Ec 2405 Optical Microwave Lab Manual

JUMPER SETTING DIAGRAM:

1 VEC/2011-12/ODD/ECE/VII/EC-2405

FIBER OPTIC CABLE

P2

DRIVER

FIBER OPTIC TRANSMITTER

SFH 756V TX1

SCREW

P1

BIAS

INTENSITY

A OA=dr = (MR+PN)/4

N

M

PO

RSCREEN

ILLUMINATED CIRCULAR PATCH

+5V

JP 5

+12V

JP 6

JP 8 TX

SW 8

VITX 1

SW 9TX 2

1. STUDY OF NUMERICAL APERTURE OF OPTICAL

FIBERAIM:

To measure the numerical aperture of the plastic fiber provided with

kit using 660 nm wavelength LED.

APPARATUS REQUIRED:

S.No. Name of the Equipments Quantity

1. Link – B Advance Fiber Optic

Communication Trainer Kit1

2. Power Supply 1

3. Fiber Optic Cable (Plastic) 1 meter

4. Numerical Aperture measurement

Jig 1

5. Steel Ruler 1

6. Patch Chords Required

THEORY:

Numerical aperture refers to the maximum angle at the light incident

on the fiber end is totally internal reflected and is transmitted properly along

the fiber. The cone formed by the rotation of this angle along the axis of the

fiber is the cone of acceptance of fiber. The light ray should strike the fiber

end within its cone of acceptance; else it is refracted out of the fiber core.

Numerical aperture is the measure of the power launching efficiently of an

optical fiber. When N.A. is small, then the light available from various


directions from the source, only a portion of light is accepted by an optical

fiber and the remaining is rejected.

OBSERVATION:

d

(mm)

MR

(mm)

PN

(mm)

r

(mm)NA

r = (MR+PN)

4

NA = sin θ max =


PROCEDURE:

1. Make connections as shown in figure. Connect the power supply cables

with proper polarity to Link – B Kit. While connecting this, ensure that

the power supply is OFF.

2. Keep Intensity control pot P2 towards minimum position.

3. Keep Bias control pot P1 fully clockwise position.

4. Switch ON the power supply.

5. Slightly unscrew the cap of SFH 756V (660) nm. Do not remove the cap

from the connector. Once the cap is loosened, insert the 1 Meter Fiber

into the cap. Now tighten the cap by screwing it back.

6. Insert the other end of the Fiber into the numerical aperture measurement

jig. Adjust the fiber such that its cut face is perpendicular to the axis of

the Fiber.

7. Keep the distance of about 5mm between the fiber tip and the screen.

Gently tighten the screw and thus fix the fiber in the place.

8. Increase the intensity pot P2 to get bright red light circular patch.

9. Now observe the illuminated circular patch of light on the screen.

10.Measure exactly the distance d and also the vertical and horizontal

diameters MR and PN as indicated in the Figure.

11.Mean radius is calculated using the following formula

r = (MR+PN)/4.

12.Find the numerical aperture of the fiber using the formula

NA = sin θ max = 4 VEC/2011-12/ODD/ECE/VII/EC-

2405

Where θ max is the maximum angle at which the light incident is

properly transmitted through the fiber.



RESULT :

Thus Numerical aperture of the plastic fiber provided with kit using

660 nm wavelength LED was measured as ________.


REVIEW QUESTIONS:

1. Define Numerical Aperture.

2. What is V number?

3. What is the need for cladding?

4. Define the refractive index of a medium.

5. State snell’s law.



2. FIBER OPTIC COMMUNICATION LINK

AIM:

To obtain the transmitted analog or digital signal in the fiber optic

receiver using optical fiber/glass fiber.

APPARATUS REQUIRED:


1. Link – A Fiber Optic Trainer Kit 1


3. Power Supply 1

4. 20 MHz Dual Channel Oscilloscope 1

5. Probe, Patch Chords Required

THEORY:

ANALOG LINK

Fiber Optic Links can be used for transmission for digital as well as

analog signals. Basically a fiber optic link contains three main elements, a

transmitter, an optical fiber & a receiver. The transmitter module takes the

input signal in electrical form & then transforms it into optical (light) energy

containing the same information. The optical fiber is the medium which

carries this energy to the receiver. At the receiver, light is converted back

into electrical form with the same pattern as originally fed to the transmitter.




TRANSMITTER:

Fiber optic transmitters are typically composed of a buffer, driver &

optical source. The buffer electronics provides both an electrical connection

& isolation between the transmitter & the electrical system supplying the

data. The driver electronics provides electrical power to the optical source in

a fashion that duplicates the pattern of data being fed to the transmitter.

Finally the optical source (LED) converts the electrical current to light

energy with the same pattern. The LED SFH 756V supplied with the kit

operates inside the visible light spectrum. It’s optical output is centered at

near visible wavelength of 660 nm. The emission spectrum is broad, so a

dark red glow can usually be seen when the LED is on. The LED SFH 450V

supplied wit the kit operates outside the visible light spectrum. It’s optical

output is centered at near infrared wavelength of 950 nm.

RECEIVER:

The function of the receiver is to convert the optical energy into

electrical form which is then conditioned to reproduce the transmitted

electrical signal in its original form. The detector SFH250V used in the kit

has a diode type output. The parameters usually considered in the case of

detector are it’s responsivity at peak wavelength & response time. SFH250V

has responsivity of about 4µA per 10µW of incident optical energy at 950

nm and it has rise & fall time of 0.01µsec. PIN photodiode is normally

reverse biased. When optical signal falls on the diode, reverse current start to

flow, thus diode acts as closed switch and in the absence of light intensity, it

acts as an open switch. Since PIN diode usually has low responsivity, a trans

impedance amplifier is used to convert this reverse current into voltage. This


voltage is then amplified with the help of another amplifier circuit. This

voltage is the duplication of the transmitted electrical signal.MODEL GRAPH:

FIBER OPTIC COMMUNICATION - ANALOG LINK:

FIBER OPTIC COMMUNICATION – DIGITAL LINK:


Am

plitu

de

Time Period

INPUTVoltage (V)

Time (ms)

Am

plitu

de

Time Period

OUTPUTVoltage (V)

Time (ms)

Am

plitu

de

Time Period

INPUT

Voltage (V)

Time (ms)

Am

plitu

de

Time Period

OUTPUT

Voltage (V)

Time (ms)

DIGITAL LINK

In the experiment no. 1, we have seen how analog signal can be

transmitted and received using LED, fiber and detector. The same LED,

fiber and detector can be configured for the digital applications to transmit

binary data over fiber. Thus basic elements of the link remains same even

for digital applications.

TRANSMITTER:

LED digital, DC coupled transmitters are one of the most popular

variety due to their case of fabrication. Standard TTL gate is used to drive a

NPN transistor, which modulates the LED SFH450V OR SFH756V source

(Turns it ON and OFF).

RECEIVER:

There are various methods of configure detectors to extract digital

data.

Usually detectors are of linear nature. Photodector SFH551V has TTL

type output. Usually it consist of PIN photo diode, transimpedance

amplifier and level shifter.


OBSERVATION:

ANALOG LINK:

AMPLITUDE

(volts)

TIME

(seconds)

INPUT

OUTPUT

DIGITAL LINK:

AMPLITUDE

(volts)

TIME

(seconds)

INPUT

OUTPUT



PROCEDURE:

FIBER OPTIC COMMUNICATION - ANALOG LINK:

1. Slightly unscrew the cap of LED SFH 756V TX1 (660 nm) from kit.

Do not remove the cap from the connector. Once the cap is loosened,

insert the fiber into the cap and assure that the fiber is properly fixed.

Now tight the cap by screwing it back. Keep INTENSITY pot P3 at

minimum position i.e. fully anticlockwise.

2. Make the connections and Jumper settings as shown in Figure.

Connect the power supply cables with proper polarity to kit. While

connecting this, ensure that the power supply is OFF.

3. Switch on the power supply.

4. Select the frequency range of Function Generator with the help of

Range Selection Switch SW1, frequency can be varied with Pot P2.

Adjust the voltage LEVEL of the Sine Wave with Pot P1 as per

following setting FREQUENCY: 1 KHz, LEVEL: 2Vp-p.

5. Connect SINE post of the Function Generator section to IN post of

Analog Buffer Section.

6. Connect OUT post of the Analog Buffer Section to TX IN post of

Analog Buffer Section.

7. Connect the other end of the fiber to detector SFH 250V (RX 1) in kit

very carefully as per the instructions in step 1.

8. Check the output signal of the Analog Buffer at its OUT post in Kit.

It should be same as that of the applied input signal.

9. Observe the output signal from the detector at ANALOG OUT post

on CRO by adjusting INTENSITY (Optical Power Control) Pot P3 in


kit and you should get the reproduction of the original transmitted

signal.


FIBER OPTIC COMMUNICATION – DIGITAL LINK:

1. Slightly unscrew the cap of LED SFH 756V TX1 (660 nm) from kit.

Do not remove the cap from the connector. Once the cap is loosened,

insert the fiber into the cap and assure that the fiber is properly fixed.

Now tight the cap by screwing it back.

2. Make the connections and Jumper settings as shown in Figure.

Connect the power supply cables with proper polarity to kit. While

connecting this, ensure that the power supply is OFF. Now Switch on

the power supply

3. Feed the Onboard Square (TTL) signal of about 1 KHz to IN post of

Digital Buffer Section and observe the signal at OUT post. It should

be same as that of the input signal.

4. Connect OUT post of the Digital Buffer section to TX IN post of

TRANSMITTER.

5. Connect the other end of the fiber to detector SFH 551V RX 2

(Digital Detector) in kit very carefully as per the instructions in step 1.

6. Observe the output signal from the detector at TTL OUT post on

CRO. The Transmitted signal and received signal are same. Vary the

frequency of the input signal and observe the output response.


RESULT:

Thus the transmitted analog or digital signal in the fiber optic receiver

using optical fiber (plastic) was done and has been verified.


REVIEW QUESTIONS:

1. What is the optical frequency range?

2. Name the basic principle used in optical fiber communication.

3. Give four advantages of optical fiber communication.

4. Based on the modes, what are the classifications of fiber?

5. Based on the refractive index profile, how the fiber is classified.


BLOCK DIAGRAM:

JUMPER SETTING DIAGRAM:


YELLOWWHITE

V

JP16JP17

1

2

3

4

1

2

3+

_

+_

BLACK RED

+5V

+9V

SFH 756V ANODE

Emitter of Q3 (2N2907)

Cathode of SFH 756V

Collector of Q1 (2N3904)

Cathode of SFH 450V

FIBER OPTIC CABLE

Pr10

DRIVER

FIBER OPTIC TRANSMITTER

SFH 756V

FIBER OPTIC RECEIVER

ANALOG OUT

SFH350V

DETECTOR

Pr10 Terminal

JP18

GND

Emitter of Q1 (2N3904)

1 2 3

Amplifier Output

JP20

Digital Buffer Output

Base of Q1 (2N3904)

1 2 3

3. V-I CHARACTERISTICS OF FIBER OPTIC LED &

PHOTO DETECTORAIM:

To study the characteristics of fiber optic LED and plot the graph of

forward current Vs output optical energy and also to the study the photo

detector response

APPARATUS REQUIRED:

S.No.Name of the

EquipmentsRange Quantity

1.

Link – B Fiber Optic

Communication

Trainer Kit

- 1

2. Power Supply - 1

3.Fiber Optic Cable

(Plastic)- 1 meter

4. Voltmeter (0-5)V, (0-10)V Each 1

5. Ammeter (0-50)mA 1

6.Connecting Wires,

Patch Chords- Required


MODEL GRAPH:

I vs. V Characteristics of SFH 756 V

CHARACTERISTICS OF OPTICAL POWER OF LED vs. If:


I (amp)(I vs. V)

V (volt)

PO (µW)(PO vs. If)

If (mA)

THEORY:

In Optical Fiber communication system, Electrical signal is first

converted into optical signal with the help of E/O conversion device as LED.

After this optical signal is transmitted through Optical fiber, it is retrived in

its orginial electrical form with the help O/E conversion device as

photodetector.

Different technologies employed in chip fabrication lead to significant

variation in parameters for the various emitter diodes. All the emitters

distinguish themselves in offering high output power coupled into the

important peak wavelength of emission, conversion efficiency usually

specified in terms of power launched in optical fiber peak wavelength of

emission,optical raise and fall times which put the limitation on operating

frequency, maximum forward current through LED and typical forward

voltage across LED.

Photodetectors usually comes in variety of forms

photoconductive,photovoltaic, transistor type output and diode type

output.Here also characteristics to be taken into account are response time of

the detector which puts the limitation on the operating frequency,

wavelength sensitivity and responsivity.


OBSERVATION:

CHARACTERISTICS OF LED:

LED voltage

Vd

(V)

LED Current

Id

(mA)

Optical power Of LED

Pd

(dBm)

Optical power Of LED

Pd

(mW)

TO CONVERT dBm TO Mw

CHARACTERISTICS OF DETECTOR: R= 100 Ω

LED Current

Id

(mA)

Optical power Of

LED

Pd

(mW)

Detector voltage

Vp

(V)

Detector Current

Ip

(mA)


PROCEDURE:

1. Confirm that the power switch is on OFF position.

2. Make the jumper settings as shown in the jumper diagram.

3. Insert the jumper connecting wires (provided along with the kit) in

jumper JP17 and JP16 at positions shown in figure.

4. Connect the ammeter and volt-meter with the jumper wires connected

to JP17 and JP16 as shown in figure.

5. Keep the potentiometer Pr10 in its maximum position (anti-

clockwise rotation) and Pr9 in its minimum position (clockwise

rotation). Pr10 is used to control current flowing through the LED and

Pr9 is used to vary the amplitude of the received signal at

phototransistor.

6. To get the VI characteristics of LED, rotate Pr10 slowly and measure

forward current and corresponding forward voltage. Take number of

such readings for various current values and plot VI characteristics

graph for the LED.

7. For each reading taken above, find out the power which is product of I

and V. This is the electrical power supplied to the LED.


8. With this efficiency assumed, find out optical power coupled into

plastic Optical Fiber for each of the reading in step7. Plot the graph of

forward current vs. output optical power of the LED.

9. In our experimental kit, when Pr9 is at its minimum position, 100

ohms of resistance is in series of emitter and ground of

phototransistor.

10.Connect the 1m optical Fiber Cable supplied with the kit between

LED SFH 756V (660nm) and phototransistor SFH 350V (Analog

Detector).


11.From the transfer characteristics obtained in step 8, launched known

optical energy into plastic fiber and measure output voltage at

ANALOG OUTPUT TERMINAL. Find out the current flowing

through phototransistor with this voltage value and 100 ohms of

resistance.

12.Repeat step11 for various launched Optical energy values and plot the

graph for the responsivity of phototransistor. Find out the portion

where detector response is linear.


RESULT :

Thus the characteristics of fiber optic LED and photo detector was

studied and has been verified .


REVIEW QUESTIONS:

1. Name two optical Sources.

2. What is the function of optical source?

3. Give the advantages of LED.

4. Define internal quantum efficiency for LED.

5. What is population inversion?

6. Define the modulation bandwidth of LED.



4. V-I CHARACERISTICS OF GUNN DIODE

AIM :

To study the V-I Characteristics of Gunn Diode.

COMPONENTS REQUIRED:

i. Gunn power Supply

ii. Gunn oscillator

iii. PIN modulator

iv. Isolator

v. Frequency Meter

vi. Variable Attenuator

vii. Detector Mount

viii. CRO

ix. Bayonet Neill Concelman(BNC) Connector

x. Threaded Neill Concelman(TNC) Connector

xi. Cooling Fan

xii. Waveguide Stand, Screw & Net

THEORY :

Gunn diodes are negative resistance device which are normally used

as low power oscillator at microwave frequencies in transmitter and as local

oscillator in receiver front end. J.B. Gunn in 1963 discovered microwave

oscillation. At low electric field in the material most of the electron will be

located in the lower central valley. At high electric field most of the electron

will be transferred in to the higher frequency satellite L and X valleys.


OBSERVATION :

MODEL GRAPH:


S.NoVoltage

(V)

Current

(mA)

I (amp)

THRESHOLD VOLTAGE

V (volt)

PROCEDURE:

1. Set the components as shown in block diagram.

2. Keep the control knobs of Gunn power supply (GPS) as below.

Meter Switch – off

Gunn bias knob – Fully anticlockwise

PIN Mod. Amp knob – Mid position

PIN Mod. Freq. knob – Mid position

3. Switch ON the Gunn power supply, VSWR meter and Cooling fan.

Set Gunn bias Voltage at 7.5V.

4. Set the micrometer of Gunn oscillator for required frequency of

operation.

5. Measure the operating frequency using frequency meter.

6. Measure the Gunn Diode Current corresponding to the various

Gunn bias voltage. Do not exceed the bias voltage above 10 volts.

7. Plot the voltage Vs Current and 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, Gunn diode may burn

RESULT:

Thus the V-I characteristics of Gunn Diode was studied.

Threshold voltage, Vth = Volts



REVIEW QUESTIONS:

1. Define Attenuation.

2. What are the types of attenuator?

3. Why isolators are called uniline?

4. Define Gunn Effect.

5. What is negative resistance in Gunn diode?

6. Name the semiconductor used in Gunn diode

7. What is transferred electron effect?



5. FREQUENCY AND WAVELENGTH

MEASUREMENT

AIM :

To determine the frequency and wavelength in a rectangular

waveguide working in TE10 mode.


i. Klystron power Supply

ii. Klystron tube with mount

iii. Isolator

iv. Frequency Meter

v. Variable Attenuator

vi. Detector Mount

vii. CRO

viii. Bayonet Neill Concelman(BNC) Connector

ix. Cooling Fan

x. Waveguide Stand, Screw & Net

THEORY:

For dominant TE10 mode in rectangular waveguide λ0, λg and λc are

related as below

1/ λ0 2 = 1/ λg

2 + 1/ λc 2

Where, λ0 = free space wavelength

λg = guide wavelength

λc = cutoff wavelength


CALCULATION:

Guided Wavelength λg = 2d = cm.

Cut off Wavelength λc = 2a = cm.

Where a = 22.8 mm (Broader Dimension of the rectangular

waveguide)

λ = [ (1/ λg)2+(1/λc)2 ] -1/2 cm

f = c/λ GHz.

Where c = 3×10 10 cm.

OBSERVATION:

Frequency (GHz) Probe Position (cm)Successive Difference

(cm)

d1= d2 - d1

d2= d3 - d2

d3= Avg (d ) =


For TE10 mode , λc = 2a,

a = broader dimension of waveguide

The following relationship can be proved,

c = f λ

c = velocity of light

f = frequency of oscillation

INITIAL ADJUSTMENTS:

1. Keep the variable attenuator in the minimum attenuation position.

2. Keep the control knob of klystron power supply as below, before

switching ON the device.

Beam voltage = OFF

Mod-switch = AM

Beam voltage knob = Fully anticlockwise

Repeller voltage knob = Fully anticlockwise

AM frequency & Amplitude knob = mid position

FM frequency & Amplitude knob = minimum position

PROCEDURE:

1. Set the components as shown in Block diagram.

2. Keep the control Knobs of klystron Power supply as mentioned in

the basic set up.

3. Switch ON the Klystron power supply and set the beam voltage at

250 volts.

4. Adjust the repeller Voltage (120V) to get maximum output in

CRO.



5. Tune the frequency meter knob to get a dip on CRO and note down

the frequency of oscillation directly. Detune the frequency meter.

6. Move the probe along the slotted line to a minimum output

voltage.

7. Record the probe position and let it be d1.

8. Move the probe to a next minimum position and note it as d2.

9. Calculate the Wavelength and Frequency.

10.Verify the calculated Frequency with the Frequency obtained from

Frequency meter.

RESULT:


Thus the Frequency and Wavelength in a rectangular Waveguide was

determined.

Freq = GHz , Wavelength= cm.


REVIEW QUESTIONS:

1. Give the frequency range for X, J, S- band.

2. What is an isolator?

3. Why TE01 cannot be considered as the dominant mode in

rectangular waveguide?

4. Why S-matrix is used in microwave analysis?

5. What are standing waves?

6. What is a dominant mode?



6. DETERMINATION OF TERMINATED IMPEDANCE

AIM:

To measure the impedance of the unknown microwave component


i. Gunn power Supply

ii. Gunn oscillator

iii. PIN modulator

iv. Isolator

v. Frequency Meter

vi. Variable Attenuator

vii. Slotted line section

viii. Slide screw tuner(SST)

ix. Tunable probe

x. VSWR

xi. CRO

THEORY:

The impedance at any point of a transmission line can be written in the form

R + jX. For comparison SWR can be calculated as

S = (1 + ρ) (1 – ρ)

ρ = reflection coefficient = [Z – λg] / [Z + λg]


OBSERVATION: Operating Frequency = ____________GHz

WITH LOAD WITHOUT LOAD

λg = 2(d2-d1) dmin=(d1-do)/ λgSWR

do

(cm)

d1

(cm)

d2

(cm)

Unknown impedance= Zo × normalized impedance

Where Zo= 50 ohms

Where fc=c/2a, fo = Frequency of oscillation, η=377

, ,

The normalized impedance was calculated using smith chart

From smith chart ΦL=_________

Practical:

ZL/Zo=___________

Theoretical:

ZL/Zo=___________

Z is the impedance at any point. The measurement is performed in the

following way.


The unknown device is connected to the slotted line and the SWR value and

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 of the

minima is used as reference minima and minima position obtained from the

unknown load. Let it be do. Take a smith chart, taking ‘1’ as centre, draw a circle of

radius equal to SWR value. Mark a point on circumference of chart towards load

side at a distance equal to λg. Join the centre with this point. Find the point where it

cuts the drawn circle. The co-ordination of this point will show the normalized

impedance of the load.

INITIAL SETUP IN VSWR METER:

1. Set input selector switch in 200 Ohms.

2. Keep meter selector in Normal.

3. Select the range as 50db or 40db or 30db and then vary the gain knob

(fine and coarse) to get minimum attenuation. (VSWR = 1).

PROCEDURE:

1. Set the components as shown in block diagram.




PIN bias knob - Fully anticlockwise

PIN mode frequency – Any position


3. Switch on the GPS. Set the Gunn bias voltage at 7.5V

4. Set the micrometer of Gunn oscillator for required frequency of operation.


5. Measure the operating frequency using frequency meter.

6. Then remove the CRO and connect the VSWR meter to slotted line

section.

7. Initial setup in VSWR meter has to be done without load.

8. Keep the depth of SST to around 3 to 4 mm and lock it.

9. Move the probe along the slotted line to get maximum deflection.

10.Adjust the gain control knob and variable attenuator until the meter

indicates ‘1’ on the normal db SWR scale.

11. Move the probe to next minimum position and note down the SWR value

on the scale. Also note down two successive minimum position. Let it be

‘d1’ and ‘d2’.

12. Find out the normalized impedance using Smith chart.

SWR MEASUREMENT:

A. If the reading at the minimum is lower than 3 on the top scale, set

RANGE Switch to next higher range and read the indication on the

second SWR or (3 to 10) scale of SWR.

B. If the range switch is changed by two steps used top SWR scale,

however all indication on this scale must be multiplied by 10.



RESULT:

Thus the impedance of the unknown microwave component was measured.


REVIEW QUESTIONS:

1. What is a VSWR meter?


2. Give two differences between transmission line and waveguide.

3. Name two advantages of rectangular waveguide over circular waveguide

4. What is the function of an Isolator?

5. What is the basic principle used in Isolator?



7. MEASUREMENT OF PROPAGATION LOSS AND BENDING

LOSS IN THE FIBER

AIM:

To Measure propagation loss and bending loss in the fiber.

APPARATUS REQUIRED:


7.Link – D Fiber Optic


8. Power Supply 1

9. Fiber Optic Cable (Plastic) 1,4 meter

10. Patch Chords Required

THEORY:

Losses are introduced in fiber due to various reasons. As light propagates

from one end of fiber to another end, part of it is absorbed in the material exhibiting

absorption loss. Also part of the light is reflected back or in some other direction

from the impurity particles present in the material contributing to the loss of the

signal at the other end of the fiber. In general terms it is known as propagation loss.

Plastic fibers have higher loss of the order of 180 dB/Km. Whenever the condition

for angle of incidence of the incident light is violated the losses are introduced due

to refraction of light. This occurs when fiber is subjected to bending. Lower the

radius of



curvature more is the loss. Another losses are due to the coupling of fiber at LED &

photo detector ends.

Although fibers are good at bending, each time the fiber is bent, a little light

lost.

PROCEDURE:

FOR PROPAGATION LOSS:

1. Make jumper connections as shown in jumper block diagram. Connect the

power supply cables with proper polarity to Link – D Kit. While connecting this,

ensure that the power supply is OFF.

2. Connect the AMP O/P as a constant signal to the TX I/P using a patch cord.

3. You will measure the light output using the SIGNAL STRENGTH section of the

kit. The loss will be larger for a longer piece of fiber, so you will measure the

loss of the long piece of fiber. In order to measure the loss in the fiber you first

need a reference of how much light goes in to the piece of fiber from the LIGHT

TRANSMITTER. You will use the short piece of fiber to measure this

reference.

4. Switch on the power supply. Connect the short piece of fiber to between the

transmitter TX and the receiver RX2 of the kit. Adjust the transmitter level until

the signal strength reads 6. This will be your reference value. Now connect the

long piece of fiber instead of the short piece. What reading do you get? Loss in

optical fiber systems is usually measured in dBs. Loss of fiber itself is measured

in dBs per meter.

Subtract the length of the short fiber from the length of the long fiber to get the

difference in the fiber lengths (4m-1m). The extra length of three


OBSERVATION FOR PROPAGATION LOSS:

S.No: Length of the Fiber Signal Strength

1. 1 m

2. 4 m

FORMULA:

POWER = 10 log (P2/P1) dB

Where P2 : Reference reading by 1 meter fiber

P1 : Reading obtained after replacing the fiber.

Fiber loss (dB/m) = Power /Difference in fiber length

= (dB/m)


meters is what created the extra loss you measured. Then take the signal strength

reading you obtained for the loss of the long fiber and convert it to dB using the

Equation. Finally divide the dB reading by the length to get the loss in dB per

meter.

The reason for converting to dB per meter is that now in order to find the loss

of any length of fiber you just have to multiply the dB per meter by the length of

the fiber. For e.g. If you have a 10 meter long piece of fiber the loss will be

0.6 dB per meter * 10 meters = 6dB

FOR BENDING LOSS:

1. Make jumper connections as shown in jumper block diagram. Connect the

power supply cables with proper polarity to Link – D Kit. While connecting this,

ensure that the power supply is OFF.

2. Connect the AMP O/P as a constant signal to the TX I/P using a patch cord.

You will measure the light output using the SIGNAL STRENGTH section of the

kit.

3. Switch ON the power supply. Connect the long piece of fiber to between the

light transmitter TX and the photo detector receiver RX2 so there are no sharp

bends in the fiber between them.

4. Adjust the transmitter power so that the SIGNAL STRENGTH reading is 6.

Now take the portion of the fiber and loop it to match the bends as shown in a

diagram. As you match each bends write down the reading


OBSERVATION FOR BENDING LOSS:

S.No: Bending Diameter in cm Signal Strength

1.

2.

3.

4.

5.

BEND vs SIGNAL STRENGTH:


NO BEND

BEND 1

BEND 2

BEND 3

BEND 4

SIGNAL STRENGTH

from SIGNAL STRENGTH indicator. What happens as bends the fibers? Don’t

bend the fiber too tightly or it may not come back to shape.

5. If you were designing the fiber optic communications system, you would need

to known the relationship between the size of the bend and the light loss from

the bend.

RESULT:

Thus the fiber propagation and bending loss was studied.



REVIEW QUESTIONS:

1. When bending loss (or) Radiative loss occurs?

2. Name the two types of bending loss.

3. What is Intermodal Dispersion?

4. What is Intramodal Dispersion?

5. What is bandwidth – distance product?



8. MEASUREMENT OF BIT ERROR RATE

AIM:

To Measure bit error rate.

APPARATUS REQUIRED:


11.Link – B Advance Fiber Optic


12. Power Supply 1


14.20 MHz Dual channel

Oscilloscope1

15. Probes, Patch Chords Required

THEORY:

BIT ERROR RATE:

In telecommunication transmission, the bit error rate (BER) is a Ratio of bits

that have errors relative to the total number of bits received in a transmission. The

BER is an indication of how often a packet of other data unit has to be retransmitted

because of an error. Too high a BER may indicate that a slower data rate would

actually improve overall transmission time for a given amount of transmitted data

since the BER might be reduced, lowering the number of packets that had to be

resent.


OBSERVATION:

Tb = 320Kbits

S.No: Error Counter Eb BER

1.

2.

3.

4.

5.

BER = Eb/Tb

Where Eb – Errored bits

Tb – Total bits Transmitted in a period of time t seconds.


Measuring Bit Error Rate:

A BERT (bit error rate tester) is a procedure or device that measures the BER

for a given transmission. The BER, or quality of the digital link, is calculated from

the number of bits received in error divided by the number of bits transmitted.

BER = (Bits in error) / (Total bits transmitted)

PROCEDURE:

1. Make connections as shown in figure. Connect the power supply cables with

proper polarity to Link – B Kit. While connecting this, ensure that the power

supply is OFF.

2. Keep PRBS switch SW7 as shown in figure to generate PRBS signal.

3. Keep switch SW8 towards TX position.

4. Keep switch SW9 towards TX1 position.

5. Keep the switch SW10 at fiber optic receiver output to TTL position.

6. Select PRBS generator clock at 32 KHz by keeping jumper JP4 at 32K position.

7. Keep Jumper JP5 towards +5V position.

8. Keep Jumper JP6 shorted.

9. Keep Jumper JP8 towards Pulse position.

10.Switch ON the power supply.

11.Connect the post DATA OUT of PRBS Generator to the IN post of digital

buffer.

12.Connect OUT post of digital buffer to TX IN post.

13.Slightly unscrew the cap of SFH 756V (660) nm. Do not remove the cap from

the connector. Once the cap is loosened, insert the one Meter Fiber into the cap.

Now tighten the cap by screwing it back.



14.Slightly unscrew the cap of RX1 Photo Transistor with TTL logic output SFH

551V. Do not remove the cap from the connector. Once the cap is loosened,

insert the other end of fiber into the cap. Now tighten the cap by screwing it

back.

15.Connect detected signal TTL OUT to Bit Error Rate event counter DATA IN

post & post IN of Noise Source.

16.Connect post OUT of Noise Source to post RXDATA IN of Bit Error Rate

event counter.

17.Connect post CLK OUT of PRBS Generator to post CLK IN of Bit Error Rate

event counter.

18.Press Switch SW 11 to start counter.

19.Vary pot P3 for Noise Level to observe effect of noise level on the error count.

20.Observe the Error Count LED’s for the error count in received signal in time 10

seconds as shown in figure.

RESULT:

Thus Bit error rate for given Sequence was measured.



REVIEW QUESTIONS:

1. Define bit error rate (BER)

2. What are the typical error rates for optical fiber telecommunication

systems?

3. Why transimpedance amplifier is commonly used in optical

communication receiver?

4. What devices are used as pre-amplifiers for Giga bits/sec. data rate?



9. STUDY OF EYE PATTERN

AIM:

To Study eye pattern using fiber optic link.

APPARATUS REQUIRED:


1.Link – B Advance Fiber Optic


2. Power Supply 1


4.20 MHz Dual channel

Oscilloscope1

5. Probes, Patch Chords Required

THEORY:

The eye-pattern technique is a simple but powerful measurement method for

assessing the data-handling ability of a digital transmission system. This method

has been used extensively for evaluating the performance of wire systems and can

also be applied to optical fiber data links. The eye-pattern measurements are made

in the time domain and allow the effects of waveform distortion to be shown

immediately on an oscilloscope.


MODEL GRAPH:

EYE PATTERN

INTERPRETATION OF EYE PATTERN:


Noise Margin

Sampling periodof receiving signal

Sensitivity to Timing end

Distortion of zero crossing

NoiseMargin

Distortion at Sampling Time

Time interval over Which received signal is Sampled

To measure system performance with the eye-pattern method, a variety of

word patterns should be provided. A convenient approach is to generate a random

data signal, because this is the characteristic of data streams found in practice. This

type of signal generates ones and zeros at a uniform rate but in a random manner. A

variety of pseudorandom pattern generators are available for this purpose.

A pseudorandom bit sequence comprises four different 2-bit-long

combinations, eight different 3-bit-long combinations, sixteen different 4-bit-long

combinations, and so on (that is, sequences of different N-bit-long combinations)

up to a limit set by the instrument. After this limit has been generated, the data

sequence will repeat.

PROCEDURE:

1. Make connections as shown in figure. Connect the power supply cables with

proper polarity to Link – B Kit. While connecting this, ensure that the power

supply is OFF.

2. Keep switch SW7 as shown in figure to generate PRBS signal.

3. Keep switch SW8 towards TX position.

4. Keep switch SW9 towards TX1 position.

5. Keep the switch SW10 to EYE PATTERN position.

6. Select PRBS generator clock at 32 KHz by keeping jumper JP4 at 32K position.

7. Keep Jumper JP5 towards +5V position.

8. Keep Jumper JP6 shorted.

9. Keep Jumper JP8 towards TTL position.

10.Switch ON the power supply.


OBSERVATION:

PRBS Generator

Frequency

Noise Margin

(V)

Sampling period of

Received Signal

(sec)

32 KHz

64 KHz

128 KHz


11.Connect the post DATA OUT of PRBS Generator to the IN post of

digital buffer.

12.Connect OUT post of digital buffer to TX IN post.

13.Slightly unscrew the cap of SFH 756V (660) nm. Do not remove the cap

from the connector. Once the cap is loosened, insert the one Meter Fiber

into the cap. Now tighten the cap by screwing it back.

14.Slightly unscrew the cap of RX1 Photo Transistor with TTL logic output

SFH 551V. Do not remove the cap from the connector. Once the cap is

loosened, insert the other end of fiber into the cap. Now tighten the cap

by screwing it back.

15.Connect CLK OUT of PRBS Generator to EXT.TRG. Of Oscilloscope.

16.Connect detected signal TTL OUT to vertical channel Y input of

oscilloscope. Then observe EYE PATTERN by selecting EXT.TRG.

KNOB on oscilloscope as shown in figure. Observe the Eye Pattern for

different clock frequencies. As clock frequency increases the EYE

opening becomes smaller.

RESULT :

Thus Eye Pattern was studied using Fiber optic Link.



REVIEW QUESTIONS:

1. What is the significance of eye pattern?

2. What is intersymbol interference?

3. How the performance of analog receiver and digital receiver is

measured?

4. What does pseudorandom means?



10. MEASUREMENT OF RADIATION PATTERN OF

HORN ANTENNA

AIM:

To measure the radiation pattern of a waveguide Horn Antenna.


i. Klystron Power Supply

ii. Klystron Mount with Tube 2K25

iii. Isolator

iv. Variable Attenuator

v. Frequency Meter

vi. Two pyramidal Horn Antenna

vii. Tunable Detector Mount

viii. VSWR Meter,CRO

ix. Bayonet Neill Concelman(BNC) Connector

x. Cooling Fan

xi. Radiation pattern Twin Table

xii. Waveguide Stand, Screw & Net

THEORY:

Horn antenna is an opened out waveguide. A waveguide is capable of

radiating radiation into open space provided the same is excited at one end

and opened at the other end. The radiation is much greater through

waveguide than transmission line. In waveguide, a small portion of the

incident wave is radiated and large portion is reflected back by the open

circuit. To minimize the reflections of the guided wave, the region between


MODEL GRAPH: (Polar port)


θ

0

–3

–G

Main lobe of antenna With Gain G dB

Lobe of omni directional antenna

Side Lobe

Back Lobe

the waveguide at the throat and free space at the aperture could be given a

gradual exponential taper.

HPBW of E direction, θE = 56λ/h degree.

HPBW of H direction, θH = 67λ/w degree

The horn antenna is most useful for broadband signals. The horn

antenna serves as a feed element for large radio astronomy, communication

dishes and satellite tracking throughout the world. As it is widely used at

micro frequencies, it may be considered as an aperture antenna.

FORMAULA:

r ≥2D2/λo, λo = C/f ( for rectangular horn antenna)

Where

r– Distance between transmitter and receiver horn antenna.

D– Size of the broad wall of horn antenna.(10.1 cm)

λo– Free space wavelength. C = 3×108 m/s. (Velocity of light)

f – Frequency of oscillation in GHz.




3. Select the range as 50db or 40db or 30db and then vary the gain

knob (fine and coarse) to get minimum attenuation. (VSWR = 1).


OBSERVATION:

Operating Frequency = GHz.

Right Left

Angle θ

(Degree)

Power

(dB)

Relative Power

(dB)

Angle θ

(Degree)

Power

(dB)

Relative Power

(dB)

CALCULATION:-

λo = C/f =

r = 2D2/λo = cm


INITIAL ADJUSTMENTS IN KLYSTRON POWER SUPPLY:




Beam voltage = OFF

Mod-switch = AM



AM freq. & Amp. Knob = Around mid position

FM freq. & Amp. knob = minimum position

PROCEDURE:



the basic set up.

3. Replace the transmitting horn by detector mount or keep the

transmitting and receiving antenna at close position.

4. Switch ON the VSWR meter, CRO, cooling fan & Klystron power

supply and set the beam voltage at 250 volts.


CRO.

6. Tune the frequency meter knob to get a ‘dip’ on CRO and note

down the frequency of oscillation directly. Detune the frequency

meter.


7. Using the formula r = 2D2/λo, Calculate the distance between

antennas and keeping the axis of both horns in same line.


8. Then remove the CRO and connect the VSWR meter to Tunable

Detector mount.

9. Obtain full scale deflection (0dB) on normal dB scale (0-10dB)

and change the appropriate range dB position to get the deflection

on scale (do not touch the gain control knob)

10.Note the range dB position and deflection of VSWR meter.

11.Tune the receiving horn to the left in 100 steps up to 400 and note

down the corresponding VSWR dB reading in the normal dB

range. (When necessary, change the range switch to next higher

range and add 10dB to observed value.)

12.Repeat the above step but this time turn the receiving horn to the

right and note down the readings.

13.Plot a relative power pattern i.e. Output vs. angle.

14.From the diagram determine 3dB–width (beam width) of the horn

antenna.


RESULT:

Thus the radiation pattern of the pyramidal horn antenna was

measured.

HPBW =


REVIEW QUESTIONS:

1. State Hygen’s principle.

2. Define an antenna.

3. Name the types of horn Antenna.

4. Define 3dB Beamwidth


1


1. MEASUREMENT OF RADIATION OF

PARABOLIC REFLECTORAIM:

To measure the radiation pattern of a Parabolic Reflector.


i. Klystron Power Supply

ii. Klystron Mount with Tube 2K25

iii. Isolator


v. Frequency Meter

vi. One Horn Antenna

vii. Parabolic Reflector

viii. Tunable Detector Mount

ix. VSWR Meter, CRO

x. Bayonet Neill Concelman (BNC) Connector

xi. Cooling Fan

xii. Radiation pattern Twin Table

xiii. Waveguide Stand, Screw & Net

THEORY:

.To improve the overall radiation characteristic of the reflector

antenna, the parabolic structure is frequently used. Basically a parabola is a

locus of a point which moves in such a way that the distance if the point

from fixed point called focus plus the distance from the straight line called

directrix is constant. When the beam of parallel rays is incident on a


MODEL GRAPH: (Polar port)


θ

0

–3

–G

Main lobe of antenna With Gain G dB

Lobe of omni directional antenna

Side Lobe

Back Lobe

Parabolic reflector, then the radiations focus at a focal point. This principle

is used in the receiving antenna.

FORMAULA:

r ≥2D2/λo, λo = C/f ( for rectangular horn antenna)

Where

r– Distance between transmitter and receiver horn antenna.

D– Size of the broad wall of horn antenna.(10.1 cm)

λo– Free space wavelength. C = 3×108 m/s. (Velocity of light)

f – Frequency of oscillation in GHz.






INITIAL ADJUSTMENTS IN KLYSTRON POWER SUPPLY:




Beam voltage = OFF

Mod-switch = AM



AM freq. & Amp. Knob = Around mid position


FM freq. & Amp. Knob = minimum position

OBSERVATION:

Operating Frequency = GHz.

Right Left

Angle θ

(Degree)

Power

(dB)

Relative Power

(dB)

Angle θ

(Degree)

Power

(dB)

Relative Power

(dB)

CALCULATION:-

λo = C/f =

r = 2D2/λo = cm


PROCEDURE:



the basic set up.

3. Replace the transmitting horn by detector mount or keep the

transmitting and receiving antenna at close position.

4. Switch ON the VSWR meter, CRO, cooling fan & Klystron power

supply and set the beam voltage at 250 volts.


CRO.

6. Tune the frequency meter knob to get a ‘dip’ on CRO and note

down the frequency of oscillation directly. Detune the frequency

meter.

7. Using the formula r = 2D2/λo, Calculate the distance between

antennas and keeping the axis of antennas in same line.


Detector mount.

9. Obtain full scale deflection (0dB) on normal dB scale (0-10dB)

and change the appropriate range dB position to get the deflection

on scale (do not touch the gain control knob)

10.Note the range dB position and deflection of VSWR meter.

11.Tune the receiving parabolic reflector to the left in 100 steps up to

400 and note down the corresponding VSWR dB reading in the


normal dB range. (When necessary, change the range switch to

next higher range and add 10dB to observed value.)

12.Repeat the above step but this time turn the receiving parabolic

reflector to the right and note down the readings.


13.Plot a relative power pattern i.e. Output vs. angle.

14.From the diagram determine 3dB–width (beam width) of the

Parabolic Reflector.


RESULT:

Thus the radiation pattern of the parabolic reflector was measured.

HPBW =


REVIEW QUESTIONS:

1. Define Radiation Pattern.

2. Define Front to Back Ratio.

3. Define Radiation Resistance.

4. Give the relation between Gain & Directivity.

5. Name the types of Parabolic Reflectors.



12. VSWR MEASUREMENT

AIM:

To determine the Standing Wave Ratio and Reflection co-efficient.


i. Gunn Power Supply

ii. Gunn Oscillator

iii. PIN Modulator

iv. Isolator


vi. Frequency Meter

vii. Slide Screw Tuner


ix. VSWR Meter, CRO

x. Bayonet Neill Concelman(BNC) Connector

xi. Threaded Neill Concelman(TNC) Connector

xii. Cooling Fan

xiii. Waveguide Stand, Screw & Net

THEORY:

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

considered as the sum of two traveling waves the ‘Incident Wave, which

Propagates from the source to the load and the reflected wave which

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

of incident wave from a discontinuity in the line or from the load impedance.

The superposition of the two traveling waves, gives rise to a standing wave


OBSERVATION:

Frequency of Oscillation = ________GHz.

No. of Threads VSWR (S)Reflection Co-efficient

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


along the line. The maximum field strength is found where the waves are in

phase and minimum where the two waves add in opposite phase. The

distance between two successive minimum (or maximum) is half the guide

wavelength on the line. The ratio of electrical field strength of reflected and

incident wave is called reflection coefficient.

The voltage standing wave Ratio (VSWR) is defined as ratio between

maximum and minimum field strength along the line

Hence VSWR denoted by S is as follows

S = Emax/Emin

= |Ei| + |Er|/|Ei| – |Er|

Where Ei = Incident Voltage

Er = Reflected Voltage

Reflection Coefficient, ρ is

ρ = Er/Ei = (ZL–ZO) / (ZL+ZO)

Where ZL is the load impedance, Zo is characteristics impedance.

The above equation gives following equation

(ρ) = (S–1)/(S+1)








PROCEDURE:

1. Setup the equipments as shown in block diagram.








4. Tune the frequency meter to get a ‘dip’ on the CRO. Measure the

operating frequency using frequency meter and detune the frequency

meter.


Detector mount.

6. If necessary change the range dB-switch, Variable attenuator position

and gain control knob to get deflection in the scale of VSWR meter.

7. Adjust the VSWR meter gain control knob or variable attenuator until

the meter indicates 1.0 on normal VSWR Scale.

8. Set the depth of S.S Tuner to around 3-4 mm. Read the VSWR on

scale and record it.

9. Repeat the above step for change of S.S. Tuner probe depth and

record the corresponding SWR.


10.If the reading at the minimum is lower than 3 on the top scale, set

RANGE Switch to next higher range and read the indication on the

second SWR or (3 to 10) scale of SWR.


11.If the range switch is changed by two steps used top SWR scale,

however all indication on this scale must be multiplied by 10.

12.Using the formula, K=S-1/S+1, find the reflection co-efficient.


RESULT:

Thus the Standing Wave Ratio was measured and Reflection

Co-efficient was verified.


REVIEW QUESTIONS:

1. What should be the value of S for Low VSWR measurement and High

VSWR measurement?

2. What is the value of VSWR for a perfectly matched system?

3. Give two limitations of VSWR measurement


DIRECTIONAL COUPLER:


PORT 1 PORT 2

PORT 3

PORT 4

13. MULTIHOLE DIRECTIONAL COUPLER

AIM:

To measure coupling factor, insertion loss, isolation and directivity of

Multihole directional coupler.


i. Gunn Power Supply

ii. Gunn Oscillator

iii. PIN Modulator

iv. Isolator


vi. Frequency Meter

vii. Multihole Directional Coupler


ix. Matched Termination

x. VSWR Meter, CRO

xi. Bayonet Neill Concelman(BNC) Connector

xii. Threaded Neill Concelman(TNC) Connector

xiii. Cooling Fan

xiv. Waveguide Stand, Screw & Net

THEORY:

A directional coupler is a device with which it is possible to measure

the incident and reflected wave separately. It consist of two transmission

lines the main arm and auxiliary arm, electromagnetically coupled to each



other. The power entering, in the main-arm gets divided between port 2 and

3, and almost no power comes out in port (4) Power entering at port (2) is

divided between port (1) and (4)

The coupling factor is defined as

Coupling (dB) = 10 log 10 [P1/P3] where port 2 is terminated.

Isolation (dB) = 10 log 10 [P2/P3] where P1 is matched.

With built-in termination and power entering at Port 1, the directivity

of the coupler is a measure of separation between incident wave and the

reflected wave. Directivity is measured indirectly as follows:

Hence Directivity D (dB) = Isolation – Coupling

= 10 log 10 [P2/P1]

Insertion loss = 10 log 10 [P1/P2]






PROCEDURE:

1. Setup the equipments as shown in block diagram.









OBSERVATION:

Frequency of Oscillation = GHz.

X = dB (Without Directional Coupler)

Z = dB (o/p at port 3, Terminate at port 2, I/p at port 1)

Y = dB (o/p at port 2, Terminate at port 3, I/p at port 1)

Yd = dB (o/p at port 1, Terminate at port 3, I/p at

port 2)

Coupling Factor, C = X–Y = dB

Insertion loss, = X–Z = dB

Isolation I = X–Yd = dB

Directivity D = Y–Yd = dB


4. Tune the frequency meter to get a ‘dip’ on the CRO. Measure the

operating frequency using frequency meter and detune the frequency

meter.


Detector mount.

6. Remove the multihole directional coupler and connect the detector

mount of the frequency meter.

7. 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)

8. Insert the directional coupler as shown in block diagram 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).

9. Note down the reading on VSWR meter on the scale with the help of

range-dB switch if required. (Let it be Y).

10.Calculate coupling factor which will be X–Y=C(dB)

11.Now carefully disconnect the detector from the auxiliary port 3 and

match termination from port 2 without disturbing the set-up.

12.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.

13.Compute insertion loss X–Z in dB.


14.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 port 3. (Without disturbing the position of variable

attenuator and gain control knob of VSWR meter.)


15.Measure and note down the reading on VSWR meter. Let it be Yd. X–

Yd gives Isolation I (dB).

16.Compute the directivity as Y–Yd = I – C


RESULT:

Thus the measuring of

Coupling Factor, C = dB

Insertion loss, = dB

Isolation I = dB

Directivity D = dB

Of Multihole directional coupler were calculated.


REVIEW QUESTIONS:

1. Define coupling factor & Directivity.

2. Name the four types of Directional Coupler.

3. Define Directional coupler.



14. POWER MEASUREMENT

AIM:

To draw the Attenuation characteristics by measuring power using

power meter.


i. Microwave source

ii. Microwave power meter

iii. Waveguide to Coax Adapter


v. Thermocouple mount

vi. Waveguide Stand, Screw & Net

THEORY:

The output power level of a system or component is frequently the

critical factor in the design and ultimately the purchase and performance of

almost all radio frequency and microwave equipment. The convenient unit

for power measurement is dBm. The formula for dBm is the ratio of one

power level P to the reference level where Pref is always one milliwatt. dBm

is used as a measure of absolute power.

Positive dBm means “dB above one milliwatt” & negative dBm is

interpreted as “dB below one milliwatt”. The advantages of the term dBm is

that it uses compact numbers and allows the use of addition instead of

multiplication when cascading gains or losses in a transmission system.


MODEL GRAPH:

OBSERVATION:

Attenuator (Probe depth)

(mm)

Power meter reading

(dBm)


Pow

er (d

Bm

)

Attenuation (mm)

PROCEDURE:

1. Give the connections as shown in the block diagram.

2. The menu switch in the power meter is used to select the different

menu options like measurement units, averaging time etc. press enter

after each settings.

3. To determine the attenuation Characteristics, slightly increase the

prove depth in the Variable Attenuator and note down the

corresponding power in the power meter.

4. A graph is plotted between Attenuation and power.

RESULT:


Thus the attenuator characteristic by measuring power using power

meter was drawn.


REVIEW QUESTIONS:

1. Name the classifications of power measurement.

2. What is a Bolometer? Name the types.

3. What is the advantage of thermistor in microwave

powermeasurement?



BLOCK DIAGRAM:


KLYSTRON POWERSUPPLY

KLYSTRON MOUNT

WITHTUBE

ISOLATOR VARIABLE ATTENUATOR

FREQUENCY METER

TUNABLE DETECTOR

MOUNT

CRO

2K 25

15. MODE CHARACTERISTICS OF REFLEX

KLYSTRONAIM :

To Study the Mode characteristics of the reflex klystron tube


i. Klystron power Supply

ii. Klystron tube with mount

iii. Isolator

iv. Frequency Meter


vi. Detector Mount

vii. CRO


ix. Cooling Fan


THEORY:

The Reflex Klystron makes the use of velocity modulation to

transform a continuous electron beam into microwave power. Electrons

emitted from the cathode are accelerated & passed through the positive

resonator towards negative reflector, which retards and, finally, reflects the

electrons and the electrons turn back through the resonator. Suppose an RF-

field exists between the resonators, the electrons travelling forward will be

accelerated of retarded, as the voltage at the resonator changes in amplitude.

The accelerated electrons leave at the reduced velocity. The electrons


OBSERVATION:

Beam Voltage:________V

Beam Current:________mA

S.No. Negative Repeller Voltage(V)

Frequency(GHz)

Output Voltage(mV)


leaving the resonator will need different time to return, due to change in

velocities. As a result, returning electrons group together in bunches, As the

electron bunches pass through resonator, they interact with voltage at

resonator grids. If the bunches pass the grid at such a time that the electrons

are slowed down by the voltage then energy will be delivered to the

resonator; and Klystron will oscillate.

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.

INITIAL ADJUSTMENTS:




Beam voltage = OFF

Mod-switch = AM



AM frequency & Amplitude knob = mid position

FM frequency & Amplitude knob = minimum position


Repeller Voltage (V)

Out

put V

olta

ge (V

)

Repeller Voltage (V)

Freq

uenc

y C

hang

e (M

Hz)

MODEL GRAPH:


PROCEDURE:

1. Connect the components as shown in Block diagram.


the basic set up.

3. Switch ON the Klystron power supply and set the beam voltage at

250 volts.

4. Check & measure the beam current whether it is less than 30mA.

5. By changing repeller Voltage from –10V to –180V to get

maximum output in CRO and measure the corresponding output

voltage.

6. Tune the frequency meter to get a dip on CRO and note down the

corresponding frequency of oscillation directly. Detune the

frequency meter.

7. Get two readings below and above the mode.

8. Plot the Negative repeller voltage Vs ouput voltage readings on the

graph.




RESULT:

Thus the mode characteristics of Reflex Klystron was studied.


BLOCK DIAGRAM:


MICROWAVE SOURCE ISOLATOR

VARIABLE ATTENUATOR

FREQUENCY METER

MATCHED LOAD

ISOLATORSLOTTED

LINE SECTION

TUNABLE PROBE

VSWR METER

16. S–PARAMETER MEASUREMENT OF ISOLATOR

AIM :

To measure the S–parameter of isolator


i. Microwave source (Gunn, Klystron)

ii. Isolator

iii. Frequency Meter


v. Slotted line section with tunable probe

vi. Detector Mount

vii. CRO / VSWR


ix. Cooling Fan


THEORY:

ISOLATOR:

An isolator is a two-port device that transfers energy from input to

output with little attenuation and from output to input with very high

attenuation

The isolator can be derived form a three-port circulator by simply

placing a matched load (reflection less termination) on one port.

The important isolator parameters are:

A. Insertion loss:


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

power supplied by source to the input port, measured with other ports

terminated in the matched load. It is expressed in dB.

READINGS:

Input Power at Output Powers at VSWRPort 1 Port 2

Port 1

Port 2

S PARAMETERS :

or ----------1.1

---------- 1.2

---------2.1

Where Pi = power output at port i, Pj = power input at port j

The S matrix of Isolator


B. Isolation:

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

the input. This ratio is expressed in dB. The isolation of a circulator is

measured with the third port terminated in a matched load.

C. Input VSWR:

The input VSWR of an isolator or circulator is the ratio of voltage

maximum to voltage minimum of the standing wave existing is the

line with all parts except the test port are matched

PROCEDURE:

A. MEASUREMENT OF INSERTION LOSS, ISOLATION AND

SCATTERING PARAMETERS

1. Set up the components and equipment and connect the detector mount

to the slotted section as shown in figure. The output of the detector

mount should be connected with VSWR meter.

2. Energize the microwave source for maximum output for a particular

frequency of operation. Tune the detector mount for maximum output

in the VSWR Meter.

3. Set reference level 0dB of power in 30dB range in VSWR meter with

the help of variable attenuator and gain control knob of VSWR meter.

4. Carefully remove the detector mount from slotted line without

disturbing the position of variable attenuator and gain control knob.

5. Insert the isolator between slotted line and detector mount. Keeping

input port (1) to slotted line and detector at its output port (2).


6. Record the reading in the VSWR meter. If necessary change range-db

switch to high or lower position and taking 10db change for one step

change of switch position.


7. Similarly measure the power through port (2) terminating port (1) in

matched termination. Note the readings in Table.

Insertion loss = 10 log10 (P1/P2) = 10 log10 (I1/I2)

Isolation = 10 log10 (P1/P3) = 10 log10 (I1/I3)

B. INPUT VSWR MEASUREMENT:

1. Set up the components and equipment as shown in the fig.2 with input

port 1 of isolator towards slotted line and matched termination on

other ports of it.

2. Energize the microwave source for particular operation of frequency.

3. With the help of slotted line, probe and VSWR meter find out SWR

of port of the isolator as described earlier for low and medium SWR

measurements.

4. The above procedure can be repeated for other ports or for other

frequencies.


RESULT:Thus the S-parameters of isolator were measured.


BENCH SET-UP:

FIG.1 SET UP FOR MEASUREMENT OF INSERTION LOSS, ISOLATION & SCATTERING PARAMETERS


Circulator1 2 3

Detector mount

Microwave Source

(RKO/GO)

Isolator Variable Attenuator

Frequency Meter

Slotted line VSWR meter

Detector mount

Circulator1 2 3

Matched Termination

Matched Termination

Detector mount

VSWR meter

VSWR meter

17. S–PARAMETER MEASUREMENT OF CIRCULATOR

AIM :

To study the operation of ferrite circulator and hence measure

i. Insertion loss ii. Isolation iii. And to determining S parameters

COMPONENT REQUIRED:

i. Microwave Source (RKO/GO)

ii. Isolator

iii. Variable Attenuator

iv. Frequency meter

v. Slotted line with Tunable probe

vi. detector mount

vii. VSWR meter

viii. Circulator and

ix. Matched Terminations-2.

THEORY: The circulator is a multi port junction that permits transmission in

certain ways. The wave incident at nth port can be coupled to (n+1) th port

only.

FIG. Y JUNCTION CIRCULATOR


BENCH SET-UP:

FIG.2 SET UP FOR MEASUREMENT OF VSWR OF CIRCULATOR


Microwave Source

(RKO/GO)

IsolatorVariable

AttenuatorFrequency

MeterSlotted line

V.S.W.R meter

TunableProbe

Matched Termination

Circulator1 2

3

Matched Termination

Following are the basic parameters of isolator and circulator.

INSERTION LOSS:

The ratio of the power supplied by a source to the input port to the

power detected by a detector in the coupling arm. i.e output arm with other

port terminated in the matched load, is defined as INSERTION LOSS or

FORWARD LOSS.

ISOLATION:

It is the ratio of the power fed to input arm to the power detected by a

detector at not coupled port with other port terminated with the matched

port.

INPUT VSWR:

The input of circulator is the ratio of voltage maximum to voltage

minimum of the standing wave existing on the line, when one port of it

terminates the line and others have matched termination.

PROCEDURE:

A. MEASUREMENT OF INSERTION LOSS, ISOLATION AND

SCATTERING PARAMETERS

1. Set up the components and equipment and connect the detector mount

to the slotted section as shown in fig.1. The output of the detector

mount should be connected with VSWR meter.

2. Energize the microwave source for maximum output for a particular

frequency of operation. Tune the detector mount for maximum output

in the VSWR Meter.



3. Set reference level 0dB of power in 30dB range in VSWR meter with

the help of variable attenuator and gain control knob of VSWR meter.

4. Carefully remove the detector mount from slotted line without

disturbing the position of variable attenuator and gain control knob.

5. Insert the circulator between slotted line and detector mount. Keeping

input port (1) to slotted line and detector at its output port (2). A

matched termination should be placed at third port (3).

6. Record the reading in the VSWR meter. If necessary change range-db

switch to high or lower position and taking 10db change for one step

change of switch position.

7. Similarly measure the power through port (3) terminating port (2) in

matched termination. Note the readings in Table.

Insertion loss = 10 log10 (P1/P2) = 10 log10 (I1/I2)

Isolation = 10 log10 (P1/P3) = 10 log10 (I1/I3)

8. Repeat the steps 5 to 7 by feeding power at ports 2 and 3. Note the

reading.

B. INPUT VSWR MEASUREMENT:

1. Set up the components and equipment as shown in the fig.2 with input

port 1 of circulator towards slotted line and matched termination on

other ports of it.

2. Energize the microwave source for particular operation of frequency.


3. With the help of slotted line, probe and VSWR meter find out SWR

of port 1 of the circulator as described earlier for low and medium

SWR measurements.

4. The above procedure can be repeated for other ports or for other

frequencies.

READINGS:TABLE-1

Input Power at Output Powers at VSWRPort 1 Port 2 Port 3

Port 1

Port 2

Port 3

S PARAMETERS :

Or ----------1.1

---------- 1.2

---------2.1



The S matrix of circulator


RESULT:Thus the S-parameters of circulator were measured


REVIEW QUESTIONS:

1. Verify Carlin’s Theorem.

2. Construct 4 port circulator with 3 port circulators.

3. What are the basic properties of ferrites which make them useful at

Microwave frequencies?

4. How does a circulator is differ from Magic Tee?



Microwave Source

Isolator Variable Attenuator

Frequency Meter

Slotted Line

Detector

Tunable Probe

VSWR Meter

CRO

2

Tee Junctions

1

4 3

Matched Load

Detector Mount

Matched Load

BLOCK DIAGRAM:


18. S-MATRIX OF E-PLANE, H-PLANE AND MAGIC

TEEAIM :

To measure the S-matrix of E-plane, H-plane and Magic Tee.


i. Microwave source (Gunn, Klystron)

ii. Isolator

iii. Frequency Meter


v. Slotted line section with tunable probe

vi. E-plane Tee, H-plane tee, Magic tee

vii. Detector Mount

viii. CRO / VSWR

ix. Bayonet Neill Concelman (BNC) Connector

x. Cooling Fan

xi. Waveguide Stand, Screw & Net

THEORY:

The device magic tee is a combination of the E and H plane Tee. Arm

3, the H-arm forms an H-plane Tee and arm 4, E-arm forms an E-plane Tee

combination of arm1 and 2 as side of collinear arms. If the power is fed in

arm3 (H-arm), the electric field divides equally between arm 1 and 2 with

the same phase and no electric field exits in arm4. If power is fed in arm 4

(E-arm), it divides equally in to arm 1 and 2 but out of phase with no power


READINGS:TABLE-1

Input Power at

Output Powers at VSWRPort 1 Port 2 Port 3 Port 4Port 1

Port 2

Port 3

Port 4

S PARAMETERS :

Or ----------1.1

---------- 1.2

---------2.1


to arm 3, further , if the power is fed in arm1 and 2 simultaneously it is

added in arm 3(H-arm) and it is subtracted in E-arm i.e. arm 4 159 VEC/2011-12/ODD/ECE/VII/EC-

2405

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 ratio of the power

supplied by the generator connected to the E-arm (port 4) to the power

detected at H-arm (port 3) when side arms 1 and 2 terminated in matched

load

Hence Isolation (dB) = 10 log10 [P4/P3]

Similarly, Isolation between other parts may also be defined.

C. Coupling Factor:

It is defined as Cij = 10-α/20

Where α is 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 delivered to arm i and P4 is power detected at j

arm.


The S matrix of Magic Tee

The S matrix of E-Plane and H-Plane Tee

PROCEDURE:

A. VSWR measurement of the ports:


1. Connect the components as shown in Block diagram. Keeping E-

arm towards slotted line and matched termination to other ports.

2. Energize the microwave source for particular frequency of operation. Detune the frequency meter

3. Measure the VSWR of E-arms as described in measurement of SWR for low and medium value.

4. 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. Energize the microwave source 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 the 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 the 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 for other frequencies.



RESULT:

Thus the S-parameters of E-plane, H-plane and magic Tee was

measured.


BLOCKDIAGRAM:


He-Ne LASER SOURCE

LASER SOURCE LASER HOLDER ASSEMBLY

LASER TO FIBER COUPLER HOLDER

ASSEMBLY

FIBER HOLDER ASSEMBLY

SCREEN

19. MODE OBSERVATION IN FIBER OPTIC CABLE

AIM:

Observation of lower order Linearly Polarized (LP) modes.

APPARATUS REQUIRED:

S.No. Name of the Equipments Specification Quantity

6. Laser source (633nm-1mW) 2mW 1

7. Source to Fiber Coupler 1

8. Single Mode Fiber SMF 9/125µm 1 meter

9. Fiber Holding Stand 1

10. Opaque Screen 1

11. Multimode Fiber 62.5/125µm 1meter

THEORY:

The central spot carries 95% of the intensity for laser beams with

Gaussian profile.

I=I0e-z(r/w) 2

Where e=2.718 beam of natural algorithm accepted definition of a

radius of a Gaussian beam is the distance at which beam intensity has

dropped to 1/e2=0.135 times its peak value I0. This radius called spot size.

The spot diameter is W.

Spot diameter (d) micron=focal length of the Lanes (f) mm X Laser

Beam full divergence angle (DA) mrad.


OBSERVATION:

Single mode Fiber:

a = 4.5µm (core radius)

NA = 0.11

V = 4.91

From figure only 4 LP modes propagate.

Total number of modes = V2/2

No. of modes = 12

Multimode Fiber:

a = 31.25µm (core radius)

NA = 0.11

V = 34.12

Total number of modes = V2/2 = (34.12)2/2

No. of modes = 582.11


In order to achieve maximum coupling efficiency, the fiber core

diameter has to be bigger than the spot diameter.

If NArays ≤ NAfiber and spot diameter (w) ≤ fiber core diameter (d), then

all of the laser light will be coupled into the fiber. 90% coupling efficiency

into the single mode fiber from the Ne-Ne lasers is achievable. For

beginners, coupling efficiency of 50% is considered to be a good result.

Operation Principle of Laser to Fiber Source Coupler

The source coupler is comprised of two base plates. One of the base

plates contains a focusing lens and a female connector receptacle. The other

base plate is attached onto the laser. An O-ring is sandwiched between the

base plates. Threaded screws interconnect the two base plats. A screwdriver

to alter the angular orientation of one base plate relative to the other can then

adjust the screws.

For small tilt angles, the resolution of the coupler Δz is determined by

Δz–fΔx /L. where Δx is the resolution of the screws and L is the lever arm.

For 80TPI (threads per inch) screws, a lens with 1mm focal length, and

20mm lever arm Δz = 1mm 2 micron/20mm = 0.1micron.

The number of modes propagating through the fiber depends on V-

number. If the fiber whose V-number is less than 2.405, it allows to

propagate single mode through it, so it is called as Single Mode Fiber. This

time you will start with a fiber, which has V-number slightly greater than

2.405. Such a fiber is Multimode fiber, but the number of allowed modes is

small enough so that they may be individually identified when the output of

the fiber is examined.


LOWER ORDER LINEARLY POLARISED MODES OF

OPTICAL FIBER


0 1 2 3 4 5

LP01

LP11 LP21

LP02

V=number

When V-number is less than 2.405, then only a single mode may propagate

in the fiber wave-guide. This mode is HE11 mode or LP01 – Linearly

Polarized mode.

When V-number>2.405, other modes may propagate in the fiber. The

first LP mode, which comes in at V=2.405, is the LP11 mode, the next lowest

mode in the weakly guiding approximation.

When V is slightly greater than 2.405 i.e. V=4.91 then 4 Linearly

Polarized modes will propagate through fiber.

LP02: Degenerated twice: 2 modes

LP11: 4 times degenerated: 4 modes

LP02: Degenerated twice: 2 modes

LP21: 4 times degenerated: 4 modes

Total 12 modes can propagate through fiber. This number is identical

to that given by formula: Ma=V2/2=12

The electromagnetic field distributions of these modes are as shown

figure. We have a fiber with the proper V-number; varying the position and

angle at which a tightly focused beam of the proper wavelengths is projected

onto the fiber core can selectively launch these modes.

PROCEDURE:

1. Keep Optical Bread board onto original and flat table surface, so

that is will not toggle.

2. Fix the pre-fitted cylindrical head of the He-Ne laser source on to

the surface of the breadboard from the bottom side with the help of

Allen screws provided with it. Confirm the rigid ness of the mount.


3. Fix the laser to the fiber coupler mount on to the breadboard with

the base plate orientation of it towards He-Ne laser exit.

IRRADIANCE PATTERN OF SOME LOWER ORDER LINEARLY

POLARIZED MODE


LP01

LP11

LP02 LP21

4. Turn on the He-Ne laser and locate the beam spot on to the central

portion of the laser-fiber coupling lens assembly by adjusting the

vertical and horizontal travel arrangement provided with the

mount. Tighten the screws of the vertical and horizontal slots.

5. Now look for the back reflection of the He-Ne spot from the rod

lens of the coupler. In case if you found the back spot, away from

the exit of the cylindrical laser head of the laser, adjust the back-

reflected spot going back in exit hole by slowly moving the four

screws provided for the laser mount.

6. Confirm the central alignment of the laser beam at the exit of the

laser fiber coupler by putting a white card sheet and zooming the

spot on to it. In case the spot is found off-center, adjust it to the

center by slightly moving the screws of the laser mount.

7. Put the multimode optical patch cord on to the laser-fiber coupler

exit and fix the other end of the fiber in the fiber holding stand by

moving the grub screws provided with the holder.

8. You will see the bright laser-beam spot coming out of the fiber.

Adjust the height of exit tip of the fiber to about 50mm. Min. from

the white sheet of the paper.

9. Now you will see a bright round shape circular spot with laser

speckle pattern on to the screen. If multimode pattern can be

refined screws provided with laser-fiber coupler. Slightly adjusting


or moving the screws on the laser mount can also view the change

in pattern of this multimode spot.

10.Once you observe the multimode pattern, change multimode fiber

optic patch cord with single mode fiber patch cord.


11.As soon as you place the single mode patch cord, you will see the

blur pattern of the various single mode patterns on to the screen.

That is, single circular two lobes, three lobes and four lobes

patterns can be very well observed by slightly adjusting the Allen

screws of the laser-fiber coupler.


RESULT:

Thus the lower order linearly polarized modes were observed.

TECHNICAL SPECIFICATIONS

Plastic Fiber

Step index, Multimode.

Numerical Aperture: 0.50

Acceptance Angle :600

Fiber diameter:1000 microns

Outer diameter: 2.2mm

Glass Fiber(Multimode)

Type: Multimode, Step index

Numerical Aperture: 0.2 +/- 0.015

Core diameter : 62.5microns

Clad diameter : 125 microns

Glass Fiber(Single mode)

Type: Single mode, Simplex

Core diameter : 9 microns

Clad diameter : 125 microns

Optical Transmitter

SFH 450V: 950nm Infrared


SFH 756V: 660nm Visible(Red)

Optical Receiver

SFH 250V/350V :Photo transistor Detector (Analog)

SFH 551V: Photo Detector with logic output.

OTDR: Optical Time Domain Reflecto meter

Microwave componentsRectangular waveguide:

Band

Name

Frequency

(GHz)

Inside

(cm)

Outside

(cm)

Height

(a)

Width

(2a)

Height

(a)

Width

(2a)

C 3.95-5.85 2.215 4.755 2.540 5.080

J 5.85-8.2 1.580 3.484 1.905 3.81

X 8.2-12.4 1.016 2.286 1.27 2.54

Ku 12.4-13.0 0.790 1.58 0.993 1.783

Detector Mount : Crystal Diode (1N 23)



Ec 2405 Optical Microwave Lab Manual

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Ec 2405 Optical Microwave Lab Manual