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 θ1 = n2 . sin θ2

n1, n2 refractive indices of initial and secondary materials.

θ 1,θ 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 (Q2) 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 4μA per 10μ

W of incident optical energy at 950 nm and it has rise & fall time of 0.01μS.

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 = Sinθmax = r/√d2+r2 where θmax 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 μW. This means that the

electrical power at 10 mA current is converted to 200 μW 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 μA).

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

λd /2 = (d1 – d2)

Where d1, d2 are the distances between 2 successive maxima / minima.

For TE10 mode.

λc = 2am

, m = 1 in TE10 mode.

λ o - Free space wavelength

λg - Guide wave length

λ c - 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 = cλ0

= c√ 1λg2 +

1λ c2

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) = EmaxEmin

= |E I|+|Er||E I|−|Er|

EI = incident voltage

Er = reflected voltage

Reflection coefficient

S = EvEi

= Z−ZoZ+Zo

|S| = s – 1s+1

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 λg.

6. Calculate the SWR as:

SWR =λ g

π (d1 – d2)

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

2D2

λo(For rectangular horn antenna)

Gain calculated as :- Pt = P r λοG1G2

(4 π s )2

Pt = Transmitted power

Pr = Received power

λο = 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.