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MW & OC LAB MANUAL ECE DEPARTMENT

1 SPHOORTHY Engg.College.

SPHOORTHY ENGINEERING COLLEGENadargul (V), Saroornagar (M), R.R. (Dist.), A.P.

LABORATORY MANUAL

For

MICROWAVE & OPTICALCOMMUNICATIONS

(FOR IV ECE-REGULATION R05)

Department OfELECTRONICS & COMMUNICATION ENGINEERING

Academic Year: 2009-2010.

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INDEX

Principal Head of the Department(Dr.SYED S BASHA, M.E., Ph.D.) (Mr.T.RAVICHANDRA BABU)

S.NO. NAME OF THE EXPERIMENT PAGE

NO.

1. STUDY OF REFLEX KLYSTRON

CHARACTERISTICS

3

2.STUDY OF GUNN DIODE CHARACTERISTICS

9

3. FREQUENCY AND WAVELENGTH

MEASUREMENT

13

4.IMPEDANCE MEASUREMENT

17

5.VSWR MEASUREMENT

21

6.DIRECTIONAL COUPLERS

26

7.CIRCULATOR

31

8.MAGIC TEE

36

9.WAVEGUIDE PARAMETERS MEASUREMENT

42

10.ATTENUATION MEASUREMENT

47

11. CHRACTERISATION OF 660 & 850 nm LEDs 51

12

CHARACTERISTICS OF LASER DIODES

54

13 INTENSITY MODULATION OF LASER 57

14NUMERICAL APERTURE

59

15LOSSES IN OPTICAL FIBRES

62

16DIGITAL OPTICAL TRANSMISSION LINK

66

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STUDY OF REFLEX KLYSTRON CHARACTERISTICS

Experiment No. 1

AIM:

1. To study the mode characteristics of a Reflex Klystron

2. To determine transit time and electronic tuning.

EQUIPMENT:

1. Klystron power supply

2. Klystron mount with Klystron 723 A/B or 2K25

3. Variable attenuator

4. Frequency meter5. Detector mount

6. VSWR meter

7. Fan or blower

8. Wave guide support

9. Multi meter

10. Isolator

THEORY:

The Reflex Klystron is a microwave device that makes use of velocity modulation to

transform a continuous electron beam into microwave power. It is easily tuned. Its oscillation

frequency can be varied over a wide band and it can be pulse and frequency modulated.

Electrons emitted from the cathode are accelerated and passed through the positive

resonator grids towards the reflector. The reflector is at a negative voltage w.r.t. cathode and

consequently it retards and finally reflects the electrons which then turn back through the

resonator grids. Suppose the Klystron starts to oscillate. Then a high field exists between the

resonator grids. The electrons traveling forward will be either accelerated or retarded as the

voltage between the grids changes in amplitude. Accelerated electrons leave the grids will

need different time to return (i.e., have different transit times). As a result electrons group

together in bunches. This variation in velocity of the electron is called velocity modulation.

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As the electron bunches pass through the resonator grids they interact with the voltage

between the grids. If the bunches pass through at a time such that the electron are slowed

down by the grid voltage, energy will be delivered and the

Klystron will oscillate. Strongest oscillation will occur when the transit time in the

reflector resonator region is (n+3/4) cycle of the resonator frequency, where n is an integer

including zero. If the bunches pass through the grids as a time such that electrons are

accelerated by the grid voltage, energy will be removed from the resonator and no oscillation

will occur.

It can be seen that oscillations will occur at many different reflector voltages

(Corresponding to different transit times). The Klystron is said to be oscillate in differentmodes. The dimensions of the resonator of the resonator cavity primarily determine the

frequency.

So, by the variation of the resonator cavity, mechanical tuning of the Klystron is

possible. But as can be seen, as a small frequency change can also be obtained by adjusting

the reflector voltage (or the resonator voltage). This is called electronic tuning.

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SET UP FOR REFLEX KLYSTRON

BLOCK DIAGRAM:

PROCEDURE:

1. The equipment is setup as shown in the block diagram.

2. The attenuator is set to the maximum position.

3. The Mod Switch of KPS is set to CW position, beam voltage control knob to

fully anticlockwise and reflector voltage control knob to fully clockwise and the

meter switch to OFF Switch.4. The knob of frequency meter is rotated at one side fully.

5. The multi meter is kept in D.C. A range of 250 A.6. The KPS, VSWR and cooling fan for the Klystron tube are switched on.

7. The meter switch is set to beam voltage position and the beam voltage knob is

rotated in clockwise direction slowly up to 300V meter reading and the beam

current position is observed. The beam current should not increase more than

30mA.

8. The reflector voltage is changed slowly. The voltage is set to max deflection in themeter. If no deflection is obtained multi meter switch is changed to position of 50

A.9. The plunger of klystron mount is tuned for the maximum o/p.

10. The knob of frequency meter is rotated slowly and stopped at a position, where there

is less o/p current on multi meter. Read directly the frequency between two

horizontal line and vertical marker from frequency meter.

11. For different values of the reflector voltage the corresponding current and frequencyare tabulated.

12. Graph is plotted between repeller voltage and current.

Frequency

Meter

Klystron

power

supply

Detector

mountVSWR

meter

Multi

meter

Oscilloscope

Variable

Attenuator

Isolator

Klystron

Mount

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MODEL WAVEFORMS

mw

20

VOLTS

-50 -100 -150 -200

MHz

50

VOLTS0

-50

fig -2

MODES OF 2K25

REFLECTOR

VOLTAGE

FREQUENCY

CHANGE

OUTPUT

POWER

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OBSERVATIONS:

Initial Beam Voltage = _________________

Beam Current = _________________

Repeller Voltage = _________________

S.No. Reflector Voltage

in (volts)

Output power

in mW

Frequency

in GHz1.

2.

3.

4.

5.

6.

7.

8.

9.10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.33.

34.

35.

36.

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CALCULATIONS:

Transit time tr= (n+3/4)/fon where n is any integer

n=1 (assume)

fon operating frequency in GHz

Electronic tuning = (f2-f1)/v2-v1

PRECAUTIONS:

1. For stable operation the Klystron is allowed to warm up to 10 minutes before

the experiment is conducted.

2. The attenuator position should not be disturbed after adjusting for maximum

power output.

3. Loose connections between the components should be avoided.

RESULT

Thus the followings are observed & studied

1. The transiting time and electronic tuning of the Reflex Klystron are found.

2. V- I Characteristics of Reflex Klystron Oscillator is studied.

XXX

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STUDY OF GUNN OSCILLATOR

Experiment No: 2

AIM:

To study the V- I characteristics of Gunn Oscillator

EQUIMENT:

1. Gunn power Supply

2. Gunn oscillator


4. Wave guide support

5. Frequency meter

6. Detector mount

7. Ammeter

THEORY:

The Gunn diode is embedded in a single structured crystal assembly which oscillates

by it self at microwave frequencies. The diode assembly known as Gunn diode consists of

Gallium Arsenide sandwich made of intermediate resistivity material placed between two

other low resistivity materials.

When a Gunn diode is biased the disturbance created at the cathode gives raise high

field region which travels towards anode. At anode this domain disappears while another is

originated. The time taken by the domain to travel between the two electrodes determines the

oscillation frequency. When the diode is placed in a resonant frequency of the cavity rather

than the diode itself. In this case the mode oscillations are not transit time mode.

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SET UP FOR GUNN OSCILLATOR

BLOCK DIAGRAM

FIG NO 1

Threshold Voltage

I

V

Fig 2 V I Characteristics of Gunn Oscillator

Gunn

Oscillator

Isolator

Gunn

power

supply

Matched

Termina-

tion

Variable

attenuator

Frequency

meter

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PROCEDURE:

I. GENERAL:

1. The equipment is set as shown in the block diagram.

2. The attenuator is set to the maximum position.

3. The Gunn diode Oscillator is connected correctly to the BNC connector

4. The two knobs on the power supply are turned fully in anti-clock

wise direction.

5. The micrometer on the wave guide cavity Gunn oscillator is set

approximately to 13.63 mm.

II. THE VOLT- AMPERE CHARACTERISTIC:

1. The equipment is set as shown in figure.

2. The voltage is increased in steps of 0.5V and corresponding current from theGunn power supply is noted by switching alternatively to current and

voltage position.

3. The readings are tabulated.

4. Graph is drawn with voltage on the X axis and input current on the Y

axis.

5. Graph is drawn with voltage on the X axis and output current on the Y

axis.

OBSERVATIONS:

S.No. Voltage(in volts) Input

Current

(in mA)

1.

2.

3.

4.

5.6.

7.

8.

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PRECAUTIONS:

1. The bias is kept course and the fine control knobs of the power meter are kept in

the maximum position before the meter is switched on.


power output.

3. Loose connection between the components should be avoided.

APPLICATIONS:

1. Broadband linear amplifier (replacing TWTs).

2. As pump source in parametric amplifiers.

3. Low and medium power oscillator in microwave receivers.

4. In Radar transmitters (Police Radar, CW Doppler Radar).

RESULT:

The Volt ampere characteristics of Gunn oscillator is observed.

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FREQUENCY AND WAVELENGTH MEASUREMENT

Experiment No: 3

AIM:

To determine the frequency and wavelength in a rectangular waveguide working in

TE10 mode.

EQUIPMENTS:

1. Klystron Power Supply

2. Klystron mount with Klystron tube


4. Frequency meter

5. Isolator

6. Slotted section

7. VSWR meter

8. Movable short

9. Termination

10. Waveguide stand

THEORY:

For dominant TE10 mode in rectangular waveguide o, g and c are related as

1/ o2

= (1/ g2

+ 1/ c2

)Where g guide wave length

o free space wave lengthc Cutoff wave length and its formula is given below as

c = 2ab/ (m2b2 +n2a2)For TE10 mode m=1 and n=0 therefore cutoff wavelength will be

c = 2a where is a broader dimension of waveguide.Frequency is measured by using formula

f= c/ oWavelength of a wave guide can be calculated by formula

g = o/ (1-(o/ c)2).The above formula shows that guide wavelength is greater than the free space wavelength. At

the cutoff wave length no field variations occur along the waveguide i.e. no energy is

propagated. Other parameters i.e. Phase velocity, phase constant, intrinsic impedance group

velocity can be calculated by using below formulas:

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p = / = c/(1- [fc/f]2) where c velocity of light = 3x 108 m/secgp= c

2

ZTE = / (1- [fc/f]2) where intrinsic impedance of free space =120 or 377

Graph is drawn between 1/ g2

on X- axis and 1/ o2

on Y axis. The Y intercept isnoted.

Graph is drawn between on X- axis and on Y axis.

SET UP FOR FREQUENCY AND WAVELENGTH MEASUREMENT

BLOCK DIAGRAM:

Frequency

Meter

Klystron

powersupply

Matched

Termination

VSWR meter

Movable

Short

Tunable

Prote

IsolatorVariable

Attenuator

Klystron

Mount

Slotted

Line

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PROCEDURE:

I. GENERAL:

1. The equipments are set as shown in the block diagram.

2. The variable attenuator is set at maximum position.

3. The control knobs of VSWR meter are kept as below:

i. Range 50db position

ii. I/P Switch Crystal low impedance.

iii. Meter switch Normal position

iv. Gain ( coarse & fine) Mid position.

4. The control knobs of klystron power supply are kept as below:

i. Meter switch OFF

ii. Mod switch AM

iii. Beam voltage knob fully anticlockwise

iv. Reflector voltage fully clockwise.v. AM amplitude knob around fully clock wise.

vi. AM frequency knob around mid position.

5. The klystron power supply, VSWR meter and cooling fan are switched on.

6. The meter switch of power supply is turned to beam voltage position and

beam voltage is set to 300V with help of beam voltage knob.

7. The reflector voltage is adjusted to get some deflection in VSWR meter.

8. The deflection in VSWR is maximized by adjusting AM amplitude and

frequency control knob of power supply.

9. The plunger of klystron mount is tuned for maximum deflection.

10. The probe is also tuned for maximum deflection in VSWR meter.

II . FREQUENCY MEASUREMENT:

1. The frequency meter is tuned to get dip on the VSWR scale.

2. The frequency meter is tuned to obtain minimum deflection.

3. The corresponding frequency is noted.

III. WAVELENGTH MEASUREMENT:

1. The termination is replaced with the movable short.

2. The frequency meter is detuned.3. The deflection in VSWR is varied by moving the probe along the slotted

line.

4. The probe is moved to a minimum deflection point. Accurate reading is got

by increasing the VSWR meter gain when close to minimum.

5. The probe position is recorded.

6. The probe is moved into the next minimum point and the probe position is

recorded.

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7. The guide wavelength is equal to twice the distance between the minima.

8. The waveguide inner broad dimensions a is measured which will be

around 2.286cm.

9. The frequency is calculated using formula f=c/[(1/g)2 +(1/2a)2].

OBSERVATIONS:

PRECAUTIONS:

1. For stable operation the Klystron is allowed to warm up to 10 minutes before

the experiment is conducted.2. The attenuator position should not be disturbed after adjusting for maximum

power output.


RESULT:

Frequency, free space wavelength, guide wave length, phase shift constant, phase

velocity, group velocity are calculated and compared the theoretical and practical values.

Theoretical Value ofg = __________________.Practical value of g= __________________ .

Operating

frequency(inGHz)

Observed

minima incm

g/2 in cm gin

cm

finGHz

=2fin 109

rad/s

1/oin

cm-2

1/gin

cm-2

=2/gin

rad/cm

px1010

cm/s

gx1010cm/s

1 2 3 2-1

3-2

Avg

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IMPEDENCE MEASUREMENT

Experiment No: 4

AIM:

To measure an unknown impedance with smith chart.

EQUIPMENTS:


2. Klystrons mount with Klystron 2K25.


4. Frequency meter

5. Isolator.

6. Slotted Line.

7. VSWR meter

8. Termination

9. Waveguide stand

10.Probe

11. S-S Tuner

THEORY:

The standing wave is the result of interaction between the incident wave and thereflected wave. In the matched case (i.e. no reflected wave) the ratio between the electric and

magnetic field is sane at all the points along the line. This ratio is directly related to the

characteristic impedance of the line Zo. if a reflected wave exists, the ratio is no longer same

along the line i.e. the impedance level varies periodically. The impedance at any point of a

transmission line can be written in the form of R+jX.

For comparison SWR can be calculated as

S= (1+||)/(1-||)

where reflection coefficient = (Z-Zo)/ (Z+Zo)

Zo characteristic impedance of w/g at operating

frequency.

Z impedance at any point.

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The measurement of impedance is done in following way:

The unknown device is connected to the slotted line and the SWR =So and the

position of one minima is determined. Then unknown device is replaced by movable short to

the slotted line. Two successive minima positions are noted. The twice of the difference

between minima position will be guide wavelength. One minima is used as reference for

impedance measurement. Find the difference of reference minima and minima position

obtained from unknown load. Let it bed. Take a smith chart, taking 1+j0 as centre, draw a

circle of radius equal to So. mark a point on circumference of chart towards load side at a

distance equal to g. join the centre with this point. Find the point where it cuts the drawncircle. The co-ordination of this point will show the normalized impedance of load.

SET UP FOR IMPEDANCE MEASUREMENT

BLOCK DIAGRAM

Variable

attenuator

Klystronpower

supply VSWRmeter

Movable

Short

Probe

Slotted

Line Termination

S-S

tuner

Klystron

Mount Isolator

Frequency

Meter

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PROCEDURE:

1. The equipments are set as shown in block diagram.

2. The variable attenuator is set to maximum position.

3. The control knobs of VSWR meter is set as below:

a. Range db 50db position

b. Input Switch Crystal low impedance

c. Meter Switch Normal position

d. Gain (Coarse and fine) Mid position4. The control knobs of klystron power supply is set as below:

i. Meter switch OFF

ii. Mod switch AM

iii. Beam voltage knob fully anticlockwiseiv. Reflector voltage fully clockwise.

v. AM amplitude knob around fully clock wise.



6. The meter switch of power supply is turned to beam voltage position and beam

voltage is set to 300V with help of beam voltage knob.


8. The deflection in VSWR is maximized by adjusting AM amplitude and frequency

control knob of power supply.



11. The reflector voltage knob is tuned for maximum deflection.

12. The frequency meter is tuned to get dip on the VSWR scale and the corresponding

frequency is noted.

13. The depth of pin of S-S tuner is kept around 3-4 mm and it is locked.

14. The probe is moved along the slotted line to get maximum deflection.

15. VSWR meter gain control knob and variable attenuator is adjusted until, the meter

indicates 1.0 on the normal upper SWR scale.

16. The probe is moved to next minima point and corresponding SWR = So and probe

position (say d3) is noted.

17. The S-S tuner and matched termination is replaced by movable short at slotted line.

At this point the plunger of short should be at zero.

18. The position of two successive minima is noted. Let it be d1 and d2. Hence g =2(d1-d2).

19. Calculate d/ g.20. The normalized impedance is computed using smith chart as described in theory.

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OBSERVATIONS:

With Movable short:

Dip in VSWR is Observed at = _____________GHz.

First minima, d1 = _____________cm.

Second minima, d2 = _____________cm.

Guide wave length g = 2(d1-d2) = _____________cm.With unknown impedance:

Let d1be the reference point.

VSWR Value at minima position= _____________.

Minima position d3 = _____________cm.

d = d3-d1 = _____________cm.

RESULT:

The impedance of unknown load is measured.

Measured impedance value is _____________ ohms.

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VSWR MEASUREMENT

Experiment No: 5

AIM:

To determine the standing wave ratio and reflection coefficient.

EQUIPMENTS:

1. Klystron tube


3. VSWR meter4. Klystron Mount

5. Isolator

6. Frequency meter


8. Slotted line

9. Tunable probe

10. Wave guide stand

11. S-S tuner

12. Movable short

13. BNC Cable

THEORY:

The electromagnetic field at any point of transmission line, may be considered

as a traveling waves: Incident Wave propagates from generator and the reflected wave

propagates towards the generator. The reflected wave is set up by reflection of incident wave

from a discontinuity on the line or from the load impedance. The magnitude and phase of

reflected wave depends upon amplitude and phase of the reflecting impedance. The presence

of two traveling waves, gives rise to standing wave along with the line. The maximum field

strength is found where two waves are in phase and minimum where the two waves adds in

opposite phase. The distance between two successive minimum(or maximum) is half the

guide wave length on the line. The ratio of electrical field strength of reflected and incidentwave is called reflection coefficient. The voltage standing ratio (VSWR) is defined as ratio

between maximum and minimum field strength along the line.

Hence VSWR, S= Emax/Emin = (|Ei|+|Er|)/ (|Ei| -|Er| )

Reflection Coefficient, =Er/Ei = {Z Zo}/ {Z + Zo}Where Z is the impedance at a point on line, Zo is characteristic impedance.

The above equation gives following equation:

|| = [S-1]/[S+1]

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SET UP FOR VSWR MEASUREMENT

BLOCK DIAGRAM

PROCEDURE:

I. GENERAL:

1. The equipments is set as shown in block diagram.


3. The control knobs of VSWR meter is set as below:a. Range db 40db/50db position



d. Gain (Coarse and fine) Mid position

4. The control knobs of klystron power supply is set as below:

vii. Meter switch OFF

viii. Mod switch AM

ix. Beam voltage knob fully anticlockwisex. Reflector voltage fully clockwise.

xi. AM amplitude knob around fully clock wise.

xii. AM frequency knob around mid position.


6. The meter switch of power supply is turned to beam voltage position and beam

voltage is set to 300V with help of beam voltage knob.

7. The reflector voltage is adjusted to get some deflection in VSWR meter.8. The output is tuned by tuning reflector voltage, AM amplitude and frequency

control knob of power supply.


VSWR

meter

Probe

Termination

S-S

tuner

Slotted

Line

Variable

attenuator

Frequency

MeterIsolator

Klystron

Mount

Klystron

supply

power

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11. To get deflection in the scale of VSWR the range db switch, variable

attenuator position and gain control knob is adjusted if necessary.

12. The deflection in VSWR can be varied by moving the probe along the slotted

line.

. MEASUREMENT OF LOW AND MEDIUM VSWR:

1. The probe is moved along the slotted line to get maximum deflection in VSWR

meter.

2. VSWR meter gain control knob or variable attenuator is adjusted until, the

meter indicates 1.0 on the normal upper SWR scale.

3. The probe is moved to next minima point with out disturbing all the control

knobs and corresponding VSWR is recorded.

4. The above step is repeated for change of S-S tuner probe depth and

corresponding VSWR is recorded.5. If the VSWR is between 3.2 and 10, then range dB switch is changed to next

higher position and VSWR is read from this second scale ranging from 3 t0 10.

III. MEASUREMENT OF HIGH VSWR (Double Minimum Method):

1. The depth of S-S tuner is set slightly more for maximum deflection.

2. The probe is moved along the slotted line till a minimum is indicated.3. The VSWR meter gain control knob and variable attenuator is adjusted to

obtain a reading of 3db of normal db of VSWR Meter.

4. The probe is moved to the left on slotted line, until full scale deflection is

obtained, i.e. 0db on 0-10db scale. The corresponding probe position is noted.Let it be d1.

5. The step 3 and 4 are repeated and then the probe is moved to right along with

slotted line until full scale deflection is obtained on 0- 10 db normal db scale.

Let it be d2.

6. The S-S tuner and terminator is replaced by movable short.

7. The distance between two successive minima position of probe is measured.

Twice this distance gives guide wavelength g.8. VSWR is computed by following equation:

S = g/[ (d1-d2)].

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MODEL WAVEFORMS

O/p Voltage

Vx = 2 Vmin

Vmin

d1 d2

Probe position

Double Minimum method

O/p

Vmax

Vmin g/4

g/2

Standing Wave

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OBSERVATIONS:

With S-S tuner and Termination:

First minima position d1

= ____________________cm.

Second minima position d2 = ____________________cm.

With Movable Short:First minima position d3 = ____________________cm.

Second minima position d4 = ____________________cm.Guide wavelength, g = 2(d3-d4) = ____________________cm

VSWR is computed as follows:VSWR = g/(d1-d2) =____________________.

RESULT:

Thus The VSWR is measured.

Measured value of VSWR = _______________.

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DIRECTIONAL COUPLER

Experiment No: 6

AIM:

To study directional coupler and to find their S matrices.

EQUIPMENTS:

1. Gunn power supply

2. Gunn Oscillator

3. Isolator


5. Frequency meter

6. Directional Coupler7. Detector

8. VSWR meter

9. Matched load

10. Fan11. Waveguide support

THEORY:

DIRECTIONAL COUPLER:

A director coupler (fig1) is a junction between 4 pairs of terminals having such

characteristics that there is free transfer of power with out reflection between terminals C & D

and no transfer of power between terminals A & C or between B & D. Degree of coupling

between A & D and between B & C depends upon the structure of the unit.

The important performance factors of a directional coupler are:

a. Coupling factor

b. Directivity

c. Insertion loss

d. Bandwidth

e. Frequency sensitivity

f. TWO HOLE DIRECTIONAL COUPLER:

g.h. The two hole directional coupler is a four port component (fig2). Two

holes P & Q are located inside the coupler. The holes P& Q are spaced g/4

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apart. As there is flow of energy from port1 to port2, there is some diversion of

energy into holes P&Q. If diameters of P&Q are same, then the amount of

energy through P&Q will be same. At P&Q, the energy is further bifurcated into

two portions going towards port3 and port4. Now the phase difference

between the portions of energy going from P & Q towards port3 is zero, hence

the two signals components add up; where as the components having the

direction towards port4 are out of phase by (2/g)* 2*PQ = radians. Hencethey cancel each other if their magnitudes are same, and this is the reason for

absence of signal for port4.

i.

j. Coupling factor in db, C=10log10(P1/P3)

k. Where P3power delivered to a matched load at terminal3 when

power P1entersthrough terminal1 with matched loads at 2 & 4.

l. Directivity in db, D =10log10 (P3/P4)

m. Where P3 and P4 are powers delivered in matched loads at

terminals 3 & 4 respectively with a matched load at terminal2.

n.o. Coupling factor is a measure of energy levels in primary and secondary

waveguides. Directivity is a measure of how well the forward traveling wave in

primary wave guide couples only to the desired terminals of a secondary wave

guide.

p.

q. The Scattering matrix of an ideal directional coupler is

r.

s. 0 C1 jC2 0

t. C1 0 0 jC2u. [S] = jC2 0 0 C1

v. 0 jC2 C1 0w.

x. where C2 = (1-C12)

1/2

SET UP FOR DIRECTIONAL COUPLER

A B

C D

Fig 1

Directional

Coupler

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3 4

P Q

g/4

1 2

TWO HOLE DIRECTIONAL COUPLER

Fig 2

BLOCK DIAGRAM

Fig 3

Gunn

Oscillator

Isolator

Gunn

power

supply

VSWR

Variable

attenuator DetectorDirectional

Coupler

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PROCEDURE:

I. GENERAL:

1. The equipment is set up as shown in fig 3.

2. The rotary wane attenuator is set at 20 db and the variable attenuator is set at

approximately 10 db.

3. The Gunn oscillator is tuned to 9 GHz.

II . MEASUREMENT OF COUPLING AND DIRECTIVITY:

1. The Gunn oscillator is tuned to 9 GHz.

2. The attenuator is kept in the maximum position.

3. A bias voltage of 7v is applied to the Gunn.

4. The power is fed through port 1 and the powers at port2 and port 3 are

measured. Let the powers of port 2 and port 3 be P2 and P3.

5. The directional coupler is reversed and the power is fed through port2. Thepower in port 4, P4 is measured.

6. The coupling factor and directivity of the directional coupler are calculated.

OBSERVATIONS:

Operating frequency= ___________GHz.

Power at port1 P1 = ___________ mw.




Coupling factor C = 10 log10(P1/P3) = _______________dB.

Directivity D = 10 log10(P4/P3) = _______________dB.

To determine Scattering matrices parameters S12, S13, S14

1. 20 log10 S12 = -10 log (P1/P2) = _________________.

S12 =100.5(log (P

1/P

2)

=__________________

2. 20 log10 S13 = -10 log10(P1/P3) =__________________.

S13 =100.5(log (P

1/P

3)

=__________________.

3. 20 log10 S14 = -10 log10(P4/P3) =__________________.

S14 =100.5(log (P

4/P

3)

=__________________.

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PRECAUTIONS:

1. Loose connections must be avoided.

2. The directional coupler should carefully handled while inserting it into the circuit.

APPLICATIONS:

Directional couplers are widely used in impedance bridges for microwave

measurements and for power monitoring.

RESULT:

The characteristic of the directional coupler is studied.

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CIRCULATOR

Experiment No: 7

AIM:

To study Circulator and to find their S matrices.

EQUIPMENTS:


2. Klystron mount with Klystron 2K25

3. Isolator


5. Frequency meter6. Circulator

7. Detector

8. VSWR meter

9. Matched load10. Fan

11. Waveguide support

THEORY:

A Circulator is a multi port junction in which the wave can travel from one port to next

immediate port in one direction only as shown in fig (1).

Three port circulator:

A three port circulator is formed by a 120 degree H-plane wave-guide or strip line

symmetrical Y-junction with a center ferrite post. A steady magnetic field Ho is applied along

the axis of post as shown in (wave guide type circulator) fig 2.

For a perfectly matched, loss less, non reciprocal three port circulator, the S matrix

is

0 1 0[S] = 1 0 0

0 1 0

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The important circulator parameters are:

1. Insertion loss:

Insertion loss is the ratio of power detected at the output port to the power supplied

by the source to the input port, measured with other ports terminated in the matched load.

It is expressed in db.

2. Isolation:

Isolation is the ratio of power applied at the output to that measured at the input.

The isolation of a circulator is measured with the third port terminative in a matched

load. It is expressed in dB.

3. The input VSWR:

The S input VSWR of a circulator is the ratio of voltage maximum to voltageminimum of the standing wave existing in the line with all ports expect the test port are

matched.

Since in practical losses are always present, the performance is limited by finite

isolation and non zero insertion loss. Typical characteristics can be represented by

Insertion loss < 1 dB

Isolation = 30 40 dB

VSWR < 1.5

SET UP FOR CIRCULATOR

Port 1

Port 2 Port 3

Fig 1

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HO 1

Conductor

Effect of biased ferric

Ferrite

3 2

fig 2: Waveguide type circulator

SET UP FOR CIRCULATOR

BLOCK DIAGRAM:

Fig - 3

Frequency

Meter

Klystron

Power

Supply

Tunable

Crystal

DetectorVSWR Meter

Variable

AttenuatorIsolator

Klystron

Mount

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SETUP FOR CIRCULTOR FOR MEASURING ISOLATION

BLOCK DIAGRAM:

Fig - 4

PROCEDURE:

I.GENERAL:


2. The Gunn oscillator is switched on and tuned to 9 GHz

II . MEASUREMENT OF ISOLATION IN A CIRCULATOR:


2. A reference power of 8mW is fed to port1. The powers at port2 and port 3 are

measured.

3. 8mW is fed to port 2. The powers at port3 and port1 are measured.

4. 8mW is fed to port 3. The powers at port2 and port1 are measured.

5. Isolation between the ports is calculated.

OBSERVATIONS:

S11 S12 S13[S] = S21 S22 S23

S31 S32 S33

Input power at P1 = 8mW or -20dB

Output power at P2 = _______________.(say x db).

Output power at P3 = _______________.(say y db).

Frequency

Meter

Klystron

power

supply

VSWR meter

Tunable

Crystal

Detector

CirculatorVariable

AttenuatorIsolator

Klystron

Mount

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Input power at P2 = 8mW or -20 db.

Output power at P3 = _______________.( say z db).

Output power at P1 = _______________.(say a db).

Input power at P3 = 8mW or 20db.

Output power at P2 = ________________.(say b db).

Output power at P1 = ________________.(say c db).

To determine Scattering matrices parameters S12, S13, S21, S23, S31, S32

1. 20 log10 S12 = -10 log (P1/P2) = (-20-x)db

S12 =100.5(log (P

1/P

2)= 10

0.5(-20-x)=____________.

2. 20 log10 S13 = -10 log10(P1/P3) = (-20 y)db

S13 =100.5(log (P1/P3) = 100.5(-20-y) =____________.

3. 20 log10 S21 = -10 log10(P2/P1) = (-20 z)db

S21 =100.5(log (P

2/P

1)= 10

0.5(-20-z)=____________.

4. 20 log10 S23 = -10 log10(P2/P3) = (-20 a)db

S23 =100.5(log (P

2/P

3)= 10

0.5(-20-a)=____________.

5. 20 log10 S31 = -10 log10(P3/P1) = (-20 b)db

S31 =100.5(log (P

3/P

1)= 10

0.5(-20-b)=____________.

6. 20 log10 S32 = -10 log10(P3/P2) = (-20 c)db

S32 =100.5(log (P

3/P

2)= 10

0.5(-20-c)=____________.

.PRECAUTIONS:


2. The Circulator should carefully handled while inserting it into the circuit.

RESULT:

The characteristics of the circulator is studied

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MAGIC TEEExperiment No: 8

AIM:

To study Magic Tee and to find their S matrices.

EQUIPMENTS:


2. Klystron mount with Klystron 2K25

3. Isolator


5. Frequency meter6. Circulator

7. Detector

8. VSWR meter

9. Matched load

10. Fan

11. Waveguide support

THEORY:

A magic T is a combination of an E plane tee and an H plane tee. It acts as a 4

port hybrid circuit, which in general form is shown in fig 1.

The characteristic of the hybrid circuit are such that if power enter the circuit through

arm A or C; the power is delivered entirely to arms B & D, with no power transmission from

port A to port C or C to A. Also power entering through arm B or arm D is entirely to arms A

& C, with no direct transfer from B to D.

Fig 2 show a magic T with a combination of an E plane and an H plane. The

collinear arms are called the side arms implying that it is usually one of the other two arms

which face the viewer. The arm which makes on H plane tee which side arm is called H

arm or shunt arm. The forth arm makes an E plane tee with the side arm and is called as E

arm. The shunt and series arms are cross polarized that is the voltage vectors in these twoarms are perpendicular to each other. Therefore as long as there is nothing within the junction

to the polarization, there can be no coupling between these two arms. The E & H arms are

matched by employing posts & irises to minimize the reflections from these two ports.

The magic T associated with hybrid junction is the way in which the power divides

in the various arms. The signal fed into the shunt or H arm divides itself equally and in

phase in the two side arms with no coupling in the E arm. When the signal is fed into series

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or E arm it also divides itself equally in the two arms but this time the two halves are

180oout of phase and there is no coupling to the H arm. If the power fed into one of the side

arms, it divides equally into the shunt & the series arms and there is no combine in phase o/p

at in the H arm & 180o

out of phase in the E arm.

A magic T is normally characterized by two quantities:

1. Isolation between E & H arms

2. Power division in the collinear arms.

Isolation between the E & H arms:

If PE is the power into E arm and PH is the power flowing out the H arm, the isolation

between the E & H arms is given by

Isolation (db) = 10 log10(PH/PE).

It is assumed that both the collinear arms are terminated.

In the other case Isolation (db) = 10 log10(PE/PH).For a well designed magic T, the isolation between E & H arms could be greater

than 20 db.

Power division:

The power fed into either the E arm or H arm should divide itself equally in both

the side arms, when the opposite arms are terminated. If PE is the power into E arm and Pc1and Pc2 are the power in the side arms, then the ratio of the power coupled inside arms to that

the relation gives entering in the E- arm.

Coupling in db = 10 log10(PC1/PH) = 10 log10(PC2/PH).The Scattering matrix of the magic T shown in figure is given by

0 1 1 0

2 1 0 0 1[S] = 2 1 0 0 -1

0 1 -1 0

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SET UP FOR MAGIC TEE

A B

C D

Fig 1

(3) E arm

(2) Collinear arm

(4) H - arm

(1) Collinear

arm

fig - 2

Hybrid Circuit

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SET UP FOR MAGIC TEE

BLOCK DIAGRAM

Fig 3

SET UP FOR MAGIC TEE FOR MEASURING ISOLATION AND COUPLING

BLOCK DIAGRAM

Fig 4

KlystronPower

Supply

Isolator

Variable

attenuator

Klystron

Mount

Frequency

meter

Tunable

Crystal

Detector

VSWR

Meter

Klystron

Power

Supply

Isolator

Variable

attenuator

Klystron

Mount

Frequency

meter

Magic

Tee

VSWRMeter

Tunable

Crystal

Detector

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PROCEDURE:

I. GENERAL:

1. The equipment is set up as shown in fig

2. The oscillator is tuned and switched to 9 GHz.

3. The Gunn power supply is set for square wave operations.

II. MEASUREMENT OF ISOLATION BETWEEN E & H ARMS:


2. A reference power of 8mW is fed through collinear arm 1.

3. The power at the collinear arm2and H arm are measured.

4. Isolation between E & H arm are calculated.

III. MEASUREMENT COUPLING IN COLLINEAR ARMS:


2. A reference power of 8mW is fed through H arm.

3. The power at the collinear arm1and arm2 and at E arm are measured.

4. Coupling between H & collinear arm are calculated.

OBSERVATIONS:

1. Power fed to port1(side arm1) = 8mW or -20db.

Power at port2(side arm2) = __________db. = P21

Power at port3(H arm ) = __________db. = P31

Power at port4(E arm ) = __________db. = P41

2. Power fed to port3 (H arm) = 8mW or -20db.



Power at port4(E arm ) = __________db. = P24

3. Power fed to port 4(E arm) = 8mW or -20db



Power at port3(H arm ) = __________db. = P43

S Parameters are determined as follows:

20 log S12 = P12 db.

S12 = 100.05P

12 = _______________.

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20 log S14 = P14 db.

S14 = 100.05P

14 = _______________.

20 log S13 = P13 db.

S13 = 100.05P

13 =________________.

20 log S34 = P34 db.

S34 = 100.05P

34 =________________.

20 log S32 = P32 db.

S32 = 100.05P

32 =________________.

20 log S42 = P42 db.

S42 = 100.05P

42 =________________.

.

PRECAUTIONS:


2. The magic - Tee should carefully handled while inserting it into the circuit.

APPLICATIONS:

1. It is used as a mixer.2. It is used as a duplexer.

3. It is used in measurement of impedance.

RESULT:

The characteristics of the magic T is studied

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WAVEGUIDE PARAMETERS MEASUREMENT

Experiment No: 9

AIM:

To determine the frequency and wavelength in a rectangular waveguide working in

TE10 mode.

EQUIPMENTS:


2. Klystron mount with Klystron tube

3. Variable attenuator4. Frequency meter

5. Isolator

6. Slotted section

7. VSWR meter

8. Movable short

9. Termination

10.Waveguide stand

THEORY:

Important waveguide parameters include:1. Cut off wavelength

2. Guide wavelength

3. Group and phase velocities

4. Characteristic impedance

Cut off Wavelength:

It is defined as wavelength of a wave above which wave does not exist in the

waveguide. Both for the TEmn and TMmn cut off wavelength is given by

c = 2ab/(m2b2 +n2a2)In the experiment rectangular waveguide is working in TE10 mode hence cut

of wavelength in above formula get reduce to c = 2a.

Guide Wavelength:

Guide wavelength is the wavelength of the traveling wave propagating inside

the waveguide. It is always different from the free space

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wavelength. The guide wavelength, free space wavelength and guide wavelength is

related by:

g = o/ (1-(o/ c)2)Group and Phase velocities:

Phase velocity is defined as velocity with which wave changes its phase. It is

the product of guide wavelength and frequency. Since g > o it appears as if p isgreater than speed of light. This appears to contradict the law that no signal can be

transmitted faster than the speed of light. In waveguides also, it is found that

modulation does not travel at a phase velocity. When modulated carrier travels through

a waveguide, the modulation envelope travels with a velocity much less than that of

carrier and even less than speed of light. The velocity of modulation envelope is called

Group velocity. The relation between group velocity and phase velocity is given as

gp= c2

p = / = c/ (1- [fc/f]2)g = d/d = c(1- [fc/f]

2

)where c velocity of light = 3x 10

8m/sec

Characteristic Impedance:

The generalized expression for the characteristic impedance of waveguide for

TE mode is given as:

ZTE =[377(/)(bgo)]The characteristic wave impedance for TEmn modes is related to free space

impedance is given by:

ZTE = / (1- [fc/f]2)where intrinsic impedance of free space =120 or 377

The frequency of a wave is calculated by formula f = c/oWhere 1/ o = (1/ g2 + 1/ c2)

g guide wave lengtho free space wave lengthc Cutoff wave length

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SET UP FOR MEASUREMENT OF WAVEGUIDE PARAMETERS

BLOCK DIAGRAM:

PROCEDURE:

I. GENERAL:

1. The equipments are set as shown in the block diagram.

2. The variable attenuator is set at maximum position.

3. The control knobs of VSWR meter are kept as below:

i. Range 50db position

ii. I/P Switch Crystal low impedance.

iii. Meter switch Normal position

iv. Gain ( coarse & fine) Mid position.

4. The control knobs of klystron power supply are kept as below:

i. Meter switch OFF

ii. Mod switch AM


iv. Reflector voltage fully clockwise.v. AM amplitude knob around fully clock wise.






Klystron

Mount

Variable

Attenuator

Frequency

Meter

Klystron

power

supply

Slotted

Line Termination

VSWR

meter

Movable

Short

Isolator

Detector

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8. The deflection in VSWR is maximized by adjusting AM amplitude and




II . WAVEGUIDE PARAMETERS MEASUREMENT:

1. The frequency meter is tuned to get dip on the VSWR scale.

2. The frequency meter is tuned to obtain minimum deflection.

3. The corresponding frequency is noted.

4. The termination is replaced with the movable short.

5. The frequency meter is detuned.

6. The deflection in VSWR is varied by moving the probe along the slotted

line.

7. The probe is moved to a minimum deflection point. Accurate reading is got

by increasing the VSWR meter gain when close to minimum.

8. The probe position is recorded.9. The probe is moved into the next minimum point and the probe position is

recorded.

10. The guide wavelength is equal to twice the distance between the minima.

11. The waveguide inner broad dimensions a is measured which will be

around 2.286cm.

12. The frequency, impedance, group velocity, phase velocity and

characteristics impedance is calculated.

OBSERVATIONS:

Theoretical Value of g = __________________.Practical value of g = __________________.Phase velocity p =___________________.Characteristic impedance ZTE =___________________.

Group velocity g =___________________.

Operating

frequency(GHz)

Observe

d

minima(cm)

g/2 (cm) g(cm)

fGHz

=2fin 109

rad/s

1/o2

in cm-21/g

2

(cm-2

)

=2/g(rad/cm)

px1010

cm/s

gx1010c

m/s

ZTE=/(1-[fc/f]

2)

1 2 3 2-1

3-2

Avg

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Cutoff wavelength c =___________________.

PRECAUTIONS:

1. For stable operation the Klystron is allowed to warm up to 10 minutes before the

experiment is conducted.

2. The attenuator position should not be disturbed after adjusting for maximum power

output.


4. Detuning the frequency meter should not be forgotten

RESULT:

Thus the Frequency, free space wavelength, guide wave length, phase shift constant,phase velocity, group velocity are calculated and compared the theoretical and practical

values.XXX

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attenuator, the vane position is fixed where as in variable attenuator, its position can be

changed by the help of micrometer or by other methods.

SET UP FOR MEASUREMENT OF ATTENUATION OF VARIABLE ATTENUATOR

BLOCK DIAGRAM:

PROCEDURE:

GENERAL:

1. The equipments is set as shown in block diagram.


3. The control knobs of VSWR meter is set as below:

a. Range db 40db/50db position



d. Gain (Coarse and fine) Mid position

4. The control knobs of klystron power supply is set as below:i. Meter switch OFF

ii. Mod switch AM


FrequencyMeter

Klystron

power

supply

SlottedLine Detector

Mount

VSWR meter

Movable

Short

Detector

VariableAttenuatorIsolator

KlystronMount

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iv. Reflector voltage fully clockwise.

v. AM amplitude knob around fully clock wise.






8. The output is tuned by tuning reflector voltage, AM amplitude and



10.To get deflection in the scale of VSWR the range db switch, variable

attenuator position and gain control knob is adjusted if necessary.

11. The deflection in VSWR can be varied by moving the probe along the

slotted line.

ATTENUATION MEASUREMENT:

1. The detector mount connected to the slotted line is tuned for maximum

deflection on VSWR meter.

2. Set any reference level on the VSWR meter with the help of variable

attenuator (not the test attenuator) and gain control knob of VSWR meter.

Let it be P1.

3. Now carefully disconnect the detector mount from slotted line with out

disturbing any position obtained in step2. Place the test attenuator to the

slotted line and detector mount to the other port of test attenuator. Record

the reading of VSWR meter. Let it be P2. The attenuation value of tested

variable attenuator for any particular position of micrometer reading is

obtained by P1 P2 dB.

OBSERVATIONS:

VSWR value without test attenuator P1 = _____________.

VSWR value with test attenuator P2 = _____________.

Attenuation of test attenuator = P1 P2 = _____________.

PRECAUTIONS:

1. For stable operation the Klystron is allowed to warm up to 10 minutes

before the experiment is conducted.


power output.


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RESULT:

The attenuation of test attenuator is measured

Attenuation of test attenuator = _____________.

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CHRACTERISATION OF 660 & 850 NM LEDS

ExperimentNo:11

AIM:

The aim of the experiment is to study the relationship between the LED dc forward current

and the LED optical power output and determine the linearity of the device at 660nm as

well as 850nm. The conversion efficiencies of the two LEDs will also be compared.

EQUIPMENT:

1.Fiber optic analog transmission Kit TNS 20EA-TX2.Fiber optic analog transmission Kit TNS 20EA-RX

3.One meter PMMA fiber patch card

4.Inline SMA adaptors

THOERY:

LEDs and laser diodes are the commonly used sources in optical communication

systems, whether the system transmits digital or analogue signals. In the case of analogue

transmission, direct intensity modulation of the optical source is possible, provided the

optical output from the source can be varied linearly as a function of the modulating

electrical signal amplitude. LEDs have a linear optical output with relation to the forward

current over a certain region of operation. It may be mentioned that in many low-cost, short-

haul and small bandwidth applications, LEDs at 660 nm, 850 nm and 1300nm are popular.

While direct intensity modulation is simple to realize, higher performance is achieved by fm

modulating the base-band signal prior to intensity modulation.

The relationship between an LED optical output Po and the LED forward current I F is given

by Po = K.IF (over a limited range), where K is a constant.

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BLOCK DIAGRAM:

PROCEDURE:

The schematic diagram for characterization of the LED is shown below and is self

explanatory.

The step by step procedure is given here:

Step1: Connect one end of Cable 1 to the 660nm LED port of TNS20EA TX and

the other end to the FO PIN (power meter) port of TNS20EA-RX.

Step2: Set DMM 1 to the 2000mV range and connect it to the terminals Po (Po1 &

Po2) on the RX unit. The power meter is ready for use. Po = (Reading)/10 dBm

Step3: Set DMM2 to the 200.0 mV range and connect it between the Vo1 and

Gnd terminals in the TX unit. If1 = Vo1 (mv)/100 in ma.

Step4: Adjust the SET Po knob on the TX unit to the extreme anticlockwise

Position to reduce If1 to 0. The reading on the power meter should be out of range.

Step 5: Slowly turn the SET Po knob clockwise to increase If1. The power meter

should read -30.0dB approximately. From here change If1 in suitable steps and note

the power meter readings, Po. Record up to the extreme clock-wise position.Step 6: Repeat the complete experiment for 850nm LED and tabulate the

Readings for Vo2 (between terminals Vo2 and Gnd) & Po. If2=Vo2(mv)/100 in ma.

Apply the correction of 2.2 dB discussed in Experiment1 for the 850nm LED.

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OBSERVATIONS FOR 660nm

Sl No V01 (mV) If1=Vo1/100(ma) Po(dBm)

1

23

4

5

6

OBSERVATIONS FOR 850 nm

Sl No Vo2(mV) If2=Vo2/100(ma) Po(dBm)Po(dBm)

Corrected

1

2

3

4

5

6

RESULT:

Studied the relationship between the LED dc forward current and the

LED optical power output and determined the linearity of the device at 660nm and

850nm. The conversion efficiencies of the two LEDs are compared.

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CHARACTERISTICS OF LASER DIODES

ExperimentNo:12

AIM:

The aim of the experiment is to study the Optical Power (Po) of a Laser Diode vs Laser

Diode Forward Current (IF)

EQUIPMENT:

1. Laser Diode Design Module TNS 20EL-TX

2.Laser Diode Design Module TNS 20EA-RX

3.Two meter PMMA fiber patch card


THOERY:

Laser Diodes (LDs) are used in telecom, data communication and video communication

applications involving high speeds and long hauls. Most single mode optical fiber

communication systems use lasers in the 1300nm and 1550 nm windows. Lasers with very

small line-widths also facilitate realization of wavelength division multiplexing (WDM) for

high density communication over a singe fiber. The inherent properties of LDs that make

them suitable for such applications are, high coupled optical power into the fiber (greater

than 1 mw), high stability of optical intensity, small line-widths (less than 0.05 nm in special

devices), high speed (several GHz) and high linearity (over a specified region suitable for

analogue transmission). Special lasers also provide for regeneration/amplification of optical

signals within an optical fiber. These fibers are known as erbium doped fiber amplifiers.

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LDs for communication applications are commonly available in the wavelength regions

650nm, 780nm, 850nm, 980nm, 1300nm and 1550nm.

BLOCK DIAGRAM:

PROCEDURE:

The schematic diagram for study of the LD Po as a function of LD forward current IF is

shown below and is self explanatory.

Step1: Connect the 2-metre PMMA FO cable (Cab1) to TX Unit of TNS20EL and couple the

laser beam to the power meter on the RX Unit as shown. Select ACC Mode of operation.

Step2: Set DMM 1 to the 200 mV range and connect it to the Vo/Gnd terminals. This will

monitor if in ma, given by Vo (mV)/100. Set DMM2 to 2000 mV range and connect it to the

Po1/Po2 terminals. This will provide Po in dBm when divided by 10.

Step3: Adjust the SET Po knob to extreme counterclockwise position to reduce IF to 0 ma.

The power meter reading will normally be below 50 dBm or outside the measuring limits

of the power meter.

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Step4: Slowly turn the SET Po Knob clockwise to increase IF and thus Po. Note IF and Po

readings. Take closer readings prior to and above the laser threshold. Current, Po will

rapidly increase with small increase in If.

OBSERVATIONS (ACC Mode/PMMA Cable)

Sl No Vo(mV) IF=Vo/100(ma) Po (dBm)

1

2

3

4

RESULT:

Studied the Optical Power (Po) of a Laser Diode vs Laser Diode Forward

Current (IF) Characteristics

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INTENSITY MODULATION OF LASER OUTPUT THROUGH AN OPTIACL

FIBER

ExperimentNo:13

AIM:

The aim of the experiment is to study the Gain Characteristics of a FO linear Intensity

Modulation System Vin(ac) vs Vout(ac) for fixed carrier power Po .

EQUIPMENT:

1. Laser Diode Design Module TNS 20EL-TX



4.Inline SMA Adaptors

THOERY:

Intensity modulation methods are the most popular of techniques used in optical

communication, whether the input signal is in the analogue or digital from. The baseband

signal, in number applications, is first modulated using one of the several electronic

methods available prior to signal transmission. The electronically modulated signal is then

used as the modulating signal for the light. While non-linear intensity modulation will be

acceptable for digital or frequency modulated signals, linear intensity modulation is

essential if a baseband signal is to be used for direct intensity modulation of a light source.

An ideal linear intensity modulation/demodulation system would employ optoelectronic

components and circuitry which will have linear characteristics in a specified range of

operation. The optical output from the modulator, Po, will be directly proportional to Vin

(modulating signal). The electrical output Vout, from the demodulator will be directly

proportional to the incident optical power Pin. With the loss in the optical path (optical fiber

cable etc) being a constant, we will obtain Vout directly proportional to Vin.

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BLOCK DIAGRAM:

PROCEDURE:

(a) Select Rin such that the Vout(dc)=1Vdc (approximately) for carrier power, Po,

corresponding to If=10ma(dc) at the modulator side. This will ensure distortion free

reception of the optical signal. However the required gain and bandwidth may not

be obtained in this case.

(b) Alternately, select Rin such that the Vout(ac)=Vin(ac). This gives a unity gain for the

full transmission system. However, clipping of the signal may appear if the Vout(dc)

component is too high. Secondly, selection of bandwidth may not be possible as it

varies inversely as Rin. We will now study these factors experimentally.

OBSERVATIONS: Vout Vs Vin

Frequency, fo =2KHz; Carrier Level Po=-15.0dBm

Sl. No Vin (mVp-p) Vout (mVp-p) Vo/Vin

1

2

3

4

5

RESULT:

Studied the Gain Characteristics of a FO linear Intensity Modulation System Vin(ac) vs

Vout(ac) for fixed carrier power Po .

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DETERMINATION OF NUMERICAL APERTURE OF OPTICAL FIBRES

ExperimentNo:14

AIM:

The aim of the experiment is to determine the numerical aperture of the optical fibers

available

EQUIPMENT:

1.Laser Diode Design Module TNS 20EL-TX




Numerical Aperture Measurement Jig

THOERY:

Numerical aperture of any optical system is a measure of how much light can be collected

by the optical system. It is the product of the refractive index of the incident medium and

the sine of the maximum ray angle.

NA = ni.sinmax; ni for air is 1, hence NA = sinmax

For a step-index fibre, as in the present case, the numerical aperture is given by N=(N core2

ncladding2)1/2

For very small differences in refractive indices the equation reduces to

NA = ncore (2)1/2, where is the fractional difference in refractive indices. I and record

the manufactures NA, ncladding and ncore, and .

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OBSERVATIONS:

Sl. No L (mm) W(mm) NA (degrees)

1 10 10 0.447 26.5

2 15 14 0.423 25.0

3 20 20 0.447 26.5

4 25 24 0.432 25.64

5 30 - - -

RESULT:

Numerical aperture of the available optical fibers is Determined

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LOSSES IN OPTICAL FIBRES AT 660NM & 850NM

ExperimentNo:15

AIM:

The aim of the experiment is to study various types of losses that occur in optical fibers and

measure losses in dB of two optical fiber patch cords at two wavelengths, namely, 660nm

and 850nm. The coefficients of attenuation per meter at these wavelengths are to be

computed from the results.

EQUIPMENT:

1.Fiber optic analog transmission Kit TNS 20EA-TX

2.Fiber optic analog transmission Kit TNS 20EA-RX

3.One meter& two meter PMMA fiber patch card

4.Inline SMA Adaptors

THOERY:

Attenuation in an optical fiber is a result of a number of effects. This aspect is well covered

in the books referred to in Appendix II. We will confine our study to measurement of

attenuation in two cables (Cable1 and Cable2) employing and SMA-SMA In-line-adaptor.

We will also compute loss per meter of fiber in dB. We will also study the spectral response

of the fiber at 2 wavelengths, 660nm and 850 and compare with the plot in Appendix II.

The optical power at a distance, L, in an optical fiber is given by PL = Po 10 (-L10) where Po

is the launched power and is the attenuation coefficient in decibels per unit length. The

typical attenuation coefficient value for the fiber under consideration here is 0.3 dB per

meter at a wavelength of 660nm. Loss in fibers expressed in decibels is given by -10log

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(Po/PF) where, Po is the launched power and PF is power at the far end of the fiber. Typical

losses at connector junctions may very from 0.3 dB to 0.6 dB.

Losses in fibers occur at fiber-fiber joints or splices due to axial displacement, angular

displacement, separation (air core), mismatch of cores diameters, mismatch of numerical

apertures, improper cleaving and cleaning at the ends. The loss equation for a simple fiber

optic link is given as:

Pin(dBm)-Pout(dBm)= LJ1+LFIB1+LJ2+ LFIB1+LJ3(db): where, LJ1(db) is the loss at the LED-

connector junction, LFIB1 (dB) is the loss in cable1, LJ2 (dB) is the insertion loss at a splice or

in-line adaptor, LFIB2 (dB) is the loss cable2 and LJ3 (dB) is the loss at the connector-detector

junction.

BLOCK DIAGRAM:

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PROCEDURE:

The schematic diagram of the optical fiber loss measurement system is shown below and is

self explanatory. The step by step procedure is given here:

Step 1: Connect one and of Cable1 to the 660nm LED port of the TNS20EA-TX and theother end to the FO PIN port (power meter port) of TNS20EA-RX.

Step2: Set the DMM to the 2000 mV range. Connect the terminals marked Po on TNS20EA-

RX to the DMM the power meter is now ready for use.

Step3: Connect the optical fiber patchcord, Cable1 securely, as shown, after relieving all

twists and strains on the fibre. While connecting the cable please note that minimum force

should be applied. At the same time ensure that the connector is not loosely coupled to

the receptacle. After connecting the optical fibre cable properly, adjust SET Po knob to set

power of 660nm LED to a suitable value, say, - 15.0dBm (the DMM will read 150 mV). Note

this as P01

Step 4:Wind one turn of the fiber on the mandrel, and note the new reading of the power

meter Po2. Now the loss due to bending and strain on the plastic fiber is Po1-Po2dB. For

more accurate readout set the DMM to the 200.0mV range and take the measurement.

Typically the loss due to the strain and bending the fiber is 0.3 to 0.8 db.

Step5: Next remove the mandrel and relieve Cable1 of all twists and strains. Note the

reading P01. Repeat the measurement with Cable2 (5 meters) and note the reading Po2. Use

the in-line SMA adaptor and connect the two cables in series as shown. Note the

measurement Po3.

Loss in Cable1=Po3-Po2-Lila Loss in Cable2=Po3Po1-Lila

Assuming a loss of 06 to 1.0dB in the in-line adaptor (Lila=1.0dB), we obtain the loss in

each cable. The difference in the losses in the two cables will be equal to the loss in 4 metersof fiber (assuming that the losses at connector junctions are the same for both the cables).

The experiment may be repeated in the higher sensitivity range of 200.0mV. The experiment

also may be repeated for other Po settings such as -20dBm, -25 dBm, -30dBm etc.

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Sl No Po1

(dBm)

Po2

(dBm)

Po3

(dBm)

Loss in

Cable 1

(dB)

Loss in

Cable2

(dB)

Loss in 4

metres

fibre (dB)

Loss per

metre (dB)

at 660nm

1 -15.0

2 -20.0

3 -25.0

4

Step6: Repeat the entire experiment with LED2 at 850nm and tabulate in 1.4.2

NOTE:

The power meter has been calibrated internally to read power in dBm at 660nm. However

the calibration has to be redone manually for measurements at 850nm. The PIN has a 66%

higher sensitivity at850nm as compared to 660nm for the same input optical power. This

corresponds to a sensitivity that is higher by 2.2dB. To calibrate the power meter at 850nm,

deduct 2.2dB from the measured reading. In computing losses in cables and fibers this gets

eliminated while solving the equations.


Sl No Po1

(dBm)

Po2

(dBm)

Po3

(dBm)

Loss in

Cable 1

(dB)

Loss in

Cable2

(dB)

Loss in 4

metres

fibre (dB)

Loss per

metre (dB)

at 850nm

1 -15.0

2 -20.0

3 -25.0

4

RESULT:Studied the various types of losses that occur in optical fibers and measured the losses in

dB of two optical fiber patch cords at two wavelengths, namely, 660nm and 850nm. The

coefficients of attenuation per meter at these wavelengths are computed from the results.

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ExperimentNo:16

DESIGN OF FIBER OPTIC DIGITAL LINK FOR TRANSMISSIONOF DIGITAL SIGNALS

AIM :

Design of optic digital transmission system

EQUIPMENT:

1. Fiber optic digital transmitter receiver trainer.

2. Cathode ray oscilloscope3. Probes.

THEORY:

The key sections of a optical fiber are a transmitter consisting of a light source and its

associated drive circuitry, a cable offering mechanical and environmental protection to the

optical fibers contained inside, and a receiver consisting of a photo detector plus amplification

and signal restoring circuitry. Additional components include optical amplifiers, connectors,

splices, couplers and regenerators. One of the principle characteristics of an optical fiber is its

attenuation as a function of wavelength. Once the cable is installed, a light source i.e.

dimensionally compatible with fiber core is used to launch optical power into the fiber.Semiconductor Light emitting diodes(LEDs) and Laser diodes are suitable for this purpose,

since their light output can be modulated rapidly by simply varying bias current at the desired

transmitter rate, there by producing optical signal. The electric input signal to the transmitter

circuitry for the optical source can be either analog or digital form.

After optical signal launched into a fiber it will become progressively attenuated and

distorted with increase distance because of scattering, absorption and dispersion mechanism

in the glass material. At the receiver photodiode will detect the weakened optical signal

emerging from the fiber end and convert it to electrical current. The design of an optical

receiver is inherently more complex than that of transmitter, since it has to interpret the

content of the weakened and degraded signal received by the photo detector.

The principle figure of merit for a receiver is the minimum power necessary at the desireddata rate to attain either given error probability for digital system or a specified signal to noise

ratio for an analog system. The ability of a receiver to achieve a certain performance level

depends on photo detector type, the effects of noise in a system and characteristics of the

successive amplifier stages in the RX.

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PROCEDURE:

1. Connect one end of the cable to the LED port of the FT2107 - Tx and other end to

FO port of the FT2106 - Rx.

2. Connect NRZ encoder output to the Vin on the transmitter side. Also connect it to

channel one of a dual trace oscilloscope. Connect Vo

on the receiver side to

channel2 of CRO.

3. Connect output of comparator on receiver side to NRZ of line decoder of receiver.

4. Set R in to 200 using DMM to measure the resistance.5. Turn on the receiver and transmitter units. The NRZ waveform should appear on

channel1. It should be 5KHz square wave. In case waveform doesnt appear,

RESET the encoder micro oscillator once.

6. Adjust Rth until the waveform on channel2 is almost identical to the input. Draw

the transmitted and received waveforms. The input frequency and output frequency

must be same.

7. Next remove the oscilloscope probe from Vo and connect to Vin to observe the

waveform at the output of the detector. Change input resistance Rin to change gainof detector and note the amplitude and shape at V in. When Rin is decreased the

amplitude of Vin decrease. But there is reduction distortion as well.

8. Repeat the set 7 by setting Rin to some other value and then adjusting Rth to obtain

the received waveforms as close to the transmitted one. In each case draw the

transmitted and received waveforms.

OBSERVATIONS:

Part 1:

Input frequency :__________________KHz

Output frequency :__________________KHz.Part 2:

S.No. R in (in ohms) Vin (in Volts)

RESULT:

Thus digital optical fiber transmitter/ receiver system characteristics are studied.

XXX

m & oc

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