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 .Where as 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.
Crystal
Measuring
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MW
Variable
Frequency
Slotted
Isolator
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A
m
rs
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1. Klystron Power Supply:
l
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a
a
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Klystron Power Supply generates voltages required for driving the reflex Klystron
t
t
r
tube like 2k25 .Itois stable, regulated and short circuit
protected power supply. It has built on
o
facility of squarer wave and saw tooth generators
r 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.
Power
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I
n
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tn
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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 =
2eVo
m
e = electron charge
m = mass of the electron
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.
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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=
2e(Vo  V 1sin wt )
m
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.
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
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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 measure 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.
Fig:3 Typical Mode Curves of Reflex Klystron
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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 impedance thereby not affecting the line
appreciably. However, it is negatively biased, it offers a very low impedance, almost shortcircuit 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.
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4. Isolator:
This unattenuated 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.
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.
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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.
10. 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 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.
11. 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 levels (<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.
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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
2
fc =
c m n
   
2  a  b
2
The corresponding cut off wave length,
λc =
2
2
m n
   
 a  b
2
Where c is velocity of light.
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
0
2

1
g
2

1
c 2
HYBRID TEE (Magic Tee):
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, HPlane 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
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*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:
[S] =
0 0 1

1 0 0  1
2 1  1 0

1 1 0
1
1
0

0
Fig. (a): Magic Tee
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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.
P
C= 10 log10  i  dB
 Pc 
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 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
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4) 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 Bethi - 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.
1) Insertion loss:
The ratio of power input at port n to the power detected at 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
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0 0 1 
[S]= 1 0 0
0 1 0
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 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
(viii) if desired.
xi) For the best set-up, the attenuator and must have maximum value corresponding to the
peak in the output meter.
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1. REFLEX KLYSTRON CHARACTERISTICS
1(a) Determine the output power and frequency of reflex klystron?
(b) Plot the relation between repeller voltage and power of reflex klystron?
(c)Obtain characteristics b/w output power and repeller voltage of reflex klystron?
(d) Calculate the electron tuning range (ETR) of reflex klystron using mode
characteristics?
AIM:
To study the mode Characteristics of a Reflex klystron tube and to calculate the electronic
tuning range (ETR).
EQUIPMENT:
1. Regulated klystron power supply
- 1 No
2. Reflex klystron with mount and cooling fan -1 No
3. Isolator
-1 No
4. Variable attenuator
-1 No
5. Frequency meter/wave meter
-1 No
6. Waveguide detector mount with detector
-1 No
7. VSWR meter or micro ammeter
-1 No
8. Waveguide stands and accessories
BENCH SET-UP:
Klystron
Power
Reflex
s
u
p
p
l
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PROCEDURE:
K Isolator
l
y
s
t
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n
Attenuator
Frequency
Meter
Detector
Mount
Indicator
Fig: 1
Oscillator
(A) Carrier Wave Operator
1) Assemble the equipment as shown in Fig.1 with VSWR meter as indicating meter.
2) Set the variable attenuator at the minimum position.
3) 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.
4) Rotate the knob of frequency meter at one side fully.
5) ON the klystron power supply, VSWR meter and cooling fan for the klystron tube.
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6) 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”
7) Change the repeller voltage slowly and watch on the VSWR meter for maximum
deflection in the meter. If no deflection is obtained, change the range of meter.
8) Tune the plunger of klystron mount for the maximum output.
9) Rotate the knob of frequency meter slowly and stop at that position, when there is less
output on meter. Read directly the frequency between two horizontal line and vertical marker.
10) Change the repeller voltage and read the Power and frequency for each repeller voltage
and plot the graph between frequency and voltage, Power and voltage.
(B) Mode Study on Oscilloscope:
1) Assemble the equipment as shown in Fig.1 with VSWR meter as indicating meter.
2) Set the variable attenuator at the minimum position.
3) Set the MOD switch of klystron power supply to FM-MOD/AM-Mod position, with
FM/AM amplitude knob and FM/AM frequency knob at mid position, keep the 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.
4) keep the time/div. scale of oscilloscope around 100 Hz frequency and Volt/Div. to lower
scale.
5) ON the klystron power supply and cooling fan for the klystron tube.
6) 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”
7) Change the repeller voltage slowly and watch on the VSWR meter for maximum
deflection in the meter. If no deflection is obtained, change the range of meter.
8) Tune the plunger of klystron mount for the maximum output.
9) Now remove the BMC cable from VSWR meter and connect it to CRO.
10) Keep amplitude knob of FM/AM modulator to maximum position.
11) Change the repeller voltage slowly and watch the amplitude of FM/AM modulation on
the Oscilloscope, Note the amplitude of output wave.
12) Draw the graph between output power and repeller voltage.
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MODEL GRAPH:
Fig.2: Typical mode curves for a reflex klystron
TABLE:
Beam Current = 19mA, Beam Voltage = 295V
1(a)
S.No
Mode 1
Repeller Volage
(inVolts)
-256v
-242v
-231v
-227v
-205v
CRO/VSWR meter reading(in Frequency meter reading
V/dB)
(in Ghz)
0
0
0.32mv
10.245
0.5mv
10.22
7.58mv
10.21
0
0
Mode 2
-204v
-202v
-195v
-190v
-160v
0
0.1mv
0.38mv
7.22mv
0
0
10.24
10.23
10.23
0
Mode 3
-159v
-156v
-143v
-132v
-117v
0
0.18mv
0.33mv
0.21mv
0
0
10.21
10.21
10.2
0
1(b)
S.No Repeller Voltage CRO/VSWR meter reading Power
(inVolts)
(in V/dB)
P = V*I
1
-256V
0
0
2
-231V
0.5mv
9.5w
3
-202V
0.1mv
1.9
4
-156V
0.18mv
3.42
5
-132V
0.21mv
3.99
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1(c)
S.No Repeller Voltage Frequency meter reading
(inVolts)
(in Ghz)
1
-117V
0
2
-143V
10.21
3
-190V
10.23
4
-227V
10.21
5
-256V
0
Power
P = V*I
0
6.27
5.32
7.98
0
1(d) Calculate Electronic Tuning Range, i.e., the frequency band from one end of the mode
to Another , from the graph of VR vs frequency The formula for electronic
Tuning range is given as
ETR 
S.No
Mode 1
Mode2
Mode3
dVR
df
Repeller Voltage
(inVolts)
-256V
-205V
-204V
-190V
-159V
-117V
ETR
51
14
42
Note: As the repeller voltage increases mode number decreases and power increases.
Inference:
1. Mode charts for Reflex Klystron are drawn.
2. The Electronic tuning range is calculated.
VIVA QUESTIONS:
1. How bunching takes place in a reflex klystron?
2. Why efficiency of the klystrons is low? Write the expression for it
3. What is the effect of cavity gap on electron bunching?
4. How are the electrons in the reflected beam collected in a reflex klystron?
5. Is some beam focusing arrangement needed in anode-reflector space?
6. What do you mean by velocity and density modulations? How do these differ from
frequency and phase modulations?
7. Why is it necessary to cool the klystrons?
8. The two cavity Klystron uses what cavity as an output cavity?
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2. DIRECTIONAL COUPLER CHARACTERISTICS
2(a) Calculate the directivity at all 4-ports of Directional Coupler?
(b) Calculate the isolation level at all 4-ports of Directional Coupler?
(c) Calculate the coupling coefficient at all 4-ports of Directional Coupler?
(d) Determine the scattering matrix at all 4-ports of Directional Coupler?
AIM:
To calculate the Isolation, coupling coefficients, and directivity,
EQUIPMENT:
1. Regulated klystron power supply
- 1 No
2. Reflex klystron with mount and cooling fan -1 No
3. Isolator
-1 No
4. Variable attenuator
-1 No
5. Frequency meter/wave meter
-1 No
6. Waveguide detector mount with detector
-1 No
7. VSWR meter or micro ammeter
-1 No
8. Matched Terminations
- 3 No
9. Two hole Directional Coupler
- 1 No
10. Slotted section
- 1 No
11. Waveguide stands and accessories
BENCH SET-UP:
Reflex
Isolator
1
2K
l
y
s
t
r
o
PROCEDURE:n
Oscillator
Attenuator
Frequency
Meter
Fig: 1
Slotted
Matched
Indicating
Directional
S
e
c
t
i
o
n
t
e
r
mMount
Ci
on
ua
pt
li
o
e
n
r
1) Assemble the set up as shown in fig. 1 by connecting mount detector initially instead of
Directional Coupler.
2) By taking care about Reflex klystron, energize reflex klystron to obtain maximum power
in the VSWR meter.
3) Adjust variable attenuator for reasonable power level say 30db. Record the power level.
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MWE & DC LABORATORY
m
e
t
e
r
This is power level at the output of the slotted section and hence it is the input power, Pi
to the Directional Coupler in the set up
4) Carefully remove the detector set up and insert the Directional Coupler as in the set up
with port 3 terminated with matched load.
5) Determine power at port 2 in decibels by noting the change in the output level on the
indicating meter, Let it be P2.
6) Interchange the positions of the detector set up and matched load and determine power in
db by noting the change in output power level(with reference to level in step 3) at port 3, Let
it be P3
7) Repeat steps 4 to 7 for port 2 and port 3 also.
8) Calculate the Coupling factor, Isolation and Directivity using the formulas:
Isolation i-j = 10 log 10 (Pj
/Pi)
Coupling coefficient = 10 log (Pi/Pj)
Where Pi= power delivered from port i
Pj= power detected at jth arm
10 Calculate all the input and output powers at all the ports .
11) By using the standard scattering matrix of a Directional Coupler, verify the scattering
parameters theoretically and compare both practical and theoretical values.
12) Determine the frequency of the exciting wave using frequency meter.
RESULT:
Beam voltage=295v
Beam Current=20mA
Repeller Voltage=249
Vmax=2.1*0.2v=0.42
Case 1: 2(a)
Port 1 I/P=P1=Vmax=2.1*0.2v=0.42
Port 1 I/P: 4 close, 2 Output=1.8*0.2=0.36;P12=0.36*20=7.2
2 Close,4 Close =4.5*0.2=0.9; P13=0.9*20=18
Port 3 is terminated
Port 2 I/P=P2=Vmax=2.1*0.2v=0.42
Port 2 I/P: 4 close, 1 Output=2.9*0.1=0.29; P21=0.29*20=5.8
Department of ECE MLRIT
18
MWE & DC LABORATORY
1 close,4 output=0; P21=0.29*20=5.8
Port 3 is terminated
Port 4 I/P=P1=Vmax=2.1*0.2v=0.42
Port 4 I/P: 2 close, 1 Output= 2*0.2=0.4; P21=0.4*20=8
1 Close,2 output=0;P12=0
Port 3 is terminated
Port 3 is terminated.
Case 2: 2(b)
Isolation=10 log10(Pj/pi)
1)10 log10(7.2/20)=0.36
Port 1
2) 10 log10(18/20)=0.9
3)10 log10(5.8/20)=0.29
Port 2
4)10 log10(5.8/20)=0.29
5)10 log10(8/20)=0.4
Port 3
6)10 log10(0/20)=0
Case 3: 2(c)
Coupling Coefficient =10 log10(Pi/pj)
1)10 log10(20/7.2)=2.77
Port 1
2)10 log10(20/18)=1.11
3)10 log10(20/5.8)=3.44
Port 2
4)10 log10(20/5.8)=3.44
5)10 log10(20/8)=2.5
Port 3
6)10 log10(20/0)=0
Department of ECE MLRIT
19
MWE & DC LABORATORY
Case4: 2(d)
Scattering matrix
S11 S12
S13
S14
S21 S22
S23
S24
S31
S32
S33
S34
S41
S42
S44
S44
0
0.9
=
0.36
2.77
3.4
3.4
1.11
0.29
0
2.6
2.5
0.4
0
0
0.3
2.77
VIVA QUESTIONS:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Which dimension of the waveguide determines the frequency range?
What is the primary Purpose of directional coupler?
In which direction maximum directivity of a directional coupler should be?
State the applications of directional coupler?
Give the examples of non-reciprocal devices.
How the performance of a directional coupler can be determined?
The distance between two holes in a directional coupler is_________
What is the function of absorbent material in directional coupler?
What happens to reflected energy that enters a directional coupler that is designed to
sample incident energy?
10. What will happens in waveguide when an impedance mismatch occurs?
Department of ECE MLRIT
20
MWE & DC LABORATORY
3. MEASUREMENT OF SCATTERING PARAMETERS OF A
MAGIC TEE
3(a) Calculate the directivity at all 4-ports of Magic Tee?
(b) Calculate the isolation at all 4-ports of Magic Tee?
(c) Calculate the coupling coefficient at all 4-ports of Magic Tee?
(d) Determine the scattering matrix at all 4-ports of Magic Tee?
AIM:
(a) To calculate the Isolation and coupling coefficients ,
(b) To Verify scattering parameters of a magic tee
EQUIPMENT:
1. Regulated klystron power supply
2. Reflex klystron with mount and cooling fan
3. Isolator
4. Variable attenuator
5. Frequency meter/wave meter
6. Waveguide detector mounts with detector
7. VSWR meter or micro ammeter
8. Slotted Section
9. Matched Terminations
10. Waveguide stands and accessories
- 1 No
-1 No
-1 No
-1 No
-1 No
-1 No
-1 No
-1 No
- 3 No
BENCH SET-UP:
Matched
1
Reflex
KIsolator
l
y
s
t
r
o
n
Attenuator
Oscillator
Department of ECE MLRIT
Frequency
Meter
Fig:1
21
Slotted
2
Magic Tee
S
e
c
t
i
Matched
o
n
Indicating
t
e
r
m
i Mount
n
a
t
i
o
n
T
e
r
m
i
n
a
t
i
o
n
MWE & DC LABORATORY
m
e
t
e
r
d
e
t
e
c
t
o
r
PROCEDURE:
1) Assemble the set up as shown in fig. 1by connecting mount detector initially instead of
Magic tee.
2) By taking care about Reflex klystron, energize reflex klystron to obtain maximum power
in the VSWR meter.
3) Adjust variable attenuator for reasonable power level say 30db. Record the power level.
This is power level at the output of the slotted section and hence it is the input power, Pi to
the magic tee in the set up
4) Carefully remove the detector set up and insert the magic tee as in the set up with port 3
and 4 terminated in matched loads.
5) Determine power at port 2 in decibels by noting the change in the output level on the
indicating meter, Let it be P2 .
6) Interchange the positions of the detector set up and matched load and determine power in
db by noting the change in output power level(with reference to level in step 3) at port 3, Let
it be P3
7) Interchange the positions of the detector set up and matched load and determine power in
db by noting the change in output power level (with reference to level in step 3) at port 4, let
it be P4
8) Repeat steps 4 to 7 for port 2, port 3 and port 4.
9) Calculate the Coupling factor, Isolation using the formulas:
Isolation i-j = 10 log 10 (Pj
/Pi)
Coupling coefficient = 10 log (Pi/Pj)Where Pi= power delivered from port i
Pj= power detected at jth arm
10) Calculate all the input and output powers at all the ports .
11) By using the standard scattering matrix of a magic tee, verify the scattering parameters.
12) Determine the frequency of the exciting wave using frequency meter.
RESULTS:
Beam voltage=295v
Beam Current=20mA
Repeller Voltage=249
Vmax=2.1*0.2v=0.42
Case 1: 3(a)
Port 1 I/P=P1=Vmax=2.1*0.2v=0.42
Port 1 I/P: 3,4 close, 2 Output=0.6*0.5v=0.3;P12=0.3*20=6
2,3 Close,4 output =1*0.5=0.5; P14=0.5*20=10
Department of ECE MLRIT
22
MWE & DC LABORATORY
2,4 Close,3 output =0.5*0.5=0.25; P13=0.25*20=5
Port 2 I/P=P2=Vmax=2.1*0.2v=0.42
Port 2 I/P: 1,3 close, 4 Output=0; P24=0
3,4 close,1 output=0.6*0.5=0.3; P21=0.3*20=6
1,4 close,3 output=0.6*0.5=0.3; P23=0.3*20=6
Port 3 I/P=P1=Vmax=2.1*0.2v=0.42
Port 3 I/P: 1,2 close, 4 Output=0; P34=0
1,4 Close,2 output=0.8*0.5=0.4;P32=0.4*20=8
1,4 Close,2 output=0.8*0.5=0.4;P32=0.4*20=8
Port 4I/P=P1=Vmax=2.1*0.2v=0.42
Port 4 I/P: 3,2 close, 1 Output=1.2*0.5=0.6; P41=0.6*20=12
1,2 Close,3 output=0.6*0.2=0.12;P32=0.12*20=2.4
1,3 Close,2 output=0.8*0.5=0.4;P42=0.4*20=8
Case2: 3(b)
Isolation=10 log10(Pj/pi)
1)10 log10(6/20)=5
Port 1
2) 10 log10(10/20)=4
3)10 log10(5/20)=4
4)10 log10(0/20)=0
Port 2
5)10 log10(6/20)=7
6)10 log10(6/20)=2
7)10 log10(0/20)=0
Port 3
8)10 log10(8/20)=14
9)10 log10(8/20)=4
10)10 log10(12/20)=7
Port 4
11)10 log10(2.4/20)=6
12)10 log10(8/20)=2.4
Department of ECE MLRIT
23
MWE & DC LABORATORY
Case 3: 3(c)
Coupling Coefficient =10 log10(Pi/pj)
1)10 log10(20/6)=2.8
Port 1
2)10 log10(20/10)=4
3)10 log10(20/5)=7.5
4)10 log10(20/0)=4
Port 2
5)10 log10(20/6)=5.1
6)10 log10(20/5)=7.0
7)10 log10(20/0)=0
Port 3
8)10 log10(20/8)=4
9)10 log10(20/8)=4
10)10 log10(20/12)=6
Port 4
11)10 log10(20/2.4)=2.2
12)10 log10(20/8)=4
Case 4: 3(d)
Scattering matrix
S11 S12
S13
S14
S21 S22
S23
S24
S31
S32
S33
S34
S41
S42
S43
S44
=
5
4
4
0
7
2
0
14
2.8 6.4 2.2
7.5
5
0
Department of ECE MLRIT
0
7.0
24
MWE & DC LABORATORY
VIVA QUESTIONS:
1. What is magic tee?
2. What is the magic in magic tee?
3. Magic tee is a combination of___________
a) 2 Eplane tees
b) 2 H plane tees
c) 1 E plane+ 1 Hplane
d) None
4. If the power is applied at port 4 then the power is________________
5. If the power is applied at port 1 then the power is________________
6. If the power is applied at port 2 then the power is________________
7. If the power is applied at port 3 then the power is________________
8. Which field configurations are easy to produce in waveguide?
9. Write the applications of magic Tee.
10. Which term is used to identify various field configurations that can exist in a
waveguide.
Department of ECE MLRIT
25
MWE & DC LABORATORY
4. MEASUREMENT OF SCATTERING PARAMETERS OF A
CIRCULATOR
4 (a) Calculate the i/p & o/p powers at all the ports of a circulator?
(b) Calculate the isolation at all the ports of a circulator?
(c)Calculate the coupling coefficient at all the ports of a circulator?
(d)Obtain the S-Matrix parameters at all the ports of a circulator?
AIM:
a) To calculate the Isolation and coupling coefficients ,
b) To verify the scattering parameters of a Circulator.
EQUIPMENT:
1. Regulated klystron power supply
2. Reflex klystron with mount and cooling fan
3. Isolator
4. Variable attenuator
5. Frequency meter/wave meter
6. Waveguide detector mount with detector
7. VSWR meter or micro ammeter
8. Matched Terminations
9. Circulator
10. Slotted section
11. Waveguide stands and accessories
- 1 No
-1 No
-1 No
-1 No
-1 No
-1 No
-1 No
- 3 No
- 1 No
- 1 No
BENCH SET-UP:
Indicating
Matched
Reflex
KIsolator
l
y
s
t
r
PROCEDURE:o
n
Oscillator
Attenuator
Frequency
Meter
Fig:1
1
Slotted
2
Circulator
S
e
c
t
i
o
n
t
e
r
m
i Mount
n
a
t
i
o
n
1) Assemble the set up as shown in fig. 1 by connecting mount detector initially instead of
Circulator.
2) By taking care about Reflex klystron, energize reflex klystron to obtain maximum power
in the VSWR meter.
3) Adjust variable attenuator for reasonable power level say 30db. Record the power level.
Department of ECE MLRIT
26
MWE & DC LABORATORY
m
e
t
e
r
d
e
t
e
c
t
o
r
This is power level at the output of the slotted section and hence it is the input power, Pi to
the Circulator in the set up
4) Carefully remove the detector set up and insert the circulator as in the set up with port
3terminated with matched load.
5) Determine power at port 2 in decibels by noting the change in the output level on the
indicating meter, Let it be P2 .
6) Interchange the positions of the detector set up and matched load and
determine
power in db by noting the change in output power level(with reference to level in step 3) at
port 3, Let it be P3
7) Repeat steps 4 to 7 for port 2 and port 3 also.
8) Calculate the Coupling factor, Isolation using the formulas:
Isolation i-j = 10 log 10 (Pj /Pi)
Coupling coefficient = 10 log (Pi/Pj)
Where
Pi=
power
delivered
from
port
i
th
Pj= power detected at j arm
10) Calculate all the input and output powers at all the ports .
11) By using the standard scattering matrix of a circulator, verify the scattering parameters
theoretically and compare both practical and theoretical values.
12) Determine the frequency of the exciting wave using frequency meter.
RESULTS:
Beam voltage=295v
Beam Current=20mA
Repeller Voltage=249
Vmax=2.1*0.2v=0.42
Case 1: 4(a)
Port 1 I/P=P1=Vmax=2.1*0.2v=0.42
Port 1 I/P: 3 close, 2 Output=3*0.1=0.3;P12=0.3*20=6
2 Close,3 output =1.8*0.1=0.18; P13=0.18*20=3.6
Port 2 I/P=P2=Vmax=2.1*0.2v=0.42
Port 2 I/P: 3close, 1 Output=2.4*0.1=0.24; P21=0.24*20=4.8
1 close,3 output=0.4*0.1=0.4; P23=0.4*20=8
Port 3 I/P=P3=Vmax=2.1*0.2v=0.42
Port 4 I/P: 1 close, 2 Output= 0; P32=0
2 Close,1 output=3.2*0.1=0.32;P31=0.32*20=6.4
Department of ECE MLRIT
27
MWE & DC LABORATORY
Case 2: 4(b)
Isolation=10 log10(Pj/pi)
1)10 log10(6/20)=0.3
Port 1
2) 10 log10(3.6/20)=0.18
3)10 log10(4.8/20)=5.24
Port 2
4)10 log10(8/20)=0.4
5)10 log10(0/20)=0
Port 3
6)10 log10(6.4/20)=0.32
Case 3: 4(c)
Coupling Coefficient =10 log10(Pi/pj)
1)10 log10(20/6)=3.33
Port 1
2)10 log10(20/3.6)=5.5
3)10 log10(20/4.8)=4.65
Port 2
4)10 log10(20/8)=2.5
5)10 log10(20/0)=0
Port 3
6)10 log10(20/6.4)=3.12
Case 4: 4(d)
Scattering matrix
S11 S12
S13
S21 S22
S23
S24
S31
S33
S34
S32
S14
=
0.3
3.3
0
0.18 2.5
0.32
4.6
Department of ECE MLRIT
0.4
3.12
28
MWE & DC LABORATORY
VIVA QUESTIONS:
1.
2.
3.
4.
5.
6.
7.
What is circulator?
What is the difference between circulator and Isolator?
What is the difference between circulator and Gyrator?
What is the difference between circulator and Magic Tee?
Which material is used in circulator to rotate EM wave?
If power is coupled to port 2 in circulator it appear at___________.
Circulator is also used as____
a) Isolator
b) Gyrator
c) both d) none
8. Circulator is a __________ device (reciprocal / non-reciprocal)
9. What are the applications of Circulator?
10. What is the use of Isolators in microwave generators?
Department of ECE MLRIT
29
MWE & DC LABORATORY
5. GUNN DIODE CHARACTERISTICS
5(a)Verify V-I characteristics of Gunn Diode?
(b) Calculate the modulation depth of PIN modulator for Gunn diode? Using square
wave modulation?
(c) Derive the peak voltage from V-I characteristics of Gunn diode?
(d)Calculate the threshold voltage from V-I characteristics of Gunn diode?
AIM:
To study Gunn oscillator as a source of microwave power
EQUIPMENT:
1.Gunn oscillator
-1 No
2.Gunn oscillator power supply
- 1 No
3.PIN diode modulator
- 1 No
4. Ferrite isolator
- 1 No
5.Frequency meter
- 1 No
6.Attenuator
- 1 No
7.Detector with tunable mount
- 1 No
8. VSWR meter
- 1 No
9. Cathode Ray Oscilloscope
- 1 No
10.Coaxial to waveguide adapter
- 1 No
11.Cables and accessories
BENCH SET-UP:
Indicating
m
e
t
e
r
Gunn
P
o
w
e
r
Gunn
Isolator
S
O
us
pc
pi
l
Departmentyl of ECE MLRIT
a
t
o
PIN
Variable
m
o
d
u
l
a
t 30
o
r
(CRO)
Frequency
A
M
t
e
t
t
e
e
n
r
u
MWE & DC LABORATORY
a
t
o
r
VSWR
Detecto
m
e
t
e
r
r
m
o
u
n
t
PROCEDURE:
1. Set the equipment as shown in Fig. Taking due care for biasing PIN and Gunn diodes.
2. Initially set variable attenuator for minimum attenuation.
3. Keep the control knobs for gunn power supply as below
Meter switch
- OFF
Gunn bias Knob
- Fully anti-clock wise
PIN bias Knob
- Fully anti clock wise
PIN mod Frequency - Any position
4. Set the Gunn oscillator micrometer tuning screw at suitable frequency say 9 GHz. Adjust
attenuator for suitable power level.
5. Switch On the Gunn power supply.
5(a)Voltage- Current Characteristics:
1.
Turn the meter switch of Gunn Power supply to Voltage position.
2.
Measure the Gunn diode current corresponding to various Voltages controlled by Gunn
bias knob through the panel meter and meter switch. Do not exceed the bias voltage
above 10 volts. Note the values in table 1.
3.
Plot the voltage and current readings on the graph sheet that must be as shown in fig 5.1.
4.
Measure the threshold voltage which corresponds to Maximum current.
NOTE: Do not keep Gunn bias knob position at threshold position for more than 8- 10
Seconds. Reading should be obtained as fast as possible. Otherwise, due to
excessive Heating, Gunn diode may burn.
Tabular Column:
S.no
Voltage(in Volts)
1
2
3
4
5
6
7
8
9
Department of ECE MLRIT
Current(in mA)
1
2
3
4
5
6
7
8
9
1
75
104
150
163
166
162
155
142
31
MWE & DC LABORATORY
5(b) Square Wave Modulation:
5. Keep the Meter switch to volt position and rotate Gunn bias voltage slowly so that
panel meter of Gunn power supply reads 10 V.
6. Tune the PIN modulator bias voltage and frequency knob for maximum output on the
Oscilloscope.
7. Coincide the bottom of the square wave in oscilloscope to some reference level and
note the micrometer reading of variable attenuator.
8. Now with help of variable attenuator coincide the top of square wave to SAME
reference level and note down the micrometer reading.
9. Connect VSWR meter to detector mount and note down the dB reading in VSWR
meter for both the micrometer reading of the variable attenuator.
10. The difference of both db reading of VSWR meter gives the modulation depth of PIN
modulator.
5(c)
S.no
Current(in mA)
1
2
3
4
5
6
7
8
9
Peak Voltage
(from the graph)
1
75
104
150
163
166
162
155
142
6V
5(d)
S.no
1
2
3
4
5
6
7
8
9
Voltage(in Volts)
1
2
3
4
5
6
7
8
9
Department of ECE MLRIT
Current(in mA)
1
75
104
150
163
166
162
155
142
32
Peak Voltage
(from the graph)
6V
MWE & DC LABORATORY
CALCULATIONS:
Micrometer reading when bottom of square wave coincides with reference (m1) =
Corresponding reading of VSWR meter for m1 (P1) = Micrometer reading when top of
square wave coincides with same reference (m2) = Corresponding reading of VSWR meter
for m2 (P2) = Modulation depth of PIN modulator = (P2-P1)
MODEL GRAPH:
Inferences:
The characteristics of Gunn diode are plotted and Modulation depth for PIN modulator is
calculated.
VIVA QUESTION:
1. What are various modes of Gunn diode?
2. What is a PIN diode and how does it work as amplitude modulator?
3. Why are Gunn diode devices classified as voltage controlled devices?
4. Compare and contrast Gunn diode oscillator with a reflex klystron Oscillator
5. Name some crystals from which Gunn diode may be manufactured.
6. Write the RWH criteria for negative resistance.
7. Write the criteria for classifying modes in gunn diode.
8. For LSA mode f*L > _____________ ?
9. For stable Amplification mode n0 * L = _________________________?
10. For delayed domain mode f* L lies between_______________________ ?
Department of ECE MLRIT
33
MWE & DC LABORATORY
6. ATTENUATION MEASUREMENT
6(a)Calculate the attenuation provided by variable attenuator using attenuation
measurement?
(b) Find out attenuation value for different positions of micrometer using attenuation
measurement?
(c) Calculate the attenuation provided by power ratio method using attenuation
measurement?
AIM:
To study the attenuator and to calculate the attenuation provided by variable attenuator.
EQUIPMENT:
1.Regulated klystron power supply
-1 No
2.Reflex klystron with mount and cooling fan -1 No
3.Isolator
-1 No
4.Variable attenuator
-2 No
5.Frequency meter.
-1 No
6. Slotted Line section
-1 No
7. Tunable probe
-1 No
8.Waveguide detector mount with detector
-1 No
9.V SWR meter or micro ammeter
- 1 No
10. C.R.O
- 1 No
11. Waveguide stands and accessories
BENCH SET-UP:
Klystron
Power
Reflex
s
u
p
p
l
y
K Isolator
l
y
s
t
r
o
n
Variable
Attenuator
Frequency
Meter
Slotted
Indicator
L
i
n
e
Detector
Mount
Attenuator
Oscillator
Detector
Mount
Setup 1
Department of ECE MLRIT
34
Setup 2
VSWR
meter
MWE & DC LABORATORY
THEORY:
The attenuator is a two port bi-directional device which attenuates some power when inserted
into the transmission line.
* Attenuation A(dB)= 10 log [P1/P2]
Where P1 =Power absorbed by load without attenuator in the line.
P2 = Power absorbed by load with attenuator in the line.
PROCEDURE:
For Insertion loss/ Attenuation measurement
1. Assemble the equipment as shown in setup 1.
2. Fire the reflex klystron by considering all the proper conditions.
3. Tune the detector mount for maximum deflection on VSWR meter [detector mount‟s
output should be connected to VSWR meter]
4. Set any reference level on the VSWR meter with the help of variable attenuator and gain
control knob of VSWR meter, Let it be P1.
5. Carefully disconnect the detector mount from the slotted line without disturbing any
position of the setup. Place the test Variable attenuator to the slotted line and detector
mount to other port of test variable attenuator.
6. Keep the micrometer reading of test attenuator to Zero and record the reading of VSWR
meter let it be P2. Then the Insertion Loss of the test attenuator will be (P1- P2) dB.
7. Now change the micrometer reading and record the VSWR meter reading in table. Find
out attenuation value for different position of micrometer reading and plot the graph.
TABLE:
Beam Voltage=280v, Beam Current=18 mA
Repeller voltage= -230v, P1= Vref*18mA =12.96mW
Vref= 3.6*0.2=0.72V
Department of ECE MLRIT
35
MWE & DC LABORATORY
6(a):
Sl.No
1.
2.
3.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
VSWR meter reading
P2 (mW)
12.96
12.96
12.96
12.96
12.96
12.96
12.96
12.96
12.24
10.44
8.64
6.12
4.32
3.24
1.8
1.08
0.72
0
Attenuation
(P1-P2) (mW)
0
0
0
0
0
0
0
0
0.72
2.52
4.32
6.84
8.64
9.72
11.16
11.88
12.24
12.96
6(b) :
Sl.No Micrometer reading
1.
2.
3.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
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24
23
22
21
20
15
10
9
8
7
6
5
4
3
2
1
0
VSWR meter reading
P2 (mW)
12.96
12.96
12.96
12.96
12.96
12.96
12.96
12.96
12.24
10.44
8.64
6.12
4.32
3.24
1.8
1.08
0.72
0
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MWE & DC LABORATORY
6(c):
1. 10log(12.96/12.96) = 0
2. 10log(12.96/12.96) = 0
3. 10log(12.96/12.24) = 0.21
4. 10log(12.96/10.44) = 0.93
5. 10log(12.96/8.64) = 1.76
6. 10log(12.96/1.8) = 8.57
7. 10log(12.96/0.72) = 12.52
8. 10log(12.96/0) = ∞
VIVA QUESTIONS:
1. What do you mean by attenuation?
2. What is an attenuator?
3. How does attenuator differ from an isolator?
4. How does a ferrite attenuator differ from a carbon pad?
5. Why absolute measurement of attenuation is essential?
6. Which type of waveguide attenuation have relatively high accuracy and
greater versatility and why?
7. What are various types of attenuators present in waveguide systems?
8. What is Flap attenuator?
9. What is Vane attenuator?
10. What are the various uses of attenuator?
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DIGITAL COMMUNICATION LAB
1. DELTA MODULATION
AIM:
To study the delta Modulation and Demodulation process
EQUIPMENT REQUIRED:
Delta Modulation and demodulation trainer kit
CRO
BNC probes
Patch cards.
BLOCK DIAGRAM:
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THEORY:
Delta modulation may be viewed, as a simplified form of DPCM is which two level
quietuses are used in conjunction with a fixed first order predictor. DPCM is based on the
explanation of signal correlation when base band signals are sampled at nyquist rate
correlation between the adjacent samples can be further increased by over sampling the signal
at a rate much higher than the Nyquist rate.
The higher correlation between the sampler permit one to use a simpler quantising
strategy for constructing the encoded signal. The very concept has led to the development of
delta modulation is a one bit variation of DPCM. Applying the sampled version if the
incoming message signal to a modulator that involves a summer, quantized and an
accumulator interconnected can generate delta modulation.
The key to effective use of delta modulation is the proper choice of the step sizes and
the sampling rate. The parameters must be chosen in such a way that staircase signal is close
approximation of tactual analog waveform. Since they signal has given fixed upper
frequency, we know that the fastest rate at which it can change however to account for the
fastest possible in the signal the step size or sampling frequency must be increased increasing
the sampling frequency results in the delta modulated waveforms that require a large
bandwidth increasing the step size increases the quantizing error.
PROCEDURE:
1.
2.
3.
4.
5.
6.
Switch ON the experimental board.
Connect Clock Signal to the Delta Modulator circuit.
Connect Modulating Signal to the Modulating signal input of the Delta
Modulator and observe the same on channel l of a Dual Trace Oscilloscope.
Observe the Delta Modulator output on channel II of CRO.
Connect this Delta Modulator output to the demodulator. Also connect the
clock signal to the demodulator.
Observe the Demodulator output with and without RC filter on CRO.
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MODEL GRAPH:
RESULT: Hence studied and observed delta modulation and demodulation
VIVA QUESTIONS:
1.
Define D.M.
2.
Explain the generation process of D.M
3.
What is the drawback of D.M?
4.
Compare D.M with ADM
5.
What is meant by slope over load modulation
6.
What is the advantage of D.M compare with DPCM
7.
Give the application of D.M
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1 (a)Determine the modulation index using delta modulation?
(b) Determine the demodulation index using delta modulation?
(c)Obtain delta demodulator o/p without RC filter.
(d) obtain of Delta demodulator o/p with RC filter.
AIM:
To study the delta Modulation and Demodulation process
EQUIPMENT REQUIRED:
Delta Modulation and demodulation trainer kit
CRO
BNC probes
Patch cards.
BLOCK DIAGRAM:
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PROCEDURE:
1.
2.
3.
4.
5.
6.
Switch ON the experimental board.
Connect Clock Signal to the Delta Modulator circuit.
Connect Modulating Signal to the Modulating signal input of the Delta
Modulator and observe the same on channel l of a Dual Trace Oscilloscope.
Observe the Delta Modulator output on channel II of CRO.
Connect this Delta Modulator output to the demodulator. Also connect the
clock signal to the demodulator.
Observe the Demodulator output with and without RC filter on CRO.
MODEL GRAPH:
5(a) Delta modulation:
5(b) Delta demodulation:
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5(c) Delta demodulator o/p without RC filter:
5(d) Delta demodulator o/p with RC filter:
RESULT: Hence studied and observed delta modulation and demodulation.
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2. TIME DIVISION MULTIPLEXING OF 2 BAND LIMITED
SIGNALS
AIM:
To study the time division multiplexing by applying different band limited signals
to time division multiplexer. Apply the multiplexed output to Demultiplexer and observe the
individual signals.
EQUIPMENT REQUIRED: TDM multiplexer and demultiplexer kit
CRO
BNC probes
Patch cards.
BLOCK DIAGRAM:
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THEORY:
A time division multiplex system enables the joint utilization of a common
communication channel by a plurality of independent message sources without mutual
interference among them.
Each input signal is first restricted in bandwidth by a low pass anti aliening filter to
remove the frequencies that are non-essential to an adequate signal representation. The low
pass filter outputs are then applied to commentator, which is usually implanted using
electronic switching circuitry the function of the commutator is twofold. To take a narrow
sample of each of the N input messages at rate fs that are slightly higher than 2w where W is
the cutoff frequency of the anti-aliening. To sequentially interleave there N samples inside
the sampling interval TS
In deed this later function is the essence of the time division multiplexing operation
following the communication process the multiplied signal is applied to pulse modulator, the
purpose of which is to transform the multiplied signal into a form suitable for transmission
over the communication channel it is clear that the use of time division multiplying
introduces a band width expansion factor N because the scheme must squeeze N samples
derived form N independent message sources into a time slot equal to one sampling interval
at the receiving end of the system, the receive signal is applied to pulse demodulator, which
performs the reverse operation of the pulse modulator.
The narrow samples produced at the pulse demodulator output are distributed to the
appropriate low pass reconstruction filter by means of a dissimulators which operates in
synchronism with the commutator in the transmitter the is synchronization is essential for a
satisfactory operation of the system. The way this synchronization is implemented depends
naturally on the method of pulse modulation use to transmit the multiplied sequence of
samples. The TDM systems are highly sensitive to dispersion in the common channel .so
accurate equalization of both magnitude3 and phase response of the channel is necessary to
ensure a satisfactory operation of the system.
PROCEDURE:
1. Switch on Time Division Multiplexing and De Multiplexing Trainer.
2. Connect the sine wave to channel-1, square wave to channel -2 and triangle wave to
channel3 terminals of 8 to 1 Multiplexer.
3. Observe the multiplexer output on channel -1 of a CRO.
4. Connect mux output to de-mux input.
5. Observe corresponding signal outputs at channel-2 of CRO.
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MODEL GRAPH:
RESULT:
The operation of TDM is observed and the output waveforms are verified.
VIVA QUESTIONS:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Define TDM.
Which principle is used in TDM
Compare TDM with FDM
In which area TDM is applicable
Explain the generation of TDM
Compare PAM & TDM
What is the function of commentator
What is the function of De commentator
Give the application of TDM.
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2(a) Show the multiplexing of band limited signals using TDM?
(b) Detremine demultiplexing process using 74155 IC of TDM?
(c) verify TDM for 2 band limited signal.
(d) Determine TDM with the help of waveforms?
AIM:
To study the time division multiplexing by applying different band limited signals
to time division multiplexer. Apply the multiplexed output to demultiplexer and observe the
individual signals.
EQUIPMENT REQUIRED: TDM multiplexer and demultiplexer kit
CRO
BNC probes
Patch cards.
BLOCK DIAGRAM:
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PROCEDURE:
1. Switch on Time Division Multiplexing and De Multiplexing Trainer.
2. Connect the sine wave to channel-1, square wave to channel -2 and triangle wave to
channel3 terminals of 8 to 1 Multiplexer.
3. Observe the multiplexer output on channel -1 of a CRO.
4. Connect mux output to de-mux input.
5. Observe corresponding signal outputs at channel-2 of CRO.
MODEL GRAPH:
2(a) TDM output:
2(b) De – Multiplexer output:
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2(c) TDM output by applying 2 band limited signals:
2(d) Draw the o/p waveforms from the operation of TDM:
Inputs:
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Outputs:
RESULT:
The operation of TDM is observed and the output waveforms are verified.
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3. FREQUENCY SHIFT KEYING GENERATION & DETECTION
AIM:
To generate FSK modulation and demodulation signals.
EQUIPMENT REQUIRED:
FSK modulation and demodulation kit
CRO
BNC probes
Patch cards.
BLOCK DIAGRAM:
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THEORY:
In FSK systems two sinusoidal carrier waves of same amplitude AC but different
frequencies fC1 and fC2 are used to re present binary symbols 1 and 0 respectively. I.e. S (t)
= Ac Cos (2 П fC1,t) symbol 1 = Ac Cos (2 П fC2,t)
symbol 2
The FSK is essentially a superposition of two ASK waveforms one with frequency fC1
and the other with fC2. Hence the PSD of FSK is the sum of two ASKS specter at frequencies
fC1 and fC2. The bandwidths of FSK are higher than that of psk and ask .The application of
FSK signals is in low speed digital data transmission.
Generation of FSK:
The FSK signal can be generated by applying the incoming binary data to a frequency
modulator and to other input a sinusoidal carrier wave of amplitude AC and frequency fC is
applied. As the binary data changes form one level to another (but non zero being pear) the
output changes its frequencies is the corresponding manner.
Detection of FSK:
FSK can be demodulated using synchronous or coherent detector. This type of
detection or digital communication reception is also known as correlation reception. The
coherent detection requires phase and time synchronization.
PROCEDURE:
1.
2.
3.
4.
5.
6.
Switch 'ON' the power to the Trainer.
Observe the clock frequency on the oscilloscope.
Apply the clock to the decade counter (7490). And vary the data outputs and draw
the data outs.
Select one data output of the decade counter to the data input point of the FSK
modulator and observe the same signal one channel of a dual trace oscilloscope.
Observe the output of the FSK modulator on the second channel of the CRO.
Apply the FSK modulator out put to demodulator input. Adjust the potentiometers
P1 & P2 until we get the demodulated output equivalent to the modulating data
signal.
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MODEL GRAPHS:
RESULT: -Hence generated frequency modulated and demodulated signals
VIVA QUESTIONS:
1.
2.
3.
4.
5.
Define Binary FSK signal?
What is meant by carrier swing?
Define Frequency deviation of FSK signal?
What are the advantages of this FSK signal?
Give the differences between FSK & FM?
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3(a) determine modulation using FSK?
(b)determine demodulation using FSK?
(c)Generation of FSK modulation using low carrier frequency
(d)Generation of FSK modulation using high carrier frequency
(e)write a MATLAB program for FSK?
AIM:
To generate FSK modulation and demodulation signals.
EQUIPMENT REQUIRED:
FSK modulation and demodulation kit
CRO
BNC probes
Patch cards.
BLOCK DIAGRAM:
Generation of FSK:
The FSK signal can be generated by applying the incoming binary data to a frequency
modulator and to other input a sinusoidal carrier wave of amplitude AC and frequency fC is
applied. As the binary data changes form one level to another (but non zero being pear) the
output changes its frequencies is the corresponding manner.
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Detection of FSK:
FSK can be demodulated using synchronous or coherent detector. This type of
detection or digital communication reception is also known as correlation reception. The
coherent detection requires phase and time synchronization.
PROCEDURE:
1.
2.
3.
4.
5.
6.
Switch 'ON' the power to the Trainer.
Observe the clock frequency on the oscilloscope.
Apply the clock to the decade counter (7490). And vary the data outputs and draw
the data outs.
Select one data output of the decade counter to the data input point of the FSK
modulator and observe the same signal one channel of a dual trace oscilloscope.
Observe the output of the FSK modulator on the second channel of the CRO.
Apply the FSK modulator out put to demodulator input. Adjust the potentiometers
P1 & P2 until we get the demodulated output equivalent to the modulating data
signal.
MODEL GRAPHS:
3(a) Generation of FSK modulation:
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3(b) Generation of FSK demodulation:
3(c) Generation of FSK modulation & demodulation using low carrier frequency:
3(d) Generation of FSK modulation & demodulation using high carrier frequency:
RESULT: -Hence generated frequency modulated and demodulated signals.
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A. FREQUENCY SHIFT KEYING
Aim: To generate and demodulate frequency shift keyed (FSK) signal using MATLAB
Theory
Generation of FSK
Frequency- shift keying (FSK) is a frequency modulation scheme in which digital
information is transmitted through discrete frequency changes of a carrier wave. The
simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit
binary (0s and 1s) information. With this scheme, the "1" is called the mark frequency and
the "0" is called the space frequency.
In binary FSK system, symbol 1 & 0 are distinguished from each other by transmitting one of
the two sinusoidal waves that differ in frequency by a fixed amount.
Si (t) = √2E/Tb cos 2πf1t 0≤ t ≤Tb
0
elsewhere
Where i=1, 2 & Eb=Transmitted energy/bit
Transmitted freq= ƒi = (nc+i)/Tb, and n = constant (integer), Tb = bit
interval Symbol 1 is represented by S1 (t)
Symbol 0 is represented by S0 (t)
BFSK Transmitter
Xx
c1 (t) = √2/Tb cos 2πƒ1t
Binary wave
+
(On-Off signaling
Σ
Form)
Inverter
+
FSK signal
X
c2 (t) = √2/Tb cos 2πƒ2t
The input binary sequence is represented in its ON-OFF form, with symbol 1
represented by constant amplitude of √Eb with & symbol 0 represented by zero
volts. By using inverter in the lower channel, we in effect make sure that when
symbol 1is at the input, The two frequency f1& f2 are chosen to be equal integer
multiples of the bit rate 1/Tb.By summing the upper & lower channel outputs, we
get BFSK signal.
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x1
BFSK Receiver
X
Tbƒdt
0
c1 (t)
x = x1-x2 +
Decision
E
Device
-
FSK signal
Tbƒdt
X
choose „1‟ if x >0
choose
x2 „0‟ if x < 0
c2 (t)
The receiver consists of two correlators with common inputs which are supplied with
locally generated coherent reference signals c1(t) and c2 (t).
The correlator outputs are then subtracted one from the other, and the resulting
difference x is compared with a threshold of zero volts. If x >0, the receiver decides
in favour of symbol 1 and if x <0, the receiver decides in favour of symbol 0.
Algorithm
Initialization commands
FSK modulation
1.
2.
3.
4.
5.
6.
7.
8.
Generate two carriers signal.
Start FOR loop
Generate binary data, message signal and inverted message signal
Multiply carrier 1 with message signal and carrier 2 with inverted message signal
Perform addition to get the FSK modulated signal
Plot message signal and FSK modulated signal.
End FOR loop.
Plot the binary data and carriers.
FSK demodulation
1. Start FOR loop
2. Perform correlation of FSK modulated signal with carrier 1 and carrier 2 to get two
decision variables x1 and x2.
3. Make decisionon x = x1-x2 to get demodulated binary data. If x>0, choose „1‟ else
choose „0‟.
4. Plot the demodulated binary data.
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Program
% FSK Modulation
clc;
clear all;
close all;
%GENERATE CARRIERSIGNAL
Tb=1;
fc1=2;
fc2=5;
t=0:(Tb/100):Tb;
c1=sqrt(2/Tb)*sin(2*pi*fc1*t);
c2=sqrt(2/Tb)*sin(2*pi*fc2*t);
%generate message signal
N=8;
m=rand(1,N);
t1=0;
t2=Tb;
for i=1:N
t=[t1:(Tb/100):t2]
if
m(i)>0.5
m(i)=1;
m_s=ones(1,length(t));
invm_s=zeros(1,length(t));
else
m(i)=0;
m_s=zeros(1,length(t));
invm_s=ones(1,length(t));
end
message(i,:)=m_s;
%Multiplier
fsk_sig1(i,:)=c1.*m_s;
fsk_sig2(i,:)=c2.*invm_s;
fsk=fsk_sig1+fsk_sig2;
%plotting the message signal and the modulated signal
subplot(3,2,2);
axis([0 N -2 2]);
plot(t,message(i,:),'r');
title('message signal');
xlabel('t---->');
ylabel('m(t)');
grid on;
hold on;
subplot(3,2,5);
plot(t,fsk(i,:));
title('FSK signal');
xlabel('t---->');
ylabel('s(t)');
grid on;
hold on;
t1=t1+(Tb+.01);
t2=t2+(Tb+.01);
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end
hold off
%Plotting binary data bits and carrier signal
subplot(3,2,1);
stem(m);
title('binary data');
xlabel('n---->');
ylabel('b(n)');
grid on;
subplot(3,2,3);
plot(t,c1);
title('carrier signal-1');
xlabel('t---->');
ylabel('c1(t)');
grid on;
subplot(3,2,4);
plot(t,c2);
title('carrier signal-2');
xlabel('t---->');
ylabel('c2(t)');
grid on;
% FSK Demodulation
t1=0;
t2=Tb;
for i=1:N
t=[t1:(Tb/100):t2];
%correlator
x1=sum(c1.*fsk_sig1(i,:));
x2=sum(c2.*fsk_sig2(i,:));
x=x1-x2;
%decision device
if x > 0 demod(i)=1
else
demod(i)=0;
end
t1=t1+(Tb+.01);
t2=t2+(Tb+.01);
end
%Plotting the demodulated data bits
subplot(3,2,6);
stem(demod);
title(' demodulated data');
xlabel('n---->');
ylabel('b(n)');
grid on;
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Modal Graph:
Result:
The program for FSK modulation and demodulation has been simulated in MATLAB and
necessary graphs are plotted.
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B. FREQUENCY SHIFT KEYING ( MATLAB)
Aim: To perform Frequency shift keying in MATLAB
Experimental requirements: PC loaded with MATLAB
Procedure:
1.
2.
3.
4.
Run MATLAB
Open a new script file
Write the code for frequency shift keying
Run the code for execution and obtain the necessary results
MATLAB script
clc;
clear all;
close all;
%GENERATE CARRIER SIGNAL
Tb=1;
fc1=2;
fc2=5;
t=0:(Tb/100):Tb;
c1=sqrt(2/Tb)*sin(2*pi*fc1*t);
c2=sqrt(2/Tb)*sin(2*pi*fc2*t);
%generate message signal
N=8;
m=rand(1,N);
t1=0;
t2=Tb
for i=1:N
t=[t1:(Tb/100):t2]
if m(i)>0.5 m(i)=1;
m_s=ones(1,length(t));
invm_s=zeros(1,length(t));
else
m(i)=0; m_s=zeros(1,length(t));
invm_s=ones(1,length(t));
end
message(i,:)=m_s;
%Multiplier
fsk_sig1(i,:)=c1.*m_s;
fsk_sig2(i,:)=c2.*invm_s;
fsk=fsk_sig1+fsk_sig2;
%plotting the message signal and the modulated signal
subplot(3,2,2);
axis([0 N -2 2]);
plot(t,message(i,:),'r');
title('message signal');
xlabel('t---->');
ylabel('m(t)');
grid on;
hold on;
subplot(3,2,5);
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plot(t,fsk(i,:));
title('FSK signal');
xlabel('t---->');
ylabel('s(t)');
grid on;
hold on;
t1=t1+(Tb+.01);
t2=t2+(Tb+.01);
end
holdoff
%Plotting binary data bits and carrier signal
subplot(3,2,1);stem(m);
title('binary data');
xlabel('n---->');
ylabel('b(n)');
grid on;
subplot(3,2,3);plot(t,c1);
title('carrier signal-1');
xlabel('t---->');
ylabel('c1(t)');
grid on;
subplot(3,2,4);
plot(t,c2);
title('carrier signal-2');
xlabel('t---->');
ylabel('c2(t)');
grid on;
Waveforms:
Result:
The program for FSK modulation and demodulation has been simulated in MATLAB and
necessary graphs are plotted.
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4. PHASE SHIFT KEYING GENERATION & DETECTION
AIM:
To study the operation of phase shift key Modulation and Demodulation.
EQUIPMENT REQUIRED:
PSK Modulations and Demodulation Trainer kit
CRO
BNC probes
Patch cards
BLOCK DIAGRAM:
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THEORY:
Phase shift keying or discrete phase modulation is another technique available for
communicating digital information over band pass channels. The psk is a form of angle
modulated, constant amplitude digital modulation. In binary phase shift keying two out put
phases are possible for a single carrier frequency as the input digital signal changes state, the
phase of the output carrier shifts between 1800 out of phase.
In binary phase shift keying modulation the balanced modulator acts as a phase
reversing switch. Depending on the logic condition of the digital input, the carrier is
transferred to the output wither in phase or 1800 with reference carrier oscillators and for
proper operation the digital input voltages must be greater than the peak carrier voltage as it
has to control ON-OFF of diodes. The coherent detection also called synchronous detection is
used for binary phase shift keying detection. It is more complicated than envelope detector,
and results in a lower probability of error for a give S/N input. Synchronous detection
requires a carrier recovery circuit to generate local carrier component exactly synchronized to
the transmitted carrier. The primary advantage of the psk signaling scheme lays in is superior
performance over the amplitude shift-keying scheme operating under the same peak power
limitations and noise environment.
MODEL GRAPHS:
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PROCEDURE: 1. Switch ON the experimental board.
2. Apply the carrier signal to the input of the modulator.
3. Apply the modulating data signal to the modulator input and observe this
signal on one channel l of the CRO.
4. Observe the output of the PSK modulator on the channel 2 of the CRO.
5. Apply this PSK output to the demodulator input and also apply the carrier
input.
6. Observe the demodulator output and compare it with the modulating data
signal applied to the modulator input.
RESULTS: - Hence generated Phase modulated and demodulated signals
VIVA QUESTIONS:
1.
2.
3.
4.
5.
6.
7.
Define PSK?
Explain the generation proven of PSK?
Differentiate PSK & PM?
Give the application of PSK?
PSK is which type of modulation?
Compare PSK & FSK?
Give the advantages PSK?
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4(a)determine modulation using PSK?
(b)determine demodulation using PSK?
(c)determine PSK demodulation for data generator signal?
(d)write a MATLAB program for PSK?
AIM:
To study the operation of phase shift key Modulation and Demodulation.
EQUIPMENT REQUIRED:
PSK Modulations and Demodulation Trainer kit
CRO
BNC probes
Patch cards
BLOCK DIAGRAM:
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MODEL GRAPHS:
4(a)Generate PSK modulation:
4(b)Generate PSK demodulation:
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4(c)Generation of PSK demodulator o/p with respect to the data generator signal.
PROCEDURE: a. Switch ON the experimental board.
b. Apply the carrier signal to the input of the modulator.
c. Apply the modulating data signal to the modulator input and observe this
signal on one channel l of the CRO.
d. Observe the output of the PSK modulator on the channel 2 of the CRO.
e. Apply this PSK output to the demodulator input and also apply the carrier
input.
f. Observe the demodulator output and compare it with the modulating data
signal applied to the modulator input.
RESULT:
Hence generated Phase modulated and demodulated signals
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A. PHASE SHIFT KEYING
Aim: To generate and demodulate phase shift keyed (PSK) signal using MATLAB
Generation of PSK signal
PSK is a digital modulation scheme that conveys data by changing, or modulating,
the phase of a reference signal (the carrier wave). PSK uses a finite number of phases, each
assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of
bits. Each pattern of bits forms the symbol that is represented by the particular phase. The
demodulator, which is designed specifically for the symbol-set used by the modulator,
determines the phase of the received signal and maps it back to the symbol it represents, thus
recovering the original data.
In a coherent binary PSK system, the pair of signal S1(t) and S2 (t) used to represent binary
symbols 1 & 0 are defined by
(t) = √2Eb/ TSb1 Cos 2πfct
(t) =√2Eb/TbS(2πf
where 0 ≤ t< Tb and
2
ct+π) = - √ 2Eb/Tb Cos 2πfct
Eb = Transmitted signed energy for bit
The carrier frequency fc =n/Tb for some fixed integer n.
Antipodal Signal:
The pair of sinusoidal waves that differ only in a relative phase shift of 180° are called
antipodal signals.
BPSK Transmitter
Binary Wave
Product
(Polar form)
Product
BPSK signal
Modulator
c1 (t) = √2/Tb cos 2πfct
The input binary symbols are represented in polar form with symbols 1 & 0 represented by
constant amplitude levels √Eb & -√Eb. This binary wave is multiplied by a sinusoidal carrier
in a product modulator. The result in a BSPK signal.
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BSPK Receiver:
PSK signal ∫ X
dt
c1 (t).
x
∫
Decision
device
dt
Decision device
Choose „1‟ if x > 0
Choose „0‟ if x < 0
The received BPSK signal is applied to a correlator which is also supplied with a
locally generated reference signal c1 (t). The correlated o/p is compared with a threshold of
zero volts. If x> 0, the receiver decides in favour of symbol 1. If x< 0, it decides in favour of
symbol 0.
Algorithm
Initialization commands
PSK modulation
1.
2.
3.
4.
5.
6.
7.
Generate carrier signal.
Start FOR loop
Generate binary data, message signal in polar form
Generate PSK modulated signal.
Plot message signal and PSK modulated signal.
End FOR loop.
Plot the binary data and carrier.
PSK demodulation
1. Start FOR loop Perform correlation of PSK signal with carrier to get decision variable
2. Make decision to get demodulated binary data. If x>0, choose „1‟ else choose „0‟ Plot the
demodulated binary data.
Program
% PSK modulation
clc;
clear all;
close all;
%GENERATE CARRIER SIGNAL
Tb=1;
t=0:Tb/100:Tb;
fc=2;
c=sqrt(2/Tb)*sin(2*pi*fc*t);
%generate message signal
N=8;
m=rand(1,N);
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t1=0;t2=Tb
for i=1:N;
t=[t1:.01:t2] ;
if
m(i)>0.5 m(i)=1;
m_s=ones(1,length(t));
else
m(i)=0; m_s=-1*ones(1,length(t));
end
message(i,:)=m_s;
%product of carrier and message signal
bpsk_sig(i,:)=c.*m_s;
%Plot the message and BPSK modulated signal
subplot(5,1,2);
axis([0 N -2 2]);
plot(t,message(i,:),'r');
title('message signal(POLAR form)');
xlabel('t--->');
ylabel('m(t)');
grid on;
hold on;
subplot(5,1,4);
plot(t,bpsk_sig(i,:));
title('BPSK signal');
xlabel('t--->');
ylabel('s(t)');
grid on;
hold on;
t1=t1+1.01;
t2=t2+1.01;
end
hold off
%plot the input binary data and carrier signal
subplot(5,1,1);
stem(m);
title('binary data bits');
xlabel('n--->');
ylabel('b(n)');
grid on;
subplot(5,1,3);
plot(t,c);
title('carrier signal');
xlabel('t--->');
ylabel('c(t)');
grid on;
% PSK Demodulation
t1=0;
t2=Tb;
for i=1:N
t=[t1:.01:t2] ;
%correlator
x=sum(c.*bpsk_sig(i,:));
%decision device
if
x>0 demod(i)=1;
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else
demod(i)=0;
end
t1=t1+1.01;
t2=t2+1.01;
end
%plot the demodulated data bits
subplot(5,1,5);
stem(demod);
title('demodulated data');
xlabel('n--->');
ylabel('b(n)');
grid on;
Modal Graphs
Result
The program for PSK modulation and demodulation has been simulated in MATLAB and
necessary graphs are plotted.
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B. PHASE SHIFT KEYING
Aim: To perform phase shift keying in MATLAB
Experimental requirements: PC loaded with MATLAB software
Procedure:
1.
2.
3.
4.
Run MATLAB
Open a new script file
Write the code for phase shift keying
Run the code for execution and obtain the necessary results
MATLAB script:
clear;
clc;
b = input('Enter the Bit stream \n ');
%b = [0 1 0 1 1 1 0];
n = length(b);
t = 0:.01:n;
x = 1:1:(n+1)*100;
for i = 1:n
if (b(i)==0)b_p(i)= -1;
else
b_p(i) = 1;
end
for j = i:.1:i+1 bw(x(i*100:(i+1)*100)) = b_p(i);
end
end
bw = bw(100:end);
sint = sin(2*pi*t);
st = bw.*sint;
subplot(3,1,1);
plot(t,bw);
gridon ;
axis([0 n -2 +2]) ;
subplot(3,1,2) ;
plot(t,sint);
gridon ;
axis([0 n -2 +2]);
subplot(3,1,3);
plot(t,st);
gridon ;
axis([0 n -2 +2])
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Waveforms:
Result:
The program for PSK modulation and demodulation has been simulated in MATLAB and
necessary graphs are plotted.
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5. AMPLITUDE SHIFT KEYING GENERATION & DETECTION
AIM:
To observe the variation in amplitude of carrier signal corresponding to applied binary
sequence.
EQUIPMENT REQUIRED:
ASK Modulation &demodulation trainer kit
Function generator
CRO
BNC cable
Patch cards
BLOCK DIAGRAM:
THEORY:
The binary ASK system was one of the earliest forms of digital modulation used in
wireless telegraphy. In a system transmitting a sinusoidal carrier wave of fixed amplitude Ac
and fixed frequency Fc represents binary symbol. For the bit duration Tb are when an binary
symbol is represented by switching off the carrier for Tb . the signal can be generated by
simply Turing the carriers of sinusoidal oscillation ON-OFF for the prescribed periods
indicated by modulating pulse train So, it is known as ON-OFF keying (00k)
i.e. S(t) = Ac cos(2*3.14*Fc*t)
symbol 1= 0 symbol 0
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Generations of ask:
ASK applying the incoming bi8nary data and the sinusoidal carrier to the inputs of 2:1
multiplexer and control input as reelect signal can generate signal. The ASK signal which is
basically the product of binary data and sinusoidal data has PSO name as that of base band
ON-OFF signal but is shifted in frequency domain by ± Fc. The ASK output has an infinity
bandwidth but practically the bandwidth is equal top that of an ideal and band pass filter is a
approximately 3/Tb Hz.
Demodulation of ASK:
The demodulation of ASK wave can be done with the help of envelope detector /
coherent deter. This detection involves the use of linear operation here the local carries is
assumed to be in perfect synchronization with the modulating signal.
MODEL GRAPHS:
PROCEDURE:
1.
2.
3.
4.
5.
Circuit connected as shown in the figure.
Apply the binary data to the input and give NRZ-M to control input of
modulator circuit and ground the second input of modulator
Apply sine wave to second input of the modulator.
Observe the output waveform on the modulator.
Now give the modulated output to demodulator or input and check whether the
binary data is corrected or not.
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RESULTS: Hence generated Amplitude modulated and demodulated signals
VIVA QUESTIONS:
1.
2.
3.
4.
5.
6.
7.
Define ASK?
Explain the generation proven of ASK?
Differentiate ASK & AM?
Give the application of ASK?
ASK is which type of modulation?
Compare ASK & FSK?
Give the advantages ASK?
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5(a)determine modulation using ASK?
(b)determine demodulation using ASK?
(c)determine ASK modulation for data generator signal.
(d)determine ASK demodulation for data generator signal.
(e)write a MATLAB program for ASK?
AIM:
To observe the variation in amplitude of carrier signal corresponding to applied binary
sequence.
EQUIPMENT REQUIRED:
ASK Modulation &demodulation trainer kit
Function generator
CRO
BNC cable
Patch cards
BLOCK DIAGRAM:
Generations of ask:
ASK applying the incoming bi8nary data and the sinusoidal carrier to the inputs of 2:1
multiplexer and control input as reelect signal can generate signal. The ASK signal which is
basically the product of binary data and sinusoidal data has PSO name as that of base band
ON-OFF signal but is shifted in frequency domain by ± Fc. The ASK output has an infinity
bandwidth but practically the bandwidth is equal top that of an ideal and band pass filter is a
approximately 3/Tb Hz.
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Demodulation of ASK:
The demodulation of ASK wave can be done with the help of envelope detector /
coherent deter. This detection involves the use of linear operation here the local carries is
assumed to be in perfect synchronization with the modulating signal.
MODEL GRAPHS:
5(a)Generation of ASK modulation:
(b)Generation of ASK demodulation:
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(c)Obtain ASK modulator o/p with respect to the data generator signal.
(d)Obtain ASK demodulator o/p with respect to the data generator signal.
PROCEDURE:
1.
2.
3.
4.
5.
Circuit connected as shown in the figure.
Apply the binary data to the input and give NRZ-M to control input of
modulator circuit and ground the second input of modulator
Apply sine wave to second input of the modulator.
Observe the output waveform on the modulator.
Now give the modulated output to demodulator or input and check whether the
binary data is corrected or not.
RESULTS: Hence generated Amplitude modulated and demodulated signals
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A. AMPLITUDE SHIFT KEYING (MATLAB)
Aim: To generate and demodulate amplitude shift keyed (ASK) signal using MATLAB
Theory
Generation of ASK
Amplitude shift keying - ASK - is a modulation process, which imparts to a sinusoid
two or more discrete amplitude levels. These are related to the number of levels adopted by
the digital message. For a binary message sequence there are two levels, one of which is
typically zero. The data rate is a sub-multiple of the carrier frequency. Thus the modulated
waveform consists of bursts of a sinusoid. One of the disadvantages of ASK, compared with
FSK and PSK, for example, is that it has not got a constant envelope. This makes its
processing (eg, power amplification) more difficult, since linearity becomes an important
factor. However, it does make for ease of demodulation with an envelope detector.
Demodulation
ASK signal has a well defined envelope. Thus it is amenable to demodulation by an
envelope detector. Some sort of decision-making circuitry is necessary for detecting the
message. The signal is recovered by using a correlator and decision making circuitry is used
to recover the binary sequence.
Algorithm
Initialization commands
ASK modulation
1.
2.
3.
4.
5.
6.
7.
Generate carrier signal.
Start FOR loop
Generate binary data, message signal(on-off form)
Generate ASK modulated signal.
Plot message signal and ASK modulated signal.
End FOR loop.
Plot the binary data and carrier.
ASK demodulation
1.
2.
3.
4.
Start FOR loop
Perform correlation of ASK signal with carrier to get decision variable
Make decision to get demodulated binary data. If x>0, choose „1‟ else choose „0‟
Plot the demodulated binary data.
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Program
%ASK Modulation
clc;
clear all;
close all;
%GENERATE CARRIER SIGNAL
Tb=1;
fc=10;
t=0:Tb/100:1;
c=sqrt(2/Tb)*sin(2*pi*fc*t);
%generate message signal
N=8;
m=rand(1,N);
t1=0;
t2=Tb ;
for i=1:N
t=[t1:.01:t2];
if m(i)>0.5 m(i)=1
m_s=ones(1,length(t));
else
m(i)=0;
m_s=zeros(1,length(t));
end
message(i,:)=m_s;
%product of carrier and message
ask_sig(i,:)=c.*m_s;
t1=t1+(Tb+.01);
t2=t2+(Tb+.01);
%plot the message and ASK signal
subplot(5,1,2);
axis([0 N -2 2]);
plot(t,message(i,:),'r');
title('message signal');
xlabel('t--->');
ylabel('m(t)');
grid on;
hold on;
subplot(5,1,4);
plot(t,ask_sig(i,:));
title('ASK signal');
xlabel('t--->');
ylabel('s(t)');
grid on ;
hold on;
end
hold off
%Plot the carrier signal and input binary data
subplot(5,1,3);
plot(t,c);
title('carrier signal');
xlabel('t--->');
ylabel('c(t)');
grid on ;
subplot(5,1,1);
stem(m);
title('binary data bits');
xlabel('n--->');
ylabel('b(n)');
grid on;
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ASK Demodulation
t1=0;t2=Tb
for i=1:N
t=[t1:Tb/100:t2]
%correlator
x=sum(c.*ask_sig(i,:));
%decision device
if x>0 demod(i)=1;
else
demod(i)=0;
end
t1=t1+(Tb+.01);
t2=t2+(Tb+.01);
end
%plot demodulated binary data bits
subplot(5,1,5);
stem(demod);
title('ASK demodulated signal');
xlabel('n--->');
ylabel('b(n)');
grid on;
Model Graph:
Result
The program for ASK modulation and demodulation has been simulated in MATLAB and
necessary graphs are plotted.
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6.
DIFFERENTIAL PHASE SHIFT KEYINGMODULATION &
DEMODULATION
AIM:
To study the various steps involved in generating the differential binary signal and
differential phases shift keyed signal at the modulator end and recovering the binary signal
from the received DPSK signal.
EQUIPMENT REQUIRED:
DPSK modulations and demodulation trainer kit
CRO
BNC probes
Patch cards
BLOCKDIAGRAM:
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THEORY:
The differentially phase shift keying makes use of a technique designed to get around
the need for a coherent reference signal at the receiver. In the differential phase shift keying
scheme the phase reference for the demodulation is derived from the phase of the carrier
during the preceding signaling interval and the receiver decodes the digital information‟s
based on the differential phase. If the channel perturbations and other disturbances are slowly
varying compared to the bit rate than the phase of the RF pulse are affected by the same
manner, thus preserving the information contained in the phase difference. If the digital
information had been differentially encoded in the carrier phase the transmitter the decoding
at the receiver can be accomplished without a coherent load oscillator signal.
MODULATION:
The differential signal to the modulating signal is generated using an Exclusive OR
gate and 1-bit delay circuit (It is shown in figure). CD4051 is an analog multiplexer to which
carrier is applied with and without 1800 phase shift (created by using an operational amplifier
connected in inverting amplifier mode) to the two inputs of the ICTL084. Differential signal
generated by Ex-OR gate (IC7486) is given to the multiplier‟s control signal input.
Depending upon the level of control signal, carrier signal applied with or without phase shift
is steered to the output.1- bit delay generation of differential signal to the input is created by
using a D- flip-flop (IC7474).
DEMODULATION:
During the demodulation, the DPSK signal is converted into a +5V Square Wave
signal using a transistor and is applied to one input of an EX-OR gate. To the second input of
the gate, carrier signal is applied after conversion into a +5 V signal. So the EX-OR gate
output is equivalent to the differential signal of the modulating data. This differential data is
applied to one input of an EX-OR gate and to the second input, after 1-bit delay the same
signal is given. So the output of this Ex-OR gate is modulating signal.
PROCEDURE:
1.
2.
3.
4.
Switch ON' the experimental board.
Check the carrier signal and the data generator signals initially.
Apply the carrier signal to the carrier input of the DPSK modulator and give
the data generator to the data input of DPSK modulator and bit clock output to
the input of DPSK modulator.
Observe the DPSK modulating output with respect to the input data generator
signal of dual trace oscilloscope (observe the DPSK modulating signal on
channel l and the data generator signal on channel 2).
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5.
6.
Give the output of the DPSK modulator signal to the input of demodulator,
give the bit clock output to the bit clock in put to the demodulator and also
give the carrier
output to the carrier input of demodulator.
Observe the demodulator output with respect to data generator signal
(modulating signal)
MODEL GRAPH:
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RESULT:
Hence generated the differential binary signal and differential phases shift keyed
signal at the modulator end and recovered the binary signal from the received DPSK signal.
VIVA QUESTIONS:
1.
2.
3.
4.
5.
6.
What is the difference between PSK&DPSK?
What is the band width requirement of a DPSK?
Explain the operation of DPSK detection?
What are the advantages of DPSK?
What is meant by differential encoding?
In Differential encoding technique which type of logic gates are used?
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6(a) determine modulation using DPSK?
(b)determine demodulation using DPSK?
(c)determine DPSK demodulation for data generator signal.
(d)determine DPSK modulation for data generator signal.
AIM:
To study the various steps involved in generating the differential binary signal and
differential phases shift keyed signal at the modulator end and recovering the binary signal
from the received DPSK signal.
EQUIPMENT REQUIRED:
DPSK modulations and demodulation trainer kit
CRO
BNC probes
Patch cards
BLOCKDIAGRAM:
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MODULATION:
The differential signal to the modulating signal is generated using an Exclusive OR
gate and 1-bit delay circuit (It is shown in figure). CD4051 is an analog multiplexer to which
carrier is applied with and without 1800 phase shift (created by using an operational amplifier
connected in inverting amplifier mode) to the two inputs of the ICTL084. Differential signal
generated by Ex-OR gate (IC7486) is given to the multiplier‟s control signal input.
Depending upon the level of control signal, carrier signal applied with or without phase shift
is steered to the output.1- bit delay generation of differential signal to the input is created by
using a D- flip-flop (IC7474).
DEMODULATION:
During the demodulation, the DPSK signal is converted into a +5V Square Wave
signal using a transistor and is applied to one input of an EX-OR gate. To the second input of
the gate, carrier signal is applied after conversion into a +5 V signal. So the EX-OR gate
output is equivalent to the differential signal of the modulating data. This differential data is
applied to one input of an EX-OR gate and to the second input, after 1-bit delay the same
signal is given. So the output of this Ex-OR gate is modulating signal.
PROCEDURE:
1.
2.
3.
4.
5.
6.
Switch ON' the experimental board.
Check the carrier signal and the data generator signals initially.
Apply the carrier signal to the carrier input of the DPSK modulator and give
the data generator to the data input of DPSK modulator and bit clock output to
the input of DPSK modulator.
Observe the DPSK modulating output with respect to the input data generator
signal of dual trace oscilloscope (observe the DPSK modulating signal on
channel l and the data generator signal on channel 2).
Give the output of the DPSK modulator signal to the input of demodulator,
give the bit clock output to the bit clock in put to the demodulator and also
give the carrier
output to the carrier input of demodulator.
Observe the demodulator output with respect to data generator signal
(modulating signal)
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MODEL GRAPH:
6(a) Generation of DPSK modulation:
(b)Generation of DPSK demodulation:
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(c)Generation of DPSK demodulation o/p with respect to the data generator signal:
(d)Generation of DPSK modulation o/p with respect to the differential data generator
signal:
RESULT:
Hence generated the differential binary signal and differential phases shift keyed
signal at the modulator end and recovered the binary signal from the received DPSK signal.
VIVA QUESTIONS:
1. What is the difference between PSK&DPSK?
2. What is the band width requirement of a DPSK?
3. Explain the operation of DPSK detection?
4. What are the advantages of DPSK?
5. What is meant by differential encoding?
6. In Differential encoding technique which type of logic gates are used?
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