Jawaharlal Nehru Engineering College Laboratory Manual Optical & Microwave Communications For Final Year Students Manual made by Prof.S.D.Jadhav ©Author JNEC, Aurangabad
1 Technical Document This technical document is a series of Laboratory manuals of Electronics and Telecommunication Department and is a certified of Jawaharlal Nehru Engineering College. The care has been taken to make the document error free. But still if any error is found, kindly bring it to the notice of subject teacher and HOD. Recommended by HOD Approved by, Principal Copies: 1. Departmental Library 2. Laboratory 3. HOD 4. Principal
2 FOREWARD It is my great pleasure to present this laboratory manual for final year students for the subject of Optical fiber and microwave Communications keeping in view the vast coverage required for visualization of concept of Optical fiber and Microwave Communications. As a student, many of you may be wondering with some of the questions in your mind regarding the subject and exactly what has been tried to answer through this manual. Faculty members are also advised that covering these aspects in initial stage itself,will greatly relieve them in future as much of the load will be taken care by the enthusiasm energies of the students once they are conceptually clear. H.O.D
3 LABORATORY MANUAL CONTENTS This manual is intended for the Final Year students of Engineering in the subject of O&MC. This manual typically contains practical/Lab sessions related O&MC covering various aspects of the subject to enhance understanding. Students are advised to go thoroughly through this manual rather than only topics mentioned in the syllabus as practical aspects are the key to understand and conceptual visualization of theoretical aspects covered in the books Good Luck for your enjoyable Laboratory sessions. Prof.S.D.Jadhav
4 DO’s and Don’ts in Laboratory: 1. Do not handle the equipment without reading the instructions/Instruction manuals. 2. Read carefully the power ratings of the equipment before it is switched on. For Indian equipments, the power ratings are normally230V/50Hz.If you have equipment with115V/60Hz ratings do not insert power plug, as our normal power supply is 230V/50Hz,Which will damage the equipment. 3. Observe the type of sockets to avoid mechanical damage. 4. Do not forcefully place the connectors. 5. Strictly observe the instructions given by the teacher/lab instructor.. Instruction for Laboratory Teachers: 1. Lab work completed during prior session should be corrected during the next lab session. 2. Students should be guided and helped whenever they face difficulties. 3. The promptness of submission should be encouraged by way of marking and evaluation patterns that will benefit the sincere students.
5 SUBJECT INDEX Lab Experiments 1. Study Optical fiber 2. Study Optical fiber Connectors and Splices 3. Study Optical Time Domain Reflectometer (OTDR) 4. Study Sources of light for Optical fiber 5. Study the various UHF components 6. Measurement of transmission line characteristics 7. Study of Gunn diode and plotting its VI characteristics 8. Study Microwave TEE’s 9. Study of Microwave Antennas
6 Experiment No.1 Study of Optical Fiber Aim: To study Optical fiber. Apparatus: Optical fiber, Cutter, light source, etc Theory: An optical fiber (or fiber) is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber­optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers. Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fibers which support many propagation paths or transverse modes are called multi­ mode fibers (MMF), while those which can only support a single mode are called single­ mode fibers (SMF). Multi­mode fibers generally have a larger core diameter, and are used for short­distance communication links and for applications where high power must be transmitted. Single­mode fibers are used for most communication links longer than 550 meters (1,800 ft). Principle of operation An optical fiber is a cylindrical dielectric waveguide (non conducting waveguide) that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step­index fiber, or gradual, in graded­index fiber
7 Total internal reflection Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs. When light traveling in a dense medium hits a boundary at a steep angle (larger than the "critical angle" for the boundary), the light will be completely reflected. This effect is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding. In simpler terms, there is a maximum angle from the fiber axis at which light may enter the fiber so that it will propagate, or travel, in the core of the fiber. The sine of this maximum angle is the numerical aperture (NA) of the fiber. Fiber with a larger NA requires less precision to splice and work with than fiber with a smaller NA. Single­mode fiber has a small NA.
8 Fig1.Cross Section of Optical Fiber Special­purpose fiber Some special­purpose optical fiber is constructed with a non­cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross­section. These include polarization­maintaining fiber and fiber designed to suppress whispering gallery mode propagation. Photonic crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). Such fiber uses diffraction effects instead of or in addition to total internal reflection, to confine light to the fiber's core. The properties of the fiber can be tailored to a wide variety of applications.
9 Materials Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer­ wavelength infrared applications. Like other glasses, these glasses have a refractive index of about 1.5. Typically the difference between core and cladding is less than one percent. Properties of Optical Fiber. 1.Numerical Aperture of any type of fiber is defined as: where n1 =is the refractive index along the central axis of the fiber(core). n 2= refractive index of cladding 2. Attenuation 3. Dispersion 3. Fiber strength 4. Band width parameters 5.Rise Time
10 Applications and Advantages 1. Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. 2. It is especially advantageous for long­distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters. 3. Additionally, the per­channel light signals propagating in the fiber can be modulated at rates as high as 111 gigabits per second, ] although 10 or 40 Gb/s is typical in deployed systems. 4. Each fiber can carry many independent channels, each using a different wavelength of light (wavelength­division multiplexing (WDM)). 5. The net data rate (data rate without overhead bytes) per fiber is the per­channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 2008). The current laboratory fiber optic data rate record, is multiplexing 155 channels, each carrying 100 Gbps over a 7000 km fiber. Conclusion:­Hence Optical fiber is studied in detail.
11 Experiment No.2 Study of Optical Fiber Connectors and Splices Aim: To study Optical fiber Connectors and Splices Apparatus: Optical fiber, Connectors and splices. Theory: An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so that light can pass. Most optical fiber connectors are spring­ loaded: The fiber end faces of the two connectors are pressed together, resulting in a direct glass to glass or plastic to plastic, respectively, contact, avoiding any glass to air or plastic to air interfaces, which would result in higher connector losses. Connectorization and Splicing of optical Fiber. In any fiber optic system, one will find the need of splices and connectors. Splices are required during i9nstallation and again during services, if the cables are damaged and fibers are broken, Connectors are invariably used to connect fiber to the terminal equipment. Each splice or connector gives rise to additional attenuation and the need to minimize such losses requires a careful preparation of the ends of the fiber. Low losses are obtained only if the fiber ends are clean, smooth and perpendicular to the fiber axis. CONNECTORIZATION:­ It is the process of terminating the fiber by a connector. Normally a source and a detector are mounted inn a standard bulkhead, into which the fiber of the system. Having connector at the end, is plugged. Such an arrangement permits individual units and components to be tested separately and replace if necessary. Moreover this arrangement also allows maximum coupling of light. Many different designs of connectors have been developed. Most use a female for fiber alignment, although some designs use three spheres to centre the fiber and a double cone to align the connectors. Some of the more sophisticated types intended for use in high speed where back reflections must be minimized, allow physical contact between the two.
12 SMA connector is commonly used with multimode fibers. It has a 9mm long ferrule with a precision bore designed to match the cladding diameter and a standard SMA threaded sleeve for connection. A typical insertion loss is in the region of1dB initially, but mechanical wear &tear of the fiber during its life involves thousands of disconnections and re connections causing losses to increase. The ST connector is intended for use with multimode fibers. It is relatively easy to terminate and employ a bayonet coupling collar somewhat similar to BNC co­axial connector. Typical insertion losses of 0.5dB can be obtained in clean conditions. Some relatively inexpensive, bi­conical, plastic, snap­in connectors have been developed, of which the type SC is one. Another standard is the two fiber connector specified for the FDDI high capacity LAN. Note:­ Draw the diagram of Lens type Connector and ferrule type connector Conclusion: Thus, Fiber connector and splices is studied successfully.
13 Experiment No.3 Study of OTDR Aim: To study Optical Time Domain Reflectometer (OTDR) Theory: The OTDR or backscatter method utilizes the light scattered in the fiber by Rayleigh scattering. Figure below shows the block diagram of operating principle of OTDR. Coupler Fiber Pulsed Laser APD Photodetector Box Car Integrator Log Amplifier Chart Recorder
Fig 1. Block diagram of operating principle of OTDR 14 This Technique provides measurement of the attenuation on an optical fiber link. A light pulse is launched into the fiber in the forward direction from an injection laser using either directional coupler or a system of external lenses using a beam splitter. The backscattered light is detected using an Avalanche Photodiode receiver which drives an integrator in order to improve the received signal to noise ratio by giving arithmetic average over a number of measurements taken at one point within the fiber. This is necessary as the received optical power from a particular point along the fiber is very low. The signal from the Integrator is fed through a logarithmic amplifier and averaged measurements for location for successive points within the fiber are plotted on a strip chart recorder. This provides location­dependant attenuation values which gives an overall picture of the optical loss down the fiber link. Conclusion: Thus the Operating principle of OTDR is studied in detail.
15 Experiment No.4 Sources of light for Optical fiber Aim: To study Sources of light for Optical fiber Theory: Optical source is often considered to be the active component of an OFC system. Its function is to convert electrical energy in the form of current into optical energy, in efficient manner into the fiber. Three main types of optical fibers sources are 1. Wideband continous spectra sources(incandescent lamps) 2. Monochromatic incoherent sources (Light Emitting Diodes) 3. Monochromatic coherent sources (Lasers) For optical Fiber communications LED’s and LASERS are preferred sources. 1. Light Emitting Diodes: Construction and working principle: The LED consists of an encapsulated chip of semiconductor diode with a suitable lens. The length of Anode terminal is greater than cathode terminal. LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm 2 ) with integrated optical components to shape its radiation pattern and assist in reflection.
16 Fig 1.Working Principle of LED Material for LED In case of LED different materials are used to get the radiation in infrared region and in the visible region. To get radiation in infrared region Ga As material is used Sometimes the combination Ga As with indium and aluminium is used. It gives the wavelength as follows: In Ga As­­­­­­8500 Angstrom Al Ga as­­­­­­­9000 Angstrom
17 Advantages of LED 1. They are small in size and light in weight. 2. They are mechanically rugged and have low operating temperature. 3. No complex driving circuitry is required. 4. Have high switching speed and are available in different colours. 5. Linearity is more and compatible with integrated circuits. Disadvantages of LED 1. Output power gets affected by the temperature variation. 2. Quantum efficiency is low. 3. Gets damaged because of overvoltage and over current. Fig 2.Different types of LED
18 2. LASER: ‐ (Light Amplification by Stimulated Emission of Radiation) A laser (Light Amplification by Stimulated Emission of Radiation)is a device that emits light (electromagnetic radiation) through a process called stimulated emission. Laser light is usually spatially coherent, which means that the light either is emitted in a narrow, low­divergence beam, or can be converted into one with the help of optical components such as lenses. More generally, coherent light typically means the source produces light waves that are in step. They have the same frequencies and identical phase. ABSORPTION, SPONTANEOUS AND STIMULATED EMISSION In general, when an electron is in an excited energy state, it must eventually decay to a lower level, giving off a photon of radiation. This event is called “spontaneous emission,” and the photon is emitted in a random direction and a random phase. The average time it takes for the electron to decay is called the time constant for spontaneous emission, and is represented by t. On the other hand, if an electron is in energy state E2, and its decay path is to E1, but, before it has a chance to spontaneously decay, a photon happens to pass by whose energy is approximately E24E1, there is a probability that the passing photon will cause the electron to decay in such a manner that a photon is emitted at exactly the same wavelength, in exactly the same direction, and with exactly the same phase as the passing photon. This process is called “stimulated emission.” Absorption, spontaneous emission, and stimulated emission are illustrated in figure .Now consider the group of atoms shown in figure below. All begin in exactly the same excited state, and most are effectively within the stimulation range of a passing photon. We also will assume that t is very long, and that the probability for stimulated emission is 100 percent. The incoming (stimulating) photon interacts with the first atom, causing stimulated emission of a coherent photon; these two photons then interact with the next two atoms in line, and the result is four coherent photons, on down the line. At the end of the process, we will have eleven coherent photons, all with identical phases and all traveling in the same direction. In other words, the initial photon has been “amplified” by a factor of eleven. Note that the energy to put these atoms in excited states is provided externally by some energy source which is usually referred to as the “pump” source.
19 Fig 3. Absorbtion, Spontaneous emission and stimulated emission mechanism POPULATION INVERSION Atomic energy states are much more complex than indicated by the description above. There are many more energy levels, and each one has its own time constants for decay. The four­level energy diagram shown in figure 4. is representative of some real lasers. The electron is pumped (excited) into an upper level E4 by some mechanism (for example, a collision with another atom or absorption of high­energy radiation). It then decays to E3, then to E2, and finally to the ground state E1. Let us assume that the time it takes to decay from E2 to E1 is much longer than the time it takes to decay from E2 to E1. In a large population of such atoms, at equilibrium and with a continuous pumping process, a population inversion will occur between the E3 and E2 energy states, and a photon entering the population
20 will be amplified coherently. Fig.4 Amplification by stimulated emission Advantages of LASER over other Light Sources: 1. LASER light has narrow spectral bandwidth. 2. Light is coherent and monochromatic 3. LASER light has good directionality. 4. More percentage of the LASER light is in the visible range as compared to conventional lamps. 5. LASER has high quantum efficiency and high modulation rate. 6. LASERS are point source of light. 7. LASER has excellent stability. 8. LASER light can be modulated externally or it has ability of direct modulation.
21 Types of LASERs According to the type of material used for the formation of LASER beam, the LASERs are classified as the solid state laser, gaseous laser, power lasers and semiconductor LASERs. A] Solid State LASERS 1. Ruby Laser 2. Nd: YAG Laser B] Semiconductor LASER C] Gas LASERs 1. Helium­Neon Lasers 2. Carbon Dioxide Laser Conclusion: Thus, sources of light are studied in detail.
22 Experiment No.5 Study Of various UHF components Aim: To study the various UHF components. List of Components:­ 1) Rectangular wave guide 2) Circular wave guide 3) Wave guide stand 4) Flanges 5) Fixed attenuator 6) Micrometer type frequency meter 7) Broad band tuned probe 8) Wave guide matched detector mount 9) Wave guide detector mount (tunable) 10) Precision slide screw tuners 11) Klystron mount 12) Three port ferrite circulator 13) E­H tuners 14) H plane Tee 15) E plane Tee 16) Directional coupler 17) Isolator 18) Match termination 19) Horn antenna 20) Sectoral horn antenna 21) Pyramidal antenna 22) Wave guide twist 23) Gunn oscillator 24) PIN modulator 25) VSWR meter 26) Klystron power supply 27) Gunn power supply Theory: ­ Following information regarding the component should be written. Model name and frequency range. Draw the diagram of each component Write specification of each component as given in the manual. Write application of each Component. Conclusion: ­ Thus studied UHF components.
23 Experiment No.6 Relationship between frequency of oscillation & repeller voltage of Reflex klystron Aim:­ To verify relationship between frequency of oscillation & repeller voltage of Reflex klystron. Apparatus: Reflex Klystron, Klystron power supply, Isolator, frequency meter, Variable attenuator, Detector mount, VSWR meter, BNC cable. Block Diagram:­ Theory:­ The reflex klystron make the use of velocity modulation to transform a continues electron beam in to microwave power. Electron emitted from the cathode are accelerated and passed through the positive resonator toward negative reflector, which retard and finally reflects electron and electron return back through the resonator. Suppose an hi field exist between the resonator .The electron traveling forward will be accelerated or retarded .As the voltage at the resonator change in amplitude. The accelerated electron leave the resonator at the increased velocity and the retarded electron leave at the reduced velocity .The electrons leaving the resonator will need different time to return due to change in velocities .As a result returning electron group together in bunches. As the electron bunches pass through resonator they interact with
24 voltage at resonator grids. If the bunches pass the grid at such time that the electrons are slowed down by the voltage energy will be delivered to the resonator and klystron will oscillate. The frequency is preliminary determined by the dimension of resonant cavity. Hence by changing the volume of resonator, mechanical tuning range of klystron is possible. Also a small frequency change can be obtained by adjusting the reflector voltage. This is called electronic tuning. Observation: ­ Beam voltage= Beam current= Repeller voltage= Repeller voltage Frequency Procedure:­ 1) Connect the equipment &component s as shown in the figure 2) Set the variable attenuator to around zero position & set the range switch of VSWR meter to 40­db positions. 3) Anti­clockwise direction, repeller voltage knob to minimum position. 4) On the klystron power supply, VSWR meter &cooling fan .Set the beam voltage to 250v and limiting beam current to less than 5) Gradually increase repeller voltage &look for sudden deflection in VSWR meter. 6) Note the corresponding frequency with the help of frequency meter. Also note the repeller voltage. 7) Slightly vary the repeller voltage on either side of this reading. Note the corresponding variation of the frequency. 8) Find the tuning range after plotting the 3db points on the repeller voltage vs. power o/p graph. Conclusion: ­ Thus, we find tuning range for two widely different repeller voltages.
25 Experiment No.7 Gunn diode & its characteristics Aim: ­ Study of Gunn diode and plot VI characteristics of Gunn diode. Apparatus:­ Reflex Klystron ,Klystron power supply ,Isolator ,frequency meter, Variable & variable attenuator, Detector mount, VSWR meter, BNC Cable Matched load E plane, H plane & Magic Tee. Block Diagram:­ Fig 1.Set for study of a Gunn Diode Characteristics Theory:­ The Gunn oscillator is based on negative differential conductivity effect in bulk semiconductors which has two conduction band minima separated by an energy gap .A disturbance at cathode gives rise to high field region which travel’s towards the anode .When this high field domains reaches the anode, it disappears and another domain is formed at the cathode and starts moving anode and so on. The time required for domain to travel from cathode to anode gives oscillation frequency. A uniform type of uniform type of Gunn diode with same contact as the end surface. Above some critical voltage current becomes function of time .It was discovered by J B
26 Gunn. It uses bulk property of semiconductor only. So it must be associated with electron rather than holes .The voltage applied is proportional to the sample length and hence electric field is expressed in v/m. When DC voltage is applied across the side of Gunn diode, cadmium ferrite in ­ve resistance property across at particular voltage range value .As the applied potential increases i.e. greater than electric field higher electron present, hence higher current across the line in short time so acceleration occur in microwave range. Actually Frequency of oscillation in determined the time so acceleration occurs in microwave range. Actually frequency of oscillation is determined the time that the bunches of electron form and arrive at the end. Procedure: ­ 1) Switch on the Gunn power supply. 2) Adjust the bench to get maximum o/p waveform. 3) By making voltage initially zero note down the current. 4) Plot the graph of V and I Observation:­ 1. Beam voltage= 2. Beam current= Conclusion: ­ Thus the V­I characteristics of Gunn diode is studied.
27 Experiment No.8 Study of Microwave TEE i.e. E plane, H plane & Magic Tee. Aim: ­To measure the power distribution of various magic Tee i.e. E plane, H plane & Magic Tee. Apparatus: ­ Reflex Klystron, Klystron power supply, Isolator, frequency meter, Variable & variable attenuator, Detector mount, VSWR meter BNC, Cable Matched load E plane, H plane & Magic Tee. Theory:­ Wave­guide Tee’s are used for connecting a branch section of wave­guide in series or parallel with the main wave­guide. Tees are also be used as power divider field. 1) Input VSWR­ Value of SWR corresponding to each port as a load to the line while other ports are terminated in matched load. 2) Isolation­ The isolation between E and H arm is defined as the ration of the power supplied by the generator connected to the E port 4 to the power detected at H arm port 3 Isolation=10 log10P4/P3 3) Coupling coefficient­ It is defined as Cij=10 –_/20 Where _ is attenuation /isolation in dB when it is input arm and j is output arm Thus _= 10 log Pi/Pj
28 Where Pi is power delivered to arm i and Pj is power detected at j arm E plane Tee­ Model 6031 E plane Tee is a type T junction & consist of 3 section wave guide joint together in order to divide & compare power levels .The signals entering first part of the P junction will be equally divided at 2nd 3rd port of magnitude but opposite in direction. H plane Tee­Model 3065 H plane TEE are shunt type T­junction that is used in conjunction with VSWR meter, Frequency meter &other detector devices. Magic Tee – Model 3045 E­H consist of section of wave­guide with both series & shunt wave­guide are mounted at exact mid point of the main arm. This becomes four terminal devices where one terminal is isolated from the i/p. VSWR of 1.40 over +­ 15%freq range. This is achieved by inserting &connecting piece with stub. Procedure: ­ H­plane Tee: ­ a) Give i/p at port 1 b) Observe o/p on VSWR meter at port 2&3. E plane Tee a) Give i/p at port 1. b) Observe output at port Magic Tee a) Give i/p at port 1. b) Observe the output at port 2,3&4 c) Give i/p at port 4. d) Observe the o/p at port 1,2&3.
29 Observation:­ Beam voltage= Beam current= Repeller voltage= a) H plane Tee 1. Input at port 1= 2. Output At port 2= At port 3= b) E plane Tee 1. Input at port 1= 2. Output At port2= At port 3= c) Magic Tee 1. Input at port 1= 2. Output At port 2= At port 3= At port 4= 3. Input at port 4= 4. Output At port 1= At port 2= At port 3= Conclusion:­Discuss the power distribution in each Tee.
30 Experiment No.9 STUDY OF ANTENNAS Aim: ­To study the various antennas. Theory:­ Antennas are used at all frequency but in actual practice the frequency on which it operates depends on its shape to the large extent. Antenna types are:­ 1) Horn antenna­ A horn antenna may be regarded as a flared out or open out wave guide A wave guide is capable of radiating in to open space provided the same is excited at one end and open at other end. However the radiation is much greater through wave­guide than the two­wire transmission the line in waveguide is small in portion of incident wave is radiated and large portion is reflected back by the open circuit. 2) Parabolic reflector or microwave dish­ A parabola is a two­dimensional plane curve .A practical reflector is a three dimensional curved surface. Therefore rotating a parabola about its axis .The surface so generated is called as “Parabolic” Which is also called as “Microwave Dish or Parabolic Reflector” forms practical reflector. Parabolic produces a parallel beam of circular cross section because the mouth of parabolic is circular. 3) Hertz antenna­ It is also a half wave dipole antenna .The dipole antenna dates back to the early half RF experiments in the center so that RF power can be applied to it .One can think of the half wave dipoles an open circuited transmission line that has been spread out so that the transmission line that has been spread out so that transmission can be spread out in space .A dipole can be of any length commonly is just under ½ wavelength long. Conclusion: ­ Thus the different antennas are studied.
31 Quiz on the subject Q1. What is reflex Klystron? Q2. What are disadvantages of reflex klystron? Q3.What are applications of klystrons? Q4.Define directional coupler. Q5. What are performance characteristics of directional coupler? Q6.What are different types of Tee? Q7.What do you mean by ‘Magic’ Tee?
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