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Page 1: Dc Lab Manual

Digital Communication Lab

DIGITAL COMMUNICATION LAB (07EC61)

CYCLE-1

1. Modulation and demodulation of a BPSK signal.2. Determination of modes, transit time, electronic tuning range and

Sensitivity of a Reflex Klystron.3. Determination of V-I characteristics of a Gunn diode, measurement of

guide wavelength (λg), frequency and VSWR.4. a. DPSK encoder and decoder using module.

b. QPSK encoder and decoder using module.

CYCLE-2

5. a. Design and implementation of ASK modulator and demodulator.b. FSK Generation and Detection using module.

6. Measurement of Directivity and Gain of a Horn Antenna (X-Band). 7. Characterization of optical Fibers: Calculation of Launching angle,

Critical angle, Numerical aperture and different types of losses. 8. a. Measurement of resonance characteristics of Microstrip ring resonator

(C-Band).b. Measurement of Power division and isolation Characteristics of Microstrip 3dB Power divider (C-Band).

CYCLE-3

9. Determination of coupling coefficient, Insertion loss and Isolation of Magic Tee and Directional coupler(Waveguide)

10. Measurement of Directivity and Gain of Printed Dipole antenna and Rectangular Microstrip patch antenna (X-Band).

11.Time Division Multiplexing& Demultiplexing, Frequency Division multiplexing & demultiplexing using OFC link.

Prof and Head

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Digital Communication Lab

EXPERIMENT 1

MODULATION AND DEMODULATION OF A BPSK SIGNAL

Aim: To generate and detect a BPSK signal using kit.

Apparatus: BPSK modulator kit, Op-Amp (µA741), DC power supply, OA79 Diode, Cathode ray oscilloscope, Resistors and capacitors as indicated in the circuit diagram.

BPSK Generation:

Fig1.1 BPSK generation circuit. BPSK detection:

Fig1.2: BPSK detector circuit.

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Procedure

1. Apply sinusoidal signal (Carrier) and Square wave (Message) signal to the Modulator kit as shown in fig1.1.

2. Connect -6V and +12V DC supply to the modulator kit.

3. Observe the BPSK modulated signal at the output of the kit. Amplitude and frequency of the modulated signal are noted down.

4. Apply the BPSK modulated signal and a carrier signal to the input of the demodulated circuit as shown in fig1.2.

5. Verify the outputs of the adder and the envelope detector before verifying the output of the comparator.

6. Plot the input and output waveforms displayed on the CRO on a graph. Input waveform and expected output waveforms are shown in fig 1.3 and 1.4 respectively.

Fig 1.3.Base band information sequence – 0010110010

Fig1.4. Binary PSK modulated signal (180 phase shifts at bit edges)

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Digital Communication Lab

EXPERIMENT 2

TO STUDY THE CHARACTERISTICS OF REFLEX KLYSTRON

Aim: To conduct a suitable experiment on reflex klystron, plot its mode curves and determine its Transit time, Electronic tuning range, Sensitivity, Peak output power for different modes, and Frequency variation for any one mode.

Apparatus: Klystron power supply, Isolator, Frequency meter, Variable attenuator, X-band detector, Waveguide-to-BNC adaptor and Oscilloscope.

Block diagram

Fig2.1: Experimental setup of a reflex klystron oscillator.

Procedure:1. Equipments are connected as shown in the Fig. 2.1.2. Keep the repeller voltage at maximum, beam voltage at minimum before switching on power

supply and also switch on the fan.3. Switch on klystron power supply and increase the beam voltage to 250V. Note down beam

current.4. Adjust the repeller voltage and detector knob to get maximum output on CRO/SWR meter

keeping frequency meter detuned.5. Repeller voltage is increased and slowly reduced in steps of 10V and at each step note down

the output voltage on CRO or output power on SWR meter along with frequency in frequency meter.

6. To measure operating frequency, the frequency meter is tuned to get the dip on the CRO and frequency is read directly from the frequency meter.

7. To find the guided wave length, move the carriage on the slotted line to get the maximum output and note down the reading on the scale on slotted line and vernier scale, say d1 in cm. Move the carriage to the right or to the left to get the next maximum output position, say d2 in cm. The guide wave length

= 2(d1~d2) cm

8. To find VSWR, move the carriage to the maximum output position and set the VSWR to 1 on the VSWR meter by adjusting the gain. Move the carriage to minimum output position. The reading of the VSWR meter gives the VSWR.

9. Note down the repeller voltage, SWR power and Frequency for different modes in the tabular column.

10. The VSWR can also be found alternatively. Find the maximum output voltage and minimum output voltage.

VSWR = Vmax / Vmin

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Digital Communication Lab

11. Calculate the mode number, transit time of each mode, electronic tuning range and electronic tuning sensitivity. Sample calculation is shown.

12. Plot the output power versus repeller voltage to get mode curves. Also plot the frequency versus repeller voltage. Expected graphs are shown in fig 2.2.

Tabular column:

S.No. Repeller voltage (V) SWR power Frequency meter reading (GHz).

Fig2.2: Mode curves of a klystron

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Digital Communication Lab

NOTE: Even though there should be little danger from microwave radiation hazards in the lab, the following work habits are recommended whenever working with RF or microwave equipment:• Never look into the open end of a waveguide or transmission line that is connected to other equipment.• Do not place any part of your body against the open end of a waveguide or transmission line.• Turn off the microwave power source when assembling or disassembling components.

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Digital Communication Lab

EXPERIMENT 3Determination of V-I characteristics of a Gunn diode, measurement of guide

wavelength, frequency and VSWR

Aim: Conduct an experiment to plot the V-I characteristics of a GUNN diode and to determine the threshold voltage, measure operating frequency, guided wavelength and VSWR.

Apparatus: GUNN power supply, GUNN oscillator, PIN modulator, Attenuator, Frequency meter, VSWR meter/ power supply.

Block Diagram:

Fig3.1: GUNN diode experimental setup.

Procedure:1. Setup the equipment as shown in fig 3.1.2. Bias the GUNN diode and P-I-N diode.3. Adjust the attenuator and P-I-N modulator to get maximum output on the CRO.

Change the GUNN biasing in steps of 0.5V and record the corresponding current in table.

4. Draw the V-I characteristics and find the threshold voltage VTH and compare it with the ideal graph (Fig 3.2).

5. To measure operating frequency, tune the frequency meter to get the dip on CRO and frequency is read directly from the frequency meter making GUNN diode to operate in negative resistance region.

6. Find the guided wavelength and cutoff wavelength then calculate the theoretical operating frequency and compare it with the measured frequency.

7. Measure the VSWR by using VSWR meter.

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GUNN power supply

GUNN oscillator

Ferrite isolator

PIN Modulator Attenuator

Frequency meter

Slotted section with carriage

Crystal detector

SWR / Power meter / CRO

Matched Load

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Fig 3.2: V-I Characteristics of GUNN diode

Tabular column

Bias Voltage (Volts) Current (mA)

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I (mA)

V

Vth VV

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Digital Communication Lab

EXPERIMENT 4

GENERATION AND DETECTION OF QPSK AND DPSK SIGNAL

a. GENERATION AND DETECTION OF QPSK

Aim: To generate QPSK wave and detect it using QPSK module.

Apparatus: QPSK Modem Kit, Power supply with regulated supply of +5V, + 12V, CRO, and Jumper wires.

QPSK Kit Description

QPSK TransmitterXR 2206 generates a master clock of frequency 10 KHz. The clock divider circuit consists of two numbers of 74HC161. Patch cord is used for selecting data rate between 600 bps or 300 bps. A 1C 74HC161 form a divide by 8 circuits which is used for getting a word pulse (WP).CD4014 generates the data. It converts the 8 bit parallel data in serial form. Data pattern can be selected through the DIP switch SW1. QPSK system (fig4.1) requires four signals –sin, sin, cos and –cos which are generated using four number of UA741 through signal processing operation like inversion and differentiation. 74HC161 and CD 4094 form a two bit shift register used for serial to parallel conversion (Bit splitter). The two bit parallel output is used for selecting one of the four signal generated by IC’s UA741. CD14053 and UA741 form a multiplexer and adder which is used for selecting one of the four signals of the QPSK modulation depends on the value of two bits of B0 and B1.

Fig4.1: Block diagram of a QPSK transmitter module.

QPSK Receiver

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QPSK receiver (fig4.2) consists of band pass filter and two parallel branches of multiplier, a low pass filter and a comparator. In coming QPSK signal is fed two parallel branches of multiplier, LPF and level converter. Multiplier is used to remove the carrier frequency and recover the and band signal. Then it is passed through a LPF to restrict the noise and made to fall within the base band signal bandwidth. The level converter is enables the decision circuit to decide ‘1’ or ‘0’ of transmitted bits. The local carrier is used in the multiplier are sine and cos signal, which ultimately generates two bit streams B0 and B1 at the output of level converters. These outputs are then fed to 2 bit parallel to serial bit combiner to recover the original data.

Fig4.2: Block diagram of a QPSK receiver module

ProcedureTransmitter

1. Connect the power supply to the QPSK Kit by using connecter wire +5V, +12 V, -12V (Fig4.1).

2. Select the input bit stream by combination of dip switches here input 8 bits data is selected. Select the proper transmission rate 600bps or 1200 bps.

3. Select NRZ (L) data at the output of data generator.4. Measure the clock signal, word pulse and NRZ(L) input data stream. If

transmission rate is 1200 bps then Word pulse width is (1/1200=833 μSec ).5. Check the odd stream and even stream data output 6. If binary input data { 1 1 0 1 1 0 0 0} the odd stream B 1= 1 1 0 0 11 00 and B0= 1 1

1 1 0 0 0 0 as seen in figure7. The four carrier signal generator with phase is selected according to the combination

of the dibits of input data stream (odd and even stream).8. The output QPSK signal is verified with reference of Word pulse. Here word pulse is

the start of 8 bits input data

Receiver1. The QPSK modulated signal is fed to the receiver input (fig4.2). 2. Here odd stream B1 offset and even stream B0 offset is used to track the transmitter

odd stream and even stream. So connect transmitter odd stream to one channel of CRO and receiver odd stream to another channel of CRO, and check the same bits pattern and repeat same for even stream.

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3. Verify the demodulated output with transmitted message signal. 4. The input waveform and expected output waveforms are shown in fig 4.3.

Fig4.3:QPSK output signal with constellation diagram

b. GENERATION AND DETECTION OF DPSK

Aim: To generate DPSK wave and detect it using DPSK module.

Apparatus: DPSK Modem Kit, Power supply with regulated supply of +5V, + 12V, CRO, and Jumper wires.

DPSK Kit Description

DPSK TransmitterThe block diagram of the DPSK transmitter module is shown in fig4.4. XR 2206 generates a master clock of frequency 10 KHz. The clock divider consisting of 74HC160, 74HCHC04 and 74HC161 generates all the systems clocks. Patch cord is used for selecting data rate between 300bps and 600bps. 74HC161 forms a divided by 8 circuits which is used for getting a word pulse. CD4014 generates the data. It converts the data. It converts the 8 bit parallel data in to serial form. Data pattern can be selected through the dip switch. Patch cord is used for selecting the internal or external data source. The internal source provides data output in the NRZ form. NRZ data is generated internally by the dip switch. By keeping the switches in either '1' or '0' (i.e. ON or OFF) position, any data pattern can be selected. The selected data from the dip switches is parallel data which is converted in to serial data by data generator block. The output of the data generator is in NRZ form which is pre-coded. The 10 KHz sine wave is passed through an inverter block to produce sine signal. Both sine and sine are fed to CD4053 which is a 2:1 multiplexer. The NRZ data is also fed into the multiplexer as select signal. The output of the multiplexer is available on pad marked DPSK O/P.

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DPSK ReceiverDPSK receiver (Fig4.5) itself consists of a band pass filter (LM318/741), multiplier, a low pass filter and a comparator (LM311). The multiplier receives its inputs as incoming DPSK signal and an internal 10 KHz sine wave signal. When the incoming DPSK signal has a sine component during a clock cycle, the comparator output will be higher than the one when the incoming signal. (DPSK) has sine in it. The output bit stream from level converter circuit is differentially coded signal. The original data is recovered using differential decoding (inverse operation).Multi turn pots have been provided with comparator IC's to make tuning easier and by doing so required demodulated output will be obtained at the output of the comparator.

Fig4.4: Block diagram of a DPSK transmitter module.

Fig4.5: Block diagram of a DPSK receiver module

Procedure Transmitter

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1. Connect the power supply to the DPSK Kit by using connecter wire +5V, +12 V, -12V. 2. Select the input bit stream by combination of dip switches here input 8 bits data is selected. If

binary input data bk{ 1 0 0 1 0 0 1 1 } here encoded bit generated by XOR with pre-coded bit ‘0’.

3. Select the required data rate either 600 bps or 300 bps by connecting jumper wire4. By using XOR gate and 1 bit delay circuit, we can generate encoded bit stream using pre-

coded bit ‘0’.5. Whenever the incoming bit is ‘1’ there is change in phase ( ‘π’) with respect to previous bit.

If the incoming bit is ‘0’ then the phase is unchanged ( ‘0’) with respect to previous bit.6. The DPSK waveform is displayed on CRO. The DPSK modulated wave form phase changes

has to be verified according to input data stream. In this example there are four phase changes. The data is repeated for different input data pattern.

Receiver1. The DPSK modulated signal is given to the adder circuit with or without noise. Default we

choose without noise for initial verification of demodulated signal.2. This signal is passed through BPF (Band pass filter) to minimise noise effect.3. The output of the BPF is applied at the input of the multiplier with reference carrier.4. The output of the multiplier is passed through a filter to eliminate higher frequency

component to the comparator with proper Vref to get perfect digital data.5. The filter output is connected to the comparator. This data is encoded using XOR and 1-bit

delay circuit. The DPSK output waveform is shown in fig4.6. 6. The decoded data at XOR is latched at the output observed on CRO.

Fig4.6: Binary DPSK signal.

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EXPERIMENT 5

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Digital Communication Lab

GENERATION AND DETECTION OF ASK AND FSK SIGNAL

a. Generation and detection of Amplitude Shift Keying

Aim: To design and demonstrate an ASK modulation and demodulation

Apparatus: SL100 Transistor, Op-Amp (µA741), DC power supply, OA79 Diode, Cathode ray oscilloscope, Resistors and capacitors as indicated in the circuit diagram.

ASK Generation:

Fig5.1: ASK generation circuit.

Design:

Given, Ic(sat) = 2mA; hfe(min)=30; Vbe(sat)=0.7V; Vce(sat) =0.2V.

Re=V/Ic =Vc--Vce(sat)/Ic = 8-0.2/(2x10-3) =3.9 K Ω ; Choose Re as 3.3 k Ω, a standard value

Rb = Vm/Ice(sat)/hfe(min) = 10-0.7/2x10-3/30 =139.5 K Ω ; Choose Rb as 140 KΩ, a standard value

ASK Detection:

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Fig5.2: ASK detection circuit.Procedure

1. Rig up the circuit as shown in the fig5.1.2. The message signal, a square wave of 4V, 500Hz is fed to the base of the transistor.3. The carrier signal a sinusoidal wave of 2V, 2 KHz is fed to the collector circuit of the

transistor.4. The output i.e., the ASK signal is taken across the resistor RE and is viewed on CRO.5. The ASK signal is fed to the input of the detector circuit of fig5.2.6. The output of the envelope detector is passed through the comparator.7. The output of the comparator is recovered and is compared with the input message

signal. The input and output waveforms are shown in fig5.3.

Fig5.3: Message signal, ASK modulated signal and ASK demodulated signal

b. Generation and detection of Frequency Shift Keying

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Aim: To design and demonstrate an FSK modulation and demodulation

Apparatus: IC-CD4053, Op-Amp (µA741), DC power supply, OA79 Diode, Cathode ray oscilloscope, Resistors and capacitors as indicated in the circuit diagram.

FSK Generation and Detection

Fig5.4: FSK generation circuit

Fig5.5: FSK demodulation circuit

Procedure:

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1. Rig up the circuit as shown in the fig5.4.2. The message signal, a square wave of 5V, 200Hz is fed to the pin 11 of CD4053. 3. The sinusoidal carrier signal of two different frequencies (one is 2 KHz and other is

20 KHz) with amplitude of 2V each is fed to pin numbers 12 and 13 respectively. 4. The output i.e., the FSK signal is taken across pin number 14 and is viewed on CRO.5. The FSK signal is fed to the input of the detector circuit of fig5.5.6. The FSK signal is low pass filtered and passed to envelope detector followed by

comparator.7. The output of the comparator is recovered and is compared with the input message

signal. The expected waveforms are shown in fig5.6.

Fig5.6: FSK output waveform.

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EXPERIMENT 6

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Digital Communication Lab

Measurement of Directivity and Gain of a Horn Antenna

Aim: To conduct a suitable experiment on Horn antenna, plot its radiation pattern and determine its directivity and gain.

Apparatus: Klystron power supply, Isolator, Frequency meter, Variable attenuator, X-band detector, Horn antenna (2no’s), Waveguide-to-BNC adaptor and Oscilloscope.

Block diagram:

Fig6.1: Experimental setup for radiation pattern measurement

Procedure:1. Power up klystron oscillator, and maximize the power on the power meter by

adjusting the repeller voltage. Note the input power.

2. Connect the detector o/p to CRO and tune the frequency meter till a dip in the square wave is observed. Read the corresponding frequency.

3. Remove the detector and connect the transmitting horn antenna. Set transmitting and

receiving horn antennas in zero degree alignment separated by (far field), where

‘D’ is the max dimensions of Horn antenna.

4. Keep both transmitting and receiving antennas in H-plane co-polarization.

5. Rotate the receiving antenna in steps of 5 degrees on both sides (clockwise and anticlockwise) and note down the corresponding power received on the power meter/ CRO.

6. Using 90 deg –twister waveguide section, change the transmitting and receiving antenna to E-plane co-polarization.

7. Repeat step 5.

8. Plot the horn antenna radiation pattern in both E-plane and H-plane using polar plot as well as linear plot.

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9. Determine half power beamwidth, Directivity from the radiation pattern.

10. Compare the theoretical values of directivity and beamwidth.

11. Calculate gain of an antenna from Friss transmission formula.

12. Expected radiation pattern of a pyramidal horn antenna is shown in fig6.2.

Basic precautions to be taken: 1. Power flowing out of horn antenna may damage the retina of the eye, Do not see

directly inside the horn antenna.

2. Materials present in the vicinity of the experimental setup should be absorbing ones. Keep reflecting objects away from the experiment.

Observations and Calculations:

1. Theoretical beamwidth and

2. Power transmitted =____________dB

3. Frequency f0=______________GHz

4. Directivity =

5. Power gain G=

Tabular column: Power in E plane Power in H plane

Angle (degrees)

Left Right Left Right

0510152025

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Digital Communication Lab

Fig 6.2: Expected Radiation pattern of a pyramidal horn antenna in polar plot.

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Digital Communication Lab

EXPERIMENT 7

Characterization of optical Fibers: Calculation of numerical aperture and different types of losses.

Aim: The objective of this experiment is to measure the propagation loss, bending Loss, and to calculate numerical aperture and the angle subtended

Apparatus: FCL-01 & FCL-02 kit, 1 & 3 Meter Fiber cable, Patch chords, Power Supply, Oscilloscope, NA JIG (Precision Jig No.1), Ruler.

Optical communication module:

Fig7.1: Optical fiber communication link

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Fig7.2: Block diagram for setting up fiber optic analog link

Procedure:

Measurement of propagation loss/ Attenuation

1. Make connections as shown in fig.7.1. Connect the power supply cables with proper polarity to FCL-01 & FCL-02 Kits. While connecting this, ensure that the power supply is OFF.

2. Keep the jumpers JP1, JP2, JP3 & JP4 on FCL-01, and JP1 & JP2 on FCL-02 as shown in fig.7.1.

3. Keep switch S2 in VI position on FCL-01 and Switch on the power supply.4. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the

connector. Once the cap is loosened, insert the 1 meter fiber into the cap. Now tighten the cap by screwing it back.

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5. Now rotate the Optical Power Control pot P3 in FCL-01 in anticlockwise direction. This ensures minimum current flow through LED.

6. Slightly unscrew the cap of Photo Diode SFH250V. Do not remove the cap from the connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back.

7. Keep Switch SW1 to SIGNAL STRENGTH position in FCL-02.8. Connect the output of Photo Diode detector post OUT to post IN of Signal Strength

Indicator block.9. Observe the signal strength LED’s, adjust the TRANSMITTER LEVEL using

Intensity control pot P3 until you get the reading of all LED's glow.10. We will measure the light output using the SIGNAL STRENGTH section of the kit.

The loss will be larger for a longer piece of fiber, so you will measure the loss of the long piece of fiber. In order to measure the loss in the fiber you first need a reference of how much light goes in to the piece of fiber from the LIGHT TRANSMITTER. You will use the short piece of fiber to measure this reference.

11. Now remove the 1 meter fiber and insert 3meter fiber.12. Loss in optical fiber systems is usually measured in dB. Loss of fiber itself is

measured in dB per meter.

Alternative Approach for measuring Attenuation1. Setup the analog link as shown in the block diagram 7.2

2. Use an optical fiber of length L1m and note down output voltage V1

3. Repeat the above step with a fiber of length L2 m. so V2 is the output voltage

4. Calculate attenuation using the formula

Attenuation Loss (A) =

Measurement of Bending Loss1. Setup the analog link as shown in the block diagram.7.2

2. Use an optical fiber link of length 1 m

3. Don't bend the fiber too tightly or it may not come back to shape.

4. Measure the output voltage V01 using a smaller bend for optical fiber link with diameter d1 mm.

5. Measure the output voltage V02 using a larger bend for optical fiber with diameter d2 mm

6. Bending Loss (B) =

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Fig7.3: Block diagram for numerical aperture measurement

Measurement of numerical aperture and angle subtended

1. Make connections as shown in fig.7.3. Connect the power supply cables with proper polarity to FCL-01 Kit. While connecting this, ensure that the power supply is OFF.

2. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the fiber into the cap. Now tighten the cap by screwing it back.

3. Keep the jumpers JP1, JP2 & JP4 on FCL-01 as shown in fig.7.3.

4. Keep switch S2 in VI position on FCL-01.

5. Switch on the power supply.

6. Insert the other end of the fiber into the numerical aperture measurement Jig Hold the white sheet facing the fiber. Adjust the fiber such that its cut face is perpendicular to the axis of the fiber.

7. Keep the distance of about 10 mm between the fiber tip and the screen. Gently tighten the screw and thus fix the fiber in the place.

8. Observe the bright red light spot on the screen by varying Intensity pot P3 and Bias pot P4.

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9. Mark the circular portion using a pencil and measure its diameter d1 cm

10. Measure the distance between the fiber and the sheet of paper h1 cm

11. Similarly , measure the diameter d2 for a different height h2

12. Using Formula Calculate Numerical Aperture and angle subtended

Numerical aperture (NA) =

Where ,

,

Angle subtended (θ0) =

Results: Attenuation ‘A’ =………………dB/m

Bending Loss ‘B’=…………...…V/m

Numerical Aperture NA=………..

Angle subtended θ0=……………deg

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EXPERIMENT 8

Characteristics of microstrip ring resonator and microstrip 3dB power divider

Aim: Measurement of resonance characteristics of microstrip ring resonator and Measurement of power division and isolation characteristics of microstrip 3dB power divider

a. Measurement of resonance characteristics of microstrip ring resonator

Apparatus: Voltage controlled oscillator, Detector, isolator, attenuator, microstrip ring resonator.

Block diagram:

Fig8.1: Measurement setup based on Voltage Controlled Oscillator (VCO)

Procedure:1. Set up the system as shown in Figure 8.1

2. Measure the input power by connecting a simple transmission line.

3. Measure the forward power by noting the reading of the detector connected to the Microstrip ring resonator circuit (DUT)

4. Repeat the above two steps at 5-10 different frequencies by tuning the VCO.

5. Plot the characteristics (forward power v/s frequency) of the microstrip ring resonator

6. From the plot, determine the resonant frequency of the microstrip ring resonator.

b. Measurement of power division and isolation characteristics of microstrip 3dB power divider

Apparatus: Voltage controlled oscillator, Detector, isolator, attenuator, microstrip 3dB power divider.

Procedure:1. Set up the system as shown in Figure 8.1

2. Terminate port 3 in 50-ohm matched load.

3. Measure the input power fed to port 1 of the Microstrip power divider circuit at a selected VCO frequency.

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4. Measure the power coupled to port 2 of the microstrip power divider circuit.

5. Measure the power coupled to port 3 (Match terminate port 2).

6. By terminating port 1, feed the power to port 2 and measure power available at port 3 and calculate the isolation.

7. The PCB structures of a transmission line, Ring resonator and power divider are shown in fig 8.2 and 8.3 respectively. The sample characteristics of a ring resonator are shown in fig8.4.

Fig8.2: Printed circuit boards of (a) 50-ohm through line and (b) Ring resonator

Fig8.3: Microstrip power divider circuit without resistor in the test jig.

Fig8.4: Simulated transmission characteristics of the final fabricated ring resonator structure

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Design of a 50-Ohm Microstrip Line:A substrate of 0.762 mm thickness and relative dielectric constant =3.2 is selected. For Z0=50-ohms, we get w/h= 2.407.

This gives width of the microstrip conductor=1.834 mm.

Calculations:a) Ring resonator

Resonant frequency from the Graphb) Power divider

Equal power divisionIsolation b/w port2 and port3

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EXPERIMENT 9DETERMINATION OF COUPLING COEFFICIENT, INSERTION

LOSS OF MAGIC TEE AND DIRECTIONAL COUPLER

MAGIC TEE

Aim: To conduct an experiment and determine Isolation, Power division between E/H plane and Insertion loss of a Magic Tee. Also construct an S-matrix for the same.

Apparatus: Klystron power supply, klystron oscillator, Isolator, Attenuator, Frequency meter, magic tee, crystal detector, VSWR/Power meter/CRO, Matched load.

Fig 9.1: Magic Tee

Fig9.2: Experimental setup of a magic Tee

Procedure:1. Equipments are connected as shown in the Fig. 9.2.2. Feed the microwave power at the given port1 and measure the output power at port2 while

terminating the other ports with matched loads. Similarly measure the output power at port3 and port 4 by terminating the other ports with matched load.

3. Calculate the Insertion loss, Isolation and Power division4. The input power can be measured by removing the magic tee and connecting the crystal

detector and CRO directly to frequency meter.

Calculations:

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Reflex klystron oscillator

oscillator

Isolator

Matched load

Matched load

VSWR/ CRO

Magic tee

Crystal detectorAttenuator

Frequency meter

KlystronPowerSupply

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Power division:

Feed the power at port3 (H-arm), and note down the power at port1 and 2 respectively by terminating the other two ports with matched load.

DIRECTIONAL COUPLER

Aim: To study characteristics of a Waveguide Directional Coupler and find Coupling coefficient, Insertion loss, Isolation. Also construct the S-matrix for a directional coupler.

Apparatus: Klystron power supply, klystron oscillator, Isolator, Attenuator, Frequency meter, Directional coupler, Crystal detector, VSWR/Power meter/CRO, Matched load.

Fig9.3: Layout of a three-port directional coupler

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Procedure:1. Set up the system as shown in Figure9.2 and connect a directional coupler in place of

Magic tee. 2. Fire the klystron and set it to oscillate in one of the modes. Measure the maximum

Power and frequency of oscillations.3. Measure the forward power at port2, measure the coupled power at port3 by feeding a

power through port1. Determine the insertion loss and coupling factor.4. Determine the isolation by feeding the power to port2 and measuring the output

power at port3.

Calculations: With respect to the notations of fig 9.3, the parameters of a directional coupler are defined as,

Insertion Loss (IL) = 10*log(P1/P2)=-20*log(S21)

Coupling Factor (CF) = 10*log(P1/P3)=-20*log(S31)

Isolation (I) = 10*log(P2/P3) = - 20*log(S32)

Expected results:

1. Coupling coefficient = 10 dB2. Insertion loss < 1 dB3. Isolation > 40 dB

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EXPERIMENT 10Measurement of Directivity and Gain of Printed Dipole antenna and

Rectangular Microstrip patch antenna (X-Band).

Aim: To conduct a suitable experiment on Microstrip antenna and printed dipole antenna, plot its radiation pattern and determine the directivity and gain.

Apparatus: Klystron power supply, Isolator, Frequency meter, Variable attenuator, X-band detector, Horn antenna, Microstrip patch antenna, Printed dipole, Waveguide-to-BNC adaptor and Oscilloscope, SMA connector, RF cables, Power meter and adapters.

Block Diagram

Fig 10.1: Experimental setup for radiation pattern measurement

Procedure:

1. Set up the apparatus as shown in Fig.10.1. Mount microstrip patch antenna (receiving antenna) on a rotatable stand.

2. Keep the distance between the two antennas sufficiently large such that they are in the far-field zone. Set the antennas for measurement in the E-plane.

3. Set the source to the frequency (say 10 GHz) at which the radiation pattern is to be measured. Align the two antennas for maximum reading on the power meter. This is the peak position of the main beam. Note this power as the reference level say P0 at 0 degree position.

4. The E-plane and H-plane orientations of microstrip patch and printed dipole antenna (Receiving antennas) with respect to transmitting horn antenna are shown in fig 10.2 and 10.3 respectively.

5. Rotate the test (receiving) antenna clockwise in small steps (5o or 10o) to 90o and note the readings on the power meter at every step.

6. Return to the 0o position. The power meter should read the reference level power. Repeat the measurements by rotating the antenna anti-clockwise in small steps till -90o and record the readings at every step. Plot the E-plane radiation pattern.

7. Repeat the measurements for the H-plane and plot the pattern (to verify the results refer to the section on characteristics of the printed antennas).

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8. Connect the printed dipole antenna as a receiver and repeat the steps 5, 6, and 7.

9. Plot the radiation pattern of microstrip patch antenna and dipole antenna in E-plane and H-plane.

10. Calculate the Gain and directivity from the radiation pattern.

Fig 10.2: E- and H-plane measurement setup for rectangular microstrip patch antenna.

Fig 10.3: E- and H-plane measurement setup for printed dipole antenna.

Tabular column:

Pr in E plane Pr in H planeAngle (degrees)

Left Right Left Right

0510152025

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EXPERIMENT 11

Time Division Multiplexing& Demultiplexing, Frequency Division multiplexing & demultiplexing using OFC link

Aim: To perform frequency and time division multiplexing and demultiplexing over Fiber optic analog link.

Apparatus: FCL-03, FG-02 with power cable, 1 Meter Fiber cable, Patch chords, Power Supply (Use only one provided), 20 MHz Dual Channel Oscilloscope.

Frequency division multiplexing and de-multiplexing

Procedure:1. Make connections as shown in fig.11.1. Connect the power supply cables with proper polarity to FCL-03 Kit. While connecting this, ensure that the power supply is OFF.2. Connect Function Generator FG-02 to FCL-03 using power cable.3. Keep the jumpers JP2 & JP3 on FCL-03 as shown in fig.11.1.4. Switch on the power supply.5. Keep the function generator JP1 shorted & JP2, JP3 open.6. Keep the function generator JP4 in 1-10 KHz position.7. Connect the OUT Signal from FG-02 to the CH1 post of FDM Transmitter on FCL-03 and keep the signal frequency at 1 KHz & Amplitude at 0.5Vpp8. Connect the 2 KHz, 0.5Vpp signal from FG-02 as a constant signal to the CH2 post of FDM Transmitter on FCL-03.9. Connect the OUT post of FDM Transmitter to the IN post of Analog Buffer on FCL-03.10. Then set carrier frequency of MOD I of about 10 KHz with the help of P1 and carrier freq. of MOD II of about 20 KHz with the help of pot P2.11. Then observe the signal at Band Pass Filter-1 OUT it should be maximum signal transmission at center freq. fc of about 10 KHz.12. Then observe the signal at Band Pass Filter-2 OUT it should be maximum signal transmission at center freq. fc of about 20 KHz.13. Then observe signal at outpost of summation block as shown in waveform Fig. 11.2.14. Connect the output of Analog Buffer post OUT to post TX IN.15. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the fiber into the cap. Now tighten the cap by screwing it back.16. Now rotate the Optical Power Control pot P3 in FCL-03 in anticlockwise direction. This ensures minimum current flow through LED.17. Slightly unscrew the cap of RX2 Photo Diode SFH250V. Do not remove the cap from the connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back.

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18. Observe the output signal from the detector at ANALOG OUT post on Oscilloscope by adjusting Optical Power Control Pot P3 and you should get the reproduction of the original transmitted signal.19. Connect the output of detector post ANALOG OUT to post IN of FDM Receiver.20. Observe the demultiplexed & demodulated signal at CH1 & CH2 output posts of FDM Receiver, fine tune carrier frequency of modulator so as it will give clear reproduction of input signal as shown in Fig.11.3.21. Connect CH1 & CH2 post to IN post of filter 1 & filter 2 respectively.22. Observe the signal at OUT post of filter 1 & filter 2 as a reproduction of original signal.

Fig 11.1 Block diagram Frequency division multiplexing and de-multiplexing

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Fig 11.2 FDM Transmitter Waveform

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Fig 11.3 FDM Receiver Waveform

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Time division multiplexing and de-multiplexing (Analog)

Equipments: FCL-01 & FCL-02, FG-01 with power cable, 20 MHz Dual Channel, oscilloscope, 1 meter Fiber cable, Patch chords, and Power supply (Use only one provided)

Procedure:1. Refer to fig 11.4 and make the following connections.2. Connect the power supply with proper polarity to FCL-01 and FCL-02. While connecting this, ensure that the power supply if OFF.3. Connect Function Generator FG-01 to FCL-01 using power cable.4. Keep the jumpers JP1.JP2.JP3 & JP4 on FCL-01 as shown in fig. 11.4.5. Keep the jumpers JP1 & JP2 on FCL.-02 as shown in fig. 11.4.6. Keep switch S2 in TX IN position on FCL-01.7. Switch on the power supply.8. Connect four sinusoidal signals of different frequencies as 250 Hz, 500 Hz, 1 KHz & 2 KHz generated on FG-01 to CH1, CH2, and CH3 & CH4 inputs of Time Division Multiplexing section on FCL-01 respectively. The amplitude of these signals can be varied with the help of potentiometers P3, P4, P5 and P6. Observe these signals on Oscilloscope and adjust their amplitude to 2 Vp-p.9. Observe the TDM output at OUT post of Time Division Multiplexing section as shown in Fig. 11.5.10. Connect the output of Time Division Multiplexing section post OUT to post IN of Analog Buffer on FCL-01.11. Connect the output of Analog Buffer post OUT to post TX IN.12. Connect post CLK on FCL-01 to post CLK l/P on FCL-02.13. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the 1 meter fiber into the cap. Now tighten the cap by screwing it back.14. Slightly unscrew the cap of Photo Diode SFH250V. Do not remove the cap from the connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back.15. Keep switches SW2 in ANALOG OUT position on FCL-02.16. Connect the output of Photo Diode detector post OUT to post DEMUX IN of Time Division De-multiplexing Section.17. Connect the output of Time Division De-multiplexing Section CH1, CH2, CH3 & CH4 to input of 4th order low pass filters IN1, IN2, IN3 & IN4 respectively.18. Observe four different reconstructed signals at the output channels marked as OUT1, OUT2, OUT3 & OUT4 of 4th order low pass filters in FCL-02 as shown in fig 11.6.19. Perform the above procedure again for all the combinations of Transmitter & Receiver.

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Fig 11.4: Block Diagram of Time Division Multiplexing and De-Multiplexing

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Fig 11.5 TDM Transmitter Waveform

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Fig 11.6 TDM Receiver Waveform

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Time division multiplexing and De multiplexing (Digital)

Aim: The objective of this experiment is to study simultaneous transmission of several signals using synchronous time division multiplexing

Equipment: FCL-04, FCL-02 with power cable, 1 meter Fiber cable, Telephone handsetsPower supply, 20 MHz dual channel oscilloscope

Procedure 1. Make connection as shown in diagram (Separate Manual). Connect the power

supply cables with proper polarity to FCL-04 Kit. While connecting this, ensure that the power supply is OFF

2. Keep all switch faults in off position

3. Keep the switch SW5 to VOICE IN position.

4. Keep the switch SW7 to TTL IN position.

5. Keep the jumpers JP2 towards DCLK position.

6. Keep the jumpers JP3 towards TX DATA Position

7. Switch ON the power supply.

8. Connect the post MCDTX to the TX IN position on FCL-04

9. Slightly unscrew the cap of LED SFH450V (950 nm). Do not remove the cap from the connector. Once the cap is loosened, insert the fiber into the cap. Now tighten the cap by screwing it back.

10. Slightly unscrew the cap of photo transistor with TTL logic output. Do not remove the cap from connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back.

11. Connect detected signal TTL post to post MCDRX

12. Connect telephone handsets to posts HS1 & HS2.

13. Set MARKER TX1 & MARKER TX2 each for bit pattern show in diagram

14. Set MARKER RX1 & MARKER RX2 each for bit pattern shown in diagram

15. Observe the TDM data at TDMTX on oscilloscope

16. Carefully observe the time division duration for which channel is selected. Observe & measure the frame period.

17. Press either of channel keys (CH2, CH5 &CH6)

18. Observe the Manchester coded data at MCDTX. This data is transmitted through the fiber.

19. The received data which is still in Manchester coded form is available at MCDRX & TDMRX signals with respect to TDMTX.

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