LAB MANUAL FOR ” EC2405-OPTICAL AND MICROWAVE LABORATORY” VII Semester

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

VELALAR COLLEGE OF ENGINEERING & TECHNOLOGY (Affiliated to Anna University, Chennai) Thindal, Erode-638012 Prepared by K.Senthil Prakash, Asst. Prof. (Sr. Gr.) S.MahendraKumar, Asst. Prof. (Sr. Gr.)

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SYLLABUS MICROWAVE EXPERIMENTS: 1. Reflex Klystron – Mode characteristics. 2. Gunn Diode – Characteristics. 3. VSWR, Frequency and Wave Length Measurement. 4. Directional Coupler – Directivity and Coupling Coefficient – S – parameter measurement. 5. Isolator and Circulator – S - parameter measurement. 6. Attenuation and Power measurement. 7. S - matrix Characterization of E-Plane T, H-Plane T and Magic T. 8. Radiation Pattern of Antennas. 9. Antenna Gain Measurement. OPTICAL EXPERIMENTS: 1. DC characteristics of LED and PIN Photo Diode. 2. Mode Characteristics of Fibers. 3. Measurement of Connector and Bending Losses. 4. Fiber Optic Analog and Digital Link. 5. Numerical Aperture Determination for Fibers. 6. Attenuation Measurement in Fibers.

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Contents Exp. No

Experiment Name

Page No.

1

Study of Microwave Components.

1

2

Mode Characteristics of Reflex Klystron Oscillator.

9

3

Characteristics of Gunn Diode Oscillator.

15

4

VSWR, Frequency and Wave Length Measurement.

19

5

S-Parameter Measurement in Directional Coupler.

25

6

S-Parameter Measurement in Isolator and Circulator.

29

7

Attenuation & Power Measurement.

35

8

S Matrix Characterization of E- plane & H-plane Tees.

39

9

S Matrix Characterization of Magic Tee.

45

10

Radiation Pattern & Gain of a Horn Antenna.

51

11

Radiation Pattern & Gain of a Parabolic Antenna.

55

12

Impedance Measurement by Slotted Line Method.

59

13

Measurement of Numerical Aperture of Optical Fiber

63

14

Measurement of Losses in the FIBER

67

15

DC characteristics of Fiber Optic LED and Photo Detector

73

16

Setting up a Fiber optic Analog Link

77

17

Setting up a Fiber Optic Digital Link

81

18

Study of Eye Pattern

85

19

Measurement of Attenuation in Fibers.

89

20

Mode Characteristics of Fiber.

93

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Ex. No: 1

STUDY OF MICROWAVE COMPONENTS

AIM To study the microwave components in the laboratory. COMPONENTS  Gunn Diode  Reflex Klystron  Isolator  Circulator  Variable attenuator  Frequency meter  Short termination  Matched termination  Directional Coupler  Horn antenna  Magic tee  E & H Plane Tee  Detector mount THEORY: GUNN DIODE Gunn diode is negative resistance device used as low power oscillator at microwave frequencies in transmitter. It is also used as local oscillator is receiver front end. J.B gunn discovered microwave oscillator GaAs and Inp. These are semiconductors having a closely packed energy valley in the conduction band. When DC voltage is applied across the material and electric field is essential across it. At low electric field in the material most of the electric field is transferred into high-energy state.

REFLEX KLYSTRON It is low power lower efficient microwave oscillator. It has as electron gun. The filament is made up of tungsten and it is heated. Frequency range is 4 Ghz to 200Ghz. Power output level is 3 watts in Xband and 10m Watts at 220GHz. Typically 100m Watts efficiency is 10%. The necessary Condition is that magnitude of the negative real part of the electronic admittance should not be less than the total conductance of the cavity circuits.

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ISOLATOR An isolator is a two-port device that transmits microwave or radio frequency power in one direction only. It is used to shield equipment on its input side, from the effects of conditions on its output side; for example, to prevent a microwave source being detuned by a mismatched load. To achieve nonreciprocity, an isolator must necessarily incorporate a non-reciprocal material. At microwave frequencies this material is invariably a ferrite which is biased by a static magnetic field. The ferrite is positioned within the isolator such that the microwave signal presents it with a rotating magnetic field, with the rotation axis aligned with the direction of the static bias field. The behaviour of the ferrite depends on the sense of rotation with respect to the bias field, and hence is different for microwave signals travelling in opposite directions. Depending on the exact operating conditions, the signal travelling in one direction may either be phase-shifted, displaced from the ferrite or absorbed. CIRCULATOR It is defined as port arrangement such that the energy entering into the port is coupled and to adjacent port but not coupled to other ports. VARIABLE ATTENUATOR An attenuator is an electronic device that reduces the amplitude or power of a signal without appreciably distorting its waveform. An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.Attenuators are usually passive devices made from simple voltage divider networks. Switching between different resistances forms adjustable stepped attenuators and continuously adjustable ones using potentiometers. For higher frequencies precisely matched low VSWR resistance networks are used. Fixed attenuators in circuits are used to lower voltage, dissipate power, and to improve impedance matching. In measuring signals, attenuator pads or adaptors are used to lower the amplitude of the signal a known amount to enable measurements, or to protect the measuring device from signal levels that might damage it. Attenuators are also used to 'match' impedances by lowering apparent SWR.

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FIXED ATTENUATORS With the help of our experienced engineers, we are able to design and develop a wide and comprehensive range of Fixed Attenuators, which is available at market leading prices. This range of fixed attenuators is highly acclaimed in the industry, owing to its application in networks, telecommunication, instruments and allied fronts. The offered range of fixed attenuators is applauded for its below cited features: High attenuation precision Excellent stability Excellent reliability. FREQUENCY METER The frequency meter is classified into two categories namely direct and indirect frequency meter. Moving a plunger can vary the distance between the shorted tuning and diode. The timing arrangement helps the user to read just the distance from the short circuit wherever the signal frequency. The detector output is normally available in at the coaxial connector, the crystal diode act as a square law device. The response of the diode to the power is dependent on resistance of the mount the diode used for detection in X band is IN238. MATCHED TERMINATION This is also a termination of load for microwave setup, standing wave occurs when a load does not completely absorb the power reaching it. Microwave measurement requires a termination resulting in maximum reflection, when matched terminations serve the purpose.

MOVABLE SHORTS: We are highly appreciated in the domestic and international market for an unparalleled range of MovableShorts. These products are utilized in different experiments such as tostudy the characteristics of reflex klystron and frequency, guide wavelength and free space wave length. In addition to this, the offered range is skillfully developed by our diligent engineers, who possess commendable experience, indepth knowledge and expertise in this domain. DIRECTIONAL COUPLER Power dividers (also power splitters and, when used in reverse, power combiners) and directional couplers are passive devices used in the field of radio technology. They couple a defined amount of the electromagnetic power in a transmission line to another port where it can be used in another circuit. An

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essential feature of directional couplers is that they only couple power flowing in one direction. Power entering the output port is not coupled. Directional couplers are most frequently constructed from two coupled transmission lines set close enough together such that energy passing through one is coupled to the other. This technique is favoured due to the microwave frequencies the devices are commonly employed with. However, lumped component devices are also possible at lower frequencies. Directional couplers and power dividers have many applications, these include; providing a signal sample for measurement or monitoring, feedback, combining feeds to and from antennae, and providing taps for cable distributed systems such as cable TV. HORN ANTENNA A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct the radio waves. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feeders (called feed horns) for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns, automatic door openers, and microwave radiometers. Their advantages are moderate directivity (gain), low SWR, broad bandwidth, and simple construction and adjustment.

MAGIC TEE The device magic tee is combination of E and H plane. They have arm 3, H arm forms an H-plane tee and arm 4, E arms an E Plane tee. If Power is fed into arm 3 the electric field divides equally between arm 1 and arm 2 with the same phase and no output at arm 4. If the power is fed into the arm 4.it divides equally into arm 1 & 2 but out of phase with no power at arm 3. For that if the power is fed in from arm 1 & 2 it is added in arm 3 and it is subtracted from arm 4.

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E-PLANE TEE The side arm is known as E- arm (or) side arm. When TE10 mode is made to propagate into the port 3 , the output at port 1 and port 2 will have a phase shift of 180 0 (ie ) the electric field line change their direction when they come out of port 1 and port 2 . E- Plane is also known as voltage (or) Series junction symmetrical about the centre arm.

H- PLANE TEE The port 1 and port 2 of the main Wave guide are called collinear arms and the port 3 is known as the side arm (or) H-arm. This is called H-Plane Tee because the axis of the side arm is parallel to the planes of the main transmission lines. All the 3 -Arms of the H – Plane tees lines in the plane of the magnetic field and it divides itself into arms and hence it is known as the current junction .If two input waves are fed into port 1 and port 2 of the collinear arms, the output at port 3 will be additive and in phase .If the input is fed at the port 3 of the side arm, the way equally split in port 1 and port 2 will be in phase and equal in magnitude.

DETECTOR MOUNT The crystal mount provides a complete DC path for rectification. But this system is affected if frequency is changed. The crystal detector can be used for detection of microwave power as well as for maxing microwave signal at input stage at receiver. The output signal can be coupled through a BNC connector. 8

SLOTTED SECTION Our organization is counted amongst the most distinguished manufacturers and traders of an extensive range of Slotted Sections. This range of slotted sections is widely applicable in different engineering and construction industries. These products are offered in different customized forms and specifications in accordance with the emerging requirements of the clients. Moreover, this range is best suited for microwave experiments and is utilized for reflection coefficient. TUNABLE PROBE It is used with slotted section. They are for exploring the energy as an electric field in a suitable fabricated section of wave-guide. The dept generation into a wave-guide section is adjustable by the knob of the probe. This probe picks up the RF power from the time and power is rectified by crystal power, which is then fed to VSWR meter.

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RESULT Thus the Microwave components were studied in the laboratory

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EXPERIMENTAL SETUP:

Microwave bench setup for study of klystron modes

MODEL GRAPH

11

Ex. No: 2

MODE CHARACTERISTICS OF REFLEX KLYSTRON OSCILLATOR

AIM To determine the mode characteristics of reflex klystron tube oscillator and to determine its Mode Number, Electronic Tuning Range and Electronic Tuning Sensitivity. EQUIPMENTS REQUIRED

1. Klystron Power Supply 2. Reflex Klystron 3. Isolator 4. Frequency meter 5. Variable attenuator 6. CRO 7. Power Meter 8. Detector Mount THEORY The reflex klystron works under the principle of velocity modulation, which results current density modulation, to transfer a continuous electron beam in to microwave power. Electrons from the cathode are accelerated and passed through resonator towards the negative reflector which reflects the electron beam back to the cavity. At the positive cycle of the RF signal the electrons are accelerated which increases the velocity of the electron beam. At the negative cycle of the RF signal the electrons are retarded. The electron beam interaction with zero crossings of the RF field travel in the cavity gap with unchanged velocity. The accelerated, retarded and unchanged velocity electrons bunch at the positive half cycle of the RF noise and deliver its energy, make the sustained oscillations. PROCEDURE 1. Set the equipments as shown in figure. 2. Set up the variable attenuator at minimum position. 3. Keep the knob of klystron power supply as bellow Mod switch – AM Beam Voltage knob- Fully anticlockwise. AM amplitude – around fully clockwise 12

TABULATION: Beam voltage:_________ S.No.

Beam Current:________

Negative Repeller Voltage

Power Output

Wave meter reading

(Volts)

(mW)

Frequency (GHz)

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AM freq. knob - around mid position. 4. Switch On the klystron power supply and cooling fan. 5. Switch ON the beam voltage/current knob and set beam current. 6. Adjust the reflector voltage knob to set maximum output in CRO. 7.Maximize

the

output

voltage

with

AM

amplitude

and

frequency

control knob of power supply. 8. Tune the plunger of klystron mount for maximum output. 9. Change the repeller voltage knob towards Clockwise directions and note down output power, repeller voltage and find frequency. 10. Tune the frequency meter and obtain the frequency for corresponding repeller voltage and note down the frequency when dip in the CRO. 11. Plot the output power Vs repeller voltage and repeller voltage Vs frequency graph.

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RESULT: Thus the mode characteristics of reflex klystron have been verified.

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EXPERIMENTAL SETUP:

Microwave bench setup for study of Gunn Oscillator Characteristics.

MODEL GRAPH

17

Ex. No: 3

CHARACTERISTICS OF GUNN DIODE OSCILLATOR

AIM To determine the characteristics of Gunn diode oscillator and to find the threshold voltage. EQUIPMENT REQUIRED 1. Gunn diode 2. Gunn power supply 3. Isolator 4. Variable Attenuator 5. Pin Modulator 6. Detector Mount 7. CRO THEORY The Gunn diode oscillator is based on negative differential conducting effect in bulk semi conductor which has two conduction bands separate by an energy gap (greater than thermal energies). A disturbance at the cathode rise to high field region which travels towards the anode. When this field domain reaches anode, it disappears and another domain is formed at the cathode and starts moving towards the anode and so on. The time required for domain to travel from cathode to anode (transit time) gives oscillator frequency. In a given oscillator the Gunn diode is placed in a resonant cavity dimension. The oscillator frequency is determined in cavity dimension. Although Gunn oscillator can be amplitude modulated with the bias voltage when we have used a PIN modulation in square wave modulation of the signal coming from the Gunn diode. A measure of the square wave capability is the modulation depth is the output ratio between ON and OFF state. PROCEDURE 1.Set the components as shown in figure. 2.Keep the control knobs of Gunn power supply as below, i) Meter switch off ii) Gunn bias knob –fully anticlockwise iii) PIN diode frequency-any position.

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TABULATION: S.No.

Gunn Bias Voltage(V)

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Gunn Diode Current(mA)

3. Set the micrometer of Gunn oscillator for required frequency of operation. 4. Switch ON power supply 5. Measure the Gunn diode current corresponding to the various Gunn bias voltage through the digital panel meter and meter switch do not exceed the bias voltage current. 6. Plot the voltage and current readings on the graph as shown in the Figure. 7. Measure the threshold voltage with corresponding to maintain maximum current.

RESULT Thus the Gunn diode oscillator characteristic was obtained and its threshold voltage was determined. Threshold Voltage = ………………. Volts

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EXPERIMENTAL SETUP

21

Ex.No: 4

VSWR, FREQUENCY AND WAVE LENGTH MEASUREMENT

AIM: To determine the VSWR, Frequency and Wave Length Measurement in a rectangular wave guide working in TE 10 mode. EQUIPMENT REQUIRED: 1. Klystron power supply 2. Reflex Klystron 3. Isolator 4. Frequency meter 5. Variable attenuator 6. Slotted section & Tunable probe 7. Movable short load 8. CRO 9. V.S.W.R Meter. PROCEDURE: Set the equipments as Keep variable attenuator in the minimum attenuation position. Keep the control knob of VSWR meter as below. Range db

:

40 db to 50 db

Input switch

:

Low impedance

Meter switch

:

Normal position

Gain

:

Mid position

Keep control knobs of klystron power supply as given below: Beam Voltage

:

Off

Mod-switch

:

AM

Beam voltage knob

:

Full anticlockwise

Reflector voltage knob

:

Full clockwise

Am amplitude knob

:

Full clockwise

Am frequency & amplitude knob

:

Mid position

Switch on the klystron power supply, vswr meter and cooling fan. 22

TABULATION

First minima d1 in cm

Second minima d2 in cm

λg =2(d2 –d1) cm

CALCULATION: Practical Frequency: λg =2(d2 –d1)= λc = 2*a = where a=2.28cm

Calculate the frequency, F=C\ 0, Where 0

1/

= free space wavelength. 2 0 =

1/ ( g) 2 + 1/( c)2

C= velocity of light F= C*

1/ ( g) 2 + 1/( c)2

Where, C=3*108 m /s.

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VSWR

Frequency in GHz

Switch on the beam voltage switch and set beam voltage at 300V Rotate the reflector voltage knob to get deflection in vswr meter. Tune the output by tuning the reflector voltage, amplitude and frequency of am modulation. Tune plunger of klystron mount and probe for maximum deflection in vswr meter. If required change the range db switch variable attenuator position and gain control knob to get deflection in the scale of vswr meter. As we move probe along the slotted line, the deflection will change. Measurement of VSWR

Compute vswr from the following equation. VSWR = λg / π (d1 – d2) = λg / π (Δx) Where λg is the guide wavelength, d1 and d2 are locations of double minimum points.

Measurement of Frequency and Wave Length Tune the frequency meter knob to get dip on the CRO and note down frequency from frequency meter. Move the probe to next minima position and note down the successive minima distances in the slotted section; let it be d. Note the positions of two successive minima. Calculate λg. calculate the cutoff wavelength (λc). λc = 2*a Where a =broad dimension of wave guide a = inner broad dimension of 22.85 or 22.86 mm for X band. λg = 2*(d2 – d1) Where d1 is the 1st maximum obtained in slotted section. d2 is the 2nd maximum obtained in slotted section.

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RESULT: Thus the VSWR, Frequency and Wave Length has been measured.

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EXPERIMENTAL SETUP:

27

Ex.No: 5

S-PARAMETER MEASUREMENT IN DIRECTIONAL COUPLER

AIM To study the power distribution in a multi-hole directional coupler and to determine its Coupling coefficient, Directivity and S-parameters. EQUIPMENTS REQUIRED 1. Klystron power supply 2. Reflex Klystron 3. Isolator 4. Vatiable attenuator 5. Slottedline and Tunable probe 6. Detector mount 7. matched termination 8. MHD coupler 9. VSWR meter 10. Power Meter THEORY A directional coupler is a hybrid waveguide joint which couples power in an auxiliary waveguide arm in one direction. It is a four-port device but one of the ports is terminated into a matched load. An ideal directional coupler has the following characteristics: If power is fed into port(1), the power is coupled in ports(2), and (3), i.e., power flows in the forward direction of the auxiliary arm port (3) but no power couples in port (4), i.e., in backward direction. Similarly power fed in (2) couples into ports(1) and (4) and not in (3). All the four ports are matched, i.e., if there of them are terminated in matched loads, the fourth is automatically terminated in a matched load. If power couples in reverse direction, i.e., power fed in (1) appears in ports (2) and (4) and nothing in (3), then such type of coupler is known as backward directional coupler. The conclusion is that in then auxiliary section the power is only one direction. PROCEDURE 1. Setup the components and equipments as shown in figure. 2. Energize the microwave source for a particular frequency. 28

CALCULATION: Input Power

=

Output Power at port 2

=

Coupling Power at port 4 = Back Power at port 3

=

Directivity

=

20 log (p4/p3)

Coupling Factor

=

20 log (p1/p4)

Isolation Factor

=

20 log (p1/p3)

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3. Measure the Vmax and Vmin for corresponding ports by connecting loads to other ports. 4. Calculate the reflection co-efficient which gives the value of S-parameter. 5. Find the upper matrix values by appropriate connections. 6. From the S-parameter value calculate coupling factor, Isolation, directivity and Insertion loss.

RESULT Thus the power distribution in a multi-hole directional coupler was studied. Also, its main and auxiliary line VSWRs, Coupling factor, Directivity and S-parameters were determined.

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Sii Measurement

Sij Measurement

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Ex.No: 6

S-PARAMETER MEASUREMENT IN ISOLATOR AND CIRCULATOR

AIM : To measure the S-parameter of the Isolator and Circulator. APPARATUS REQUIRED :

1. Klystron Power Supply 2. Reflex Klystron 3. Isolator 4. Circulator 5. Slotted Section & Tunable probe, 6. Variable Attenuator, 7. Detector mount, 8. VSWR 9. Power Meter 10. CRO 11. Matched Termination THEORY : ISOLATOR :The isolator is a two-port device with small insertion loss in forward direction and a large in reverse attenuation. CIRCULATOR : The circulator is a multi port junction that permits transmissionin certain ways. A wave incident in port 1 is coupled to port 2 only, a wave incident at port 2 is coupled to port3 only and so on . Following is the basic parameters of isolator and circulator for study. A. Insertion loss :The ratio of power supplied by a source to the input port to the power detected by a detector in the coupling arm, i.e., output arm with other port terminated in the matched load, is defined as insertion loss or forward loss. B. Isolation :It is the ratio of power fed to input arm to the input power detected at notcoupled port with other port terminated in the matched load.. C. Input VSWR :The input VSWR of an isolator or circulator is the ratio of voltage maximum to voltage minimum of the standing wave existing on the line, when one port of it terminates the line and others have matched termination.

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OBSERVATIONS AND CALCULATIONS

33

PROCEDURE (a) Input VSWR Measurement (1) Set up the components and equipments as shown above with input port of isolator or circulator towards slotted line and matched load on other ports of it. (2) Energize the microwave source for particular operation of frequency. (3) With the help of slotted line, probe and VSWR meter, find out SWR of the isolator or circulator as describe earlier for low and medium SWR measurements. (4) The above procedure can be repeated for other ports or for other frequencies. (b) Measurement of Insertion loss &Isolation : (1) Remove the probe and isolator or circulator from slotted line and connect the detector mount to the slotted section. The output of the detector mount should be connected with VSWR meter. (2) Energize the microwave source for max. output for a particular frequency of operation.Tune the detector mount for max. output in VSWR meter. (3) Set any reference level of power in VSWR meter with the help of variable attenuator, gain control knob of VSWR meter and note down the reading (let it be P1). (4) Carefully remove the detector mount from slotted line without disturbing the positionof set up. Insert the isolator / circulator between slotted line and detector mount. Keeping input port to slotted line and detector at its output port. A matched termination should be placed at third port in case of circulator. (5) Record the readings in the VSWR meter. If necessary change range – db switch to highor lower position and taking 10 db change for one set change of switch position (let itbe P2). (6) Compute insertion loss on P1-P2 in db. (7) For measurement of isolation, the isolator or circulator has to be connected reverse, i.e., output port to slotted line and detector to input port with other port terminated by matched termination. After setting a reference level without isolator or circulator in the set up as described in insertion loss measurement. Let same P1 level is set . (8) Record the reading of VSWR meter after inserting the isolator or circulator (let it beP3). (9) Compute isolation as P1 – P3 in db. (10) The same experiment can be done for other ports of circulator. (11) Repeat the same for other frequency.

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RESULT:

Thus the power distribution in circulator and Isolator and its S-parameters were determined.

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BENCH SETUP DIAGRAM FOR ATTENUATION MEASUREMENT

37

Ex.no:7

ATTENUATION & POWER MEASUREMENT

AIM: To measure the attenuation introduced by the given fixed attenuator. COMPONENTS REQUIRED: 1. Klystron power supply 2. Reflex Klystron 3. Isolator 4. Variable Attenuator 5. Frequency meter 6. DUT (Fixed Attenuator) 7. Power Meter 8. CRO THEORY With the help of our experienced engineers, we are able to design and develop a wide and comprehensive range of Fixed Attenuators, which is available at market leading prices. This range of fixed attenuators is highly acclaimed in the industry, owing to its application in networks, telecommunication, instruments and allied fronts. The offered range of fixed attenuators is applauded for its below cited features: High attenuation precision Excellent stability Excellent reliability. FORMULA: Attenuation = 10log (P2 / P1) dB PROCEDURE: 1. Arrange the bench setup as shown in figure 1 and measure the input power entering into the wave guide (P1). 2. Reconnect the circuit as shown in the figure 2 and find the power (P2) at the output of the given wave guide. 3. Using formula find the attenuation introduced by the wave guide.

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OBSERVATION AND CALCULATION:

Input Power

Output Power (fixed

Attenuation =

P1 in mW

attenuator) P2 in mW

10log (P2 / P1) dB

S.No

39

RESULT: Thus the attenuation introduced by the given fixed attenuator was found and verified.

40

EXPERIMENTAL SETUP:

41

Ex.No: 8

S MATRIX CHARACTERIZATION OF E- PLANE & H-PLANE TEES

AIM To study the E-plane and H-plane tees and to find the coupling factor, directivity and scattering matrix. EQUIPMENT REQUIRED 1. Klystron power supply 2. Reflex Klystron 3. Isolator 4. Variable attenuator 5. Frequency meter 6. Slotted line 7. E Plane Tee & H Plane Tee 8. Power meter 9. CRO 10. Matched Termination

THEORY H-PLANE TEE An auxiliary wave guide arm perpendicular to the narrow wall of a main guide. Thus it is 3 port device in which axis of the auxiliary or side arm is parallel to the plane of magnetic field of the magnitude and the coupling from the main guide to the branch guide and the arm 3 by means of magnetic field therefore H is also known as H-plane Tee. The perpendicular arm is generally taken as input and other two arms are in shunt to the input and hence it is called as shunt Tee. E-PLANE TEE An auxiliary waveguide arm is fastened to the broader wall of the main guide. Thus it is also a 3 port device in which the auxiliary arm is parallel to the plane of electric field of main guide and the coupling from the main guide to the auxiliary guide is by means of electric field. There fore it is also known as E-plane. It is called as series tee, because the load which is connected to its branches appears to be in series. 42

OBSERVATION AND CALCULATION

43

PROCEDURE 1. Input is fed into the port 3 of the Tee section. 2. Keeping the end p2 matched with a matched load, power output at p1 of the Tee junction is measured. 3. Reversing the setup the input is now fed to the reversed input port and the output at the secondary exit port is measured. 4. The readings are tabulated and the calculations are done. 5. Same procedure is repeated with H-plane Tee. 6. Using the power obtained from various ports the S-matrix is calculated.

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45

RESULT Thus E- and H-plane Tees were studied and their coupling factor, directivity and S-parameters were determined. 46

EXPERIMENTAL SETUP:

47

Ex.No: 9

S MATRIX CHARACTERIZATION OF MAGIC TEE

Date: AIM To study the power distribution in a magic (E-H or hybrid) tee and to obtain the values of isolation, coupling coefficients, input VSWRs and scattering matrix. EQUIPMENT REQUIRED 11. Klystron power supply 12. Reflex Klystron 13. Isolator 14. Variable attenuator 15. Frequency meter 16. Slotted line 17. Magic Tee 18. Power meter 19. CRO 20. Matched Termination THEORY The device magic tee is a combination of the E and H plane tee. Arm 3 is the H-arm and arm 4 is the E-arm. If the power is fed, into arm 4 (H-arm) the electric field divides equally between arm 1 and 2 with the same phase, and no electric field exits in arm 3. If the power is fed in arm 3 (H-arm), it divides equally in to arm 1 and 2 but out of phase with no power to arm 4. Further, if the power is fed in arm 1 and 2, with same magnitude and phase, simultaneously will be added in the H-arm and subtracted at Earm. PROCEDURE VSWR MEASUREMENT AT THE PORTS 1. Set up the components and equipments as shown in figure. Keeping E-arm towards slotted line and matched termination to other ports. 2. Energize the microwave source for particular frequency of operation. 3. Measure the VSWR of E-arm as described in measurement of SWR for low and medium value. 48

OBSERVATION AND CALCULATION

49

4. Connect another arm to slotted line and terminate the other port with matched termination. Measure the VSWR as above. Similarly, VSWR of any port can be measured.

MEASUREMENT OF ISOLATION AND COUPLING FACTOR 1. Remove the tunable probe and Magic Tee from the slotted line and connect the detector mount to slotted line. 2. Energize the microwave source for particular frequency of operation and the detector mount for maximum output. 3. With the help of variable attenuator and gain control knob of VSWR meter and note down. Let it be P3. 4. Without disturbing the position of the variable attenuator and gain control knob carefully place the magic Tee. 5. Tee after slotted line keeping H-arm connected to slotted line, detector to E-arm matched termination to arm 1 and 2.Note down the reading of VSWR meter Let it P4. 6. Determine the isolation between port 3 and 4 as P3-P4 in dB. 7. Determine the coupling coefficient from equation given in the theory part. 8. The same experiment may be repeated for other ports also. 9. Repeat the above experiment for other frequencies. MEASUREMENT OF INSERTION DIRECTIVITY 1. Set up the components and equipments as shown in the fig. 2. Energize the microwave source for particular frequency of operation. 3. Remove the multiple directional coupler and connect the detector coupler and connect mount of the frequency meter. Tune the detector for maximum output. 4. Set any reference level of power on VSWR meter with the help of variable attenuator, gain control knob of VSWR meter, and note down the reading. 5. Insert the directional coupler as shown in second fig 3 with detector to the auxiliary port 3 and matched termination to port 2, without changing the position of variable attenuator and gain control knob of VSWR meter. 6. Note down the reading on VSWR meter on the scale with the help of range-db switch if required. Let it be Y. 7. Calculate coupling factor which will be X-Y=C(db). 8. Now carefully disconnect the detector from the auxiliary port 3 and match termination from port 2 without disturbing the set-up. 50

9. Connect the matched termination to the auxiliary port 3 and detector to port 2 and measure the reading on VSWR meter suppose it is Z. 10. Compute insertion loss X-Z in db. 11. Repeat the step from 1 to 4.

51

12. Connect the direction coupler in the reverse direction, i.e. port 2 to frequency meter side. Matched termination to port 1 and detector mount to port 3. Without disturbing the position of the variable attenuator and gain control knob of VSWR meter. 13. Measure and note down the reading on VSWR meter. Let it be Yd. X-Yd gives isolation I (db). 14. Compute the directivity as Y-Yd=I-C 15. Repeat the same for other frequencies. 16. Calculate the Coupling Factor and Directivity using the formulae Coupling factor=10 log (Pin/Paux) dB Directivity D=10 log(Paux(forward)/Paux(reverse)) dB 17. from coupling factor and directivity, obtain the Scattering parameters as follows, Coupling Factor = -20 log (S41) dB Directivity

= 20 log (S31 / S41) dB

RESULT Thus the power distribution in a magic (E-H or hybrid) tee was studied and the values of isolation, coupling coefficients, input VSWRs and scattering matrix were obtained.

52

EXPERIMENTAL SETUP

53

Ex.No:10

RADIATION PATTERN & GAIN OF A HORN ANTENNA

AIM To measure the polar pattern and gain of a pyramidal horn antenna. EQUIPMENT REQUIRED 21. Klystron power supply 22. Reflex Klystron 23. Isolator 24. Variable attenuator 25. Frequency meter 26. Pyramidal horn antennas 27. Power meter THEORY Horn antenna is a rectangular waveguide with one end is stretched either in the broad dimensions a or b. It is classified according to its construction like, If it is prolonged in the breath a, it is known as H-plane horn antenna. If it is stretched in width b, then it is called as H-plane horn antenna. If it is prolonged in both directions, it is known as pyramidal horn antenna. The measurement may be considered either in the far field distance or near field distance. Far field distance is calculated by the formula d = 2d2/λ0, where d is the largest dimension of the antenna and λ0 is the free space wavelength. Antenna measurement may be either indoor or outdoor environment. If the size of the antenna is larger, it will give more directive radiation beam.Horn antenna is mainly used as feed element for parabolic dish antennas ( Cassegrain feed), to increase the spill over efficiency. PROCEDURE 1. Set up the equipments as shown in figure keeping the axis of both antennas in same line. 2. Energize the klystron oscillator for maximum and measure the input power. 3. Place the transmitting and receiving antenna and measure the received power.

54

TABULATION Transmitted Power Pt = …….. m Watts Received Power

Frequency = ………. GHz

Pr = …….. m Watts

S.No

Angle in Degrees

Power in Clockwise

MODEL GRAPH:

55

Power in Anticlockwise

4. Rotate the receiving antenna and measure the power. 5. Calculate the gain for each reading. 6. Plot the values on the polar sheet. 7. From the plot determine 3dB width /beam width of the parabolid.

CALCULATION

Antenna Gain (G) =

(4πS / λo) × Pr/Pt

Gain in dB = 20 log (G) Where: Pt is transmitted power Pr is received power S is distance between two antennas

λo is free space wavelength

RESULT Thus the gain and beam-width of the pyramidal horn antenna was measured and the polar pattern was also drawn. 56

EXPERIMENTAL SETUP

57

Ex.no.11

RADIATION PATTERN & GAIN OF A PARABOLIC ANTENNA

AIM: To obtain the radiation pattern & gain of a parabolic reflector antenna

APPARATUS REQUIRED: 1. Klystron power supply 2. Reflex Klystron 3. Isolator 4. Frequency meter 5. CRO 6. Variable attenuator 7. Horn antennas 8. Parabolic reflector 9. Power Meter

THEORY: A parabolic may be defined as a locus of points which moves in such a way that its distance from a straight line is constant .The open mouth D of the parabola is known as the aperture .The ratio of local length to the aperture is F/D known as F over D. ratio. Its value usually between 0.25 to 0.50, focusing (or) beam for motion action of the parabolic reflector can be under stand by focusing source of radiation at the focus.

58

TABULATION: S.No

Angle in Degrees

Power (dB)

Power (dB)

Clockwise

Anticlockwise

MODEL GRAPH:

59

PROCEDURE: 1.

Setup the equipments as shown in the block diagram and keep the axis of both the antenna in the same axis line.

2.

Switch ON the power supply keeping the knob on the front panel in beam off position.

3.

Wait for few minutes and then change the knob to beam on position.

4.

Set the beam voltage to 260 V by varying beam voltage control knob.

5.

Check the beam current whether it is less than 30 mA.

6.

Tune the frequency meter knob to get a dip on the CRO and note down the frequency directly from the frequency meter.

7.

Now rotate the receiving parabolic antenna clockwise and anti clockwise and note the corresponding power meter reading. Repeat this step in 20 to 50 Steps up to 400 to 500.

8.

Draw the relative power pattern, i.e., Output Vs Angle.

RESULT: Thus the radiation pattern of parabolic reflector antenna and its gain was obtained.

60

EXPERIMENTAL SETUP:

61

Ex.No: 12

IMPEDANCE MEASUREMENT BY SLOTTED LINE METHOD

AIM To measure an unknown impedance using the slotted line and verify it by using smith chart. EQUIPMENT REQUIRED Klystron tube 2K25,Klystron power supply skps-600,Klystron mount –XM-251,Isolator XI 621,Frequency meter XF10,Variable attenuator XA520,Slotted line XS565,Tunable probe XP655,VSWR meter,Waveguide stand SU535,Triner XT441,Movable short THEORY The impedance at any point on a transmission line can be written in the form R+jX for comparison SWR can be calculated as S = 1+| R| / 1-|R|, where, reflection co-efficient R = (Z-Z0) / (Z+Z0), Z0 is the characteristics impedance of waveguide at operating frequency. The unknown device is connected to the slotted line and the position of one minima is determined. The unknown device is replaced by a movable short to the slotted line. Two successive minima positions are noted. The choice of the difference between minima position will be guide wave length. One of the minima is used as reference for impedance measurement. To find the difference of the reference minima and minima position obtained from unknown load. Let it be „d‟ take a smith chart, taking 1 as centre , draw a circle of radius equal to s0.mark a point on the circumference of smith chart towards load at a distance equal to d / λg. PROCEDURE 1. Set the equipments as shown in figure. 2. Set up the variable attenuator at minimum position. 3. Keep the knob of klystron power supply as bellow i. Mod switch – AM ii. Beam Voltage knob- Fully anticlockwise. iii. AM amplitude – around fully clockwise iv. AM freq. knob - around mid position. 4. Switch On the klystron power supply and cooling fan. 5. Connect the matched load to the slotted section and obtain the dip frequency in the CRO tuning the frequency meter. 62

63

6. Remove the matched load and connect the movable short with the slotted section and move the slotted section towards load/generator and note down the successive minima‟s distances. 7. From the successive minima distances calculate the guide wave length λ g.

λg= 2 ( X1 ~ X2),

where X1& X2 are the distances of two successive minima‟s of short circuit. 8. Remove the movable short and connect the Horn antenna as load i. (unknown impedance) and move the slotted section towards ii. load/generator and note down the successive minima‟s distances. 9. From the successive minima distances calculate dmin.

dmin= ( d1-d2), where d1& d2 are the

distances of two successive minima‟s of Horn Note down the maximum and minimum amplitude and calculate the VSWR (S). S = Vmax/ Vmin 10. From the above readings calculate the unknown impedance and verify the result by using the Smith chart. 11. The calculation of unknown impedance: i.

Magnitude of reflection co-efficient |Γ| = (S-1)/(S+1)

ii.

Phase constant β = 2π/λg (radians)

iii.

Angle of reflection co-efficient θ = π +2βdmin (radians)

iv.

Reflection co-efficient = |Γ| еjθ

v.

Characteristics impedance of waveguide Z0= η(λg/ λ0) Ω

vi.

Load impedance ZL = Z0 * {(1+Γ)/ (1-Γ)} Ω

vii.

Normalized Load impedance = ZL/Z0.

RESULT Thus the unknown load impedance was measured using slotted line method and verified

64

65

Ex. No: 13 MEASUREMENT OF NUMERICAL APERTURE OF OPTICAL FIBER OBJECTIVE: The objective of this experiment is to measure the numerical aperture of the plastic fiber provided with the kit using 660nm wavelength LED. THEORY: Numerical aperture refers to the angle at which the light incident on the fiber end is totally internally reflected and is transmitted properly along the fiber. The cone formed by the rotation of this angle along the axis of the fiber is the cone of acceptance of the fiber. The light ray should strike the fiber end within its cone of acceptance; else it is refracted out of the fiber core. CONSIDERATIONS IN A MEASUREMENT: 1) It is very important that the optical source should be properly aligned with the cable & the distance from the launched point & the cable be properly selected to ensure that the maximum amount of optical power is transferred to the cable. 2) This experiment is best performed in a less illuminated room. EQUIPMENTS: FCL-01 1 meter fiber cable NA JIG (Precision Jig No.1) Ruler Power Supply (Use only the one provided)

NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1) 2) 3) 4) 5) 6) 7)

Make connections as shown in figure. Connect the power supply cables with proper polarity to FCL-01 Kit. While connecting this, ensure that the power supply is OFF. 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. Keep the jumpers JP1, JP2 & JP4 on FCL-01 as shown in figure. Keep switch S2 in VI position on FCL-01. Switch ON the power supply. 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. 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.

66

TABULATION: Sr. No

MR in cm

PN in cm

Radius (r) in Distance (d) in NA= r / (d2 + r2 ) cm cm

1.

1.3

1.3

0.65

0.7

0.68

2.

1.5

1.5

0.75

0.9

0.64

3.

1.7

1.7

0.85

1.2

0.578

4.

1.9

1.9

0.95

1.4

0.561

5

2.1

2.1

1.05

1.8

0.503 Mean NA

SAMPLE CALCULATION MR=1.3 PN=1.3 r= (MR+PN)/4= (1.3+1.3)/4 r = 0.65 cm d = 0.7 cm NA = r / (d2 + r2 ) = 0.65/√ 0.72 +0.652

NA= 0.68

67

: 0.592

8) 9) 10) 11)

Observe the bright red light spot on the screen by varying Intensity pot P3 and Bias pot P4. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN as indicated in the figure1. Mean radius is calculated using the following formula r = (MR+PN) / 4 Find the numerical aperture of the fiber using the formula NA = sin max = r / (d2 + r2) Where fiber.

max

is the maximum angle at which the light incident is properly transmitted through the

Result: Thus the numerical aperture of the fiber cable is measured and it is NA = _________

68

69

Ex.No: 14 MEASUREMENT OF LOSSES IN THE FIBER OBJECTIVE: The objective of this experiment is to measure the following losses in the fiber. 1. Propagation loss 2. Bending loss 3. Connector loss EQUIPMENTS: FCL-01 & FCL-02 1 & 3 meter fiber cable 0.5 meter connectorized fibers Patch chords Power supply 20 MHz Dual Channel Oscilloscope

THEORY: Optical fibers are available in different variety of materials. These materials are usually selected by taking into account their absorption characteristics for different wavelengths of light, in case of optical fiber, since the signal is transmitted in the form of light, which is completely different in nature as that of electrons, one has to consider the interaction of matter with the radiation to study the losses in the fiber. Losses are introduced in the fiber due to various reasons. As light propagates from one end of the fiber end to another end, part of it is absorbed in the material exhibiting absorption loss. Also part of the light is reflected back or in some other direction from the impurity particles in the material contributing to the loss of the signal at the other end of the fiber. In general terms it is known as propagation loss. Plastic fiber has the higher loss of the order of 180dB/km.Whenever the condition for angle of incidence of the incident light is violated the losses are introduced due to refraction of light. This occurs when the fiber is subjected to bending. Lower the radius of curvature more is the loss. Another loss is due to the coupling of fiber at LED and Photo detector ends. When light travels down optical fibers, some of the light is absorbed by the glass or plastic. When designing the optical fiber, you need to know the size of this loss to calculate the maximum distance the signal will travel.

70

TABULATION: S.No

Bending diameter in cm

Signal strength (No of LED’s that glow)

1 2 3 4 5 6 7

71

A. MEASUREMENT OF PROPAGATION LOSS PROCEDURE: 1. Make connections as shown in figure. Connect the power supply cables with proper polarity to FCL-01& FCL02.Ensure that supply is OFF. 2. Keep the jumpers JP1, JP2, JP3 AND JP4 on FCL-01. 3. Keep the jumpers JP1 & JP2 on FCL02. 4. Keep switch in the VI position. 5. Switch ON the Power supply 6. Slightly unscrew the cap of LED. Do not remove the cap from the connector. Once the cap is loosened, insert the 1 meter cable into the cap. Now tighten the cap by screwing it back. 7. Now rotate the optical power control pot P3 in FCL-01 in anti-clockwise direction. This ensures the minimum current flow through LED. 8. Slightly unscrew the cap of photo diode SFH 250V. Do not remove the cap from the connector once the cap is loosened; insert the 1 meter cable into the cap. Now tighten the cap by screwing it back. 9. Keep switch SW1 in the signal strength position in FCL02 10. Connect he output of photo diode detector post OUT to post IN of the signal strength indicator block. 11. 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. 12. 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 a longer 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. 13. Now remove the 1 meter fiber and insert 3 meter fiber. 14. What reading do you get? Loss in optical fiber systems is usually measured in dBs. Loss of fiber itself is measured in dBs per meter. Subtract the length of the short fiber from the length of the long fiber to get the difference in the fiber lengths (3m-1m). The extra length of two meters is what created the extra loss you measured. Then take the signal strength reading you obtained for the loss of the long fiber and convert it to dB using the eq.1. Finally divide the dB reading by the length to get the loss in dB per meter. Equation 1.0: Power =10 log (p2/p1) dB =10 log (8/6) dB =1.25 dB P2=reference reading by 1 meter fiber. P1=reading obtained after replacing 3 meter fiber. For example your signal strength reading in 6, and then your loss in dB would be 1.25 dB. Taking 1.25/2 gives 0.625 dB per meter.

72

TABULATION: S.No

Fiber cable type

1.

1 meter fiber

2.

0.5 meter connectorized fibers

Signal strength

73

The reason for converting to dB per meter is that now in order to find the loss of any length of the fiber you just have to multiply the dB per meter by the length of the fiber. For e.g. If you have a 10 meter long piece of fiber the loss will be 0.625 dB per meter * 10 meters=6.25 dB

B. MEASUREMENT OF BENDING LOSS 1. Keep the connections with 1 meter fiber as per the above procedure. 2. Adjust the transmitter power so that the SIGNAL STRENGTH reading is 8. Now take the portion of the fiber and loop it to match the bends as shown in figure. As you match each bends write down the reading from SIGNAL STRENGTH indicator. What happens when bend in the fiber? Do not bend the fiber too come back to shape. 3. If you were designing the fiber optic communication systems, you would need to know the relationship between the size of the bend and the light loss from the bend. In order to describe this relationship you can measure the loss for different bends and plot them on a graph Do you notice a pattern to the numbers? Do they steadily increase or decrease? Can you predict what the readings would be for other bends?

C.MEASURMENT OF CONNECTOR LOSS 1.Keep the connections with 1 meter fiber as per the aboove procedure . 2.Adjust the transmitter power so that the SIGNAL STRENGTH reading is 8. 3.Remove the 1 meter fiber and insert 0.5 meter connectorized fibers through connecting sleeve .What reading you get on the signal strength ? Now take your loss from this measurment ,say 7.0 dB and subtract it from 8 dB .Your connector loss is then 8.0 dB – 7.0 dB = 1 dB this is actual connector loss.

Result: Thus the propagation loss, bending loss and connector loss is measured for the given fiber optical cable. 74

75

Ex. No: 15 DC CHARACTERISTICS OF FIBER OPTIC LED AND PHOTO DETECTOR OBJECTIVE: To study the characteristics of fiber optic LED and plot the graph of forward current v/s output optical energy and also to study the photo detector response. THEORY: In optical fiber communication system, electrical signal is first converted into optical signal with the help of E/O conversion device as LED. After this optical signal is transmitted through optical fiber, it is retrieved in its original electrical form with the help O/E conversion device as photo detector. Different technologies employed in chip fabrication lead to significant variation in parameters for the various emitter diodes .All the emitters themselves in offering high o/p power coupled into the plastic fiber. Data sheets for LED s usually specific electrical and optical characteristics ,out of which are important peak wavelength of emission ,conversion efficiency ( usually specified in terms of power launched in optical fiber for forward current), optical rise and fall ties which put the limitation on operating frequency),max forward current through LED and typical forward voltage across LED. Photodetectors usually comes in variety of forms like photoconductive transistor type output and diode type o/p. Here also characteristics to be taken into account are response time of the detector which puts limitation on the operating frequency, wavelength sensitivity and responsibility EQUIPMENTS: FCL -01 &FCL -02 1METER FIBER CABLE Patch chords. Jumper to crocodile wires Power supply (use only 1 provided) 20 MHz Dual channel Oscilloscope. Current Meter. Voltmeter NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown in fig connect the power supply with proper polarity to FCL -01 & FCL -02 kits. While connecting this ensures that the power supply is off. 2. Slightly unscrew the cap of LED SFH756V (660 nm). Do not remove the cap from connector. Once the cap is loosened insert the 1 meter fiber into cap. Now tighten the cap by screwing it back. 3. Slightly unscrew the cap of PHOTODIODE .Do not remove the cap from connector. Once the cap is loosened insert the 1meter fiber into cap. Now tighten the cap by screwing it back. 4. Keep the jumper JP1, JP2, JP3& JP4 on FCL-01 as shown in fig 3.1

76

CHARACTERISTICS OF FIBER OPTIC LED & DETECTOR Sr .No

Vf

If

Pi=Vf *If

Po=Pi *1.5%

R=0.8mA*Po/10 μW

(V)

(mA)

(mW)

(μW)

(mA)

I=o/p current (μA)

1.

1.6

2.5

4

4.6

0.368

15

2.

1.65

5

8.25

9.49

0.759

50

3.

1.7

10

17

19.55

1.564

75

4.

1.75

17.5

30.625

35.22

2.818

140

5.

1.8

27.5

49.5

56.92

4.554

190

77

5. 6. 7. 8. 9. 10. 11.

12. 13. 14. 15. 16.

Keep the jumper JP1, JP2, on FCL-02 as shown in fig 3.1 Keep switch S2 in VI position on FCL-01 Connect voltmeter & current meter as per the polarities shown in fig 3.1 Switch ON the power supply Keep the potentiometer P3 in its maximum position. P3 is used to control current flowing through the Led Keep the potentiometer P4 fully clockwise rotation.P4 is used to control bias voltage of LED To get the VI characteristics of LED, rotate P3 slowly and measure fwd current & corresponding fwd voltage. take no of such readings for various current values & plot VI characteristics graph of the LED For each reading taken above, find out the power, which is product of I & V. this, the electrical power supply to the LED. With this efficiency assumed, find out optical power coupled into plastic optical fiber for the each of the reading. plot the graph of fed current v/s o/p optical power of the LED Similarly measure the current at the detector Plot the graph of the Receiver current v/s o/p optical power of the LED Perform the above procedure again all the combination of transmitter & receiver

Vf = Forward voltage of LED SFH 756 If = Forward current of LED SFH 756 Pi = Vf * If (electrical power) Po = Pi*1.15 % (optical power of LED 756.) R = 0.8 mA*PO/ 10μW (Responsively) I =O/p current of photodiode.

Result: Thus the VI characteristic of LED was obtained & the responsivity of photo detector was plotted. Cutin Voltage of LED =1.65V.

78

79

Ex.No. 16 SETTING UP A FIBER OPTIC ANALOG LINK OBJECTIVE: The objective of this experiment is to study an 660nm & 950nm fiber analog link and to study the frequency response of the phototransistor detector. In this experiment you will study the relationship between the input signal and received signal. EQUIPMENTS • Link-B kit with power supply • Patch chords • 20MHz dual channel oscilloscope • 1MHz function generator • 1-Meter fiber cable NOTE: Keep all switch faults in off position. THEORY: Fiber optic links can be used for transmission of digital as well as analog signals. Basically a fiber optic link contains three main elements, a transmitter, an optical fiber, & a receiver. The transmitter module takes the input signal in electrical form & then transforms it into optical (light) energy containing the same information. The optical fiber is the medium which carriers this energy to the receiver. At the receiver, light is converted back into electrical form with the same pattern as originally fed to the transmitter. TRANSMITTER Fiber optic transmitters are typically composed of a buffer, driver, & Optical source. The buffer electronics provides both an electronics connection & isolation between the transmitter & the electrical system supplying the data. The driver electronics provides electrical power to the Optical source in a fashion that duplicates the pattern of the data being fed to the transmitter. Finally the optical source (LED) converts the electrical current to light energy with the same pattern. The LED SFH450V (660nm) supplied with this kit operates outside the visible light spectrum. Its optical output is centered at near infrared wavelength of 950nm. The LED SFH756V(660nm) supplied with this kit operates at the visible light spectrum. Its optical output is centered at wavelength of 660nm. RECEIVER The function of the receiver is to convert the optical energy into electrical form, which is then conditioned to reproduce the transmitted electrical signal in its original form. The detector SFH350V(photo transistor detector) used in the kit has s transistor type output. The parameters usually considered in the case of detector are its responsivity at peak wavelength & response time. SFH350V(photo transistor detector) has responsivity of about 0.8ma/10uW at 660nm. But its response time is quite large & thus has lower bandwidth of about 300KHz.

80

81

When optical signal falls on the base of the transistor detector, proportional current flows through its emitter generating the voltage across the resistance connected between the emitter & ground. This voltage is the duplication of the transmitted electrical signal, which can be amplified.

PROCEDURE • Make connections as shown in FIG.1.1. Connect the power supply cables with proper polarity to Link-b kit. While connecting this, ensure that the power supply is OFF. • Keep switch SW8 towards TX position. • Keep switch SW9 towards TX1 position. • Keep jumper JP5 towards +12V position. • Keep jumpers JP6, JP9, JP10 shorted. • Keep jumper JP8 towards sine position. • Keep intensity control pot P2 towards minimum position. • Switch ON the power supply. • Feed about 2Vpp sinusoidal signal of 1KHz from the function generator to the IN post of analog buffer. • Connect the output post OUT of analog buffer to the post TX IN of transmitter. • Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the one-meter fiber into the cap. Now tighten the cap by screwing it back. • Connect the other end of the fiber to detect the SFH350V (photo transistor detector) very carefully as per the instructions in the above step. • Observe the detector signal at post ANALOG OUT on oscilloscope as shown in FIG 1.2. adjust intensity control pot P2 optical power control potentiometer so that you receive signal of 2Vpp amplitude. • To measure the analog bandwidth of the phototransistor, vary the input signal frequency and observe the detected signal at various frequencies. • Plot the detected signal against applied signal frequency and from the plot determine the 3dB down frequency. • Repeat the same procedure as above for second transmitter SFH450V by making the following changes. Analog bandwidth of SFH350 for TX1 SFH756 is about 300KHz while for TX2 SFH450 is below 300KHz. • Keep switch SW9 towards TX2 position. • Keep jumper JP7 towards +12V position.

Result: Thus fiber optic analog link has been established to transfer the data 82

83

Ex. No :17

SETTING UP A FIBER OPTIC DIGITAL LINK

OBJECTIVE: The objective of their experiment is to study a 660nm & 950nm Fiber Optic Digital Link. Here you will study how digital signal can be transmitted over fiber cable &reproduced at the receiver end. EQUIPMENTS: 1.

Link B Kit with power supply

2.

Patch chords

3.

20Mhz Dual Channel Oscilloscope

4.

1-Mhz Function generator

5.

1-Meter Fiber Cable

THEORY: In the Experiment No.1 we have seen how analog signals can be transmitted & received using LED, Fiber& Detector can be configured for the digital applications to transmit binary data over Fiber. Thus the basic elements of the link remain the same even for digital application. Transmitter: LED, digital DC coupled transmitters are one of the most popular varieties due to their ease of fabrication. We have used a standard TTl gate to drive a NPN transistor, which modulates the LED SFH450V of SFH 756V source. (turns it ON & OFF). Receiver: SFH-551V is a digital optodetector. It delivers a digital output, which can be processed directly with little additional external circuitry. The integrated circuit inside the SFH551V optodetector comprises the photodiode device, a trans-impedance amplifier, a comparator and a level shifter. The photo diode converts the detected light into a photocurrent. With the aid of an integrated light emanating from the plastic Fiber is almost entirely focused on the surface of the diode. At the next stage the trans-impedance amplifier converts the photocurrent into a voltage In the comparator, the voltage is compared to the reference voltage. In over to ensure good synchronism between the reference and the trans-impedance output voltage, the former is derived from a second circuit of a similar kind, which incorporates a “blind” photodiode. 84

85

The comparator derives a level shifter with an open collector output stages. Here a catch diode (similar to Schottky-TTL) prevents the saturation of the output transistor, thus limiting the output voltage to the supply voltage. NOTE: Keep All the Switch Faults in OFF Position. PROCEDURE: •

Make connections as shown in the fig.2.1. Connect the power supply cables with proper polarity to Link-b kit. While connecting this, make sure that the power supply is OFF.

•

Switch on the power supply.

•

Feed TTl square wave signal of 1Khz from the function generator to the IN post of Digital Buffer.

•

Connect the output post OUT of Digital Buffer to the post TX IN of transmitter.

•

Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the counter. Once the cap is loosened, insert the One Meter Fiber into the cap. Now tighten the cap by screwing it back.

•

Connect the other end of the fiber to detector SFH551V very carefully as per the instructions in above step.

•

Observe the detected signal at the post TTL OUT on oscilloscope as shown in fig.2.2.

•

To measure the digital bandwidth of the phototransistor, vary the input signal frequency and observe the detected signal at various frequencies.

•

Determine the frequency at which the detector stops recovering the signal.

•

This determines the maximum bit rate on the digital link.

•

Keep switch SW9 towards TX2.

•

Keep jumper JP7 towards +5V position.

•

Repeat the same procedure above the second transmitter SFH4501V by making the following changes.

•

The digital bandwidth of SFH551 for TX1 SFH756 is 32Mhz &for SFH450 it is 1MHz.

Result: Thus fiber optic Digital link has been established to transfer the data .

86

87

Ex.No:18

STUDY OF EYE PATTERN

OBJECTIVE: The objective of this experiment is to study eye pattern using fiber optic link. EQUIPMENTS: •

Link-B kit with power supply

•

Patch chords

•

1 Meter fiber cable

•

20MHz dual channel oscilloscope

NOTE: keep all switch faults in OFF position.

THEORY: The eye-pattern technique is a simple but powerful measurement method for assessing the datahandling ability of a digital transmission system. This method has been used extensively for evaluating the performance of wire systems and can also be applied to optical fiber data links. The eye-pattern measurements are made in the time domain and allow the effects of waveform distortion to be shown immediately on an oscilloscope. An eye-pattern can be observed with the basic equipment shown in fig.12.1. The output from a pseudorandom data pattern generator is applied to the vertical input of an oscilloscope and the data rate is used to trigger the horizontal sweep. This results in the type of pattern shown in fig.12.2, which is called the eye pattern because the display shape resembles a human eye. To see how the display pattern is formed, consider eight possible 4-bit-long NRZ combinations. When these sixteen combinations are superimposed simultaneously, an eye pattern as shown in fig.12.2 is formed. To measure system performance with the eye-pattern method, a variety of word patterns should be provided. A convenient approach is to generate a random data signal, because this is the characteristic of data streams found in practice. This type of signal generates ones and zeros at a uniform rate but in a random manner. A variety of pseudorandom pattern generators are available for this purpose. The word pseudorandom means that the generated combination or sequence of ones and zeros will eventually repeat but that it is sufficiently random for test purposes. A pseudorandom bit sequence comprises four different 2-bit-long combinations, eight different 3-bit-long combinations, sixteen different 4-bit-long combination and so on(that is sequences of different N-bit-long combination) up to a limit set by the instrument. After this limit has been generated, the data sequence will repeat. A great deal of system performance information can be deduced from the eye-pattern display. To interpret the eye-pattern, follow the procedure ahead.

88

89

PROCEDURE: •

Make connections as shown in figure. Connect the power supply cables with proper polarity to Link-B kit. While connecting this, ensure that the power supply is OFF.

•

Keep switch SW7 as shown in figure to generate PRBS signal.

•

Keep switch SW8 towards TX position.

•

Keep switch SW9 towards TX1 position.

•

Keep the switch SW10 to EYE-PATTERN position.

•

Select PRBS generator clock ay 32KHz by keeping jumper JP4 at 32K position.

•

Keep jumper JP5 towards +5V position.

•

Keep jumper JP6 shorted.

•

Keep jumper JP8 towards TTL position.

•

Switch ON the power supply.

•

Connect the post DATA OUT of PRBS generator to the IN post of digital buffer.

•

Connect OUT post of digital buffer to TX IN post.

•

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

•

Slightly unscrew the cap of RX1 photo transistor with TTL logic output SFH551V. 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.

•

Connect CLK OUT of PRBS generator to EXT.TRIG. of oscilloscope.

•

Connect detected signal TTL OUT to vertical channel Y input of oscilloscope. Then observe EYE PAATERN by selecting EXT.TRIG KNOB on oscilloscope as shown in figure. Observe the eye pattern for different clock frequencies. As clock frequency increases the EYE opening becomes smaller.

Result : Thus system performance was measured with the eye - pattern.

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MEASUREMENT OF ATTENUATION

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MEASUREMENT OF ATTENUATION IN FIBERS

Ex.No: 19 AIM

The aim of the experiment is to measure the attenuation in the optical fiber using a laser source. EQUIPMENT REQUIRED i)

Fiber Optic Trainer Kit

ii)

Optical fiber cable

iii)

JIG

THEORY ATTENUATION The power coming out of the fiber should be less than the power entering it called attenuation. If the fibre should be less than communication attenuation is decrease in the light power or intensity during light propagation along a fiber. Here the light loss caused by the violation of the total internal reflection concept due to improper fibre coupling called coupling loss. PROCEDURE 1. Establish the analog link, set the sinusoidal signal amplitude and frequency to 1VPP and 1KHz respectively using variable control POTs on VOFT-06 unit connect I/O3 output with oscilloscope using BNC –BNC cable 2. Connect the 1m fiber cable between optical Tx1 an optical Rx1. Turn GAIN control POT so as to make 4VPP at the receiver unit 3. Replace a 3m fiber cable instead of 1m fiber cable. Note down output signal amplitude level without altering receiver gain and input signal amplitude and find out attenuation los for 3m fiber cable as α=-10log(Vo/Vin)

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TABULATION: Fiber Length

Vin amp

α=-10log(Vo/Vin)

Vout time

amp

93

Time

RESULT Thus the study of attenuation for the optical fiber was performed.

94

95

MODE CHARACTERISTICS OF FIBER

Ex.no:20

AIM To study the mode characteristics of single mode fiber APPARATUS REQUIRED 1. Advanced fiber optic communication trainer link 2. 1m and 3m fiber cable 3. CRO THEORY In the single mode fiber there are actually two independent degenerate propagation modes. These modes are very similar but their polarization planes are orthogonal. Those may be chosen arbitrarily as their horizontal and vertical polarization either one of these polarization modes constitute the fundamental mode. Suppose we arbitrarily choose one of the modes to have its traverse electric field polarized along the x direction and the other independent orthogonal nodes to be polarized in y direction.

PROCEDURE 1. Make the jumper connections for 660nm wavelength source, connect a 1m fiber cable between optical TX1 and NA setup 2. Insert the fiber cable in numerical aperture setup 3. Now a circular red spot is shown in graph attached with the base of NA setup. Measure the circle in horizontally and vertically and find out mean radius of circular spot as, γ=(DE+BC)/4 4. Find out the numerical aperture for a distance as NA = r/(sqrt(d2+r2)) Where d is a distance in cm,r is mean radius of circular spot 5. The refractive index of the cladding for a given fiber is 1.402, now find out the refractive index of the core using the formula NA =sqrt(n12- n22) Where n1 is refractive index of core,n2refractive index of cladding and NA is numerical aperture of fiber 6. Calculate V- number as follows V=(

)

Where d is the diameter of core, λ is the wavelength of source 7. Now calculate the number of modes,

N=V2/2 96

97

RESULT Thus the mode characteristics of single mode fiber was studied and verified. 98