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Mw&oc manual

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The document outlines the contents of microwave and optical fiber lab experiments, including experiments measuring characteristics of devices like Gunn diodes, klystrons, and optical fibers as well as calibrating attenuators and measuring antenna patterns. It also provides descriptions of the components and functioning of an optical fiber trainer kit, including fiber preparation and characteristics of transmitters, receivers, and other devices used in optical communication experiments.

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Contents 1.Microwave lab experiments 1. GUNN diode characteristics. 2. Reflex Klystron Mode Characteristics 3. VSWR and Frequency measurement. 4. Verify the relation between Guide wave length, free space wave length and cut off wave length for rectangular wave guide. 5. Measurement of E-plane and H-plane characteristics. 6. Directional Coupler Characteristics. 7. Unknown load impedance measurement using smith chart and verification using transmission line equation. 8. Measurement of dielectric constant for given solid dielectric cell. 9. Magic-Tee characteristics. 10. Antenna Pattern Measurement. 11. Calibration of attenuator. 2.Optical Experiments: Familiarisation of optical fibre trainer kit 1. Measurement of Numerical Aperture of a fiber, after preparing the fiber ends. 2. Measurement of attenuation per unit length of a fiber using the cutback method. 3. Preparation of a Splice joint and measurement of the splice loss. 4. Characteristics of LASER diode 6. Characteristics of fibre optic LED and photodetector 7. Characteristics of Avalanche Photo Diode (APD) and measure the responsivity. 8. Measurement of fiber characteristics, fiber damage and splice loss/connector loss by Optical Time Domain Reflectometer (OTDR) technique.
INTRODUCTION TO OPTICAL FIBRE INTRODUCTION Before fibre optics came along the primary means of real time communication was electrical in nature. It was accomplished using copper wire or by transmitting electromagnetic waves. Fibre optics changed that by providing a means of sending information over significant distances – using light energy. It is very reliable and cost effective. Light as utilized for communication has a major advantage because it can be manipulated at significant higher frequencies that electrical signals can. For example, a fibre optic cable can carry up to 100 million times more information than a telephone line. It has low energy loss and wider bandwidth. Principle of Operation Light travels in straight line through most optical materials, but that’s not necessarily the case at the junction of two materials of different refractive indices. In the fig. the light ray travel through air actually is bent as it enters the water. Amount of bending depends on the refractive indices of the two materials involved and also on the angle of incoming ray of light. The relationship between the incident and refracted ray is given by Snell’s law. n1.sin 1 = n2 . sin 2 n1, n2 refractive indices of initial and secondary materials. 1, 2 incident and transmitted angles. Snell’s law says that reflection of light cannot take place when the angle of incidence grows too large. If the angle of incidence exceeds a certain value, light cannot exit. i.e. reflected. The angle that is reflected is equal to angle of incidence. This phenomenon is called total internal reflection. It is what keeps light inside an optical fibre.
Types of Optical Fibre The simplest one consists of two concentric layers of transparent materials. The core transports the light. The cladding must have a lower refractive index than the core. Optical fibre is generally made from either plastic or glass. The plastic fibre is generally limited to uses involved in distances of less than 100 mtrs because of high loss. Glass fibre has very low attenuation, hard to cut and more expensive. The core fibre is made of silica dopped with impurities. The cladding is typically made from pure silica. The outer buffer coating is a plastic cover. Single mode v/s Multimode The term multimode means that the diameter of the fibre optic core is large enough to propagate more than one mode. So the pulse that is transmitted down, the fibre tends to become stretched over distance. This modal dispersion. Single mode fibre is designed to propagate only one mode of light. So it is not affected by modal dispersion and has higher bandwidth capacity. They are more sensitive to back reflections from connectors and sharp cable bends. Advantages of fibre optics Much greater Bandwidth. Immunity to electrical disturbances ground loops, cross talks etc:-. In addition no emi. Much lighter. Better in hostile environment, not affected as much by temperature, water etc:-. Low transmission loss. Better security as it is not possible to simply bridge onto the facility and monitor the traffic.
FAMILIARISATION OF FIBER OPTIC TRAINER KIT Fibre Optic Trainer Kit Link – A The purpose of FIBRE OPTIC TRAINER KIT is to provide an experience on the various fibre optic and digital communication technique. The experimental setup includes Trainer Kit Link A Plastic Fibres of 1 mtr & 3 mtr length. NA JIG Steel Rule Speaker and Microphone Power Supply Serial Cables Shorting Link Jumper to crocodile Optical Fibre Preparation Instructions Cut off the ends of the cable with a single edge razor or sharp knife at precise 90 angle. Wet the polishing paper with water or light oil and place it on a flat surface. Hold the optical fibre upright at right angle to the paper and polish the fibre tip with a gentle ―figure 8‖ motion. Using a 18 gauge wire stripper, remove 3mm of the jacket from the end of the fibre. Do not nick the buffer in the process to minimize light loss.
Function Generator The integrated circuit IC L 8038 generates sine wave and square wave forms at their respective posts. The frequency is variable ranging from 1 Hz to 100 KHz. The frequency of since wave is controlled by pot and capacitors. The frequency range could be selected with help of range selector switch. The presets adjust the symmetry of the sine signal. The amplitude of sine wave is controlled by pot. Buffer IC 74HC04 is used as TTL Buffer. IC’s IC LF357(U4) and IC LF 357(U5) are collectively used as ANALOG Buffer. Fibre Optics Buffer The transmitter module takes the input signal in electrical form and then transforms it into optical (light) energy containing the same information. The optical fibre is the medium which carries this energy to the receiver. Transmitter – LED, digital, DC coupled transmitters are one of the most popular variety due to their ease of fabrication. A standard TTL gate to drive a NPN transistor, which modulates the LED SFH450v source (Turns it ON and OFF). Fibre optic transmitters are typically composed of a buffer, driver and optical source. The buffer electronics provides both an electrical connection and isolation between the transmitter and the electrical system supplying the data. The driver electronics provides electrical power to the optical source in a fashion that duplicates the pattern of data being fed to transmitter. Finally the optical source (LED) converts the electrical current to light energy with same pattern. The LED SFH450v supplied with link – A operated outside the visible light spectrum. Its optical source (LED) output is centred at near infrared wavelength of 950nm. The emission spectrum is broad so a faint red glow can usually be seen when LED is on a dark room. The LED used in link A is coupled to transistor driver in common emitter mode. In the absence of input signal half of the supply voltage appears at the base of transistor. This biases the transistor near midpoint within the active region for linear applications. The LED emits constant intensity of light at this time. When the signal is
applied to the amplifier it overrides the dc level to the base of transistor which causes the Q point of transistor to oscillate about the midpoint. So the intensity of LED varies about its previous constant value. The variation in the intensity has linear relation with input electrical signal. NPN transistor (Q 2) emitter is modulated by changing potentiometer P4 value. Optical signal is then carried over by the optical fibre. Another source used is LED 756v at 660nm wavelength which is visible red light source. A standard TTL drives NPN transistor (Q2), which modulates the LED SFH756v source (turns it OFF and ON). Selection between different sources is done through jumpers provided onboard. Fibre Optics Receiver At the receiver, light is converted back into electrical form with the same pattern as originally fed to the transmitter. The function of the receiver is to convert the optical energy into electrical form, which is then conditioned to reproduce the electrical signal transmitted in its original form. The detector SFH250v use in Link A has a diode type output. The parameters usually considered in case of detector are its responsivity at peak wavelength and response time. SFH250v used in link A has responsivity of about 4 per 10 W of incident optical energy at 950 nm and it has rise & fall time of 0.01 S. PIN photodiode is normally reverse biased. When optical signal falls on the diode, reverse current start to flow, thus diode acts as closed switch and in the absence of light intensity it acts as open switch. Since PIN diode usually has low responsivity, a transimpedance amplifier is used to convert this reverse current into voltage formed around IC LF356. This voltage is then amplified with help of another amplifier circuit IC LF 357(U13) and IC LF 357(U20). This voltage the duplication of transmitted electrical signal. These are various methods to extract digital data. Usually detectors are of linear nature. Photo detector having TTL type output (SFH 551/V) consists of integrated photodiode, transimpedance amplifier and level shifter.
EXPT N0. 1. STUDY OF NUMERICAL APERTURE OF OPTICAL FIBRE Aim The objective of this experiment to measure the numerical aperture of the plastic fibre provident with the kit using 660nm wavelength LED. Theory Numerical aperture refers to the maximum angle at which the light incident on the fiber end is totally internally reflected and is properly along the fiber. The cone formed by the rotation of this angle along the axis of the fiber is the cone acceptance of the fiber. The light ray should strike the fibre end within its cone of acceptance; else it is reflected out of the fibre cone. Considerations in a NA Measurement 1. It is very important that optical source should be properly selected to ensured that maximum amount of optical power is transferred to the cable. 2. This experiment is best performed in a less illuminated room. Equipments Required Kit C (Fiber link – A), 1 meter fibre cable, NA J/G, Steel Ruler, Power Supply. Procedure 1. Slightly unscrew the cap of LED SFH756 V (660nm). Do not remove cap from connector. Once the cap is loosened, insert the fibre into the cap. Now tight the cap by screwing it back.
2. Connect the power supply cables with proper polarity to kit. While connecting this, ensure that power supply is OFF. Do not apply any TTL signal from Function Generator. Make the connections from the figure. 3. Keep pot P3 fully clockwise position and P4 fully anticlockwise position. 4. Switch on the power supply. 5. Insert the other end of the fibre into the numerical aperture measurement jig. Hold the white sheet facing fibre. Adjust the fibre such that its cut face is perpendicular to the axis of the fiber. 6. Keep the distance of about 10mm between the fibre tip and screen. Gently tighten the screw and thus fix the fibre in the place. 7. Now adjust pot P4 fully clockwise position and observe the illuminated circular path of light on the screen. 8. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN indicated in fig. 9. Mean radius is calculated using formula r = (MR+PN)/4. 10. Find the numerical aperture of fibre using the formula NA = Sin max = r/ where max is maximum angle at which light incident is properly transmitted through the fibre. 11. Using the formulae V number = π d NA calculate V number λ Result The numerical aperture and V number of the plastic fibre is calculated using 660nm wave length LED. Numerical Aperture = V number =
EXPT NO. 4 CHARACTERISTICS OF OPTICAL FIBRE LED AND DETECTOR Aim To study the VI characteristics of fibre optic LED’s. Theory In Fibre optic communication system, electrical system is first converted into optical signal with help of E/O conversion device as LED. After this optical signal is transmitted in its original electrical form with help O/E conversion device as photo detector. Different technologies employed in chip fabrication lead to significant variation in parameters for various emitter diodes. All emitters distinguish themselves in offering high output power coupled into plastic fibre. Data sheets for LEDs usually specify electrical and optical chara out of which are important peak wavelength of emission, conversion efficiency, optical rise and fall times which put the limitation of operating frequency, maximum forward current through LED and typical forward voltage across LED. Photo detectors usually come in variety of forms like photoconductive, photovoltaic, transistor type output and diode type output. Here also characteristics to be taken into account are response time of detector which puts the limitation on the operating frequency. Wavelength sensitivity and responsivity. Procedure (A) CHARACTERISTICS OF FIBER OPTIC LED 1. Make the jumper and switch settings as shown in jumper diagram. keep Pot P4 fully in clockwise position. 2. Connect the ammeter with jumper connecting wires in jumpers JP3 as in diagram. 3. Connect the voltmeter with jumper wires to JP5 and JP2 at positions as in diagram.
4. Switch on power supply. Keep potentiometer P3 in its minimum position (fully anticlockwise position), P4 id used to control biasing voltage of the LED. To get the VI characteristics and optical power of SFH 756v LED. Graph for VI characteristics of SFH 756v LED. 5. For each reading taken above, find out the power, which is product of I and V. This is the electrical power supplied to LED specifies optical power supplied to LED specifies optical power coupled into plastic fibre when forward current was 10 mA as 200 W. This means that the electrical power at 10 mA current is converted to 200 W of optical energy. Hence the efficiency of LED comes out to be approx 1.15% 6. With this efficiency assumed, find out optical power coupled into plastic optical fibre for each of the reading in step 4. Plot the graph of forward current v/s output optical power of LED SFH 756v. 7. Repeat the above experiment by using SFH 450v (950nm) LED. Graph for VI characteristics of SFH 756v LED is shown. The figure shows graph of forward current v/s output optical power of LED SFH 450v. (B) CHARACTERISTICS OF DETECTOR 1. Make the jumper and switch settings as shown in the jumper diagram fig keep pot P4 in fully clockwise position. 2. Connect the ammeter with the jumper connecting wires in jumpers JP 7. 3. Connect 1 metre fibre optic cable between LED (TX 1) SFH 756v and detector (RX 1) SFH 250v 4. Switch on the power supply and measure corresponding forward current of LED (TX 1) as per table. Measure the current flowing through the detector (RX 1) SFH 250v at corresponding optical power output (Normally in A). 5. We can observe that as incident optical power on detector increases, current flowing through the detector increases.
Result The VI characteristics of fibre optic LED and detector are plotted.
EXPT NO. 2 REFLEX KLYSTRON REPELLER MODE CHARACTERISTICS Aim To study characteristics of the reflex klystron tube. Equipments Required Klystron power supply, Klystron tube with Klystron mount, Isolator, Frequency meter, Variable attenuator, detector mount, wave guide stand, VSWR meter and oscilloscope BNC cable. Theory The reflex Klystron makes use of velocity modulation to transform a continuous electron beam into microwave power. Electrons emitted from the cathode are accelerated and passed through the positive resonator towards negative reflector which retards and finally reflects the electrons and the electrons turn back through the resonator. Suppose an RF field exist between the resonators the electrons travelling forward will be accelerated or retarded as the voltage at the resonator changes in amplitude.
The accelerated electrons leave the resonator at the increased velocity and the retarded electrons leave at the retarded velocity. The electrons leaving the resonator will need different time to return due to change in velocities. As a result returning electrons group together in bunches, as the electron bunches pass through resonator, they interact with voltage at resonator grids. If the bunches pass the grid at such a time that the electrons are slowed down by the voltage be then energy will delivered to the resonator and Klystron will oscillate. The frequency is primarily determined by the dimensions of resonant cavity. Procedure Setup Set up the components and equipments as shown keep position of variable attenuator at maximum attenuation position. Set the mode selector switch to FM MOD position and FM amp and FM frequency knob at mid position, keep beam voltage control knob fully anticlockwise and reflector voltage knob to fully clockwise with meter switch to OFF position. Keep the time/division scale of oscilloscope around 100 Hz frequency measurement and v/division to lower scale Switch ON Klystron power supply and oscilloscope. Change the meter switch of Klystron power supply to beam voltage position and set beam voltage to 300v by voltage control knob. Keep amplitude knob of FM modulator to maximum position and rotate reflector voltage anticlockwise to get modes.
Result The characteristics of Reflex Klystron is obtained. `
EXPT NO. 1 GUNN DIODE CHARACTERISTICS Aim To study the V – I characteristics of gunn diode. Equipment Required Gunn Oscillator, Gunn power supply, PIN modulator, Isolator, Frequency meter, Detector mount, Wave guide stands, SWR meter. Theory Gunn oscillator is based on negative differential conductivity effect in bulk semiconductors which has two conduction bands minima separated by an energy gap. When this high field domain reaches the anode it disappears and domain is formed at the cathode and starts moving towards anode. In Gunn oscillator, gunn diode is placed in a resonant cavity. Although the Gunn oscillator can be amplitude modulated, separate PIN modulators through PIN diode for square wave modulation are used. A measure of the square wave modulation capability is the modulation depth i.e, the output ratio between ON and OFF state. Procedure Set the components and equipments. Initially set the variable attenuator for maximum attenuation. Keep the control knob of gunn power supply as Meter switch : OFF, Gunn bias knob : Fully clockwise. Keep the control knob of VSWR meter as below : Meter switch : Normal
Input switch : Low impedance Range db switch : 40 dB Gain Control knob : Fully clockwise Set the micrometer of gunn oscillator for required frequency of operation. Switch ON gunn power supply VSWR meter and cooling fan. Turn the meter switch to voltage position. Measure the gunn diode current corresponding to the variations in gunn voltage; do not exceed the bias voltage above 10 volts. Plot voltage and current reading as on graph. Measure the threshold voltage which corresponds to maximum current.
Result The characteristics of gunn oscillator have been obtained VTH =
EXPT NO. 3 VERIFY RELATIONSHIP BETWEEN λo, λg AND λc Aim To determine the frequency and wavelength in rectangular waveguide working in TE10 mode. Equipments Klystron power supply, Klystron Tube, Isolator, Fraquency meters, Variable attenuator, Slotted section, tunable probe, wavelength stand, VSWR meter, matched termination. Theory Mode represents in waveguide as either TE min/TM min. Where TE - Transverse Electric TM - Transverse Magnetic m - number of half wavelength in broader section n - number of half wavelength in shorter section = (d1 – d2) Where d1, d2 are the distances between 2 successive maxima / minima. For TE10 mode. = , m = 1 in TE10 mode. - Free space wavelength g - Guide wave length - Cutoff wavelength Procedure
Set the components and equipments. Set the variable attenuator at maximum position. Keep the controls of VSWR as follows. Range db : 50 dB Input Switch : Crystal low impedance Meter Switch : Normal position Gain : Mid position Keep the controls of Klystron Power Supply as :- Meter Switch : OFF Mode Switch : AM Beam V knob : Full anticlockwise Reflector voltage : Fully clockwise AM Knob : Around fully clockwise
AM Frequency : Around mid position Switch on Klystron Power Supply VSWR meter. Turn the meter switch to bean voltage position and repeller voltage as 300v and current 15-20 mA. Adjust repeller voltage to get some deflection in VSWR meter. Tune the plunger of Klystron for maximum deflection. Replace the termination of movable short and detune frequency meter. Move tunable probe along with slotted line to get the deflection in VSWR meter. Move probe to next minimum position. i.e. d2. Calculate guide wavelength as twice the wavelength between two successive minima. Calculate frequency using the equation. f= =c Verify with frequency obtained by frequency meter. Obtain and verify the experiment at different frequencies. Result Frequency of the rectangular waveguide is calculated from its guide and cut-off wavelength. The observed frequency is found to be equal to the obtained frequency.
EXPT NO. 3 VSWR & FREQUENCY MEASUREMENT Aim To determine the standing wave ratio and reflection coefficient. Equipments Klystron Power Supply, Klystron tube, VSWR meter, Isolator, Frequency meter, Variable attenuator, Tunable probe, SS tuner. Theory VSWR is the ratio of maximum to minimum voltage along a transmission line, as the ratio of maximum to minimum current. The em field at any point of transmission line may be considered as the sum of two travelling waves. Incident & Reflected waves. The distance between two successive minimum is half the guide wavelength. The ratio of the electric field strength of reflected and incident wave is called reflection between maximum & minimum field strength along the line. VSWR(S) = = EI = incident voltage Er = reflected voltage Reflection coefficient S = = – =
Z = impedance at a point on line Zo = Characteristic impedance Procedure Setup the equipment. Keep the variable attenuator at max position. Keep the VSWR control knob as follows : Range = (40/50) dB Input Switch = Impedance low Meter Switch = Normal Gain = Mid position Keep the control knob of Klystron Power Supply Meter Switch = OFF Mod Switch = AM Beam V knob = Fully anticlockwise Reflector V knob = Fully clockwise Switch ON the Klystron Power Supply, VSWR meter. Turn switch to beam. Tune output by tuning reflector voltage, amplitude and frequency of AM. Move the probe along with slotted line the deflection will change.
Measurement of low & medium VSWR 1. Move probe along with slotted line to maximum deflection in VSWR meter. 2. Adjust VSWR meter gain control knob until meter indicates 1 on SWR scales. 3. Read the VSWR on scale and record it. 4. Repeat the step for change of SS. 5. If VSWR is b/w 7.2 and 10, change the range dB switch to next higher position. Measurement of high VSWR 1. Set the depth of SS tuner slightly more max VSWR. 2. Move probe along slotted line until min is obtain. 3. Adjust VSWR meter gain control knob to read 3dB 4. Move the probe to left till 0 dB is obtained. Note the probe position as d1. 5. Repeat 3 & 4 and move till 0 dB. Note it as d2 Measure the distance b/w two minima. Twice this is waveguide length g. 6. Calculate the SWR as:
SWR = – Result The equipment is setup and the value is setup.
EXPT NO. 10 ANTENNA PATTERN MEASUREMENT Aim To measure the polar pattern of a horn antenna. Equipments Gunn power supply, Gunn oscillator, Frequency meter, Variable attenuator, VSWR meter. Theory The variation pattern of an antenna is a diagram of field strength (or) more often the power intensity as a function of the aspect angle at a constant distance from the radiating antenna. An antenna pattern consist of several lobes. The 3 dB beam width is the between two points on a main lobe. Far field pattern is achieved at a minimum distance of (For rectangular horn antenna) Gain calculated as :- Pt = Pt = Transmitted power Pr = Received power = Free space wavelength S = Distance b/w two antenna
Procedure Setup the experiment equipment. Energize the microwave source for maximum output at desired frequency with square wave modulation and frequency of modulation signal of gunn power supply. Obtain the full scale deflection on the normal dB scale at any range switch position of VSWR meter by gain control knob of VSWR meter. Turn the receiving horn antenna to the left in 2° or 5° steps upto 40° - 50° and note the corresponding VSWR reading in dB range. Repeat the above step, turning the receiving horn to the right end and note the reading. Draw a relative power pattern. From diagram determine 3 dB BW. Result Equipment are setup as in block diagram and polar pattern of waveguide plotted.
EXPT NO. 11 CALIBRATION OF ATTENUATOR Aim To study the fixed Attenuator. Equipments Required Microwave source, Isolator, Frequency Meter, Variable attenuator, Slotted line, Tunable probe, Detector mount, matched termination, VSWR meter, Test fixed and and variable attenuator & accessories. Theory Attenuators are 2 port directional device which attenuate powers when inserted into the termination line. Attenuation A(dB) = 10 log (P1/P2) P1 = Power absorbed or detected by load without attenuation in line. P2 = Power absorbed or detected by lead with attenuator in line. The attenuator consist of rectangular waveguide with a resistive inside it to absorb microwave power according to their position with respect to side wall of the waveguide. As electric field is maximum, at centre in TE10 mode. Moving from centre toward side walls attenuation decreases in fixed attenuators, the wave position is fixed whereas in a variable attenuator, its position can be changed by help of micrometer or other methods.
Procedure Input VSWR measurement. Connect equipments, energize microwave source is maximum power at any frequency of operation. Measure VSWR meters as described in the experiment of measurement of low & medium VSWR. Measurement of Isolation loss & Isolation Remove probe & isolator (or) circulator from slotted line & connect detector mount to slotted section. Output of detector mount should be connected VSWR meter. Energize all equipments. Set reference of power in VSWR meter with help of variable attenuator & gain control knob of VSWR. Remove the detector mount. Insert isolator/circulator between slotted lines & detector mount. Record VSWR meter (P2). Insertion loss is P1-P2 in dB. For measurement of isolation, isolator/circulator is connected in reverse. Some P1 level is set. Record off VSWR meter inserting isolator/circulator it be P2. Isolation is P1 – P3 in dB. Some is repeated for other parts of isolator. Repeat for other frequencies if required. Result Experiment is setup and fixed attenuator is studied.
EXPT NO. 6 DIRECTIONAL COUPLER CHARACTERISTICS Aim To measure coupling factor and directivity of multihole directional coupler. Equipments Required Microwave source, Isolator, Frequency Meter, Variable attenuator, Slotted line, Tunable probe, Detector mount, matched termination, MHD coupler, waveguide stand, cables and accessories VSWR meter. Theory A directional coupler is a device, with it is possible to measure the incident and reflected wave separately. It consists of two transmission line, the main arm and auxiliary arm, electromagnetically coupled to each other. The power entering Port -1. The main arms gets divided between Port-2 and 3 and almost no power comes out in Port-4. Power entering Port-2 is divided between Port-1 and Port-4, with built in termination and power is entering at Port-1. Coupling (dB) = 10 log10 (P1/P3) where Port-2 is terminated. Isolation = 10 log10 (P2/P3) P1 is matched. Directivity of coupler is measure of separation between incident and reflected wave. It is measured as the ratio of two power outputs from the auxiliary line when a given amount of power is successively applied to each terminal of main lines the port terminated by material loads. Hence Directivity (0 dB) = Isolation – coupling
= 10 log10 (P2/P1) Main line VSWR is SWR measured 100 king into the main line input terminal. When matched loads are placed. Loss = 10 log10 (P1/P2) When power is entering at Port-1. Procedure Setup all equipments. Energize the microwave source for particular frequency operation. Remove multihole directional coupler and connect the detector mount to the frequency meter. Tune the detector for the maximum output. Set any reference level of power on VSWR meter with help of attenuator gain control knob of VSWR meter and note the readings. Insert directional coupler with the detector to auxiliary Port-3 and matched termination to Port-2 without changing position of variable attenuator and gain control knob of VSWR meter. Calculate coupling factor X – Y in dB. Disconnect the detector from Port-3 and matched termination from Port-2 without disturbing setup connect the matched termination to auxiliary Port-3 and detector to Port2 and measure reading. Compute section loss in directional coupler in the reverse directional. i.e. Port-2 to frequency meter side. Measure and note down reading in VSWR. Compute the directivity Y – Yd. Repeat some for other frequency. Result Experiment is setup as block diagram and readings are obtained.
EXPT NO. 9 MAGIC TEE CHARACTERISTICS Aim Study of Magic tee Equipments Required Microwave source, Isolator, Variable attenuator, Frequency Meter, Slotted line, Tunable probe, magic tee, matched termination, waveguide stand, detector mount, VSWR meter and accessories. Theory The device magic tee is combination of E – plane and H- plane tee. Arm 3 the H-arm form on E plane tee in combination with arm 1 and arm 2 a side or collinear arms. If power is fed into arm 3 the electric field devices equally between arm 1 and arm 2 in same phase, and no electric field exists in arm 4. Reciprocity demands a coupling in Port 3, if power is fed in arm 4, it divides equally into arm 1 and arm 2 but out of phase with no power to arm 3. Procedure 1. VSWR measurement of parts.
Setup components and equipments.’ Energy microwave source for particular freq of operation and tune the detector mount for maximum output. Measure VSWR of E – arm as described in measurement of SWR for low and medium value connect another arm to slotted line and terminate other port with matched termination. Measure VSWR as above. 2. Measurement of isolation and coupling coefficient. Remove tunable probe and magic tee from the slotted line and connect the detector mount to slotted line. Energize the microwave source for particular frequency of operation and time the detector mount of maximum output. Result Experiment is setup and Magic Tee is studied.
EXPT. No:2 MEASUREMENT OF ATTENUATION / UNIT LENGTH OF AN OPTICAL FIBRE Aim: To measure attenuation / unit length of an optical fibre. Theory: Procedure: 1. Connect power supply to board. 2. Make the following connections. a) Function generator’s 1KHz sine wave o/p to i/p 1 socket of emitter1 circuit via 4mm lead. b) Connect 0.5m optic fibre between emitter1 o/p and i/p of detector1. c) Connect detector1 o/p to amplifier i/p socket via 4mm lead. 3. Switch ON the power supply. 4. Set the oscilloscope CH1 to 0.5V/div and adjust 4 – 6 div.amplitude by using X1 probe with the help of variable pot in function generator block at i/p 1 of emitter1. 5. Observe the o/p s/n from detector tp10 on CRO. 6. Adjust the amplitude of the received s/n same as that of transmitted one with the help of gain adjust pot in AC amplifier block.Note this and name it V1. 7. Now replace the previous FG cable with 1m cable without changing any previous settings. 8. Measure the amplitude at the receiver side again at o/p of amplifier1 socket tp28. Note this value and name it V2. 9. Calculate the propagation(attenuation) loss with the following formula V1 / V2 = e—α (L1 + L2) where α = loss in nepers / meter (1 neper = 8.686dB ) L1= length of shorter cable ( 0.5m ) L2= length of longer cable ( 1m ) Result : The attenuation per unit length of an optical fibre .......np/m.
Mw&oc manual
Mw&oc manual

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Mw&oc manual

  • 1. Contents 1.Microwave lab experiments 1. GUNN diode characteristics. 2. Reflex Klystron Mode Characteristics 3. VSWR and Frequency measurement. 4. Verify the relation between Guide wave length, free space wave length and cut off wave length for rectangular wave guide. 5. Measurement of E-plane and H-plane characteristics. 6. Directional Coupler Characteristics. 7. Unknown load impedance measurement using smith chart and verification using transmission line equation. 8. Measurement of dielectric constant for given solid dielectric cell. 9. Magic-Tee characteristics. 10. Antenna Pattern Measurement. 11. Calibration of attenuator. 2.Optical Experiments: Familiarisation of optical fibre trainer kit 1. Measurement of Numerical Aperture of a fiber, after preparing the fiber ends. 2. Measurement of attenuation per unit length of a fiber using the cutback method. 3. Preparation of a Splice joint and measurement of the splice loss. 4. Characteristics of LASER diode 6. Characteristics of fibre optic LED and photodetector 7. Characteristics of Avalanche Photo Diode (APD) and measure the responsivity. 8. Measurement of fiber characteristics, fiber damage and splice loss/connector loss by Optical Time Domain Reflectometer (OTDR) technique.
  • 2. INTRODUCTION TO OPTICAL FIBRE INTRODUCTION Before fibre optics came along the primary means of real time communication was electrical in nature. It was accomplished using copper wire or by transmitting electromagnetic waves. Fibre optics changed that by providing a means of sending information over significant distances – using light energy. It is very reliable and cost effective. Light as utilized for communication has a major advantage because it can be manipulated at significant higher frequencies that electrical signals can. For example, a fibre optic cable can carry up to 100 million times more information than a telephone line. It has low energy loss and wider bandwidth. Principle of Operation Light travels in straight line through most optical materials, but that’s not necessarily the case at the junction of two materials of different refractive indices. In the fig. the light ray travel through air actually is bent as it enters the water. Amount of bending depends on the refractive indices of the two materials involved and also on the angle of incoming ray of light. The relationship between the incident and refracted ray is given by Snell’s law. n1.sin 1 = n2 . sin 2 n1, n2 refractive indices of initial and secondary materials. 1, 2 incident and transmitted angles. Snell’s law says that reflection of light cannot take place when the angle of incidence grows too large. If the angle of incidence exceeds a certain value, light cannot exit. i.e. reflected. The angle that is reflected is equal to angle of incidence. This phenomenon is called total internal reflection. It is what keeps light inside an optical fibre.
  • 3. Types of Optical Fibre The simplest one consists of two concentric layers of transparent materials. The core transports the light. The cladding must have a lower refractive index than the core. Optical fibre is generally made from either plastic or glass. The plastic fibre is generally limited to uses involved in distances of less than 100 mtrs because of high loss. Glass fibre has very low attenuation, hard to cut and more expensive. The core fibre is made of silica dopped with impurities. The cladding is typically made from pure silica. The outer buffer coating is a plastic cover. Single mode v/s Multimode The term multimode means that the diameter of the fibre optic core is large enough to propagate more than one mode. So the pulse that is transmitted down, the fibre tends to become stretched over distance. This modal dispersion. Single mode fibre is designed to propagate only one mode of light. So it is not affected by modal dispersion and has higher bandwidth capacity. They are more sensitive to back reflections from connectors and sharp cable bends. Advantages of fibre optics Much greater Bandwidth. Immunity to electrical disturbances ground loops, cross talks etc:-. In addition no emi. Much lighter. Better in hostile environment, not affected as much by temperature, water etc:-. Low transmission loss. Better security as it is not possible to simply bridge onto the facility and monitor the traffic.
  • 4. FAMILIARISATION OF FIBER OPTIC TRAINER KIT Fibre Optic Trainer Kit Link – A The purpose of FIBRE OPTIC TRAINER KIT is to provide an experience on the various fibre optic and digital communication technique. The experimental setup includes Trainer Kit Link A Plastic Fibres of 1 mtr & 3 mtr length. NA JIG Steel Rule Speaker and Microphone Power Supply Serial Cables Shorting Link Jumper to crocodile Optical Fibre Preparation Instructions Cut off the ends of the cable with a single edge razor or sharp knife at precise 90 angle. Wet the polishing paper with water or light oil and place it on a flat surface. Hold the optical fibre upright at right angle to the paper and polish the fibre tip with a gentle ―figure 8‖ motion. Using a 18 gauge wire stripper, remove 3mm of the jacket from the end of the fibre. Do not nick the buffer in the process to minimize light loss.
  • 5. Function Generator The integrated circuit IC L 8038 generates sine wave and square wave forms at their respective posts. The frequency is variable ranging from 1 Hz to 100 KHz. The frequency of since wave is controlled by pot and capacitors. The frequency range could be selected with help of range selector switch. The presets adjust the symmetry of the sine signal. The amplitude of sine wave is controlled by pot. Buffer IC 74HC04 is used as TTL Buffer. IC’s IC LF357(U4) and IC LF 357(U5) are collectively used as ANALOG Buffer. Fibre Optics Buffer The transmitter module takes the input signal in electrical form and then transforms it into optical (light) energy containing the same information. The optical fibre is the medium which carries this energy to the receiver. Transmitter – LED, digital, DC coupled transmitters are one of the most popular variety due to their ease of fabrication. A standard TTL gate to drive a NPN transistor, which modulates the LED SFH450v source (Turns it ON and OFF). Fibre optic transmitters are typically composed of a buffer, driver and optical source. The buffer electronics provides both an electrical connection and isolation between the transmitter and the electrical system supplying the data. The driver electronics provides electrical power to the optical source in a fashion that duplicates the pattern of data being fed to transmitter. Finally the optical source (LED) converts the electrical current to light energy with same pattern. The LED SFH450v supplied with link – A operated outside the visible light spectrum. Its optical source (LED) output is centred at near infrared wavelength of 950nm. The emission spectrum is broad so a faint red glow can usually be seen when LED is on a dark room. The LED used in link A is coupled to transistor driver in common emitter mode. In the absence of input signal half of the supply voltage appears at the base of transistor. This biases the transistor near midpoint within the active region for linear applications. The LED emits constant intensity of light at this time. When the signal is
  • 6. applied to the amplifier it overrides the dc level to the base of transistor which causes the Q point of transistor to oscillate about the midpoint. So the intensity of LED varies about its previous constant value. The variation in the intensity has linear relation with input electrical signal. NPN transistor (Q 2) emitter is modulated by changing potentiometer P4 value. Optical signal is then carried over by the optical fibre. Another source used is LED 756v at 660nm wavelength which is visible red light source. A standard TTL drives NPN transistor (Q2), which modulates the LED SFH756v source (turns it OFF and ON). Selection between different sources is done through jumpers provided onboard. Fibre Optics Receiver At the receiver, light is converted back into electrical form with the same pattern as originally fed to the transmitter. The function of the receiver is to convert the optical energy into electrical form, which is then conditioned to reproduce the electrical signal transmitted in its original form. The detector SFH250v use in Link A has a diode type output. The parameters usually considered in case of detector are its responsivity at peak wavelength and response time. SFH250v used in link A has responsivity of about 4 per 10 W of incident optical energy at 950 nm and it has rise & fall time of 0.01 S. PIN photodiode is normally reverse biased. When optical signal falls on the diode, reverse current start to flow, thus diode acts as closed switch and in the absence of light intensity it acts as open switch. Since PIN diode usually has low responsivity, a transimpedance amplifier is used to convert this reverse current into voltage formed around IC LF356. This voltage is then amplified with help of another amplifier circuit IC LF 357(U13) and IC LF 357(U20). This voltage the duplication of transmitted electrical signal. These are various methods to extract digital data. Usually detectors are of linear nature. Photo detector having TTL type output (SFH 551/V) consists of integrated photodiode, transimpedance amplifier and level shifter.
  • 7. EXPT N0. 1. STUDY OF NUMERICAL APERTURE OF OPTICAL FIBRE Aim The objective of this experiment to measure the numerical aperture of the plastic fibre provident with the kit using 660nm wavelength LED. Theory Numerical aperture refers to the maximum angle at which the light incident on the fiber end is totally internally reflected and is properly along the fiber. The cone formed by the rotation of this angle along the axis of the fiber is the cone acceptance of the fiber. The light ray should strike the fibre end within its cone of acceptance; else it is reflected out of the fibre cone. Considerations in a NA Measurement 1. It is very important that optical source should be properly selected to ensured that maximum amount of optical power is transferred to the cable. 2. This experiment is best performed in a less illuminated room. Equipments Required Kit C (Fiber link – A), 1 meter fibre cable, NA J/G, Steel Ruler, Power Supply. Procedure 1. Slightly unscrew the cap of LED SFH756 V (660nm). Do not remove cap from connector. Once the cap is loosened, insert the fibre into the cap. Now tight the cap by screwing it back.
  • 8. 2. Connect the power supply cables with proper polarity to kit. While connecting this, ensure that power supply is OFF. Do not apply any TTL signal from Function Generator. Make the connections from the figure. 3. Keep pot P3 fully clockwise position and P4 fully anticlockwise position. 4. Switch on the power supply. 5. Insert the other end of the fibre into the numerical aperture measurement jig. Hold the white sheet facing fibre. Adjust the fibre such that its cut face is perpendicular to the axis of the fiber. 6. Keep the distance of about 10mm between the fibre tip and screen. Gently tighten the screw and thus fix the fibre in the place. 7. Now adjust pot P4 fully clockwise position and observe the illuminated circular path of light on the screen. 8. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN indicated in fig. 9. Mean radius is calculated using formula r = (MR+PN)/4. 10. Find the numerical aperture of fibre using the formula NA = Sin max = r/ where max is maximum angle at which light incident is properly transmitted through the fibre. 11. Using the formulae V number = π d NA calculate V number λ Result The numerical aperture and V number of the plastic fibre is calculated using 660nm wave length LED. Numerical Aperture = V number =
  • 9. EXPT NO. 4 CHARACTERISTICS OF OPTICAL FIBRE LED AND DETECTOR Aim To study the VI characteristics of fibre optic LED’s. Theory In Fibre optic communication system, electrical system is first converted into optical signal with help of E/O conversion device as LED. After this optical signal is transmitted in its original electrical form with help O/E conversion device as photo detector. Different technologies employed in chip fabrication lead to significant variation in parameters for various emitter diodes. All emitters distinguish themselves in offering high output power coupled into plastic fibre. Data sheets for LEDs usually specify electrical and optical chara out of which are important peak wavelength of emission, conversion efficiency, optical rise and fall times which put the limitation of operating frequency, maximum forward current through LED and typical forward voltage across LED. Photo detectors usually come in variety of forms like photoconductive, photovoltaic, transistor type output and diode type output. Here also characteristics to be taken into account are response time of detector which puts the limitation on the operating frequency. Wavelength sensitivity and responsivity. Procedure (A) CHARACTERISTICS OF FIBER OPTIC LED 1. Make the jumper and switch settings as shown in jumper diagram. keep Pot P4 fully in clockwise position. 2. Connect the ammeter with jumper connecting wires in jumpers JP3 as in diagram. 3. Connect the voltmeter with jumper wires to JP5 and JP2 at positions as in diagram.
  • 10. 4. Switch on power supply. Keep potentiometer P3 in its minimum position (fully anticlockwise position), P4 id used to control biasing voltage of the LED. To get the VI characteristics and optical power of SFH 756v LED. Graph for VI characteristics of SFH 756v LED. 5. For each reading taken above, find out the power, which is product of I and V. This is the electrical power supplied to LED specifies optical power supplied to LED specifies optical power coupled into plastic fibre when forward current was 10 mA as 200 W. This means that the electrical power at 10 mA current is converted to 200 W of optical energy. Hence the efficiency of LED comes out to be approx 1.15% 6. With this efficiency assumed, find out optical power coupled into plastic optical fibre for each of the reading in step 4. Plot the graph of forward current v/s output optical power of LED SFH 756v. 7. Repeat the above experiment by using SFH 450v (950nm) LED. Graph for VI characteristics of SFH 756v LED is shown. The figure shows graph of forward current v/s output optical power of LED SFH 450v. (B) CHARACTERISTICS OF DETECTOR 1. Make the jumper and switch settings as shown in the jumper diagram fig keep pot P4 in fully clockwise position. 2. Connect the ammeter with the jumper connecting wires in jumpers JP 7. 3. Connect 1 metre fibre optic cable between LED (TX 1) SFH 756v and detector (RX 1) SFH 250v 4. Switch on the power supply and measure corresponding forward current of LED (TX 1) as per table. Measure the current flowing through the detector (RX 1) SFH 250v at corresponding optical power output (Normally in A). 5. We can observe that as incident optical power on detector increases, current flowing through the detector increases.
  • 11. Result The VI characteristics of fibre optic LED and detector are plotted.
  • 12. EXPT NO. 2 REFLEX KLYSTRON REPELLER MODE CHARACTERISTICS Aim To study characteristics of the reflex klystron tube. Equipments Required Klystron power supply, Klystron tube with Klystron mount, Isolator, Frequency meter, Variable attenuator, detector mount, wave guide stand, VSWR meter and oscilloscope BNC cable. Theory The reflex Klystron makes use of velocity modulation to transform a continuous electron beam into microwave power. Electrons emitted from the cathode are accelerated and passed through the positive resonator towards negative reflector which retards and finally reflects the electrons and the electrons turn back through the resonator. Suppose an RF field exist between the resonators the electrons travelling forward will be accelerated or retarded as the voltage at the resonator changes in amplitude.
  • 13. The accelerated electrons leave the resonator at the increased velocity and the retarded electrons leave at the retarded velocity. The electrons leaving the resonator will need different time to return due to change in velocities. As a result returning electrons group together in bunches, as the electron bunches pass through resonator, they interact with voltage at resonator grids. If the bunches pass the grid at such a time that the electrons are slowed down by the voltage be then energy will delivered to the resonator and Klystron will oscillate. The frequency is primarily determined by the dimensions of resonant cavity. Procedure Setup Set up the components and equipments as shown keep position of variable attenuator at maximum attenuation position. Set the mode selector switch to FM MOD position and FM amp and FM frequency knob at mid position, keep beam voltage control knob fully anticlockwise and reflector voltage knob to fully clockwise with meter switch to OFF position. Keep the time/division scale of oscilloscope around 100 Hz frequency measurement and v/division to lower scale Switch ON Klystron power supply and oscilloscope. Change the meter switch of Klystron power supply to beam voltage position and set beam voltage to 300v by voltage control knob. Keep amplitude knob of FM modulator to maximum position and rotate reflector voltage anticlockwise to get modes.
  • 14. Result The characteristics of Reflex Klystron is obtained. `
  • 15. EXPT NO. 1 GUNN DIODE CHARACTERISTICS Aim To study the V – I characteristics of gunn diode. Equipment Required Gunn Oscillator, Gunn power supply, PIN modulator, Isolator, Frequency meter, Detector mount, Wave guide stands, SWR meter. Theory Gunn oscillator is based on negative differential conductivity effect in bulk semiconductors which has two conduction bands minima separated by an energy gap. When this high field domain reaches the anode it disappears and domain is formed at the cathode and starts moving towards anode. In Gunn oscillator, gunn diode is placed in a resonant cavity. Although the Gunn oscillator can be amplitude modulated, separate PIN modulators through PIN diode for square wave modulation are used. A measure of the square wave modulation capability is the modulation depth i.e, the output ratio between ON and OFF state. Procedure Set the components and equipments. Initially set the variable attenuator for maximum attenuation. Keep the control knob of gunn power supply as Meter switch : OFF, Gunn bias knob : Fully clockwise. Keep the control knob of VSWR meter as below : Meter switch : Normal
  • 16. Input switch : Low impedance Range db switch : 40 dB Gain Control knob : Fully clockwise Set the micrometer of gunn oscillator for required frequency of operation. Switch ON gunn power supply VSWR meter and cooling fan. Turn the meter switch to voltage position. Measure the gunn diode current corresponding to the variations in gunn voltage; do not exceed the bias voltage above 10 volts. Plot voltage and current reading as on graph. Measure the threshold voltage which corresponds to maximum current.
  • 17. Result The characteristics of gunn oscillator have been obtained VTH =
  • 18. EXPT NO. 3 VERIFY RELATIONSHIP BETWEEN λo, λg AND λc Aim To determine the frequency and wavelength in rectangular waveguide working in TE10 mode. Equipments Klystron power supply, Klystron Tube, Isolator, Fraquency meters, Variable attenuator, Slotted section, tunable probe, wavelength stand, VSWR meter, matched termination. Theory Mode represents in waveguide as either TE min/TM min. Where TE - Transverse Electric TM - Transverse Magnetic m - number of half wavelength in broader section n - number of half wavelength in shorter section = (d1 – d2) Where d1, d2 are the distances between 2 successive maxima / minima. For TE10 mode. = , m = 1 in TE10 mode. - Free space wavelength g - Guide wave length - Cutoff wavelength Procedure
  • 19. Set the components and equipments. Set the variable attenuator at maximum position. Keep the controls of VSWR as follows. Range db : 50 dB Input Switch : Crystal low impedance Meter Switch : Normal position Gain : Mid position Keep the controls of Klystron Power Supply as :- Meter Switch : OFF Mode Switch : AM Beam V knob : Full anticlockwise Reflector voltage : Fully clockwise AM Knob : Around fully clockwise
  • 20. AM Frequency : Around mid position Switch on Klystron Power Supply VSWR meter. Turn the meter switch to bean voltage position and repeller voltage as 300v and current 15-20 mA. Adjust repeller voltage to get some deflection in VSWR meter. Tune the plunger of Klystron for maximum deflection. Replace the termination of movable short and detune frequency meter. Move tunable probe along with slotted line to get the deflection in VSWR meter. Move probe to next minimum position. i.e. d2. Calculate guide wavelength as twice the wavelength between two successive minima. Calculate frequency using the equation. f= =c Verify with frequency obtained by frequency meter. Obtain and verify the experiment at different frequencies. Result Frequency of the rectangular waveguide is calculated from its guide and cut-off wavelength. The observed frequency is found to be equal to the obtained frequency.
  • 21. EXPT NO. 3 VSWR & FREQUENCY MEASUREMENT Aim To determine the standing wave ratio and reflection coefficient. Equipments Klystron Power Supply, Klystron tube, VSWR meter, Isolator, Frequency meter, Variable attenuator, Tunable probe, SS tuner. Theory VSWR is the ratio of maximum to minimum voltage along a transmission line, as the ratio of maximum to minimum current. The em field at any point of transmission line may be considered as the sum of two travelling waves. Incident & Reflected waves. The distance between two successive minimum is half the guide wavelength. The ratio of the electric field strength of reflected and incident wave is called reflection between maximum & minimum field strength along the line. VSWR(S) = = EI = incident voltage Er = reflected voltage Reflection coefficient S = = – =
  • 22. Z = impedance at a point on line Zo = Characteristic impedance Procedure Setup the equipment. Keep the variable attenuator at max position. Keep the VSWR control knob as follows : Range = (40/50) dB Input Switch = Impedance low Meter Switch = Normal Gain = Mid position Keep the control knob of Klystron Power Supply Meter Switch = OFF Mod Switch = AM Beam V knob = Fully anticlockwise Reflector V knob = Fully clockwise Switch ON the Klystron Power Supply, VSWR meter. Turn switch to beam. Tune output by tuning reflector voltage, amplitude and frequency of AM. Move the probe along with slotted line the deflection will change.
  • 23. Measurement of low & medium VSWR 1. Move probe along with slotted line to maximum deflection in VSWR meter. 2. Adjust VSWR meter gain control knob until meter indicates 1 on SWR scales. 3. Read the VSWR on scale and record it. 4. Repeat the step for change of SS. 5. If VSWR is b/w 7.2 and 10, change the range dB switch to next higher position. Measurement of high VSWR 1. Set the depth of SS tuner slightly more max VSWR. 2. Move probe along slotted line until min is obtain. 3. Adjust VSWR meter gain control knob to read 3dB 4. Move the probe to left till 0 dB is obtained. Note the probe position as d1. 5. Repeat 3 & 4 and move till 0 dB. Note it as d2 Measure the distance b/w two minima. Twice this is waveguide length g. 6. Calculate the SWR as:
  • 24. SWR = – Result The equipment is setup and the value is setup.
  • 25. EXPT NO. 10 ANTENNA PATTERN MEASUREMENT Aim To measure the polar pattern of a horn antenna. Equipments Gunn power supply, Gunn oscillator, Frequency meter, Variable attenuator, VSWR meter. Theory The variation pattern of an antenna is a diagram of field strength (or) more often the power intensity as a function of the aspect angle at a constant distance from the radiating antenna. An antenna pattern consist of several lobes. The 3 dB beam width is the between two points on a main lobe. Far field pattern is achieved at a minimum distance of (For rectangular horn antenna) Gain calculated as :- Pt = Pt = Transmitted power Pr = Received power = Free space wavelength S = Distance b/w two antenna
  • 26. Procedure Setup the experiment equipment. Energize the microwave source for maximum output at desired frequency with square wave modulation and frequency of modulation signal of gunn power supply. Obtain the full scale deflection on the normal dB scale at any range switch position of VSWR meter by gain control knob of VSWR meter. Turn the receiving horn antenna to the left in 2° or 5° steps upto 40° - 50° and note the corresponding VSWR reading in dB range. Repeat the above step, turning the receiving horn to the right end and note the reading. Draw a relative power pattern. From diagram determine 3 dB BW. Result Equipment are setup as in block diagram and polar pattern of waveguide plotted.
  • 27. EXPT NO. 11 CALIBRATION OF ATTENUATOR Aim To study the fixed Attenuator. Equipments Required Microwave source, Isolator, Frequency Meter, Variable attenuator, Slotted line, Tunable probe, Detector mount, matched termination, VSWR meter, Test fixed and and variable attenuator & accessories. Theory Attenuators are 2 port directional device which attenuate powers when inserted into the termination line. Attenuation A(dB) = 10 log (P1/P2) P1 = Power absorbed or detected by load without attenuation in line. P2 = Power absorbed or detected by lead with attenuator in line. The attenuator consist of rectangular waveguide with a resistive inside it to absorb microwave power according to their position with respect to side wall of the waveguide. As electric field is maximum, at centre in TE10 mode. Moving from centre toward side walls attenuation decreases in fixed attenuators, the wave position is fixed whereas in a variable attenuator, its position can be changed by help of micrometer or other methods.
  • 28. Procedure Input VSWR measurement. Connect equipments, energize microwave source is maximum power at any frequency of operation. Measure VSWR meters as described in the experiment of measurement of low & medium VSWR. Measurement of Isolation loss & Isolation Remove probe & isolator (or) circulator from slotted line & connect detector mount to slotted section. Output of detector mount should be connected VSWR meter. Energize all equipments. Set reference of power in VSWR meter with help of variable attenuator & gain control knob of VSWR. Remove the detector mount. Insert isolator/circulator between slotted lines & detector mount. Record VSWR meter (P2). Insertion loss is P1-P2 in dB. For measurement of isolation, isolator/circulator is connected in reverse. Some P1 level is set. Record off VSWR meter inserting isolator/circulator it be P2. Isolation is P1 – P3 in dB. Some is repeated for other parts of isolator. Repeat for other frequencies if required. Result Experiment is setup and fixed attenuator is studied.
  • 29. EXPT NO. 6 DIRECTIONAL COUPLER CHARACTERISTICS Aim To measure coupling factor and directivity of multihole directional coupler. Equipments Required Microwave source, Isolator, Frequency Meter, Variable attenuator, Slotted line, Tunable probe, Detector mount, matched termination, MHD coupler, waveguide stand, cables and accessories VSWR meter. Theory A directional coupler is a device, with it is possible to measure the incident and reflected wave separately. It consists of two transmission line, the main arm and auxiliary arm, electromagnetically coupled to each other. The power entering Port -1. The main arms gets divided between Port-2 and 3 and almost no power comes out in Port-4. Power entering Port-2 is divided between Port-1 and Port-4, with built in termination and power is entering at Port-1. Coupling (dB) = 10 log10 (P1/P3) where Port-2 is terminated. Isolation = 10 log10 (P2/P3) P1 is matched. Directivity of coupler is measure of separation between incident and reflected wave. It is measured as the ratio of two power outputs from the auxiliary line when a given amount of power is successively applied to each terminal of main lines the port terminated by material loads. Hence Directivity (0 dB) = Isolation – coupling
  • 30. = 10 log10 (P2/P1) Main line VSWR is SWR measured 100 king into the main line input terminal. When matched loads are placed. Loss = 10 log10 (P1/P2) When power is entering at Port-1. Procedure Setup all equipments. Energize the microwave source for particular frequency operation. Remove multihole directional coupler and connect the detector mount to the frequency meter. Tune the detector for the maximum output. Set any reference level of power on VSWR meter with help of attenuator gain control knob of VSWR meter and note the readings. Insert directional coupler with the detector to auxiliary Port-3 and matched termination to Port-2 without changing position of variable attenuator and gain control knob of VSWR meter. Calculate coupling factor X – Y in dB. Disconnect the detector from Port-3 and matched termination from Port-2 without disturbing setup connect the matched termination to auxiliary Port-3 and detector to Port2 and measure reading. Compute section loss in directional coupler in the reverse directional. i.e. Port-2 to frequency meter side. Measure and note down reading in VSWR. Compute the directivity Y – Yd. Repeat some for other frequency. Result Experiment is setup as block diagram and readings are obtained.
  • 31. EXPT NO. 9 MAGIC TEE CHARACTERISTICS Aim Study of Magic tee Equipments Required Microwave source, Isolator, Variable attenuator, Frequency Meter, Slotted line, Tunable probe, magic tee, matched termination, waveguide stand, detector mount, VSWR meter and accessories. Theory The device magic tee is combination of E – plane and H- plane tee. Arm 3 the H-arm form on E plane tee in combination with arm 1 and arm 2 a side or collinear arms. If power is fed into arm 3 the electric field devices equally between arm 1 and arm 2 in same phase, and no electric field exists in arm 4. Reciprocity demands a coupling in Port 3, if power is fed in arm 4, it divides equally into arm 1 and arm 2 but out of phase with no power to arm 3. Procedure 1. VSWR measurement of parts.
  • 32. Setup components and equipments.’ Energy microwave source for particular freq of operation and tune the detector mount for maximum output. Measure VSWR of E – arm as described in measurement of SWR for low and medium value connect another arm to slotted line and terminate other port with matched termination. Measure VSWR as above. 2. Measurement of isolation and coupling coefficient. Remove tunable probe and magic tee from the slotted line and connect the detector mount to slotted line. Energize the microwave source for particular frequency of operation and time the detector mount of maximum output. Result Experiment is setup and Magic Tee is studied.
  • 33. EXPT. No:2 MEASUREMENT OF ATTENUATION / UNIT LENGTH OF AN OPTICAL FIBRE Aim: To measure attenuation / unit length of an optical fibre. Theory: Procedure: 1. Connect power supply to board. 2. Make the following connections. a) Function generator’s 1KHz sine wave o/p to i/p 1 socket of emitter1 circuit via 4mm lead. b) Connect 0.5m optic fibre between emitter1 o/p and i/p of detector1. c) Connect detector1 o/p to amplifier i/p socket via 4mm lead. 3. Switch ON the power supply. 4. Set the oscilloscope CH1 to 0.5V/div and adjust 4 – 6 div.amplitude by using X1 probe with the help of variable pot in function generator block at i/p 1 of emitter1. 5. Observe the o/p s/n from detector tp10 on CRO. 6. Adjust the amplitude of the received s/n same as that of transmitted one with the help of gain adjust pot in AC amplifier block.Note this and name it V1. 7. Now replace the previous FG cable with 1m cable without changing any previous settings. 8. Measure the amplitude at the receiver side again at o/p of amplifier1 socket tp28. Note this value and name it V2. 9. Calculate the propagation(attenuation) loss with the following formula V1 / V2 = e—α (L1 + L2) where α = loss in nepers / meter (1 neper = 8.686dB ) L1= length of shorter cable ( 0.5m ) L2= length of longer cable ( 1m ) Result : The attenuation per unit length of an optical fibre .......np/m.