1. MICROWAVE AND OPTICAL COMMUNICATIONS LAB
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VIJAYA ENGINEERING COLLEGE
DEPARTMENT
OF
ELECTRONICS AND COMMUNICATION
ENGINEERING
MICROWAVE AND OPTICAL COMMUNICATIONS
LAB MANUAL
Class : IV B.TECH I SEM

2. MICROWAVE AND OPTICAL COMMUNICATIONS LAB
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R18 B. Tech. ECE Syllabus
EC703PC: MICROWAVE AND OPTICAL COMMUNICATIONS LAB
B. Tech IV Year I Semester L T P C
0 0 2 1
Note: Any Twelve of the following experiments
LIST OF EXPERIMENTS:
1. Reflex Klystron Characteristics.
2. Gunn Diode Characteristics.
3. Attenuation measurement
4. Directional coupler Characteristics.
5. Scattering parameters of wave guide components
6. Frequency measurement.
7. Impedance measurement
8. VSWR measurement
9. Characterization of LED.
10. Characterization of Laser Diode.
11. Intensity modulation of Laser output through an optical fiber.
12. Measurement of Data rate for Digital Optical link.
13. Measurement of Numerical Aperture of fiber cable.
14. Measurement of losses for Optical link

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Power
Crystal Measuring
MW Isolator Variable Frequency Slotted Component
DESCRIPTION OF MICROWAVE BENCH
INTRODUCTION:
Electrical measurements encountered in the microwave region of the
electromagnetic spectrum are discussed through microwave measurement
techniques. This measurement technique is vastly different from that of the
more conventional techniques. The methods are based on the wave character
of high frequency currents rather than on the low frequency technique of
direct determination of current or voltage. For example, the measurement of
power flow in a system specifies the product of the electric and magnetic
fields. Whereas the measurement of impedance determines their ratio. Thus,
these two measurements indirectly describe the distribution of the electric
field and magnetic fields in the system and provides its complete description.
This is, in fact, the approach to most of the measurements carried out in the
micro wave region of the spectrum.
Microwave Bench:
The micro wave test bench incorporates a range of instruments capable of
allowing all types of measurements that are usually required for a microwave
engineer. The bench is capable of being assembled or disassembled in a
number of ways to suit individual experiments. A general block diagram of the
test bench comprising its different units and ancillaries are shown bellow.

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1.Klystron Power Supply:
Klystron Power Supply generates voltages required for driving the reflex
Klystron tube like 2k25. It is stable, regulated and short circuit protected
power supply. It has built on facility of square wave and saw tooth generators
for amplitude and frequency modulation. The beam voltage ranges from 200V
to 450V with maximum beam current.50mA. The provision is given to vary
repeller voltage continuously from -270V DC to -10V.
2.Gunn Power Supply:
Gunn Power Supply comprises of an electronically regulated power supply and
a square wave generator designed to operate the Gunn oscillator and PIN
Modulator. The Supply Voltage ranges from 0 to 12V with a maximum current,
1A.
Reflex Klystron Oscillator:
At high frequencies, the performance of a conventional vacuum tube is
impaired due to transit time effects, lead inductance and inter-electrode
capacitance. Klystron is a microwave vacuum tube employing velocity modulation
and transit time in achieving its normal operation. The reflex type known as
reflex klystron, has been the most used source of microwave power in laboratory
(fig.1).It consists of an electron gun producing collimated electron beam. The
electron beam is accelerated towards the reflector (repellor) by a dc voltage V0,
while passing through the positive resonator grids. The velocity of the electrons in
the beam will be
v0 =
e = electron charge
m = mass of the electron
2eVo
m

5. MICROWAVE AND OPTICAL COMMUNICATIONS LAB
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Fig: 1 Reflex Klystron Tube
The repeller, which is placed at a short distance from the resonator grids, is
kept at negative potential with respect to cathode. And consequently, it retards
and finally reflects the electrons which then turn back through the resonator
grids.
Basic Theory of Operation:
To understand the operation of this device, assume that the resonator cavity is
oscillating slightly, causing an AC potential, say V1sinωt in addition to Vo, to
appear across the cavity grids. These initial oscillations could be cause by any
small disturbance in the electron beam. In the presence of the RF field, the
electrons which traverse towards the repeller will acquire the velocity
V=
Thus, we have a velocity modulated beam traveling towards the repeller, having
velocities between Vo√1+V1/Vo and Vo√1- V1/Vo, i. e electrons leaving the cavity
during the positive half cycle are accelerated while electrons leaving the cavity
during negative half cycle are decelerated. Obviously, the electrons traversing
towards the repeller with increased velocity.
i.e., faster ones shall penetrate farther into the region of the repeller field (called
drift space) as compared to the electrons traversing towards the repeller with
decreased velocity, i.e., slower ones. But the faster electrons, leaving the cavity
take longer time to return to it and the faster electrons, therefore, catch up with
slow ones. As a result, the resulting electrons group together in bunches. The
bunching action is shown in Fig.2.
2e(Vo V1sin wt)
m

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Fig 2: Bunching of Electrons in reflex Klystron Oscillator
As the electron bunches re cross the cavity, they interact with the voltage
between the Cavity grids. If the bunches pass through the grids at the time
when the grid potential is such that the electrons are severally decelerated, the
decelerated electrons give up their energy and this energy reinforces oscillations
within the cavity. Hence under these conditions, sustained oscillations are
possible. The electrons having spent much of their energy are then collected by
the positive cavity wall near the cathode. Thus, it is clear that in its normal
operation the repeller electrode does not carry any current and indeed this
electrode can severely be damaged by bombardment. To protect the repelled
from such damage, the repeller voltage VR is always applied before the
accelerating voltage Vo.
Power Frequency Characteristics:
The cavities used in reflex klystrons do not have infinite Q, as such each
mode of operation will be spread over a narrow range of repeller voltages. Fig.3
shows the variation of frequency and power output versus repeller voltages
along with mode number. It should, however, be noted that repeller voltage -
mode number correspondence is valid only at the center of mode (maximum
power) of operation. That is, the repeller voltage needed for the calculations
should measured only at the peak (top) of the mode. The variation in repeller
voltage from the peak of the mode causes change in transit time, as a result the
bunch is either not properly formed or starts de-bunching, thereby decreasing
output power and also a slight change in frequency observed.

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Fig:3 Typical Mode Curves of Reflex Klystron
Fig 4: Cross Sectional View Of 2K25 Reflex Klystron
3.Gunn oscillator:
Gunn oscillator uti1izes Gunn diode which works on the principle that
when a DC voltage is applied across a sample of n - type Gallium
Arsenide; the current oscillates at microwave frequencies. This does not
need high voltage as it is necessary for Klystrons and therefore solid state
oscillators are now finding wide applications. Normally, they are capable of
delivering 0.5 watt at 10GHz, but as the frequency of operation is
increased the microwave output power gets considerably reduced.
Gunn oscillators can also be' used as modulated microwave sources. The
modulation is generally provided by means of a PIN diode. PIN diode is a device
whose resistance varies with the bias applied to it. When waveguide line is
shunted with PIN diode and the diode is biased positively, it presents a very high

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impedance thereby not affecting the line appreciably. However, it is negatively
biased, it offers a very low impedance, almost short- circuit thereby reflecting
the microwave power incident on it. As impedance varies with bias, the signal is
amplitude modulated as the bias varies. Since heavy-power is reflected during
the negative biasing of PIN diode, so an isolator or an attenuator should
invariably be used to isolate PIN diode and avoid overloading of the latter. Gunn
oscillator can also be pulse –modulated, but it is accompanied by the frequency
modulation and frequency modulation is not good, so separate PIN modulation
is preferred.
4. Isolator:
This un attenuated device permits un attenuated transmission in one
direction (forward direction) but provides very high attenuation in the
reverse direction {backward direction). This is generally used between the
source and rest of the set up to avoid overloading of the source due to
reflected power.
5.Variable Attenuator:
The device that attenuates the signal is termed as attenuator. Attenuators are
categorized into two categories namely, the fixed attenuators and variable
attenuators. The attenuator used in the microwave set is of variable type. The
variable attenuator consists of a strip of absorbing material which is arranged in
such a way that its profusion into the guide is adjustable. Hence, the signal
power to be fed to the microwave set up can be set at the desired level.
6.Frequency Meter:
It is basically a cavity resonator. The method of measuring frequency is to
use a cavity where the size can be varied and it will resonate at a particular
frequency for given size. Cavity is attached to a guide having been excited by a
certain microwave source and is tuned to its resonant frequency. It sucks up
some signal from the guide to maintain its stored energy. Thus if a power meter
had been monitoring the signal power at the resonating condition of the cavity it
will indicate a sharp dip. The tuning of the cavity is achieved by a micrometer
screw and a curve of frequency versus screw setting is provided. The screw
setting at which the power indication dip is noted and the frequency is read
from the curve.

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7.Slotted Section:
To sample the field with in a wave guide, a narrow longitudinal slot with ends
tapered to provide smoother impedance transformation and thereby providing
minimum mismatch, is milled on the top of broader dimension of wave guide.
Such section is known as slotted wave guide section. The slot is generally so
many wave lengths long to allow many minima of standing wave pattern to be
covered. The slot location is such that its presence does not influence the field
configurations to any great degree. On this Section a probe inserted with in a
holder, is mounted on a movable carriage. The output is connected to detector
and indicating meter. For detector tuning a tuning plunger is provided instead of
a stub.
8.Matched Load:
The microwave components which absorb all power falling on them are matched
loads. These consist of wave guide sections of definite length having tapered
resistive power absorbing materials. The matched loads are essentially used to
test components and circuits for maximum power transfer.
9.Short Circuit Termination:
Wave guide short circuit terminations provide standard reflection at any desired,
precisely measurable positions. The basic idea behind it is to provide short
circuit by changing reactance of the terminations.
8.VSWR meter:
Direct-reading VSWR meter is a low-noise tuned amplifier voltmeter calibrated
in db and VSWR for use with square law detectors. A typical SWR meter has a
standard tuned frequency of 100-Hz, which is of course adjustable over a range
of about 5 to 10 per cent, for exact matching in the source modulation
frequency. Clearly the source of power to be used while using SWR meter must
be giving us a 1000-Hz square wave modulated output. The band width
facilitates single frequency measurements by reducing noise while the widest
setting accommodates a sweep rate fast enough for oscilloscope presentation.
For precise attenuation measurements, a high accuracy 60 db attenuator is
included with an expand offset feature that allows any 2 db range to be
expanded to full scale for maximum resolution. Both crystal and bolometer may
be used in conjunction with the SWR meter. There is provision for high (2,500-
10,000 ohm) and low (50-200 ohm) impedance crystal inputs. This instrument

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 m 
2
 n 
2

a
  
b

   
is the basic piece of equipment in microwave measuring techniques and is used
in measuring voltage peaks valleys, attenuation, gain and other parameters
determined by the ratio of two signals.
9.Crystal Detector:
The simplest and the most sensitive detecting element is a microwave crystal. It
is a nonlinear, non reciprocal device which rectifies the received signal and
produces a current proportional to the power input. Since the current flowing
through the crystal is proportional to the square of voltage, the crystal is
rejoined to as a square law detector. The square law detection property of a
crystal is valid at a low power level (<10 mw). However, at high and medium
power level (>10 mw), the crystal gradually becomes a linear detector.
MICROWAVE COMPONENTS
A wave guide consists of a hollow metallic tube of a rectangular or circular
shape used to guide an electromagnetic wave. Wave guides are used principally
at frequencies in the microwave region. At frequency range x band from 8 to 12
GHz, for example, standard rectangular wave guide, RG - 52/U has an inner
width 0.4 in and an inner length 0.9 in.
In wave guides the electric & magnetic fields are confined to the space within
the guides. Thus, no power is lost through radiation, and even the dielectric loss
is negligible, since the guides are normally air filled. However, there is some
power loss as heat in the walls of the guides.
It is possible to propagate several modes of Electromagnetic waves within a wave
guide. A given wave-guide has a definite cutoff frequency for each allowed mode
and behaves as a high pass filter. The dominant mode in rectangular wave
guides is TE1O mode. It is advisable to choose the dimensions of a guide in such
a way that for a given input signal only the energy of the dominant mode can be
transmitted through the guide.
The cut off frequency for m, nth mode
fc =
The corresponding cut off wave length,
λc =
2
Where c is velocity of light.
c
2
 m 2
 n 2
    
 a   b

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Vijaya Engineering College Page 11




a is inner broader dimension of wave guide.
b is inner narrow dimension of wave guide & m, n indicate mode number.
The guide wave length, λg related to free space wave length & cut off wave length
is
1 1 1
2 2 2
0 g c


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Vijaya Engineering College Page 12
Magic Tee Junction:
Wave guide junctions are used to split the line with proper consideration of
the phase. The junctions that are widely encountered in microwave techniques
are E - plane, H-Plane and Hybrid tees.
* An E-plane tee is designed by fastening a piece of a similar wave guide to
the broader wall of a wave guide section. The fastened wave guide, also known as
series arm is parallel to the plane of the electric field of the dominant TE10 mode
in the main wave-guide.
* An H-plane tee is obtained by fastening the auxiliary wave guide
perpendicular to the narrow arm of the main wave guide section. The auxiliary
arm, also known as shunt arn should lie in the H - plane of the dominant TE10
mode in the main wave guide
*Hybrid tee is a combination of the E - plane tee and H plane tee. It has certain
characteristics listed below:
1) If two waves of equal magnitude and the same phase are fed into port 1
and port 2, the output will be zero at E - arm and additive at H - arm.
2) If a wave is fed into H - arm, it will be divided equally between port 1 &
port 2 of the collinear arms and will not appear at E - arm.
3) If a wave is fed into E - arm, it will produce an output of equal magnitude
and opposite phase at port - 1 and port 2. The output at H - arm is zero.
4) If a wave is fed into one of the collinear arms at port 1 or port 2, it will not
appear in the other collinear arm at port 2 or 1, because E - am1 causes a phase
delay while the H - arm causes a phase advance.
The Scattering matrix of a Magic Tee is given as:

























0
0
2
1
2
1
0
0
2
1
2
1
2
1
2
1
0
0
2
1
2
1
0
0
]
[S

13. Microwave and Optical Communications Lab Manual
Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 13

(a) Magic Tee (b) Cut way rear view of a wave guide E-H Tee.
The hybrid tee can be used
1) In impedance bridges
2) As antenna duplexer
3) As Mixer
4) As modular, etc.
Directional Coupler (DC):
Directional coupler is a 4-port wave guide junction. It consists of a primary wave
guide and a secondary wave guide connects together through apertures. These are uni
directional devices. Directional couplers are required to satisfy (1) reciprocity (2)
conservation of energy (3) all ports matched terminated.
The characteristics of a DC can be expressed in terms of its:
1. Coupling factor: The ratio, in dB, of the power incident and the power coupled
in auxiliary arm in forward direction.
=
Where Pi = Incident power
Pc = Coupled Power
2. Directivity: The ratio expressed in decibels, of the power coupled in the
forward direction to the power coupled in the backward direction of the auxiliary

14. Microwave and Optical Communications Lab Manual
Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 14
arm with un used terminals matched terminated.
D=10log10(Pc/Pr) dB
Where Pr=Reverse Power Pc
= Coupled Power
3.Insertion loss: The Ratio, expressed in decibels, of the power incident to the
power transmitted in the main line of the coupler when auxiliary arms are matched
terminated.
I= 10 log 10 (Pi / Pi1) Where Pi1 =
Received power at the transmitted port
Isolation: The ratio, expressed in decibels of the power incident in the main arm to
the backward power coupled in the auxiliary arm, with other ports matched
terminated.
L= 10log10 (Pi/Pr) dB
For an ideal coupler D & I are infinite while C& L are Zero. Several types of
directional couplers exist, such as a two-hole directional coupler, Schwinger
directional coupler and Bethe - hole directional coupler. Directional couplers are very
good power samplers.
Circulator:
A circulator is a passive microwave component which allows complete
transmission from n to (n+ 1) port. Circulator can be constructed with the help of
magic tees & gyrator or directional coupler with phase shifter or using ferrite
material and so on. A ferrite type circulator employs ferrite material at the center of
the junction. This ferrite post will be magnetized normal to the plane of the junction.
Electromagnetic wave, which propagates through the ferrite material under goes
phase change during its transverse. The phase change is dependent upon the
intensity of the magnetic bias and the length of the ferrite rod. The bias &
dimensions of the ferrite are so chosen, such that the wave moves unidirectional
from n to (n+ 1) port.
The characteristics of the circulator:
1. Insertion loss: The ratio of power input at port n to the power detected at

15. Microwave and Optical Communications Lab Manual
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Port n+1
L= 10 log10(Pi/ Pr)
Where Pi = Incident power at port n
Pr = received power at port n+1
2. Isolation: The ratio of power at port n to the power detected at port n-l.
I=10 log10(Pi/ P3)
Where Pi = Incident power at port n
P3 = received power at port n-1
The scattering matrix of a three-port circulator
Circulators can be used as (1) de coupling isolators (2) duplexers
FIRING OF THE REFLEX KLYSTRON:
To fire the klystron correctly, adopt the following procedure.
i) Set the cooling fan to blow air across the tube and turn on the filament voltage, and
then wait for a few minutes.
ii) Set the attenuator at a suitable level, say at 3db value.
iii) Apply the repeller voltage to its maximum value, say - 250V.
iv) Set the MOD switch of klystron power supply to CW position, Beam Voltage control
knob to fully anti clock wise and reflector voltage control knob to fully clock wise and
the meter switch to OFF position.
v) Rotate the knob of frequency meter at one side fully.
vi) ON the klystron power supply, VSWR meter and cooling fan for the klystron tube.
vii) Put the meter switch to beam voltage position and rotate the beam voltage knob
clockwise slowly up to 300V meter reading, and observe beam current on the
meter by changing meter switch to Beam current position.
“The beam current should not increase more than 30 mA”
viii) Adjust the repeller voltage to have maximum power output (micro ammeter

16. Microwave and Optical Communications Lab Manual
Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 16
current)
ix) If meter goes out of scale, increase attenuation to have suitable power level.
x) Also adjust the klystron mounting plunger for maximum power output and
repeat step if desired.
For the best set-up, the attenuator. Must have maximum value corresponding to the
peak in the output meter.

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Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 17

18. Microwave and Optical Communications Lab Manual
Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 18
AIM:
To Study the characteristics of reflex klystron.
EQUIPMENTS REQUIRED:
SNo. EQUIPMENT SPECIFICATION QUANTITY
1 Klystron power supply SKPS-610 1
2 Klystron tube with Klystron Mount 2K-25, XM-251 1
3 Isolator XI-621 1
4 Frequency meter XF-710 1
5 Variable Attenuator XA-520 1
6 Detector Mount XD 451 1
7 Wave Guide Stand XU-535 2
8 Oscilloscope -- 1
9 BNC Cable -- 1
10 Cooling Fan --- 1
THEORY:
The Reflex Klystron makes the use of velocity modulation to transform a continuous electron
beam into microwave power. Electron emitted from the cathode are accelerated and passed through the
positive resonator towards negative reflector, which retards and finally, reflects the electrons and
electrons turn back through the resonator. Suppose an rf-field exists 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 an increased velocity and the retarded
electrons will leave at the reduced velocity. The electron 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 the voltage at resonator grids. If the bunches
pass the grid at such a time that
Date:
STUDY OF THE CHARACTERISTICS OF REFLEX
KLYSTRON
Ex No: 1

19. Microwave and Optical Communications Lab Manual
Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 19
M
MO
OD
DE
EL
L G
GR
RA
AP
PH
H:
:
M
ME
EA
AS
SU
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RE
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EN
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T T
TA
AB
BL
LE
E:
:
MODE
REPELLER
VOLTAGE(V)
AMPLITUDE (V) FREQUENCY(GHz)
1
2
3

20. Microwave and Optical Communications Lab Manual
Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 20
electrons are slowed down by the voltage then energy will be delivered to the resonator and klystron
will oscillate. Fig shows the relationship between output power, frequency and reflector voltages.
The frequency is primarily determined by the dimensions of resonant cavity. Hence, by
changing the volume of resonator, mechanical tuning of Klystron is possible. Also a small frequency
change can be obtained by adjusting the reflector voltage. This is called Electronic Tuning.
PROCEDURE:
1. Set up the components and equipments as shown in fig.
2. Keep the position of variable attenuator at minimum attenuation position.
3. Set mode selector switch to FM-MOD position, FM amplitude and Fm frequency knob at mid
position, keep beam voltage knob fully anticlockwise and reflector voltage knob to fully clockwise and
Beam switch to ‘OFF’ position.
4. Keep the time/division scale of oscilloscope around 100Hz frequency measurement and volt/div to
lower scale.
5. Switch ON the Klystron Power Supply and Oscilloscope.
6. Switch ON Beam voltage switch and set beam voltage to 300V by beam voltage control knob.
7. Keep amplitude knob of FM Modulator to maximum position and rotate the reflector voltage
anticlockwise to get modes as shown in fig.2 on the oscilloscope. The horizontal axis represents axis
represents reflector voltage axis and vertical represents output power.
8. By changing the reflector voltage and amplitude of FM modulation, any mode of Klystron tube can
be seen on Oscilloscope.
RESULT:

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Vijaya Engineering College DEPT.OF ECE IV-1 SEM Page 21
SET
UP
FOR
STUDY
OF
GUNN
DIODE

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Ex No: 2
CHARACTERISTICS OF GUNN DIODE
Date:
AIM:
To Study of the characteristics of Gunn diode and to determine the threshold voltage that
corresponds to maximum current.
EQUIPMENTS REQUIRED:
SNo. EQUIPMENT SPECIFICATION QUANTITY
1. Gunn power supply GS-610 1
2. Gunn oscillator XM-55 1
3. Pin modulator XM-55 1
4. Isolator XI-621 1
5. Frequency meter XF-710 1
6. Variable Attenuator XA-520 1
7. Detector Mount XD-451 1
8. VSWR Meter SW-115 1
9. BNC Cable -- 1
10. Cooling Fan --- 1
11. Wave Guide Stand --- 2
PROCEDURE:
1. Set the components as shown in the fig.
2. Keep the control knobs of Gunn power supply as below

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M
ME
EA
AS
SU
UR
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T T
TA
AB
BL
LE
E:
:
GUNN BIAS
VOLTAGE(V)
CURRENT(mA)
FREQUENCY(GHz)
POWER
LEVELS(dB)
MICROMETER
READING
FREQUENCY
IN GHz

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Meter Switch - OFF
Gunn bias knob - Fully anticlockwise
PIN bias knob - Fully anticlockwise
PIN Mode frequency - Any position
3. Set the micrometer of Gunn oscillator for required frequency of operation
4. Switch ON the Gunn power supply
5. Measure the Gunn diode current corresponding to various Gunn bias voltages through the
digital panel meter and meter switch. Do not exceed the bias voltage above 10 volts
6. Tune the output in the VSWR meter through frequency control knob of modulation
7. If required then change the range db switch of VSWR meter to higher db position to get
deflection on VSWR meter. Any level can be set through variable attenuator and gain control
knob of VSWR meter.
8. Measure the frequency meter and detune it.
9. Plot the voltage and current readings on the graph as shown in fig.
10 Measure the threshold voltage which corresponds to maximum current.
Note: Do not keep Gun bias knob position at threshold position for more than 10-15 seconds
reading should be obtained as fast as possible. Otherwise due to excessive heating, gun diode
may burn.
RESULT:

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MULTI HOLE DIRECTIONAL (MHD) COUPLER:

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Ex No: 4 STUDY OF CHARACTERISTICS OF
DIRECTIONAL COUPLER
Date:
AIM:
To study the function of multi hole directional coupler by measuring the following
parameters
i. Mainline and auxiliary-line VSWR
ii. The coupling factor and directivity of the coupler
EQUIPMENTS REQUIRED:
SNo. EQUIPMENT SPECIFICATION QUANTITY
1. Klystron power supply SKPS-610 1
2. Klystron tube with Klystron Mount 2K-25, XM-251 1
3. Isolator XI-621 1
4. Frequency meter XF-710 1
5. Variable Attenuator XA-520 1
6. Detector Mount XD 451 1
7. Matched Termination XL 400 2
8. MHD Coupler XK 620 1
9. Waveguide Stand -- 2
10. BNC Cable -- 1
11. VSWR meter -- 1
12. Cooling Fan -- 1

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M
ME
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T T
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AB
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E:
:
ATTENUATOR POWER(dB)
DIRECTIVITY
(dB)
COUPLING
FACTOR
(dB)
WITHOUT
COUPLER
WITH COUPLER
FORWARD
DIRECTION
REVERSE
DIRECTION
i-arm Auxiliary
arm
i-arm Auxiliary
arm

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THEORY:
A directional coupler is a device with which it is possible to measure the incident and
reflected wave separately. It consist of wo transmission line the main arm and auxiliary arm,
electromagnetically coupled to each other. The power entering in the main arm gets divided
between port2 and 3 and almost no power comes out in port 4. Power entering at port2 is divided
between port1 and 4.
The coupling factor is defined as
Coupling (db) = 10 log10(P1/P2)
Where port2 is terminated.
Isolation (db) = 10 log10(P2/P3)
Where P1 is matched.
With built-in termination and power entering at Port1, the directivity of the coupler is a measure
of separation between incident wave and the reflected wave.Directivity is measured indirectly,
Directivity D (db)= 10 log10(P2/P1)
Main line VSWR is SWR measured, looking into the main line input terminal when the
matched loads are placed at all other ports.
Auxiliary line VSWR is SWR measured in the auxiliary line looking into the output
terminal when the matched loads are placed on other terminals
Main line insertion loss is the attenuation introduced in the transmission line by insertion of
coupler. It is defined as
Insertion loss (dB) = 10 log10 (P1/P2)
PROCEDURE:
A. Main Line SWR Measurement
1. Set up the equipments as shown in fig
2. Energies the microwave sources for particular frequency of operation as described in
the procedures given in the operation of Klystron tube/Gunn Oscillator
3. Follow the procedure as described for VSWR measurement(low and medium SWR
measurement)

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4. Repeat the same for other frequencies.
B. Auxiliary Line SWR Measurement
1. Set up the components and equipments as shown in fig
2. Energies the microwave sources for particular frequency of operation as described in
the operation of Klystron tube/Gunn Oscillator
3. Measure SWR as described in the experiment of SWR measurement (low and medium
SWR measurement)
4. Repeat the same for other frequencies.
C. Measurement of Coupling Factor, Insertion loss, Isolation & Directivity
1. Set up the components and equipments as shown in fig
2. Energies the microwave sources for particular frequency of operation
3. Remove the multi hole directional coupler and connect the detector mount of the
Frequency meter. Tune the Detector for maximum output.
4. Set any reference level of Power on VSWR meter with the help of variable
attenuator, Gain control knob of VSWR meter and note down the
reading (reference level let X)
5. Insert the directional coupler as shown in second fig 3. With detector to the
auxiliary port 3 and matched termination to port 2, without changing the position
of variable attenuator and gain control knob of VSWR meter
6. Note down the reading on VSWR meter on the scale with the help of range – dB
switch if required. let it be Y
7. Calculate coupling factor which will be X-Y=C(dB)
8. Now carefully disconnect the detector from the auxiliary port 3 and match
termination from port 2 without disturbing the set-up
9. Connect the matched termination to the auxiliary port 3 and detector to port 2 and
measure the reading on VSWR meter, Suppose it is Z.
10. Compute the insetiopn loss X-Z dB

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11. Repeat the steps from 1 to 4.
12. Connect the directional coupler in the reverse direction i.e., port 2 to frequency
meter side. Matched termination to port 1 and detector mount to prt 3 without
disturbing the position of the variable attenuator and gain control knob of VSWR
meter.
13. Measure and note down the reading on VSWR meter. Let it be Yd. X- Yd gives
Isolation (dB)
14. Compute the Directivity as Y-Yd= I-C
15. Repeat the same for other frequencies.
RESULT:

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Ex No: 5 SCATTERING PARAMETERS OF WAVE
GUIDE COMPONENTS
Date:
AIM:
Study of Magic Tee
EQUIPMENTS REQUIRED:
SNo. EQUIPMENT SPECIFICATION QUANTITY
1. Klystron power supply SKPS-610 1
2. Klystron tube with Klystron Mount 2K-25, XM-251 1
3. Isolator XI-621 1
4. Frequency meter XF-710 1
5. Variable Attenuator XA-520 1
6. Detector Mount XD 451 1
7. Matched Termination XL 400 2
8. Magic Tee XK 620 1
9. Waveguide Stand -- 2
10. BNC Cable -- 1
11. VSWR meter -- 1
12. Cooling Fan -- 1

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M
ME
EA
AS
SU
UR
RE
EM
ME
EN
NT
T T
TA
AB
BL
LE
E:
:
Pin = dB
ORIENTATION OF MAGIC TEE
VSWR METER
READING (dB)
SCATTERING
PARAMETER
INPUT ARM OUTPUT ARM OUTPUT POWER(dB)
P01 P12
P13(E-Plane)
P14(H-Plane)
P02 P21
P23(E-Plane)
P24(H-Plane)

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THEORY:
The device magic Tee is a combination of E and H palne Tee. Arm 3 is the H-arm and
arm 4 is the E-arm. If the power is fed into arm 3 (H-arm) the electric field divides equally
between arm 1 and 2 wih the same phase, and no electric field exists in arm 4. If power is fed in
arm 4(E-arm). It divides equally into arm and 2 but out of phase with no powerto arm 3. Further,
if power is fed in arm 1 and 2 simultaneously it is added in arm 3 (H-arm) and it is subtracted in
E-arm i.e arm 4
The basic parameters to be measured for magic Tee are defined below
A. Input VSWR
Value of SWR corresponding to each port, as a load to the line while other ports are
terminated in matched load.
B. Isolation
The Isolation between E and H arms is defined as the ration of the power supplied by the
generator connected to the E-arm (port 4) to the power detected at H-arm (port3) when
side arms 1 and 2 terminated in matched load.
Hence Isolation (dB) = 10 log10(P4/P3)
Similarly, isolation between other ports may also be defined.
C. COUPLING FACTOR
It is defined as Cij= 10-α/20
Where α is the attenuation / isolation in dB when I is input arm and j is output
arm
Thus α=10 log10(P4/P3)
Where P3 is the power delievered to arm I and P4 is power detected at j arm
PROCEDURE:
A.VSWR MEASUREMENTS AT PORTS
1. Set up the components and equipments as shown in fig. Keeping E arm towards slotted
line and match the termination to other ports.
2. Energise the microwave sources for particular frequency of operation

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3. Measure VSWR of E arms as described in measurement of SWR for low and medium
value
5. Connect another arm to slotted line and terminate the other port with matched
termination. Measure the VSWR as above. Similarly, VSWR of any port can be
measured.
B. Measurement of Isolation and Coupling factor
1. Remove the tunable probe and magic Tee from the slotted line and connect the detector
mount to slotted line.
2. Energise the microwave sources for particular frequency of operation and tune the
detector mount for maximum output
3. With the help of variable attenuator and gain control knob of VSWR meter, set any
power level in VSWR meter and note down. Let it be P3.
4. Without disturbing the position of variable attenuator and gain control knob, carefully
place the Magic Tee after slotted line. Keeping H arm connected to slotted line,
detector to E arm and matched termination to arm 1 and 2. Note down the reading of
VSWR meter. Let it be P4.
5. Determine the Isolation between port 3 and 4 as P3-P4 in dB.
6. Determine th e coupling coefficient from equation given in the theory part.
7. The same experiment may be repeated for other ports also.
8. Repeat the above experiment fo r other frequencies.
RESULT:

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Ex No: 6 DETERMINTAION OF
FREQUENCY
MEASUREMENT
Date:
AIM:
mode.
To determine the frequency and wavelength in a rectangular waveguide working in TE
EQUIPMENT:
SNo. EQUIPMENT SPECIFICATION QUANTITY
1 Klystron power supply SKPS-610 1
2 Klystron tube with Klystron Mount 2K-25, XM-251 1
3 Isolator XI-621 1
4 Frequency meter XF-710 1
5 Variable Attenuator XA-520 1
6 Slotted section XS 651 1
7 Tunable Probe XP-655 1
8 VSWR Meter SW-115 1
9 Movable Short XT-4813 1
10 Wave Guide Stand XU-535 2
11 Matched Termination XL-400 1
12 Oscilloscope -- 1
13 BNC Cable -- 1
14 Cooling Fan --- 1
THEORY
For dominant TE mode rectangular waveguide Io,Igand Ic are related as below

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(1/⅄o
2
) = (1/⅄g
2
) + (1/⅄c
2
)
where Io is free space wavelength
Ig is guide wavelength
Ic is cutoff wavelength
For TE mode, I =2a where “a” is broad dimension of waveguide.
PROCEDURE
1. Setup the components and equipments as shown in figure.
2. Setup variable attenuator at minimum attenuation position.
3. Keep the control knobs of VSWR meter as below:
Range-50db
Input switch- crystal low impedance
Meter switch-normal position
Gain(Coarse & Fine)- Mid position
4. Keep the control knobs of Klystron power supply as below
Beam voltage- OFF
Mod-switch-AM
Beam Voltage knob-Fully anticlockwise
Reflector Voltage- Fully clockwise
AM- Amplitude knob- Around fully clockwise
AM- Frequency knob – Around Mid position
5. Switch ON the Klystron power supply, VSWR Meter and cooling fan switch.
6. Switch ON the beam voltage switch and set beam voltage around 250V-300V with help
of beam voltage knob.
7. Adjust the reflector voltage to get some deflection in VSWR meter.
8. Maximize the deflection with AM amplitude and frequency control knob of power
supply.
9. Tune the plunger of Klystron Mount for maximum deflection.
10. Tune the reflector voltage knob for maximum deflection .
11. Tune the probe for maximum deflection in VSWR Meter.
12. Tune the frequency meter knob to get a ‘dip’ on the VSWR scale and note down the
frequency directly from frequency meter.
13. Replace the Termination with movable short, and detune the frequency meter.
14. Move the probe along the slotted line. The deflection in VSWR meter will vary. Move
the probe to a minimum deflection position, to get accurate reading. If necessary increase
the VSWR Meter range dbswitch to higher position. Note and record the probe position.
15. Move the probe to next minimum position and record the probe position again.

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16. Calculate the guide wavelength as twice the distance between two successive minimum
position obtained as above.
17.
18. Measure the waveguide inner broad dimension ‘a’ which will be around 22.86 mm for X-
band.
19. Calculate the frequency by following equation
20. Verify the frequency obtained by frequency meter.
21. Above experiment can be verified at different frequencies.
RESULT:

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Ex No: 7 IMPEDANCE MEASUREMENT BY
SLOTTED LINE METHOD
Date:
AIM:
To measure an unknown impedance using the smith chart.
EQUIPMENTS:
SNo. EQUIPMENT SPECIFICATION QUANTITY
1 Klystron power supply SKPS-610 1
2 Klystron tube with Klystron Mount 2K-25, XM-251 1
3 Isolator XI-621 1
4 Frequency meter XF-710 1
5 Variable Attenuator XA-520 1
6 Slotted section XS 651 1
7 Tunable Probe XP-655 1
8 VSWR Meter SW-115 1
9 Movable Short XT-4813 1
10 Wave Guide Stand XU-535 2
11 Matched Termination XL-400 1
12 S S Tuner XT 441
13 Oscilloscope -- 1
14 BNC Cable -- 1
15 Cooling Fan --- 1
THEORY:
The impedance at any point on a transmission line can be written in the form R+jX

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For comparison SWR can be calculated
Where
Reflection co-efficient
Z0= characteristics impedance of w/g at operating frequency
Z= load impedance. The measurement is performed in following way.
The unknown device is connected to the slotted line and the position of one minima is
determined. The 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 guidewave length. One of the minima is used as reference for impedance measurement .find
the difference of reference minima and minima position obtained from unknown load. Let it be
‘d’. Take a smith chart , taking ‘1’ as centre, draw a circle of radius equal to S. mark a point on
circumference of smith chart towards load side at a distance equal to d/g. join the centre with this
point . find the point where it cut the drawn circle.the co-ordinates of this point will show the
normalized impedance of load.
PROCEDURE:
1. Setup the components and equipments as shown in figure.
2. Setup variable attenuator at minimum attenuation position.
3. Keep the control knobs of VSWR meter as below:
Range - 50db position
Input switch - Crystal low impedance
Meter switch - Normal position
Gain(Coarse & Fine)- Mid position
4. Keep the control knobs of Klystron power supply as below
Beam voltage - ‘OFF’
Mod-switch -AM
Beam Voltage knob-Fully anticlockwise

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Reflector Voltage- Fully clockwise
AM- Amplitude knob- Around fully clockwise
AM- Frequency knob – Around Mid position
5. Switch ‘ON’ the Klystron power supply, VSWR Meter and cooling fan switch.
6. Switch ‘ON’ the beam voltage switch and set beam voltage around 250V-300V with help
of beam voltage knob.
7. Adjust the reflector voltage to get some deflection in VSWR meter.
8. Maximize the deflection with AM amplitude and frequency control knob of power
supply.
9. Tune the plunger of Klystron Mount for maximum deflection.
10. Tune the reflector voltage knob for maximum deflection .
11. Tune the probe for maximum deflection in VSWR Meter.
12. Tune the frequency meter knob to get a ‘dip’ on the VSWR scale and note down the
frequency directly from frequency meter.
13. Keep the depth of pin S S. Tuner to around 3-4 mm and lock it.
14. Move the probe along the slotted line to get maximum deflection.
15. Adjust VSWR meter gain control knob and variable attenuator until the meter indicates
1.0 on the normal db SWR scale.
16. Move the probe to next minimum position and note down the SWR S0 on the scale .also
note down the probe position. Let it be ‘d’.
17. Remove the SS tuner and matched termination and place movable short at slotted line.
The plunger of short should be at zero.
18. Note the position of two successive minima position .let it be as d1 and d2 .Hence λg =
2(d1- d2).
19. Calculate
d
- -
λg
20. Find out the normalized impedance as described in the theory section.
21. Repeat the same experiment for other frequency if required.
RESULT:

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Ex No: 8 VSWR MEASURMENT
Date:
AIM: To measure the VSWR of given load
SNo. EQUIPMENT SPECIFICATION QUANTITY
1 Klystron power supply SKPS-610 1
2 Klystron tube with Klystron Mount 2K-25, XM-251 1
3 Isolator XI-621 1
4 Frequency meter XF-710 1
5 Variable Attenuator XA-520 1
6 Slotted section XS 651 1
7 Tunable Probe XP-655 1
8 VSWR Meter SW-115 1
9 Movable Short XT-4813 1
10 Wave Guide Stand XU-535 2
11 Matched Termination XL-400 1
12 S S Tuner XT 441
13 Oscilloscope -- 1
14 BNC Cable -- 1
15 Cooling Fan --- 1
THEORY:
The impedance at any point on a transmission line can be written in the form R+jX

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For comparison SWR can be calculated
Where
Reflection co-efficient
=
−
+
Z0= characteristics impedance of w/g at operating frequency
Z= load impedance. The measurement is performed in following way.
The unknown device is connected to the slotted line and the
position of one minima is determined. The 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 guidewave length. One of the minima is used as
reference for impedance measurement .find the difference of reference
minima and minima position obtained from unknown load. Let it be
‘d’. Take a smith chart , taking ‘1’ as centre, draw a circle of radius
equal to S. mark a point on circumference of smith chart towards load
side at a distance equal to d/g. join the centre with thispoint . find the
point where it cut the drawn circle.the co-ordinates of this point will
show the normalized impedance of load.
PROCEDURE:
1. Set the various components and instruments as per the block diagram.
2. Switch on the Klystron Power Supply Unit (PSU) and CRO
3. Set the beam voltage to 300Vand repeller voltage for maximum output.
4. Note down the maximum output (Vmax).
5. By varying the slotted section note down the minimum o/p(Vmin) .
6. Find out the VSWR of the load by the formula VSWR= Vmax/ Vmin.
7. Repeat the same procedure for other loads.
8. Compare the practical values with manufacturer’s specifications.
RESULT:

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INTRODUCTION TO OPTICALCOMMUNICATIONS
An optical fiber is a dielectric wave guide through which light can be
transmitted by total internal reflection. Usually optical fibers are flexible, thin,
and cylindrical and made of transparent materials such as glass and plastic. The
most abundant and widespread material used to make optical fiber is glass and
most often this is an oxide glass based on silica (SiO2) with some additives.
There are three types of fiber optic cables: single mode, multimode and plastic
optical fiber (POF).Single Mode cable is a single stand of glass fiber with a diameter
of 8.3 to 10 microns. (One micron is 1/250th the width of a human hair.) Multimode
cable is made of multiple strands of glass fibers, with a combined diameter in the
50-to-100 micron range. Each fiber in a multimode cable is capable of carrying a
different signal independent from those on the other fibers in the cable bundle. POF
is a newer plastic-based cable which promises performance similar to single mode
cable, but at a lower cost.
PRINCIPLES OF FIBER OPTICS:
Total internal reflection (TIR) is the most important phenomenon for the
guiding of light in optical fibers. Under the condition of total internal reflection,
light can be completely reflected at a dielectric interface without any reflective
coating. It is required for TIR that the ray of light be incidental on a dielectric
interface from the high refractive index side to the low refractive index side. Fig.
shows that TIR occurs over a certain range of incidence angles. If a ray of light
propagates at a certain angle, θ 1(θ1<θc) where θc is the critical angle from a high
refractive index medium (n1) to a low refractive medium (n2), a portion of light
will be reflected back to Medium 1 and another part of light will be refracted into
Medium 2 as shown in Fig. This behavior of light can be expressed by Snell's law:
n1 sin θ1 = n2 sin θ2 (1)
If angle θ1 is increased to θc, θ2 reaches 90º. The critical angle, θc, is defined as:
θc = sin-1
(n1/n2) (2)

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FIG1: Refraction and reflection at the interface between two
mediawith different indices of refraction (n1>n2).
(a) Incident angle θ1< θc; (b) incident angle = θc (critical angle);
(c) Incident angle = θ3>θc (total internal reflection).
At the critical angle θc, the refracted ray will travel along the boundary
surface. If the angle of incidence is increased further to θ3(θ3>θc) at the boundary
surface, the ray is totally reflected back into the higher refractive index Medium 1.
This phenomenon is called total internal reflection.
ADVANTAGES OF OPTICAL COMMUNICATIONS:
1. Less attenuation
2. Enormous Bandwidth
3. Small in size and weight
4. Security
5. Flexibility
6. Electromagnetic immunity
7. Electrical isolation
APPLICATIONS OF OPTICAL COMMUNICATIONS:
1. Military
2. Sensors
3. Networking
4. Communications

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Ex No: 9
CHARACTERIZATION OF
LED
Date:
Aim: To study the relationship between the optical power output and dc forward
current of LED and determine the linearity of the device at 660 nm as well as
850 nm.
APPARATUS:
1. LED TX Kit - λ=660 nm& 850 nm
2. LED RX Kit - λ=660 nm& 850 nm
3. Multimeter
4. Optical Fiber Cable - PMMA Type
5. CRO - 30 MHz
THEORY:
LED’s and laser diodes are the commonly used sources in optical
communication systems whether the system transmits digital or analog signals. In
the case of analog transmission, direct intensity modulation of the optical source
can be varied linearly as a function of the modulating electrical signal amplitude.
LED’s 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 LED’s at 660 nm, 1300 nm, 850 nm are
popular. While direct intensity modulation is simple to realize higher performance
is achieved by FM modulating the base band signal prior to the intensity
modulation. The relationship between an LED optical output P0 and the LED
forward current IF is given by P0= k.IF where k is a constant.
FIG1: Set up for LED Characterization

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VO
(mV)
IF=V0/100
(mA)
P0
(dBm)
VO
(mV)
IF=V0/100
(mA)
P0
(dBm)
PROCEDURE:
1. Connect one end of cable to the LED1 port of transmitter kit and the
other end to the FO PIN port of receiver kit as shown in Figure
2. Set DMM1 to the 200 mV range and connect it to P0 on the receiver
kit. The power meter is ready for use Po=(reading)/10 dBm
3. Set DMM2 to 200 mV range and connect it between the TP1 (VO)
and ground in the transmitter kit. IF=V01 (mV)/100 in mA.
4. Plug the AC mains for both units. Adjust the set gain knob on the
transmitter kit to the extreme anticlockwise position to reduce IF to
minimum. The reading on the power meter should be out of range.
5. Slowly turn the set gain knob clockwise to increase IF. The power
meter should read –30.0 dB approximately. From here change IF in
suitable steps and note the power meter readings P0.
6. Record up to the extreme clockwise position.
7. Plot a graph between P0 and IF as shown in the Fig 2.
TABULAR FORMS:
For 660 nm For 850 nm
MODEL GRAPH:

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FIG. 2 LED CHARACTERISTICS
RESULT: The optical power Vs forward current characteristics of
660 nmand 850 nm LEDs are observed and plotted.

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Ex No: 10
CHARACTERIZATION OF
LASER DIODE
Date:
AIM: To find the characteristics of Optical Power (Po) of laser diode vs. Laser
diode forward current (IF).
APPARATUS:
1. LD TX Kit - λ=660 nm
2. LED RX Kit - λ=660 nm
3. Multimeter
4. Optical Fiber Cable - PMMA Type
5. CRO - 30 MHz
THEORY:
Laser diodes (LDs) are used in telecom, data, and video communication
applications involving high speeds and long hauls. All single mode optical fiber
communication systems use lasers in the 1300 nm and 1500 nm windows. Lasers with
very small line-widths also facilitate realization of wavelength division multiplexing
(WDM) for high density communication over a single fiber. The inherent properties
of LDs that make them suitable for such applications are, high coupled optical power
in to the fiber (typically greater than 1mw), 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 analog transmission) special lasers also
provide for regeneration / amplification of optical signals within an optical fiber.
These fibers are known as erbium doped fiber amplifiers (EDPA). Specifications of a
typical laser diode are given in Appendix B.Even though a variety of laser diode
constructions are available there are a number of common features in all of
them . Very simple device (650nm
/2.5mw )is used to demonstrate the functioning of a laser diode
A laser diode has a built – in photo detector ,which one can employ
to monitor the optical intensity of the laser at a specified forward current . This
device is also effectively utilized in designing an optical negative feedback
control loop , to stabilize the optical power of a laser in the steep lasing
region . The electronic circuit scheme that employs the monitor photo diode to
provide a negative feedback for stabilization of optical power is known as the
automatic power control mode (APC) . If a closed loop employs current control
alone to set optical power then this mode is called the automatic current
control mode (ACC) . The disadvantage of ACC scheme is that the optical
power output may not be stable at a given current due to the fact that small
shifts in the lasing characteristicsoccur with temperature changes and ageing .
The disadvantage of the APC is that the optical feedback loop may cause
oscillations , if not designed properly .

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FIG. Set up for Po Vs IF Measurement
PROCEDURE:
1. Connect the 2-metre PMMA FO cable (cab 1) to TX Unit and
couple the laser light to the power meter on the RX unit as
shown . Select ACC mode of operation.
2. Set DMM1 to the 2000 mV range and on the RX side
connect to the terminals marked Po to it . Turn it on. The power
meter is now ready for use. Po= (reading)/10 dBm.
3. Set DMM2 to the 2000 mV range and connect it between Vo
and Gnd on the TX unit . (IF = Vo/100).
4. Adjust the Set IF Knob to the extreme anticlockwise position
to reduce IF to 0.
5. The power meter reading will normally be below -40 dBm or
out of range .
6. Gradually increase IF . Note IF and Po readings.
7. Plot the graph Po Vs. log IF as shown in the Fig.
8. Determine the slopes prior to lasing and after lasing. Record the
laser threshold current.
TABULAR FORM:
V(mV) IF (mA) PO (dBm)

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MODEL GRAPH:
FIG: Laser Diode Characteristics.
RESULT: The optical power Vs forward current characteristics of the
laserdiode are observed and plotted.

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12.MEASURMENT OF DATA RATE FOR DIGITAL OPTICAL LINK
AIM:
To connect the RS-232 ports of two computers using optical fiber digital link to establish a full duplex
communication and to measure the data rate at different parity bits, stop bits and data bits.
APPARATUS REQUIRED:
a. Fiber link- A kit
b. 1mt fiber cable
c. 9-pin D connector cables (2)
d. Computers PC/XT, PC, 386, 486 (or) higher version
e. Power supply
f. Patch chords
THEORY:
In optical communication the exchange of information between any two devices across a
communication channel involves some type of optical signal which carries the information. The rate at which circuits
(or) other devices operate when handling digital information is called data rate. The max rate that can be obtained over
a given channel is called channel capacity in digital link, input is a digital signal. The optical communication involves
exchange of information between any two devices across a communication channel. The data rate can be measured by
connecting optical digital link to thecomputer
PROCEDURE:
1. Slightly unscrew the cap of 660nm LED on kit. Don’t remove the cap from the connector. Once
the cap is loosened, insert the fiber into the cap. Now, tight the cap by screwing it back.
2. Make the jumper settings and connection diagrams as shown in figures 1 and establish full
duplex communication.
3. Refer to fig.2 of this experiment and make the necessary connections and connect one end of the
9 to 9 pin cable to PC COM 1 port and the other end to CN1 connector on LINK-A kit then connect
second 9 to 9 pin cable one end to second PC COM 1 port and other end to CN2 connector on LINK-A
kit. Connect the power supply cables with proper polarity to kit. While connecting this, ensure that the
power supply is OFF.
4. Connect CN1 post on the kit (RS-232 section) to IN post of digital buffer section.
5. Connect CN2 post on the kit (RS-232 section) to TTL OUT post of the receiver section.
6. Switch ON the PCs and the power supply of the kit fiber link-A.
7. After putting ON one of the PC, go to START menu, PROGRAMS, ACCESSORIES,
COMMUNICATION and then click on HYPER TERMINAL.
8. A new window will open, where in you double click on HYPERTERM, two windows will open,
one at the background and another with title connection description which will be active.
9. Enter the name in the box by which you would like to store your connections, for e.g. (PC 2 PC)

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and click Ok. Also you could select the ICON provided below. The background window title will
change to the name provided by you.
10. Then specify connect using selecting direct to COM1 or port where your cable is connected and
then click on OK.
11. Now window with title COM1 properties will appear, where port setting should be done as shown
below click on OK
12. After the above settings you click OK. The background window will become active.
13. Click on file, save as, and save it in the directory, which you want.
14. Perform the same procedure i.e.., from points 8 to 14 on the computer with whom we want
to communicate.
15. To start communicating between the two PC’s click on the transfer menu and again click on send
file. A window will be prompted having title send file name with filename and protocol.
16. Select “browse” for the file which we would like to send to the PC connected. Select the file and
click on open the file name and address will be displayed in the small window. Then select the
“Kermit” protocol (optional use protocols are S-modem, Y-modem and IKX modem).
17. To receive the file on the PC click on the transfer menu and click on receive file. A window will
be prompted having title receiving file with location at which you want to receive files and protocol.
18. Select the browser for the location where you would like to store received files. Select the folder
and click OK, the folder name and address will be displayed in the small windows protocol to be
selected should be Kermit and select and same as the file transmittingPC.
19. On the PC from which the selected file to be transmitted, click on send. A new window will open
showing file transfer status. Immediately at the receiving PC click receive (otherwise time out error
will be displayed and communication will fail). You will see a window showing the file is received in
the form of packets.
20. After the file is transferred both the windows in the two PC’s will close. Check for the received
files in the folder where the file is stored. You can do this procedure vice versa to transfer the file.
DIAGRAM OF A PC TO PC COMMUNICATION VIA FIBER
OPTIC CABLE

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OBSERVATIONS:
FULL DUPLEX COMMUNICATION:
Input characters from keyboard 1 of PC1: MICROWAVE & OPTICAL COMMUNICATION LAB
Input characters from keyboard 1 of PC1 are displayed on PC2:
Output characters of PC2: MICROWAVE & OPTICAL COMMUNICATION LAB Input characters from keyboard 2
of PC2: ECE Department
Output characters from keyboard 2 of PC2 are displayed on PC1: Output characters of PC1: ECE Department
DATA RATE MEASUREMENT:
S.No Baud rate Tx time Tx CPS Rx time Rx CPS Stop bits Data bits Parity bits
1
2
3
PRECAUTIONS:
1. Keep the jumpers properly
2. Select the patch cards according to the requirement and insert properly
3. Avoid the sharp bending of optical fiber cable
4. Insert properly RS 232 probe between PC and optical trainer kit
RESULT:

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13.MEASUREMENT OF NUMERICAL APERTURE
AIM: To estimate the Numerical Aperture of the 1mm diameter plastic fiber at650
nm.
APPARATUS: 1.OFT Trainer Kit
2. Numerical Aperture Measurement Unit
3. 1mm diameter 1m fiber
THEORY:
Numerical aperture of the fiber is a measure of the acceptance angle of light
in the fiber. Light which is launched at angles greater than this maximum acceptable
angle does not get coupled to propagating modes in the fiber, and therefore does not
reach the receiver at other end of the fiber. The NA is useful in the computation of
optical power coupled from an optical source to the fiber, from fiber to a photo
detector, and between two fibers.
PROCEDURE:
SETUP:
1. The interfaces used in the experiment are summarized in Table. Identify
them on OFT kit with the layout diagram. The block diagram is shown
in fig. ensure that the shorting plugs of Tx data shorting link S4, coded
data shorting link S6, and Tx clock shorting link S5 in the Manchester
coder block are in position. Also ensure that the shorting plug of clock
select jumper JP1 is across the posts B&A1. A TTL signal from the
multiplexer should now be driving LED2 in optical Tx2 block. This
experiment is best performed in a less illuminated room.
2. Ensure that the cut planes of the 1m plastic fiber are perpendicular to the
axis of the fiber. If required, prepare 1m of plastic fiber as per the
instructions in appendix A.
3. Insert one end of fiber in to NA measurement unit as shown in figure.
adjust the fiber such that its tip is 10mm from the screen.
4. Gently tighten the screw to hold the fiber firmly in place.
5. Connect the other end of the fiber to LED2 through the simplex
connector. The fiber will project a circular patch of red light on to the
screen. Now measure the diameter of the circular patch of red light in
two perpendicular directions (BC and DE in Fig). the mean radius of the
circular patch is given by
X = (DE +BC)/4
6. Carefully measure the distance d between the tip of the fiber and the
illuminated screen (OA in Fig). The Numerical Aperture of the fiber is
given by
NA = Sin (Ө) =X/ (√ (d2
+X2
)
7. Repeat steps 3 to 6 for different values of d. compute the average value
of Numerical aperture.

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FIG: Layout diagram

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Fig: Block diagram

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FIG: Numerical Aperture measurement unit
Fig: Circular path diameter
Fig: Total internal reflection of core cladding boundary of fiber

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TABULAR FORMS:
S.No BC DE X d NA
Table: Interface details:
Sl.
No
Identification
name
function location
1 LED2 650nm 650nm LED Optical Tx2
block
2 S6 coded data Manchester coded data shorting link
post A: coder output
Post B: Manchester coder input
posts A&B should be shorted
Manchester
coder block
3 S4 Tx data Multiplexed transmitted data
shorting link
Post A: Manchester coder unit
Post B: Manchester coder input
posts A&B should be shorted
Manchester
coder block
4 S5 Tx clock Transmitter clock shorting link
Post A: Manchester coder unit
Post B: Manchester coder input
posts A&B should be shorted
Manchester
coder block
5 JP1 clock select Transmission clock selection posts
B&A1 should be shorted
Timing and
control block
RESULT: The Numerical Aperture of the 1mm diameter plastic fiber at 650nm is
measured.

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14.MEASUREMENT OF COUPLING AND BENDING LOSSES IN
OPTICAL FIBER
Aim:
The objective of this experiment is to measure the losses in an optical fiber
communication link. The experiment not only enables one to determine the
propagation loss in the fiber, but also to get a feel for bending and coupling losses.
Equipment Required:
1. OFT.
2. Two channel, 20MHZ Oscilloscope.
3. Function generator, 1HZ-10 MHZ.
4. Fiber alignment unit.
Theory:
S.NO.
Identification
Name
Function Location
1 SW8
Analog/Digital
selection switch
should be set to
ANALOG position.
2 LED1
850nm
850nm LED Optical Tx1
Block
3 LED2
650nm
650nm LED Optical Tx2
Block
4 PD1 PIN Detector Optical
Rx1Block
5 JP2
PD1/PD2 Receiver
Select Posts B & A1
should be shorted
6 GAIN GAIN Control
Potentiometer
Optical
Rx1Block
7
P11 ANALOG
IN
Analog IN
8 P31 PIN Detector signal
after gain
Optical
Rx1Block
9 I/O1,I/O2,I/O3
Input/output BNCs
and posts for feeding
in and observing
signals

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10 S6 coded data
Manchester Coded
Data Shorting link.
Post A: Coded
output
Post B: Input to
Tx1/Tx2/Electrical
Post A & B should
be shorted.
Manchester
Coder
Block
11 S26 coded data
Received
Manchester Coded
Data shorting link
Post A: Receiver
output (Rx1/Rx2)
Post B: Input to
decoder and clock
recovery block
Post A&B should be
shorted
Decoder &
Clock
Recover
Block
Table: Interface Details.

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FIG: Block diagram

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Fig: Bending the optical fiber
Fig: Fiber Alignment using the Aligning Unit

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PROCEDURE:
1. Set the switch SW8 to the ANALOG position. Ensure that the shorting
plug of the jumper JP2 is across the posts B& A1 (for PD1). Remove the
shorting plugs from coded data shorting links. S6 in the Manchester coder
block and S26 in the Decoder& clock recovery block.
Attenuation at 850 nm:
2. Take the 1m fiber and setup and analog link using LED1 in the Optical
Tx1 block and detector PD1 in the Optical Rx1 block [850nm link]. Drive
a 1V p-p 10 KHz sinusoidal signal with zero d.c. at P11. Observe the
signal at P31 on the oscilloscope. Use the BNC I/Os for feeding in and
observing signals. Adjust the GAIN such that the received signal is not
saturated. Do not disturb the level of the signal at the function generator or
the gain setting throughout the rest of the experiment.
3. Note the peak value of the signal received at P31 and designated it as
V1. Replace the 1m fiber by the 3m fiber between LED1 and PD1. Again
note the peak value of the received signal and designate it as V3. If α is the
attenuation in the fiber and I1 and I3 are the exact length of the 1m and 3m
fibers in meters respectively, we have

Where α is in nepers/m, and P1 and P3 are the received optical
power with1m and 3m fiber respectively. Compute α in dB/m for
850nm wavelength using α’=4.343α where α is in nepers/m.
Attenuation at 650nm:
4. Now setup the 650nm link using LED2, detector PD1 and the 1m fiber.
Remove the shorting plugs from S6 and S26 and feed in a TTL signal of
10 KHz at post B of S6. Observe the signal at P31 on the oscilloscope.
Adjust the GAIN such that the received signal is not saturated. Note the
peak value of the 1m fiber with the 3m fiber between LED2 and PD1.
Again without disturbing the GAIN, note the peak value of the received
signal and designate it as V3. Compute α’ in dB/m for a 650nm
wavelength using the expressions given Step3.
Bending Loss:
5. Set up the 850nm analog link using the 1m fiber. Drive 1Vp-p sinusoidal
signal of 10 KHz with zero d.c. at P11 are observe the received signal at
P31 on the oscilloscope. Now bend the fiber in a loop as shown in Figure.
Reduce the diameter of the loop slowly and observe the reduction of the
received signal at P31. Keep reducing the diameter of the loop to about 2
cm and plot the amplitude of the received sign versus the diameter of the
loop. (Do not reduce the loop diameter to less than 1cm.)

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Coupling Loss:
6. Connect one end of the 1m fiber to LED2 and the other end to the detector
PD1. Drive the LED with a 10 KHz TTL signal at post B of S6. Note the
peak signal received at P31 and designated it as V1 [ensure that the GAIN
is low to prevent saturation.] Now disconnect the fiber from the detector.
Take the 3m fiber and connect one end to the detector PD1. The optical
signal can be seen emerging form the other end of the 1m fiber. Bring the
free ends of the two fibers as close as possible and align them as shown in
Figure using the Fiber Alignment Unit. Observe that the received signal at
P31 varies as the free ends of the fibers are brought closer and moved
apart. Note the received signal level with the best possible alignment and
designate it as V4. Using the attenuation constant value obtained in Step3,
Compute the coupling loss associated with the above coupling of the two
fibers using
V4 
   10 logV   'L3  L1 

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 1 
Where α’ is the attenuation constant in dB/m at 650nm and η is thecoupling loss in dB.
Now move the two fibers a bit apart in the Fiber Alignment Unit and notethe decrease in the
output voltage. Measure the coupling loss also.
7. With the two ends of the fiber are aligned as close as possible, place a dropof glycerine/isopropylene
through the hole provided in the Fiber Alignment unit so as to cover the fiber ends. Note that the
received signal now increases. Compute the coupling loss in the presence of a index matching fluid like
glycerin.
8. Now try aligning the two fibers without using the Fiber Alignment unit. Estimate the losses as the two
fibers are offset laterally and also when the two fibers are at an angle as shown Figure.
RESULT:
Various losses in an optical fiber communication link are
measured.