Contents1.Microwave lab experiments1. GUNN diode characteristics.2. Reflex Klystron Mode Characteristics3. VSWR and Frequency measurement.4. Verify the relation between Guide wave length, free space wave length and cut offwave 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 kit1. 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 diode6. Characteristics of fibre optic LED and photodetector7. 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 FIBREINTRODUCTION Before fibre optics came along the primary means of real timecommunication was electrical in nature. It was accomplished using copper wireor by transmitting electromagnetic waves. Fibre optics changed that byproviding a means of sending information over significant distances – usinglight energy. It is very reliable and cost effective. Light as utilized for communication has a major advantage because itcan be manipulated at significant higher frequencies that electrical signals can.For example, a fibre optic cable can carry up to 100 million times moreinformation 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 notnecessarily the case at the junction of two materials of different refractiveindices. In the fig. the light ray travel through air actually is bent as it enters thewater. Amount of bending depends on the refractive indices of the twomaterials involved and also on the angle of incoming ray of light. Therelationship between the incident and refracted ray is given by Snell’s law. n1.sin 1 = n2 . sin 2n1, 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 angleof 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 ofincidence. This phenomenon is called total internal reflection. It is what keepslight inside an optical fibre.
Types of Optical Fibre The simplest one consists of two concentric layers of transparentmaterials. The core transports the light. The cladding must have a lowerrefractive index than the core. Optical fibre is generally made from either plastic or glass. The plasticfibre is generally limited to uses involved in distances of less than 100 mtrsbecause of high loss. Glass fibre has very low attenuation, hard to cut andmore expensive. The core fibre is made of silica dopped with impurities. Thecladding is typically made from pure silica. The outer buffer coating is a plasticcover.Single mode v/s Multimode The term multimode means that the diameter of the fibre optic core islarge enough to propagate more than one mode. So the pulse that istransmitted down, the fibre tends to become stretched over distance. Thismodal dispersion. Single mode fibre is designed to propagate only one mode of light. So itis not affected by modal dispersion and has higher bandwidth capacity. Theyare 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 TRAINERKITFibre Optic Trainer Kit Link – A The purpose of FIBRE OPTIC TRAINER KIT is to provide an experienceon the various fibre optic and digital communication technique. Theexperimental 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 crocodileOptical Fibre Preparation Instructions Cut off the ends of the cable with a single edge razor or sharp knife atprecise 90 angle. Wet the polishing paper with water or light oil and place it on a flatsurface. Hold the optical fibre upright at right angle to the paper and polish thefibre tip with a gentle ―figure 8‖ motion. Using a 18 gauge wire stripper, remove 3mm of the jacket from the endof 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 waveforms at their respective posts. The frequency is variable ranging from 1 Hz to100 KHz. The frequency of since wave is controlled by pot and capacitors.The frequency range could be selected with help of range selector switch. Thepresets adjust the symmetry of the sine signal. The amplitude of sine wave iscontrolled 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 thentransforms it into optical (light) energy containing the same information. Theoptical fibre is the medium which carries this energy to the receiver.Transmitter – LED, digital, DC coupled transmitters are one of the most popularvariety due to their ease of fabrication. A standard TTL gate to drive a NPNtransistor, which modulates the LED SFH450v source (Turns it ON and OFF).Fibre optic transmitters are typically composed of a buffer, driver and opticalsource. The buffer electronics provides both an electrical connection andisolation between the transmitter and the electrical system supplying the data.The driver electronics provides electrical power to the optical source in afashion that duplicates the pattern of data being fed to transmitter. Finally theoptical source (LED) converts the electrical current to light energy with samepattern. The LED SFH450v supplied with link – A operated outside the visiblelight spectrum. Its optical source (LED) output is centred at near infraredwavelength of 950nm. The emission spectrum is broad so a faint red glow canusually be seen when LED is on a dark room. The LED used in link A iscoupled to transistor driver in common emitter mode. In the absence of inputsignal half of the supply voltage appears at the base of transistor. This biasesthe 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 whichcauses the Q point of transistor to oscillate about the midpoint. So the intensityof LED varies about its previous constant value. The variation in the intensityhas linear relation with input electrical signal. NPN transistor (Q 2) emitter ismodulated by changing potentiometer P4 value. Optical signal is then carriedover by the optical fibre. Another source used is LED 756v at 660nmwavelength which is visible red light source. A standard TTL drives NPNtransistor (Q2), which modulates the LED SFH756v source (turns it OFF andON). Selection between different sources is done through jumpers providedonboard.Fibre Optics Receiver At the receiver, light is converted back into electrical form with the samepattern as originally fed to the transmitter. The function of the receiver is toconvert the optical energy into electrical form, which is then conditioned toreproduce the electrical signal transmitted in its original form. The detectorSFH250v use in Link A has a diode type output. The parameters usuallyconsidered in case of detector are its responsivity at peak wavelength andresponse time. SFH250v used in link A has responsivity of about 4 per10 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 thediode, reverse current start to flow, thus diode acts as closed switch and in theabsence of light intensity it acts as open switch. Since PIN diode usually haslow responsivity, a transimpedance amplifier is used to convert this reversecurrent into voltage formed around IC LF356. This voltage is then amplifiedwith help of another amplifier circuit IC LF 357(U13) and IC LF 357(U20). Thisvoltage the duplication of transmitted electrical signal. These are variousmethods to extract digital data. Usually detectors are of linear nature. Photodetector 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 FIBREAim The objective of this experiment to measure the numerical aperture ofthe plastic fibre provident with the kit using 660nm wavelength LED.Theory Numerical aperture refers to the maximum angle at which the lightincident on the fiber end is totally internally reflected and is properly along thefiber. The cone formed by the rotation of this angle along the axis of the fiber isthe cone acceptance of the fiber. The light ray should strike the fibre end withinits cone of acceptance; else it is reflected out of the fibre cone.Considerations in a NA Measurement1. 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 RequiredKit C (Fiber link – A), 1 meter fibre cable, NA J/G, Steel Ruler, Power Supply.Procedure1. 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 λResult The numerical aperture and V number of the plastic fibre is calculatedusing 660nm wave length LED.Numerical Aperture =V number =
EXPT NO. 4 CHARACTERISTICS OF OPTICAL FIBRE LED AND DETECTORAimTo study the VI characteristics of fibre optic LED’s.Theory In Fibre optic communication system, electrical system is firstconverted into optical signal with help of E/O conversion device as LED. Afterthis optical signal is transmitted in its original electrical form with help O/Econversion device as photo detector. Different technologies employed in chip fabrication lead tosignificant variation in parameters for various emitter diodes. All emittersdistinguish themselves in offering high output power coupled into plastic fibre.Data sheets for LEDs usually specify electrical and optical chara out of whichare important peak wavelength of emission, conversion efficiency, optical riseand fall times which put the limitation of operating frequency, maximum forwardcurrent through LED and typical forward voltage across LED. Photo detectorsusually come in variety of forms like photoconductive, photovoltaic, transistortype output and diode type output. Here also characteristics to be taken intoaccount are response time of detector which puts the limitation on the operatingfrequency. Wavelength sensitivity and responsivity.Procedure (A) CHARACTERISTICS OF FIBER OPTIC LED1. Make the jumper and switch settings as shown in jumper diagram. keepPot 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 DETECTOR1. 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 250v4. 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 CHARACTERISTICSAimTo 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 acontinuous electron beam into microwave power. Electrons emitted from thecathode are accelerated and passed through the positive resonator towardsnegative reflector which retards and finally reflects the electrons and theelectrons turn back through the resonator. Suppose an RF field exist betweenthe resonators the electrons travelling forward will be accelerated or retardedas the voltage at the resonator changes in amplitude.
The accelerated electrons leave the resonator at the increased velocityand the retarded electrons leave at the retarded velocity. The electrons leavingthe resonator will need different time to return due to change in velocities. As aresult returning electrons group together in bunches, as the electron bunchespass through resonator, they interact with voltage at resonator grids. If thebunches pass the grid at such a time that the electrons are slowed down by thevoltage be then energy will delivered to the resonator and Klystron will oscillate.The frequency is primarily determined by the dimensions of resonant cavity.ProcedureSetupSet up the components and equipments as shown keep position of variableattenuator at maximum attenuation position. Set the mode selector switch toFM MOD position and FM amp and FM frequency knob at mid position, keepbeam voltage control knob fully anticlockwise and reflector voltage knob to fullyclockwise with meter switch to OFF position. Keep the time/division scale ofoscilloscope around 100 Hz frequency measurement and v/division to lowerscale Switch ON Klystron power supply and oscilloscope. Change the meterswitch of Klystron power supply to beam voltage position and set beam voltageto 300v by voltage control knob. Keep amplitude knob of FM modulator tomaximum position and rotate reflector voltage anticlockwise to get modes.
Result The characteristics of Reflex Klystron is obtained.`
EXPT NO. 1 GUNN DIODE CHARACTERISTICSAim To study the V – I characteristics of gunn diode.Equipment Required Gunn Oscillator, Gunn power supply, PIN modulator, Isolator, Frequencymeter, Detector mount, Wave guide stands, SWR meter.Theory Gunn oscillator is based on negative differential conductivity effect inbulk semiconductors which has two conduction bands minima separated by anenergy gap. When this high field domain reaches the anode it disappears anddomain is formed at the cathode and starts moving towards anode. In Gunn oscillator, gunn diode is placed in a resonant cavity. Althoughthe Gunn oscillator can be amplitude modulated, separate PIN modulatorsthrough PIN diode for square wave modulation are used. A measure of the square wave modulation capability is the modulationdepth i.e, the output ratio between ON and OFF state.Procedure Set the components and equipments. Initially set the variable attenuatorfor maximum attenuation. Keep the control knob of gunn power supply asMeter switch : OFF, Gunn bias knob : Fully clockwise. Keep the control knob ofVSWR meter as below : Meter switch : Normal
Input switch : Low impedance Range db switch : 40 dB Gain Control knob : Fully clockwiseSet the micrometer of gunn oscillator for required frequency of operation.Switch ON gunn power supply VSWR meter and cooling fan. Turn the meterswitch to voltage position. Measure the gunn diode current corresponding tothe 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. 3VERIFY RELATIONSHIP BETWEEN λo, λg ANDλcAim To determine the frequency and wavelength in rectangular waveguideworking in TE10 mode.Equipments Klystron power supply, Klystron Tube, Isolator, Fraquency meters,Variable attenuator, Slotted section, tunable probe, wavelength stand, VSWRmeter, 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 wavelengthProcedure
Set the components and equipments. Set the variable attenuator at maximumposition. 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 switchto bean voltage position and repeller voltage as 300v and current 15-20 mA.Adjust repeller voltage to get some deflection in VSWR meter. Tune theplunger of Klystron for maximum deflection. Replace the termination ofmovable short and detune frequency meter. Move tunable probe along with slotted line to get the deflection in VSWRmeter. Move probe to next minimum position. i.e. d2. Calculate guide wavelength as twice the wavelength between twosuccessive minima. Calculate frequency using the equation. f= =c Verify with frequency obtained by frequency meter. Obtain and verifythe experiment at different frequencies.Result Frequency of the rectangular waveguide is calculated from its guide andcut-off wavelength. The observed frequency is found to be equal to theobtained frequency.
EXPT NO. 3 VSWR & FREQUENCY MEASUREMENTAim To determine the standing wave ratio and reflection coefficient.Equipments Klystron Power Supply, Klystron tube, VSWR meter, Isolator, Frequencymeter, Variable attenuator, Tunable probe, SS tuner.Theory VSWR is the ratio of maximum to minimum voltage along a transmissionline, as the ratio of maximum to minimum current. The em field at any point of transmission line may be considered as thesum of two travelling waves. Incident & Reflected waves. The distancebetween two successive minimum is half the guide wavelength. The ratio ofthe electric field strength of reflected and incident wave is called reflectionbetween maximum & minimum field strength along the line. VSWR(S) = = EI = incident voltage Er = reflected voltageReflection coefficient S = = – =
Z = impedance at a point on line Zo = Characteristic impedanceProcedure 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 positionKeep the control knob of Klystron Power Supply Meter Switch = OFF Mod Switch = AM Beam V knob = Fully anticlockwise Reflector V knob = Fully clockwiseSwitch 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 VSWR1. 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 VSWR1. 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 3dB4. 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 MEASUREMENTAim To measure the polar pattern of a horn antenna.Equipments Gunn power supply, Gunn oscillator, Frequency meter, Variableattenuator, 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 constantdistance from the radiating antenna. An antenna pattern consist of severallobes. The 3 dB beam width is the between two points on a main lobe. Farfield 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 desiredfrequency with square wave modulation and frequency of modulation signal ofgunn power supply. Obtain the full scale deflection on the normal dB scale at any rangeswitch position of VSWR meter by gain control knob of VSWR meter. Turn the receiving horn antenna to the left in 2° or 5° steps upto40° - 50° and note the corresponding VSWR reading in dB range. Repeat theabove step, turning the receiving horn to the right end and note the reading. Draw a relative power pattern. From diagram determine 3 dB BW.ResultEquipment are setup as in block diagram and polar pattern of waveguideplotted.
EXPT NO. 11 CALIBRATION OF ATTENUATORAim To study the fixed Attenuator.Equipments Required Microwave source, Isolator, Frequency Meter, Variable attenuator,Slotted line, Tunable probe, Detector mount, matched termination, VSWRmeter, Test fixed and and variable attenuator & accessories.Theory Attenuators are 2 port directional device which attenuate powers wheninserted 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 itto absorb microwave power according to their position with respect to side wallof the waveguide. As electric field is maximum, at centre in TE10 mode.Moving from centre toward side walls attenuation decreases in fixedattenuators, the wave position is fixed whereas in a variable attenuator, itsposition can be changed by help of micrometer or other methods.
Procedure Input VSWR measurement. Connect equipments, energize microwavesource is maximum power at any frequency of operation. Measure VSWRmeters as described in the experiment of measurement of low & mediumVSWR. Measurement of Isolation loss & Isolation Remove probe & isolator (or) circulator from slotted line & connectdetector mount to slotted section. Output of detector mount should beconnected VSWR meter. Energize all equipments. Set reference of power inVSWR 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 beP2. 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 CHARACTERISTICSAim To measure coupling factor and directivity of multihole directionalcoupler.Equipments Required Microwave source, Isolator, Frequency Meter, Variable attenuator,Slotted line, Tunable probe, Detector mount, matched termination, MHDcoupler, waveguide stand, cables and accessories VSWR meter.Theory A directional coupler is a device, with it is possible to measure theincident and reflected wave separately. It consists of two transmission line, themain arm and auxiliary arm, electromagnetically coupled to each other. Thepower entering Port -1. The main arms gets divided between Port-2 and 3 andalmost no power comes out in Port-4. Power entering Port-2 is dividedbetween Port-1 and Port-4, with built in termination and power is entering atPort-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 andreflected wave. It is measured as the ratio of two power outputs from theauxiliary line when a given amount of power is successively applied to eachterminal 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 inputterminal. 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 particularfrequency operation. Remove multihole directional coupler and connect thedetector mount to the frequency meter. Tune the detector for the maximumoutput. Set any reference level of power on VSWR meter with help ofattenuator gain control knob of VSWR meter and note the readings. Insertdirectional coupler with the detector to auxiliary Port-3 and matched terminationto Port-2 without changing position of variable attenuator and gain control knobof VSWR meter. Calculate coupling factor X – Y in dB. Disconnect thedetector from Port-3 and matched termination from Port-2 without disturbingsetup connect the matched termination to auxiliary Port-3 and detector to Port2and measure reading. Compute section loss in directional coupler in thereverse directional. i.e. Port-2 to frequency meter side. Measure and notedown reading in VSWR. Compute the directivity Y – Yd. Repeat some forother frequency.Result Experiment is setup as block diagram and readings are obtained.
EXPT NO. 9 MAGIC TEE CHARACTERISTICSAim Study of Magic teeEquipments 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. Arm3 the H-arm form on E plane tee in combination with arm 1 and arm 2 a side orcollinear arms. If power is fed into arm 3 the electric field devices equallybetween 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 dividesequally into arm 1 and arm 2 but out of phase with no power to arm 3.Procedure1. VSWR measurement of parts.
Setup components and equipments.’ Energy microwave source for particular freq of operation and tune thedetector mount for maximum output. Measure VSWR of E – arm as describedin measurement of SWR for low and medium value connect another arm toslotted line and terminate other port with matched termination. Measure VSWRas above.2. Measurement of isolation and coupling coefficient. Remove tunable probe and magic tee from the slotted line and connectthe detector mount to slotted line. Energize the microwave source for particularfrequency 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 FIBREAim: 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.