal from the RF amplifier and the frequency input from the local oscillator to produce three frequencies: (i) A ‘difference’ frequency of local oscillator frequency -RF signal frequency. therefore it follows. of this has removed the unwanted components generated by the mixing process. amplified slightly. which contains three components: (i) The wanted audio information signal. GAIN preset fully clockwise (d) Speaker Switch OFF position 2. 1. (c) Output Amp. at t. (iii) A positive DC voltage level. position (b) Select `DSB MODE`. The Audio Amplifier: at the input to the amplifier. by adjusting its preset we are removing the carrier component altogether means the carrier has been`balanced`out or suppressed to leave only the two sidebands.p.The result is an output. At t. a low pass filter is used to remove the IF ripple and a capacitor blocks the DC voltage level as shown in figure.p. is the OUTPUT AMPLIFIERS output signal. 9 a sine wave frequency of 1MHz. instead of using ST-2201 Audio oscillator block. AM waveform. 4. By using Audio Input Module. Frequency and in BALANCED MODULATOR & BANDPASS FILTER CIRCUITS I block fully clockwise. This is the carrier input of our doublesideband modulator. Note that the DSBSC waveform appears. It can also reduce the effect of fluctuations in the received signal strength. Turn the Audio Oscillator blocks Amplitude. the human voice can be used as the modulating signal. 6. Turn On power to the ST-2201 board 3. (ii) Some ripple at the IF frequency. The Automatic Gain Control (AGC): The AGC circuit is used to prevent very strong signals from overloading the receiver. Monitor at t. which has been formed by amplitude-modulating the 1 Mhz carrier sine wave with the audio-frequency sine wave form the audio oscillator. which will be transmitted to the receiver 7.p. (a) AUDIO INPUT SWITCH INT. Procedure: Ensure the following conditions on ST-2201. 5.3 the output of the BALANCED MODULATOR & BANDPASS FILTER CIRCUIT 1block is a double-sideband. and put the Audio input select switch in the EXT position Experiment 2 . Procedure: Experiment 1 Double Sideband AM Generation This experiment investigates the generation of Double Sideband Suppressed Carrier (DSBSC) AM in such a way by removing the carrier from an AM waveforms. Connect the audio input module to the external audio input on the ST-2201 board. (f) TX output select switch in ANT position.Double Sideband AM Reception This experiment investigates the reception and demodulation of AM waveforms. in DIODE position. Then adjust the receiver’s tunning dial. (e) O/P Amp. (f) Audio amplifier volume preset fully counter clockwise. (d) Select DSB MODE.Tnd. (e) Detector Switch. (h) SPEAKER switch in ON position (i) On board antennae in vertical position and fully extended 2.Swt. (b) Audio input select switch in internal position. so that transmitter generates an AM signal 5.F.Ensure the following conditions on ST-2201.Turn ON power to the modules 4.psition. (c) R. (a) Audio oscillator Amplitude preset fully clockwise. (d) AGC Switch IN position.Ckt. adjust the volume preset so that receiver output clearly heard. (b) R.Now turn the GAIN preset in ST-2201 OUT AMPLIFIER block to its fully clockwise position. (g) Speaker in ON position. (g) Audio amplifier VOLUME preset in counter clockwise.Amps.in ANT. position.Now check the waveform at TP1 at ST-2201 and at TP39 at ST-2202. GAIN preset fully anti-clockwise.F. (c) Balance preset in BALANCED MOD & BPF CIRCUIT/block in fully clockwise. (h) BEAT Frequency Oscillator Switch.On the ST-2201/ ST-2202. These two are approximately same Result: Precautions (if any): - . (i) On board antennas in vertical position 3.On ST-2202 (a) RX INPUT SELECT in ANT. (This should be when the tuning dial is set to about 55 – 65) 6. 1.Amps. until the tone generated at the transmitter’s also clearly Audible at the receiver. In OFF position. GAIN preset fully clockwise. CRO. Attenuation at 850 nm: 3. Take the 1m fiber and set-up an analog link using LED1 and detector PD1 . A&B shortd c) At S26. this fiber has very low attenuation. A1&B should be shorted b) At S6. A&B shorted The block diagram of the circuit used in this experiment is shown in Fig1 2. Two optical fibres are joined using either a connector or a splice. The interfaces used in the experiment should be as: a) At JP2. as even the minutes misalignment or gap between the fibres may cause significant coupling losses. Function generator. if the fiber is bent with a radius of curvature smaller than a certain value. 1 Hz – 10 MHz Introduction: The fiber used in OFT is multimode plastic fiber with 1000 µm core diameter. bending of fiber. the propagating signal may suffer significant bending losses. splices and couplers may all contribute significantly to the losses in a fiber optic communication link. This fiber has been selected for OFT because of the ease of handling it affords. Unlike its Glass-Glass and Plastic Coated Silica fiber counterparts. However. Procedure: Set Up: 1. A small bend in a fiber will not significantly affect the propagation characteristics and therefore the losses in the fiber. Objective: (a) Propagation loss in the fiber (b) Bending loss Equipment Required: OFT. An Optical fiber is a circular waveguide. Apart from the above propagation loss in a fiber. The alignment of the cores of the two fibres is critical in both the situations.Communication System Lab Aim: To measure the losses in an optical fiber communication link. Set the switch SW8 to the ANALOG position and remove the shorting links S6 and S26. connectors. 6. Note the peak value of the signal received at P31 and designate it as V1. Bending Loss: 9. Adjust the GAIN such that the received signal is not saturated. Now bend the fiber in a loop and reduce the diameter of the loop slowly and observe the reduction of the received signal at P31.343α . Repeat steps 3. Result: Precautions (if any): . Note the peak value of the received signal and designate it as V3 . If α is the attenuation in the fiber and l1 and l3 are the exact length of the 1m and 3m fibers in meters respectively. 4 and 5 10. at P11. Do not disturb the level of the signal at the function generator or the gain setting throughout the rest the experiment. we have V3 = exp[ − α ( l 3 − l1 ) ] V1 Where α is in nepers/m. Replace the 1m fiber by the 3m fiber between LED1 and PD1. 11. and also note the diameter of loop. Plot the amplitude of the received signal versus the diameter of the loop. 8. Observe the signal at P31 on the oscilloscope.c. Drive a 1V p-p 10 KHz sinusoidal signal with zero d. 5. Compute α’ in dB/m for 850 nm wavelength using α’ = 4. 7.4. Carrier signal having frequency of 71kHz and amplitude is 5. Adjust the potentiometer in demodulation section until we get demodulated output. Modulating & modulated. while its frequency is varied as per the modulating signal. Modulating Signal Generator FM Modulator CH2 (CRO) 4. 7. For demodulation connect the kit as per figure given below. Trace it and compare with the input signal. Result: Precautions (If any): . 2. The modulation index is given by (FM) mf = Maximum frequency deviation Modulating Frequency or mf = δ fm Procedure: 1. 3. Theory: Frequency modulation is a system in which the amplitude of the modulation carrier is kept constant. Switch on the experiment kit.Communication System Lab Aim: To generate an FM signal and demodulate it. Modulating Signal Generator CH1 (CRO) FM Modulator Demodulator CH2 (CRO) CH1 (CRO) 6. 5. Equipments Required: FT-1502 Frequency Modulation and Demodulation kit. Adjust the amplitude of the modulating signal until we get undistorted FM output.6VP-P. Connect Modulating signal to the modulator input as per figure given below and observe modulating signal and FM O/P on a dual trace CRO. CRO. And trace the signal ie. Observe modulating signal having frequency of 8KHz and amplitude of 0-12VP-P. Now decrease the amplitude of the modulating signal until we get undistorted demodulation output in this condition maximum signal generator output is VP-P is due to capture range restrictions of PLL in demodulator. In frequency modulation for a given frequency deviation the modulation index varies. the system is a. b. Reactance tube modulator b. 6. FM system a. Twice the modulating frequency. Half the modulating frequency. 3. PM 7. Provides better noise immunity.) or (b. Envelope detector b. Directly c. Varactor diode modulator 9.) 11. Armstrong modulator c. Both (a. With the help of a simple mathematical expression explain the basic difference between FM and PM. In a system of modulation.Questions: 1. Low frequency term b. Pre-emphasis circuit in FM transmitter emphasises the a. Frequency deviation 4. Modulation index b. increasing the depth of modulation increases the bandwidth of transmission. One of the following is an indirect way of generating FM this is a. In an FM waveform. AM b. Require less modulating power 8. Inversely b. Demodulation of FM wave is effected by a. b. Both low and middle frequency terms d. Independently as the modulating frequency varies 5. What is meant by the following terms in connection with frequency modulation? a. . Discriminator c. 2. a. the sidebands are spaced at interval equal to a. Equal to modulating frequency. Require lower bandwidth c. Compare FM system with AM system from bandwidth point of view. Give the comparison between AM and FM systems. FM c. High frequency terms 10. Middle frequency term c. c. Indicate false statement. 8 and 16 outputs of the input clock signal. To observe the FSK modulator / demodulator output waveform. In the demodulator section high-Q turned filter is used which is tuned to any frequency divided by 2 or 8 so the filter passes one frequency and stops the other frequency than we are using a envelop detector and comparator. Observe the output of the FSK modulator on the second channel of the CRO. so depending on the level of the modulating data signal given to the FSK modulator either divided by 2 or divided by 8 frequency output of the IC 74163 and transmitted to the output of the FSK modulator. CRO. Switch on the experimental board. Adjust the potentiometer P1 and P2 until we get the demodulated O/P equivalent to the modulating data signal.4. Divided by 16 output is given to a decode counter (IC-7490) which generate the modulating data signals. Objective: 1. 2. Equipments Required: Trainer Kit FT-1506. Fig. During the demodulation connect the FSK output to the input of the demodulator.Communication System Lab Aim: Study of FSK modulation and demodulation. Result: Precautions (if any): . Basically a 555IC is connected in astable multivibrator mode. 2. Shows the circuit diagram of a FSK modulation and demodulation system. generating a clock pulse of frequency determined by the values of RT and CT this clock signal is given by to a divided by 16 counter(74163) which generates divided by 2. Apply any one data output of the decade counter (IC-7490) to the data input point of FSK modulator and observe the same signal in one channel of a dual trace oscilloscope. 4. In this system divided by 2 and 8 output are given taken as two-carrier frequency. 5. so these are given to a FSK modulator constructed by using NAND gates. its output is equivalent to the modulating data given at the input of the FSK modulator. To familiarisation with frequency shift keying method. Theory: FSK is a system of frequency modulation in the nominal unmodulated carrier frequency corresponds to mark condition and a space is represented by a downward frequency shift. 3. Procedure: 1. (4) Hold the white screen with 4 concentric circles (10. Procedure: (1) Connect power supply to the board. It shows the light collection efficiency of the fiber. Numerical aperture Jig. Theory: Numerical aperture refers to the maximum angle at which the light incident on the fibre end is totally internally reflected and is transmitted properly along the fibre. 20 & 25mm diameter) vertically at a suitable distance to make the red spot from the fibre coincide with 10mm circle.Cable W L Scale W . The cone formed by the rotation of this angle along the axis of the fibre is the cone of acceptance of the fibre. Equipments Required: ST-2502 WB-Trainer.Communication System Lab Aim: Measurement of Numerical Aperture of a Fiber using Optical Fiber Trainer Kit. Screen F. The light ray should strike the fibre end within its cone of acceptance else it is refracted out of the fibre. Hold the white screen facing the fibre such that its cut face is perpendicular to the axis of the fibre. (3) Connect one end of fiber cable to the output socket of emitter-1 circuit and the other end to the Numerical aperture measurement jig. Adjust its amplitude at 5Vp-p(e.).g.15.O. Its maximum value may be one. (2) Connect the frequency generator’s 1KHz sine wave output to input of emitter-1 Circuit. It is very important that the optical source should be properly aligned with cable and the distance from the launched point & cable be properly selected to ensure that the maximum amount of optical power is transferred to the cable. 5. (8) Tabulate the various distances and diameter of the circles made on the white screen and computes the numerical aperture from the formula given above.A. recorded in the manufacturers data sheet is 0. The N.(5) Record the distances of screen from the fiber end L and note the diameter W of the spot. (6) Compute the numerical aperture from the formula given below: W 4 L2 + W 2 N .A = = Sinθ max (7) Vary the distance between the screen and fiber optic cable and make it coincide with one of the concentric circles and note its distance. Result: Precautions (if any): . Transmitter: Fiber optic transmitters are typically composed of a buffer driver and optical source. The transmitter module takes the input signal in electrical form and then transforms it into optical (light) energy containing the same information. The transmitter section comprises of: (1) Function Generator. an optical fiber and a receiver. The output voltage available is 1KHz sinusoidal signal of adjustable amplitude and fixed amplitude 1KHz square wave signal. The fiber optic link: Emitter and detector circuit on board form the fiber optic link. The buffer provides both an electrical connection and isolation between the transmitter & the electrical system supplying the data. Finally the optical source converts the electrical current to the light energy with same pattern. The modulator section accepts the information signal and converts it into suitable form for transmission through the fiber optic link.Communication System Lab Aim: Study of an optical fiber kit and setting up of an analog/digital link. At the receiver light is converted back into electrical form with the same pattern as originally fed to the transmitter. . Commonly used optical source are light emitting diodes and a laser beam. The optics plugs into the connector provided in this part of the board. This section provides the light source for the optic fiber and the light detector at the far end of the fiber optic links. Equipment Required: ST2502WB Trainer Kit. The driver provides electrical power to optical source. which takes the energy to the receiver. Basically a fiber optics link contains three main elements. Two separate links are provided. The optical fiber is the medium. Objective (a): To study an 650nm fiber optic analog link. (3) The function generator generates the input signals that are going to be used as information to transmit through the fiber optic link. a transmitter. (2) Frequency Modulator & Pulse width modulator block. Theory: Fiber optic links can be used for transmission of digital as well as analog signals. 28) and note that Result: Precautions (if any): . 7. 1 KHz square wave output to emitter 1’s input.p. Slowly adjust the comparators bias preset. phase Locked Loop. In this experiment the trainer board is used to illustrate one-way communication between digital transmitter and receiver circuits.G. Ensure that all switch faults are off. 3. Procedure: 1. Objective (b): The objective of this experiment is to study an 650nm fiber optic Digital link.p. until DC level on the input (t.G 1KHz sine wave output to emitter 1’s input. 4. Make the following connection (as shown in diagram-2) 2.p.14). Monitor both the inputs to comparator 1 (t. Detector1’s output to comparator 1’s input.The receiver: The comparator circuit.p. Connect the F. Comparator 1’s output to Amplifier 1’s input. Observe the input to emitter (t. 2.13) lies mid way between the high and low level of the signal on the positive input (t. 8. 5. low pass filter. Make the following connection a. Detector 1’s output to Amplifier 1 input. 6.28) and note that the two signals are same. Connect the fiber optic cable between emitter output and detectors input.5) with the output from amplifier 1(t. AC Amplifier Circuits form receiver on the board. b.p. Connect the power supply to the board. It is able to undo modulation process in order to recover the original information signal.5) with the output from Amplifier 1(t. Observe the input to emitter 1 (t. 5. Connect the Optical Fiber cable between emitter output and detectors input. the two signals are same. 3. Connect the F. Switch emitter 1’s driver to Analog mode. 4. c.p. 9.p. Switch ON the power. Switch emitter 1’s driver to digital mode. Procedure: 1.13 &14). Equipment Required: Trainer kit ST2103 and ST2104. If even parity is to be establish a ‘1’ bit is added to each code word containing odd ‘1’ and a ‘0’ bit is added to each word containing even number of one’s. Objective: a. c. A better solution would be to introduce a method of error detection and correction. CRO. Parity is a method of encoding such that the number of one’s in a codeword is either even or odd. In such cases it is called as odd parity. Parity coding is normally only used on transmission systems where the probability of error occurring is low.Communication System Lab Aim: Study of Pulse Code Modulation and Demodulation. but it doesn’t solve the problem. To demodulate the PCM signal. To observe some of error correcting codes. d. The pulse code modulation/demodulation comprises of the following steps • • • • • Sampling Quantisation Encoding Decoding Reconstruction filter Coding allows us a great deal of detection and correction it generally cannot detect or correct all errors. Similarly the parity coding can ensure that the total numbers of one’s in a encoded words is odd. Detection of errors allows the system to request the retransmission of data. .e. Many different types of codes have been developed and are in use. b. In PCM system the amplitude of the sampled waveform at define time intervals is represented as a binary code. To observe multiplexed (TDM) signals To generate PCM wave and observe intermediate signals. Introduction: The basis of digital modulation system lies on pulse modulation i. a particular characteristic of pulse is varied in accordance with the information signals. commonly employed codes are • • Parity coding Hamming coding Parity Coding: It is its simplest method of error coding. D4. the parity is lost and can be detected at receiver e. Three bits Hamming code provide single bit error detection and correction. where the following parity check was carried out and the listed groups failed. D5. Group1 D6 D5 D4 C2 0 1 0 0 Failed Group2 D6 D5 D3 C1 0 1 1 1 Failed Group3 D6 D4 D3 C0 0 0 1 1 Passed . Let us encode binary value D6. For transmitting data than the format becomes D6. C1. If an error occurs in any of the digits. if Hamming code is selected. C1 and C0 are Hamming code bits. D3 D6. D5. D3 of ‘1101’ Group1 Group2 Group3 D6 1 D6 1 D6 1 D5 1 D5 1 D4 0 D4 0 D3 1 D3 1 C2 0 C1 1 C0 0 So.Hamming Coding: Hamming coding recode each word at transmitter in two way new code by stuffing the word with extra redundant bits. D4. D3 Parity Bit-C2 Parity Bit–C1 Parity Bit-C0 The groups and parity bits forms an even parity check group. than no errors has occurred in transmission and all bit values are valid. D4. C2. the data word after coding will be D6 D5 D4 D3 1 1 0 1 C2 0 C1 1 C0 0 At the receiver. Therefore only four bits are used for transmitting data. D5. Suppose a case.g. D5. C0 where C2. The code on this trainer is generated by adding parity check bit to each group as shown below Group1 Group2 Group3 D6. D4 D6. D3. The error detection/ Correction logic carries out parity checks on the three groups Group1 Group2 Group3 D6 D6 D6 D5 D5 D4 D4 D3 D3 C2 C1 C0 If none of them fails. the four digits representing a particular quantise value are taken in as three groups. Set up following initial conditions on ST2104 Trainer. All switched faults off. e. 2.p. e.1) to clock regeneration circuit input (t.8) to RX. a. PSEUDO RANDOM Sync code generator switched on c.1) . b. Make following connection between ST2103 and ST2104 (Fig. D3 and C0 are valid. c. PCM data input (t.12) This ensures that the two channels contains the same information 4. Set up the following initial conditions on ST2103 Trainer.0 input (t. DC1 & DC2 amplitude controls in function generator block in fully clockwise position. d. DC1 output to CH. Output of clock regeneration circuit (t. 1kHz & 2kHz signal levels in function generator block set to 1Vpp.p.10) to CH1 input (t. MODE switch in FAST position.p.p. Make following connections on ST2103 Trainer (Diagram-1) a.If we suppose only a single bit error the passing of group three means that all D6.46) 5.3) b. PSEUDO RANDOM Sync code generator switched on. MODE switch in FAST position. b. Error check code selector switches A&B in A=0&B=0 Position (OFF Mode) f. Error check code selector switches A&B in A=0&B=0 Position (OFF Mode) d. D4. CH. All switched faults off.0 input (t.clock input (t. Parity Check Results on ST2104 Trainer Group1 D6D5D4C2 Pass Pass Pass Pass Fail Fail Fail Fail Group2 D6D5D3C1 Pass Pass Fail Fail Pass Pass Fail Fail Group3 D6D4D3C0 Pass Fail Pass Fail Pass Fail Pass Fail Location of Error No Error C0 C1 D3 C2 D4 D5 D6 Procedure: 1. Make following connection on ST2104 Trainer (Diagram-1) a. Table given below gives the location of possible single bit errors.p.10) b. Pulse generator delay adjust control in fully clockwise position. 3.p.p. a. PCM output (t.p. c. Connect the grounds of both the trainers. 8.p.1 input of ST2103 transmitter Trainer.p. connect DC1 output from function generator block to CH.p. Even Parity: select even parity with error check code selector switches A&B at A=0 & B=1 position.a. Connect channel one of CRO to t. 7. Odd Parity: set up the error check selector A & B switches to A=1 & B =0 position on both Trainers to select the odd parity mode. Hamming code: -The position of A and B switches in error check code selector block is A=1 and B=1.33 on ST2104 By varying DC1 we can verify data is transferred correctly between two trainers. Vary the DC1 control and not the error check code generator output.p. 16 to 22) on ST2104 trainer & D/A converter input (t. ST2103 uses the least significant bit (LSB) of the 7 bit word to transmit the parity bit. data latch output (t. 6. Its value is changed to achieve the correct parity for each word. Carry out the same experiment with 1kHz sine wave applied at CH. we can verify that the data in the A/D converter block of ST2103 Trainer is always same as the data in D/A converter block of ST2104.1 input of the ST2103 Trainer. but odd parity selected this time. Turn ON the power. 11. Adjust the DC1 control such that such that the A/D converter blocks LED’s shows a data of 1101000 on D6-D0 Bits record the binary code on the error check code generator LED’s. 12. Switch ON the Hamming code error check mode on Trainer.44) in the receiver clock regeneration circuit has been correctly adjusted. 14.10 on ST2103.0 & CH. Notice the number of 1’s in the transmitted data streams is it even or odd? d. on both the trainers.p. 9. a.p. 13. Check the error check code generator output on ST2103 Trainer. . Carry out steps 8&9 again. Channel two of CRO to t. b. Turn on the power. 23 to 29) on ST2104 trainer. Ensure that the frequency of the VCO(t. Match this with your expected code. When it is correctly adjusted than LED of sync bit counter will turn on. Set up various codes from A/D converters output LED’s some containing even number of 1’s & some odd.0 and CH. 10.1) of ST2104 b.44) of ST2103 to PCM data input (t. Work out the error Bit (if any ) and than correct the data used output bits D6. pulse or analog? 5. D5. S. D5. In what way PCM is different from other modulation systems.15. What are the advantages and applications of PCM? 2. Work out a table as shown below with different values at D6. C1 and C0 depends on the value of bits D6.No Data at A/D Converter’s Output Expected Results Check on ST2103 Trainer D6 D5 D4 D3 1 2 3 C2 C1 C0 17. Draw an irregular waveform and show how it is quantised.Parity check bits C2. Results: Precautions (if any): Questions: 1. Connect 2kHz signal from the function generator block to CH0 and CH1 input of ST2103 Trainer and repeat the same process. What makes PCM a digital system? . Name the digital modulation systems other than PCM? 3. D5. 16. D4 and D3 Bits S. 4. D4 and D3. Assume that the error detection/correction logic has received a transmitted seven Bit word as shown in table below. D4 and D3 were originally at the output by the ST2103 Trainer. Set the switch position A=0 and B=0 position. 18.No Data Received 1 2 3 4 0101011 0110001 1101101 1101001 Case1 D6D5D4 C2 Fail Case2 D6D5D3 C1 Fail Case3 D6D4D3 C0 Pass Bit in error D5 Corrected output 0001011 Note: How the particulate combination of passes or failures of parity check locates a single faulty Bit. using eight standard levels. D4 and D3. Error checks code generator is only concerned with the Bits D6. D5. In PCM generation. 1/n d 1/n2 . Compander performs a. As compared to message bandwidth the PCM bandwidth is a. n2 c. Signal amplitude c. None of (a) and (b). The quantisation error changes with the number (n) of quantisation levels as a. 9. Expansion after demodulation c. Compression before modulation b. Both of the above d. PCM 10. the sampling of the signal tends to a. Intervals between levels b. PAM d. 8. Both of these. Much smaller b. n b. Much larger 7. Same c. PPM c. The quantisation error is a function of a.6. PWM b. At the receiving end. Equipments Required: Trainer kit FT1505. If we observe the PWM output. 6. Output of the demodulator is almost concides with the modulation signal but having same phase difference due to RC networks and amplifier. CRO Circuit Diagram: Introduction: Pulse Modulation may be used to transmit analog information. During the demodulation. 2.Communication System Lab Aim: Generation and Demodulation of Pulse Position Modulation Signals. PPM output clock position changed. Observe the clock generator output and modulating signal output. the original signal may be reconstituted from the received samples. 8. By varying the modulating voltage. we have fixed amplitude of each pulse. Connect the clock generator output to the clock input point and modulator output to modulation input point of PPM modulator and observe the same clock on one channel of a dual trace CRO 4. which are in the demodulator. Observe the PPM output on CRO 5. apply PPM signal to the input of demodulator and observe its output. Switch on the experimental kit. Procedure: 1. but the position of each pulse is shifted. 3. It is a system in which continuous signals are sampled at regular intervals. 7. In Pulse Position Modulation. its width varies according to the modulating voltage. Results: Precautions (if any): Questions: . the shift being proportional to the amplitude of the modulating signal at that instant. Information regarding the signal is transmitted only pulses. but its width maintains constant. By integrating the signal 5. practical sample is a. By differentiating pulse position modulation b. PDM c. Time location of Pulses edges 8.1. In PPM. None of these . PPM 3. on the one hand and frequency and amplitude modulation on the other? 2. PPMc. The pulse width modulation may be generated a. the message resides in a. Pulses b. With a monostable multivibrator c. Which performs best in the presence of noise? a. which of the following pulse systems would be affected? a. 6. PAM b. What is the fundamental difference between pulse modulation. PAM b. PDM b. PAM 4. In essence. PDM c. If the synchronisation between transmitter and receiver fails. PAM b. It is necessary to transmit a series sync pulse in a. PPM c. PWM c. PPM 7. how it is derived from PWM. Define and describe pulse position modulation and explain with waveforms. Apply this PSK output to the demodulator input and also apply the carrier input. which generate modulating data output. Observe the output of PSK modulator on the channel-2 of the CRO. The 180° phase shift to the carrier is created by an operational amplifier (IC-741). To familiarisation with phase shift keying method. During the demodulation the PSK signal is converted into square wave signal and is applied to one input of an EX-OR gate. IC-8038 is abasic waveform generator. PSK and FSK signals have a constant envelop. Square wave is used as clock input to a decade counter (IC-7490). the feature i. respectively. Switch ON the experimental board. 6. 2. so the EX-OR gate output is equivalent to the modulating data signal. Ideally. 4. 5. on second input of gate carrier signal is applied. Apply the modulating data signal to the modulator input and observe the signal on .Communication System Lab Aim: Study of PSK Modulation/Demodulation Objective: 1. Theory: Modulation is defined as the process by which some characteristics of a carrier is varied in accordance with a modulating signal. frequency shift keying(FSK) or phase shift keying(PSK). IC-CD4051 is a multiplexer to which carrier is applied with and without phase shift. which generates Sine. In digital modulating wave consist of binary data or an M-ary encoded version of it with a sinusoidal carrier. and by –ive90° for a space. To observe the PSK modulator/demodulator output waveform. 3. CRO.The result of this modulation process is amplitude shift keying(ASK). In PSK the carrier may be phase shifted by +ive90° for a mark. Apply the carrier signal to the input of the modulator. Observe the demodulator output and compare it with the modulating data signal to applied the modulator input. channel-1 of CRO. Equipment Required: Trainer kit FT-1507. 2. Modulating data input is applied to its control input.e used by modulator to distinguish one signal from another is a step change in amplitude. Sine wave generated is used as carrier signal to the system. frequency or the phase of the carrier. Procedure: 1. (Fig-1) shows the circuit diagram of PSK modulator and demodulator. Triangle and Square waveforms. 2 fm 3. 5. Decrease c. All modulation system. Quantising noise is produced in a. Mark true or false:Some times both amplitude and phase of the carrier are combined to produce amplitude phase keying (APK). 8 kHz c. Both (b) and (c) error performance 2. 4 kHz 4. fm b. a. PCM c.Questions:1. Decrease but ate the expense of an interior d. All pulse modulation system b. For transmission of normal speech signal the PCM channel leads a bandwidth of a. Increase b. By using non coherent detection complexity of the receiver. 3. 64 kHz bandwidth of a. n fm Hz b. To transmit ‘n’ signals each band limits to fm Hz by TDM will require a minimum . 4.3 of IC555. Procedure: 1. 3. 2. Connect clock generator output to the clock input point of the PWM modulator and observe the same clock on the CRO. Observe the PWM output on CRO at pin no. its width varies according to the modulating voltages. 7. Switch on the experimental kit. 6.Communication System Lab Aim: Generation and Demodulation of Pulse Width Modulation Signal. CRO Circuit Diagram: Introduction: Pulse Modulation may be used to transmit analog information. but the width of each pulse is made proportion to the amplitude of the modulating signal at that instant. In pulse width modulation. It is a system in which continuous signals are sampled at regular intervals. Output of the demodulator almost coincides with the modulating signal but having some phase difference due to RC networks and amplifiers which are in the demodulator. Information regarding the signal is transmitted only pulses. During the demodulation apply PWM signal to the input of demodulator and observe its output. Results: Precautions (if any): Questions: . Observe the clock generator and modulating signal outputs working properly. we have fixed amplitude and starting time of each pulse. At the receiving end. Equipments Required: Trainer kit FT1504. If we observe the PWM output. the original signal may be reconstituted from the received samples. 5. The width of each pulse is varied if we change the amplitude of the modulating signal. Delta 3. For nearly distortion less receives signal in pulse modulation. PAM b. More then twice the signal frequency . What is pulse width modulation? What other names does it have? 2. The major application of PWM is in a. Less then twice the signal frequency c. By integrating the signal 4. it is required that the speed should be a. PCM b. TDM b. Differential PCM c. PPM 5.1. Pulse width modulation may be generated a. Generation of PPM d. PAM 6. Detection of PPM c. With a monostable multivibrator c. PDM c. Which of the following pulse systems require highest bandwidth? a. Less then the signal frequencyb. PWM d. Indicate which of the following pulse modulation system is analog? a. By differentiating PPM b. 3. 7. To study Nyquist criteria. The display shows the reconstructed original 1 kHz sinewave (fig. which contains the information to be transmitted. is known as information signal. c. we have used sampling frequencies greater than twice the maximum input frequency.2). change the sampling frequency to 2 kHz. Display sample output (t. By successively pressing of frequency selector switch. Put the duty cycle selector switch in position 5. 4. . Link 1 kHz sinewave output to analog input. Function Generator Introduction: The signal. Link the sample output to fourth order low pass filter. 9. 8. This gives a duty cycle of 0.Communication System Lab Aim: Sampling and reconstruction of an analog signal.int’ sampling selector switch in ‘internal’ position. 6. 8 kHz. 10.p. then it can be reproduced exactly at the receiver with no distortion. Set that the ‘Ext.5. Sampling can be defined as measuring the value of an information signal at predetermined time instants. 4 kHz. Procedure: 1. b.p. Study of sampling and reconstruction.1). To observe the effect of duty cycle on the reconstruction waveform in Sample and Hold output. Display 1 kHz sinewave (t. 50% duty cycle. Turn on the Trainer (Power ON).p. The rate at which the signal is sampled is known as the sampling rate or sampling frequency. If the signal is sampled quite frequently (The limit being specified by Nyquist rate).12) and sample output (t. Select 32 kHz sampling rate. 5. CRO.37) and the output of filter (t. Our aim is to reproduce this information signal as accurately as possible at the receiving end of the communication system. Objectives: a. Observe how sampled output changes in each case and how the lower sampling frequencies introduce distortion in the reconstructed output. Remove the link from 1 kHz sinewave output to the signal input. set sampling rate of 8 kHz. To verify the Nyquist rate and see the Aliasing effect. 16 kHz and back to 32 kHz (Sampling frequency is 10% of the frequency indicated by the illuminated LED). So far. 2. The display shows 1 kHz sinewave being sampled at 32 kHz. 11.46) on the CRO. so that there are 32 samples for every cycle of the sinewave (Fig.p.37) on CRO. Equipment required: Trainer kit ST2101. Repeat with the filters of 2nd order and observe the difference. 4).p.39) on CRO.3). Follow steps 1-5 as described above. To see the effect on reconstructed waveform of the use of sample/hold circuitry and effect of sampling pulse duty cycle on the reconstructed waveform in sample and sample/hold output. 14. This also describes the phenomenon of Aliasing. Set the duty cycle selector switch to position 5 (fig. Vary the sampling frequency to illustrate how each sample is held at the sample/ hold output.46). d. observe how the sample output changes and how the amplitude of filter output changes. g.37) and the fourth order LPF filter output (t. Results: Precautions (if any): Questions: . Observe the waveform at signal input and fourth order LPF filter (t.p. a. b.46).12.46). This is due to the fact that we under sampled the input waveform overlooking the Nyquist criteria and thus the output was distorted even though the signal lie below the cut off frequency of the filter. Process is as given below.p. Observe the waveform at sampled and hold output (t.p. Obtain a 2 Volt peak. Link sample and hold output to fourth order low pass filter input. Observe the sample output (t. 2 kHz sinewave from 50Ω output of the function generator to signal input. 15. Disconnect the sample output from filter input. Vary the position of duty cycle selector switch from 0% to 90%.p. 13. c. Observe the filter output at t. f. Observe the distorted waveform at the filter output (t. Decrease the sampling rate to 32 kHz and then to 2 kHz. e.p.46 (fig. Both of these 4. . Decreases 6. c. b. Increasing the sampling frequency c. The minimum sampling frequency is called a. Improving the filter slope characteristic b. 8. What will be the effect of over sampling on the bandwidth? 7. Increases b. AM FM PCM None of these. Cross over distortion b. Carlson Frequency b. By increasing the sampling frequency. Aliasing can be reduced by a. Slope overload distortion c. If the lower sideband overlaps the baseband. d. Baud rate c. Sampling theorem find application in a. the bandwidth requirement of the transmission medium a. Nyquist sampling rate d. What is the Nyquist sampling rate of a given signal? 2. distortion is called a. Under sampling will lead to some problems.1. discuss. Cross-Talk d. Bit rate 3. Aliasing 5. Remains same c. Mode2: Two links between transmitter and receiver (Fig. The word ‘Link’ refers to one set of dedicated connections. To observe synchronisation requirement in time division multiplexing Equipment Required: Trainer kit ST2102. The most vital requirement of a time division multiplexed system is synchronization. To observe individual PAM signals. by extracting the clock information from the frame synchronisation signal.1) In this mode a separate transmission media are used to carry the information signal the clock signal and the frame synchronisation signal. 2. We can use three different modes of these information transfers. 4. This ensured by frame synchronisation signal.Communication System Lab Aim: -\ Study of TDM Pulse Amplitude Modulation/Demodulation Objective: 1.2) The number of links between transmitter and receiver can be reduced to two. CRO 30MHz Circuit Diagram: Procedure: The circuit. These two signals namely the clock signal and frame synchronisation signal may be transmitted by the transmitter along with the information signal. Clock signal and frame synchronisation signal should be transmitted by the transmitter along with the information signal. The receive clock must match with the transmitter clock. the receiver also required an information from the transmitter to identify one time slot per frame and so as to pass the time slot to correct output channel. the receiver also requires information from the transmitter to identify one timeslot per frame. Besides clock signal. Mode3: One link between transmitter and receiver (Fig. is the clock circuit for receiver clock must match with the transmitter clock. .3) The number of links connecting transmitter and receiver can be reduced to one the reduction in number of links is achieved by using one time slot to transmit synchronisation signal along with the information samples. It is accomplished by frame synchronisation signal. To observe multiplexed (TDM) signals. Mode1: Three links between transmitter and receiver (Fig. 3. To study sync and control signals. which ensures precisely timed action. Similarly view the outputs of all Receiver Low Pass Filters in turn (t.CH0 signal is used by the receiver to know which sample belongs to channel 0.41) & output (t.0 Low Pass Filter input (t. 2 KHz fully clockwise. 46.1 input socket of Transmitter block c. With the help of oscilloscope.20). observe the Tx.p. The Oscilloscope displays the extracted sample corresponding to channel 0 from the time division multiplexed sample.CH. CH. synk level. The signal at t.44. Tx. 250 Hz. Tx. Ensure that the delay control port in receiver timing logic block is fully anticlockwise. Time division multiplexed samples appear at the Tx.0 link & make following new links. sine wave which was transmitted at CH.2 input socket of transmitter block d.3 input socket of Transmitter block 6. 4. This ensures Mode1 operation of the ST2102 trainer (See Diagram 1 for interconnections) Tx. discount TX.p.20) & the Receiver”s CH. Tx. 1KHz. Make following connections a.p. 7. Display the Receiver’s Low Pass Filter’s input (t. The three links required between Transmitter & Receiver in Mode 1 of operation can be reduced to two in Mode2.CH. Out (t. Output signal (t.p.. 5. 42 shows the reconstructed ~ 250 Hz. 10. 1.0 input socket of Transmitter block b. We are using de-multiplexer to be able to distinguish the synchronisation signal from the information samples. 11.0 to Rx.p.p. 3. . Set the duty cycle control switch in position 5.41).Synchronisation signal must be different from the information samples for the receiver to distinguish it from the other samples. Clock to Rx. Clock c.48). Output to Rx.0 & RX. Clock signal is used by the receiver to synchronise it’s activity & TX. 2KHz to CH. To configure the trainer in Mode 2 of operation. Input b.p. 2. 250Hz to CH. Turn on the power to the Trainer. The Transmitter circuit samples all channels at different time intervals. Turn the all potentiometers in function generator block viz. The distinction is achieved by fixing the amplitude of the synchronisation level samples considerably greater than maximum information signal amplitude. Make the following connections a. 1KHz to CH. CH. Observe that each of the original sine wave have been correctly reconstructed. 9. 500Hz to CH.42) simultaneously on the oscilloscope.0. Turn the potentiometer mark comparator threshold level in phase locked loop timing logic block fully clockwise.0 8. 15. a.0 c. Tx. 44. remove following links. CLK It is used to clock the receiver. CH. 13.CH.3 Outputs (t. the sync pulse are transmitted along with the other samples in channel ‘0’ time slot i. These pulses are fed to the Phase Locked Loop Circuitry. CH.p. channel ‘0’ is dedicated to carry sync pulses.0 RX. Observe the Receiver’s CH. b. level related to the amplitude of the Transmitted sync pulses. Output & Transmitter’s CH. and generates sync clock signal as in Mode 2. Notice that the wave shapes are still preserved in Mode2. PLL O/P to Rx clock Also ensure that level of toggle switch in Phase Locked Loop Timing Logic is in upward position. Ensure that the toggle switch lever in Phase Locked Loop Timing Logic is in Upward Position. Block Results: Precautions (If any): . SYNC Level in Function Generator Block to Transmitter’s CH. CH. Display Tx. In this operational mode. 12. The Phase Locked Loop locks onto the Tx. which locks on to the sync pulse. CH.0 to PLL I/P b.p.CH.1 input (t.0 link i. To configure the trainer in Mode3 of operation.42) is a D. SYNC.42. CH. it tells the Receiver which of the transmitted signal belongs to channel 0. 44.e.CH. Observe the Receiver’s CH.2 & CH.3 output on the oscilloscope (t.a. b.1. 46. SYNC to RX.C.0. a.0 output (t. Now establish the following connections. which extracts the sync pulses.13) on the oscilloscope. 48) on oscilloscope. Notice that the waveshapes still preserved in Mode3.e. ~250 Hz. This serves the same purpose as TX. To transmitter’s CH. 46. b.p. 17. 14.CH. These sync pulses are fed to the voltage comparator. The configuration is as shown in Diagram 3. 16. The number of links can be further reduced to one in Mode3.1. The configuration is given in Diagram 2.0 to PLL I/P socket. Sync Level Pot should be to fully clockwise position.0 signal & produces two outputs. The threshold level of the comparator has been set such that it can easily distinguish between sync pulses & the other samples.2.CH. a.0 Input. 28 & 26 respectively.p.0 Input.p. TX. Receiver CH. 48). These signals can be examined on t. Questions: 2. Can TDM be accomplished with our pulse modulation systems like PPM and PWM? 12. PCM d. What will happen if clocks at Tx and Rx are different? 8. How do you demodulate a PAM signal? 11. FDM c. What is multiplexing? Why is it needed? 4. PWM 7. State sampling theorem. Is sampling a must for TDM technique? 10. TDM b. Quantisation noise occurs in a. What are the two basic forms of multiplexing? 5. Explain the principle of time division multiplexing. Will TDM work satisfactorily if the signals are under sampled? . 6. 3. What will happen if synchronisation gets lost? 9. 15 to 1050MHz. Objective: 1. whereby memory B can only accept copies of memory A results. push. (2) INTENS: Beam intensity adjustment. If pushed one time. To check the frequency response of a low pass filter. To understand the working of spectrum analyser. The individual spectrum components of a signal become visible on a spectrum analyzer. Spectrum analyzer and tracking generator are synchronized. (4) A/B/A-B: The instrument has two memories. Function Generator and CRO Equipments Required: Introduction: The spectrum analyzer permits the detection of spectrum components of electrical signals in the frequency range of 0. (5) AB: Allows for temporary storage of settings from memory A to memory B for comparison purposes.III YEAR Electronics & Communication Communication System Lab-II Aim: Harmonic analysis of a given signal using Spectrum Analyzer.1) (1) Power: After about 10 second the noise level will appear on the bottom base line. ‘A/B/AB’ two times. The oscilloscope would display the same signal as one resulting waveform. Using the AVERAGE function the displayed noise band can be reduced. 4. 5. (6) AVERAGE: This function allows the automatic storage of average signal level readings of the instruments. Push short to store the actual contents of A in B. The respective LED will light to show function is activated.15 to 1050MHz. To measure frequency and level of a given unknown signal. To get back to the actual signal. AB will be displayed. Controls (Fig. Spectrum analyser. To check the frequency response of a high pass filter. This generator provides sine wave within the frequency range of 0. Pushing the AVERAGE button for a short time activates the AVERAGE function. In contrast to an oscilloscope where the amplitude is displayed on the time domain. the spectrum analyzer displays amplitude on the frequency domain. 3. the instrument will automatically display stored B memory. The HM5014 includes a tracking generator. Function A-B allows for the subtraction of B results from updated measuring results stored in A. (3) FOCUS: Beam sharpness adjustment. To measure Harmonics of square wave and Triangular wave. (7) CENTER FREQUENCY: . Memory contents of B will be deleted when power is turned off. 2. Actual measurement results are always stored in A. memory A and memory B. Press again to revert to previous span. Mode. the instrument is equipped with a running Marker (X). By pushing the UP and DOWN buttons. a Marker movement is performed in very small steps. again. 120KHz. Now Center Frequency can be adjusted via tuning knob (14). The respective LED will indicate which resolution bandwidth is selected. To . 5dB/Div. Push CENTER to leave MARKER mode. The Marker can be moved in X-orientation via the tuning dial and follows the measurement curve in Y-orientation. (14) VBW-Video Filter: (11) (12) The Video Filter has the purpose of reducing video and noise bandwidth and therefore reducing noise distribution. To enter again in 10 dB/Div. At full SPAN (1000MHz) the frequency axis is scaled in 100MHz step per (vertical) graticule line. This allows for the detection of even small signals. Pushing the ZERO SPAN button activates the ZERO SPAN mode. which can be selected via the ‘RBW’ buttons. SPAN: The span of sweep of the analyzer is set via the two SPAN buttons. Select the precise Center Frequency and the SPAN as low as possible (resolution of display) so the signal can be viewed easily. The respective LED will then be lit. (8) FINE: If the FINE button is pushed (LED is lit). Button. When measuring low-level values. Button. (9) MARKER: In order to evaluate measurement curves. (13) RBW (Resolution Bandwidth): The instrument is equipped with resolution filters of 9KHz. Py pushing the 5 dB/Div. the Video Filter (low pass) can be used to reduce the noise level. ZERO SPAN: With the ZERO SPAN button a SPAN of 0 Hz is being selected.By pushing CENTER FREQ. The numeric indication of marker frequency and amplitude is displayed on-screen. The frequency reduces accordingly when moving towards the left screen edge. the vertical scale is set to 5 dB/Div. The SPAN is displayed in the upper right-hand corner of the screen and is marked with the letter ‘S’. The Marker is activated (LED lit) by pushing MARKER button . (10) Tuning Dial: The tuning dial either selects Center Frequency or Marker position. (15) ATTN: The buttons to set the input attenuation are marked ATTN. push 5 dB/Div. The frequency is displayed in the upper left-hand corner behind the letter ‘C’. depending on CENTER FREQUENCY or MARKER being activated. input for center frequency is being enabled and respective LED is lit. the attenuation can be set from 0 db to 40 dB in 10 dB steps. which might otherwise not be visible. and 400KHz. which are situated within the regular noise level. the reference level may be set between –99. which can be chosen via the UP/DOWN – buttons. The Tracking Generator is activated.2dB. (17) INPUT: Without attenuation of input signal the maximum allowable input voltage is +25V DC or +10dBm AC respectively. The reference level is always at the topmost horizontal graticule line. Then span can be reduced. Obtaining values: . These values should not be exceeded. The output level is shown in the readout. (18) ATTN. to this level all amplitude readings on screen are referenced. this is for protection of the input stage. and so that this setting can’t be set accidentally. otherwise measurement results may be incorrect. the span has to be decreased. To analyze the detected signals more closely. This is a security measure to protect any loads connected. By pushing TRACK GEN.enter 0 dB attenuation. With a maximum attenuation of the input signal (40dB) +20dBm is allowed. The output level is set using the rotary knob LEVEL (27) and the attenuator buttons (26). it is necessary to push button long.. Depending also on attenuator setting.8 dBm and +13 dBm. If no signal is visible. Now a ‘T’ will appear in the readout. (19) LEVEL With the LEVEL knob the output level of the Tracking generator can be varied in steps of 0. The output attenuator is used for reducing the output level of the Tracking Generator. the Tracking Generator is deactivated. Then the resolution bandwidth can be decreased. the center frequency has to be set so the signal is at center of screen. and one of the attenuator LED’s (26) will be lit. (20) Tracking Generator After switching on the instrument. this indicates a possible other high-amplitude input signal present but not visible in the chosen frequency range. otherwise the input stages will be damaged. also dependent on the attenuator setting. and the video filter used if necessary. In the readout this is shown by the ‘t’. the attenuation can be consecutively decreased. (16) REFERENCE With rotary knob REFERENCE the so-called reference level is set. The warning ‘uncal’ in the readout must not be displayed. the Tracking generator will be inactive. The Track Generator output attenuator HM5014 has 5 positions. If the noise band moves upward on screen when decreasing input attenuation. Measuring in full-span mode serves mostly as a quick overview. (21) Output 50Ω output of Tracking Generators. By again pushing TRACK GEN. Previous to this. uses the fine step mode. The top line has a level of –27 dBm or 10 mV (reference) 4. Assuming that the reference level is –27 dBm. Thus the signal has an amplitude of (-27 dBm) + (-16 dB) = -43dBm.For a numerical value of a measurement result the easiest way is the use of the marker. 3. Suppose you have pushed 2 switches (attenuator 10 dB each) of spectrum analyzer. Each division of graticule (vertical) is 10 dBm. All levels are in RMS reading 2. and the scale 10 dB/Div.2) 1. it is not necessary to make a correction afterwards. If a value is to be measured without using the marker. In this value the setting of the input attenuator is already included. 2. The rotary dial. Or R .(Reading from top ref. in the reference level value the setting of the input attenuation is already included. then measure the difference of the reference line to the signal. if necessary sets the marker frequency. Observe that the scale may be either 5 dB/Div. Say signal is 2 divisions down from the top line. Line) .27 dBm (-27 dB) (20 dB) (20 dB) =10 mV rms. read the value for the amplitude. The display has 8 * 10 divisions on graticule. The signal shown in the picture shows an amplitude difference of about – 16dB to the reference line. which is shown in the readout. Calculation Of Level Of Signal In Spectrum Analyzer 1. EXAMPLE (Fig. Then. This means 20 dBm down with reference. Now add to the reference the following Reference level – display level + attenuator level = . EXPERIMENT NO:1 OBJECT: To measure Harmonics of SQUARE WAVE EQUIPMENT REQUIRED: 1. Switch ON the signal source (function generator) and set as given below: FUNCTION KNOB FREQUENCY KNOB 1 MHz C. G. OBSERVATION: S. Follow steps from (E) and (G) for different frequency on function generator and note the levels. Note down the level of the highest spectral line on the CRT display and calculate the level. Spectrum analyzer 2. 1 2 3 4 5 Freq on Display Fundamental 1st Harmonic 2nd Harmonic 3rd Harmonic 4th Harmonic Level in dB . F. Set the spectrum analyzer as given below: CENTER FREQUENCY 000. NO. Signal source 3.0 ATTENUATION (-10 dB x 2) pressed SPAN WIDTH Adjust between 1to 1000 MHz/div D.MK is lit and the display shows the MARKER frequency. Connect spectrum analyzer and signal generator as shown in the fig E. BNC-BNC cable HM5005/HM5006 Function Generator HM5030-2 1 Nos. H. PROCEDURE: A. Now switch on the MARKER pushbutton . On connecting both the instruments you shall observe a spectral line other than the zero frequency Line. Switch on the spectrum analyzer B. 6. Set the spectrum analyzer as given below: CENTER FREQUENCY 000.1 OBSERVATIONS: S.Same as used in Experiment no.1 You will observe the curve as shown in the fig 6.EXPERIMENT NO: 2 OBJECT: To measure harmonics of Triangular WAVE Procedure: . Connect the given filter between the spectrum analyzer and tracking generator as shown in the fig. L 2 3 4 5 Freq on Display Fundamental 1st Harmonic 2nd Harmonic 3rd Harmonic 4th Harmonic Level in dB EXPERIMENT NO: 3 OBJECT: To check the Frequency Response of a LOW PASS filter EQUIPMENT REQUIRED: Spectrum analyzer BNC-BNC cable 2Nos.0 ATTENUATION (10 dB * 2) pressed SPAN WIDTH 20 MHz/div B. Set the tracking generator as given below: ATTENUATION ALL PRESSED ON /OFF Switch ON Level +1 dB (clockwise) C. LOW PASS filter PROCEDURE: A. NO.2 . You will observer the curve as shown in fig. 6. E.2 OBSERVATIONS: -3 dB frequency reading on display ‘X’=5. EXPERIMENT NO: 4 OBJECT: To check the frequency response of a ‘High Pass’ filter Procedure: A. In order to find the bandwidth of the given filter start moving the marker knob on RHS and note its reading at -3 dB (Marked X in the fig.2 C.D. 7.4 B.MK is lit and the display shows the marker frequency .5 MHz Result: Precautions (if any): . In order to find the bandwidth of the given filter start moving the marker Knob and note its reading at –3dB as in fir. 7. Same as used in Experiment no. Now switch on the MARKER pushbutton .2) OBSERVATIONS: On higher side the –3dB frequency on display at ‘X’=38 MHz (approx). 6 MHz (approx) -3 dB frequency reading on display ‘Y’=4.2 C.4 (Fig.6 MHz EXPERIMENT NO: 6 OBJECT: Frequency response of a ‘BAND PASS ‘ filter.1) B. In order to find the band width of the band reject filter start moving the marker knob and note its readings at –3dB point as shown in fig.1) B. 9.9. Procedure:A. Observe the curve as shown in fig.6 MHz & higher side at 4.6 MHz (approx) CALCULATIONS: Reject bandwidth of the given filter =Y-X =2 MHz (approx) With lower side at 2.2 C.3 (Fig.2 OBSERVATIONS: -3 dB frequency reading on display ‘X’=12 MHz (approx) -3 dB frequency reading on display ‘Y’=29 MHz (approx) CALCULATIONS: Pass bandwidth of the given filter =Y-X =17 MHz (approx) Result: Precautions (if any): . Same as used in Experiment no. You will observe the curve as shown in fig.2 OBSERVATIONS: -3 dB frequency reading on display ‘X’= 2. In order to find the band width of the band reject filter start moving the marker knob and note its readings at –3dB point as shown in fig. Same as used in Experiment no. 8. 8.8. 9.EXPERIMENT NO: 5 OBJECT: To check frequency response of a ‘BAND REJECT’ filter Procedure:A. (6) It changes speech of a calling party to electrical signal for transmission to distant party through the system.). Study of speech circuit using IC and its interface to the line. called the dial tone. (5) It indicates the incoming call of the called telephone by ringing bells or other audible tones. Three Telephones Instrument. Telecommunication Trainer Kit. EQUPMENTS: 20MHz Oscilloscope. a. Study of tone generation. (4) It indicates the stage of the call in progress by receiving tones indicating the status (ringing. ABOUT TELEPHONE ELECTRONICS: The public switched telephone network is one of the true marvels of the modern word. It provides the ability to interconnect any two out of more than one hundred million telephones. The most important one is: (1) It requests the use of the telephone systems when the handset is lifted. e. (2) It indicates that the system is ready for use by receiving a tone. b. This number is initiated by the caller when the number is pressed or the dial is rotated. It is simple in appearance and operation yet it performs a surprising number of functions. (3) It sends the number of the called telephone to the system. c. Yet the telephones in this network are usable by unskilled operators without formal training. d. To observe the different signaling waveforms. Let us understand the basics of telephone system THE TELEPHONE SET: Telephone sets like those used to originate and received telephone calls. To understand the basic features of EPABX. Understanding of telephone transmission. usually with in a few seconds of the request for connection. Objective: a. busy etc.Communication System Lab Aim: To understand the basic concepts and working of a telephone exchange (EPABX). Understanding of telephone transmission. (Almost any child of four or five can make a telephone call). Caller Phone Called Phone . It changes electrical signals received from the distant party to speech for the called party. It is controlled by the world’s largest network of interconnected and co-operating computers. and batteries that supply direct current to operate the telephone. The circuit between the telephone handset and the central office is open. The number of dial pulses resulting from one operation is determined by how far the dial is rotated before releasing it. In the very early days of telephony. The off-hook signal tells the exchange that some one wants to make a call. blocks the flow of DC from the battery but passes the AC ringing signal. When the connection is established. (The ringer circuit presents high impedance to speech signals so it has no effect on them). SENDING A NUMBER: Some telephone sets send the number by dial pulses while others send it by audio tone. This is called off-hook condition. One of the wires is called T (for tip) and the other is called R (for ring) that refers to the tip and ring parts of the plug used in the early manual switchboards. When the handset is removed from its cradle. This is called the on-hook condition. (8) It signals the system that a call is finished when a caller “hangs up” the handset. when the receiver was separate and hung on the switch hook when not in use as shown. (The on-hook.(7) It automatically adjusts for change in the power supplied to it. Each phone is connected to the central office through a local loop of two wire pair. . This also explains why many people still refer to the handset of as the receiver). for a telephone to be of any use. THE LOCAL LOOP: Each subscriber telephone is connected to a central office that contains switching equipment. The capacitor. however. off-hook. the two telephones communicate over transformer-coupled loop using the current supplied by the central office batteries. (The telephone number also may be referred to as an address). the ringer circuit in the telephone is always connected to the central office is open. the ringer circuit in the telephone is always connected to the central office as shown. which opens and closes the local loop circuit at a timed rate. signaling equipment. As the number of phones increased this became impractical. so the local exchange or central office was established to handle the switching and other functions. DIAL PULSING: Telephone sets that use dial pulsing have rotary dial. Of course. it must be connected to another telephone. the phone was simply wired together with no switching. The exchange returns a dial tone to the calling to let the caller know that the exchange is ready to accept a telephone number. This completes the circuits to the exchange and the current flows in the circuit. INITIATING A CALL: When the handset of the telephone is resting in its cradle. C. the spring-loaded buttons come up and the switch hook closes. however. Switches in the central office respond to the dial pulses or tones from the telephone to connect the calling phone to the called phone. the weight of the handset holds the switch hook buttons down and the switches are open. and hang-up terms came from the early days of telephony. called the “polarized ringer”. that the connection has been made. These can be used only if the central office is equipped to process the tones. these telephones set a push button keypad with twelve keys for the number 0 through 9 and the symbols • (asterisk) and # (Pound sign). and the caller gained the attention of the party at the other end by picking up the transmitter and shouting “Hello” or “Ahoy”. a busy tones generated by the central office is returned to the calling phone. If the called phone handset is off-hook when the connection is attempted. a ring back tone is returned to the calling phone to indicate that the called phone ringing.Although all network facilities are currently compatible with pulse dialing telephones with today’s standard embraces the tone method of dialing. For now. At the same time. Bell’s assistant). and schemes based on the mechanical signaling arrangements were soon invented. RINGING THE CALLED PHONE: Early telephone circuits were point-to-point (not switched). DUAL TONE MULTIFREQUENCY (DTMF): Most modern telephone sets employ the newer method of using audio tones to send the telephone number. The one common use today. or bell. a ringing signal is sent to the called phone to alert the called party that a call is waiting. Pressing one the keys causes an electronic circuit in the keypad to generate two output tones that represent the number. the loop to that phone is completed by its closed switch hook and loop current flows through the called telephone. This was not very satisfactory. ANSWERRING THE CALL: When the called party removes the handset in response to a ring. The central office then removes the ringing signal and the ring back tone from the circuit. CONNECTING THE PHONES: The central office has various switches and relays that automatically connects the calling and called phones. Otherwise. Electronic ringing circuits are quickly replacing polarized ringer in new telephone designs. was patented in 1878 by Thomas A. Watson (Mr. . Instead of a rotary dial. It converts speech (acoustical energy) in to variations in an electric current (electrical energy) by varying or modulating the loop current in accordance with the speech of the talker. Most central office exchange can handle up to 10.TALKING: The part of the telephone in to which a person talks is called the transmitter. a small amount of the transmitter signal is fed back in to the talker’s receiver. The signal produced by the transmitter is carried by the loop current variations to the receiver of the called party. different states. Also. . BEYOND THE LOCAL LOOP: Thus far. a complex network of many telephone exchanges has been established to accomplish these requirements. or countries? Over the years. The part of the telephone that converts the electric current variations in to sound that a person can hear is called the receiver.000 phones in different cities. This is called the side tone. the discussion of connecting two telephones together has been limited to local loops and a central office exchange. Speak when called party answers. Basic features of EPABX (1) Access to Trunk Line (0) (Line hunting): Extensions may be programmed to have or all trunk lines by dialing 0. use the call back facility explained in point 7. Note: in case the called Extension is busy. then Dial # Extension No.b. disconnect. (2) Access to Reserved line (9): One or two lines may be kept reserved for certain extensions. No. Extension can access this line by dialing 9. .(30. (4) Re-Dial (*): Any extension user can repeatedly dial the last no. For this follow the procedure given below. the user has to proceed as follows: Lift hand set and hear dial tone and dial Extns.. dial extension No. The last dialed number will be redialed automatically. Interrupt conversation. To use this feature operate as follows:Lift hand set. 31. (whether internal or external) without passing all the numbers again. Wait for the internal ring tone. this feature allows the caller to interrupt the conversation of the busy extension. Lift hand set and hear dial tone. (5) Barge in (# Ex): If an extension is found busy.32. The feature can be used with a warning tone or without a warning tone.33). (3) Extension to Extension Call (Ex): When one extension user wish to talk to another. lift handset and hear dial tone. and on hearing a busy tone. Disconnect previous call. Dial ‘*” key. wait for second (If the feature is with a warning tone you will hear the same and if without a warning tone you will not.).Extensions can also be denied this access. ): . this feature automatically connects. Dial # 14 and hang on.(6) Automatic Call Back on Busy Extension (# 13): If the called extension is busy. Call Transfer (HF EX. dial # 17AB. Follow Me (#16 Ex. Lift hand of your extension and hear the dial tone. your extension will ring. (Trunk Line) Gets free. as soon as the called extension gets free. To cancel this feature. All calls for AB will now ring at the extension from where the above code has been dialed. the extension to receive incoming calls directed at his original extension. hear dial tone. Dial # 0. wait for the called party to answer. this allows the extension to prevent itself from being called. (7) Automatic Call Back on Busy Trunk Line (# 13): If all/any CO. No. Lift set and obtain dial tone. of original extension being used). you will hear an internal ring tone. Dial (# 13) and hang up. Lines are/is busy. is from a different pick up group dial # 8 followed by the extension no.Jn. On hearing a busy tone wait for a few seconds for the dial tone to return then Dial # 13 and hang up. Jn. As soon as the called extension gets free. this feature allows the user to receive that call at his own extension with out physically moving to the ringing extension.\ Note: After using the follow me feature care must be taken to cancel the feature otherwise all calls will be diverted to the extension. Lift hand set where user wants to receive calls.): Incoming calls can be made to follow the extension user. Dial # 15 hang up. Call Pick-up (8 or # 8 Ex.): If another extension is ringing.Jn. To cancel this feature. lift hand set and hear dial tine. Line. Wait for the extension to ring. Line. Lift hand set. Lift hand set. dial 0 or access code for CO. wait for a few seconds for the dial tone to return and then operate as follows. Jn. If the user extension no. (12). (8) Do not Disturb (# 14) : If an extension user does not wish to called. hear dial tone and dial #0. the extension user can call others. Lift hand set and obtain dial tone. If from the same group. Lift hand set and hear dial tone. (9) Extension Privacy (#15): The feature protects an extension user from being interrupted by any other extension during a conversation. which is ringing. till the feature is cancelled. However. To cancel this feature. (11). this feature inform the user as soon as the CO. then just dial 8 and talk to the caller. Dial # 16 AB. (10). (AB is the no. In other words. If a user gets a busy tone after attempting to seize any CO. 8. Study of speech circuit using IC and its interface to the line. Speak to party B and hook flash to conference between yourself. Listen to the dial tone and dial the extension number of party B. Repeat the procedure to extend the conference to party C in the same manner. c. Dial the extension No. Wait for the internal ring tone. (13). you may do it the following way. party A goes on hold. to which you want to transfer the call. If called extension is busy then use feature No. party A and party B. The held party will hear music while on hold. Block Diagram . Conference (HF Extn.Any internal or external call received/originated at any extension can be transferred from that extension to any other extension.1 or TN 1 + HF EXT2 or TN 2): If while conversing with an outside line or an extension you want to arrange for a third or even a fourth party to conference. A maximum of 4 people can conference at any point of time. Hook Flash and heat feature mode tone. While conversing with party A use the hook flash. PROCEDURE: (1) (2) (3) Pick up hand set of extension 30 and dial 31. THE SPEECH CIRCUIT: A simplified block diagram of a speech circuits suitable for implementation as an integrated circuit is shown in built in transmit. The bridge is dynamically equivalent to a small resistant in series with the signal path. receive . These Devices have most of the required components on the chip with connections provided for outboard components such as resistors and capacitors. and equalizer circuit. and side tone circuits. which are used to “program” the chip. (4) Like above procedure we can establish speech path between CO line and extension also. It is connected to the telephone line by a conventional rectifier bridge. replace mechanical and conventional electrical devices.O. Pick up hand set at extension 31 as you pick up hand set loop between two extension is Observe the wave form on C.R. at TP14 for extension 30 and at TP 15 for extension 31. You can observe ring signal at TP15 during ringing and after pick up you can observe voice signal (Voice Frequency) at test points. External components are used to adjust transmits. receive and side tone gains and frequency responses. usually in the form of integrated circuits.THEORY: The Telephone system as it presently exists to a discussion of how it is changing and improving as electronic devices. (d) To observe the different signaling waveforms at TP1 to TP31 . as well as a DC loop interface regulator. The emphasis is on the circuits that provided two-way speech in the telephone set. Regulator circuitry sets the operating voltage in the integrated circuit and biases the speech circuits. The DC line interface controls the voltage and current characteristics of the entire speech network depending upon the value of loop current in the subscriber line. completed and speech path is established. and a high resistance in parallel to it. You can hear ring at extension 31. TP1 TP2 TP3 TP4 TP5 TP7 TP8 TP9 RING VOLTAGE I/P 15V 20Hz CLOCK INTRRUPT SIGNAL 2MHz CLOCK CLOCK RING DETECTOR SIGNAL IN COI RING DETECTOR SIGNAL IN COII TONE RECEIVED I TP12 OUTPUT OF DTMF TP13 OUTPUT OF DTMF TP14 RING SIGNAL OF EXTENSION 30 TP15 RING SIGNAL OF EXTENSION 31 TP16 RING SIGNAL OF EXTENSION 32 TP17 RING SIGNAL OF EXTENSION 33 TP18 EXCHANGE TONE TP19 DIAL TONE TP20 RING BACK SIGNAL TP21 MUSIC OUTPUT SIGNAL TP22 OUTPUT OF LATCH FR RING OF EXTENSION 30 TP23 OUTPUT OF LATCH FR RING OF EXTENSION 31 TP24 OUTPUT OF LATCH FR RING OF EXTENSION 32 TP25 OUTPUT OF LATCH FR RING OF EXTENSION 33 TP26 HOOKUP SIGNAL OF EXTENSION 1 TP27 HOOKUP SIGNAL OF EXTENSION 2 TP28 HOOKUP SIGNAL OF EXTENSION 4 TP29 HOOKUP SIGNAL OF EXTENSION 3 TP30 TRUNK ACCESS SIGNAL OF CO I TP31 TRUNK ACCESS SIGNAL OF CO II e. Study of tone generation. Theory: . ( DOT line must be connected at COI and COII). Line will ring like a normal telephone. These are analog signals that are either continuous tones or tone bursts (tones turned on and off at various rates). Tone signaling between exchanges may be in-band or out-of-band. The busy signal that tells the caller that the called appears in bursts of 0.31 and keep it aside. (2) TP9. (5) Ringing Tone: Two types of tings can be heard from the telephone instrument connected to the system. PROCEDURE AND OBERVATION: (1) Exchange dial tone: Lift the hand set of extension 30 and hear the dial tone is a continuous sound which lasts for 8seconds during which exchange waits for dialing to be initiated this signal is as shown in figure and can be observed at TP18. A from a CO jn. (4) Internal Ring Back Tone: Lift the handset of extn.5 second on time separated by an off time of 0. There are two types of busy tones one is a high speed busy tone which consists of equal duration ON and OFF signals.31 you will hear a busy tone which is a discontinuous sound(Du------Du). When your instrument is called by another internal instrument the ring will be continuous one with a one second ON and two second OFF waveform of ring signal is as shown in figure. The call progress tones are sent by the exchange to the calling phone to inform the caller about the status of the call e.30 and dial the no. This is a discontinuous sound of two frequencies sounds for one second with a tw9o second silence interval. Then lift the hand-set of extn. All of these tones are in band signaling. This tone indicates that the system is too busy.30 and dial any extn. Result: P and Dial tone: On accessing a direct line by dialing ‘0’ . E0. This waveform is as shown in figure. If no dialing takes place during this period the EPABX times the user out and starts issuing a busy tone. This signal can be observed at Precautions (if any) : . Dial tone is a continuous tone made by combining the frequencies of 350Hz and 440Hz. you will obtain the normal P and T dial tone. You will hear this tone till thee extension answers.5 second. 32 you will hear ring back tone that can be observed at TP14 for extn. The tones may be single frequency or combinations of frequencies.Various tones are used for both control and status indication. (3) Busy Tone: Lift the hand-set of extn. This tone consist of double duration ON and single duration OFF.g. Number like 31. .III Year Electronics & Communication Communication System Lab Aim: Familiarisation with transmission line trainer Kit. Objective: a. One of the simplest forms of the transmission line is the open wire line or the twisted pair. Finally the wires are separated by a medium called the dielectric. Here total effective resistance of line is 68Ω. It is BALANCED LINE but this type of line has very poor shielding properties and has a tendency to radiate. Make the connections as shown in dig. it must have resistance and inductance. Tabulate as under: . Oscilloscope CH1 shows applied input CH2 shows outputs.4V. there must be capacitance between them. 2. Since each conductor has certain length and diameter. for optimum power transfer we should have the source resistance and terminating resistance also as 68Ω. Measuring the Attenuation of a transmission line 1. The ohmic resistance R & conductance G are responsible for energy disputation in the form of heat. We must connect 18Ω Ri in series with the generator to match the line. co-axial line have extremely low radiation loss. since there are two wires close to each other. Measure signal level at Input and at 25. Another co-axial line consists of a central conductor and an outer conductor with the outer conductor referred to as shield normally grounded. 3. 100KHz and level to 0. Measuring the attenuation Equipment Required: Trainer Kit ST-2266 and CRO Introduction: Transmission lines are means of conveying signals or power from one point to another. Since the two conductors of this type of line have same relationship with respect to ground. The losses. Assuming generator resistance Rg as 50Ω. 2. Measuring the input impedance of a line b. Due to shielding. 50 75 and 100m length. 6. 5. Adjust Ri and RL for 18Ω and 68Ω respectively with the help of DMM. Set the sine-wave frequency to approx. the current leakage through it can be represented by a shunt conductance. 4. Procedure: A. which determines the attenuation characteristic are expressed in terms of attenuation “a” and can be calculated by a= 20Log(V2/V1) Where V1= amplitude of signal at i/p V2= amplitude of signal at o/p a= attenuation for given length. which cannot be prefect in its insulation. Now calculate the attenuation in its at various length by for formulae given below a=20Log(V2/V1) Measuring the input impedance a line 8. Make a connection as shown in dig. Set the i/p at 0. Repeat step 1 9. 11. Take readings of Vin & Vm (across 1Ω) on oscilloscope 13.Length (m) 25 50 75 100 V1 (input) V2 (output) 7. A 1Ω resistance in series between the generator & the transmission line as shown in fig.4VPP and frequency 100KHz of sine-wave (both measurement on CRO) 12.6 allows to measure the value of i/p current. Calculate the i/p impedance according to the following formula: Zi=Vin/I =Vin/Vm* 1Ω Note down this result Result: Precautions (if any): - . 3 10.