EC 16L2 COMMUNICATION LABORATORY I

Instructions for students.

1. Be punctual to the lab

2. You are not supposed to leave the lab in between. Leave the lab only after
getting permission from your lab in charge, after completing experiment.
3. Be ready to do at least two experiments.
4. Your staff will be evaluating you daily. So prepare well.
5. Submit your rough and fair records regularly. Remember that will help to
score marks for internals.
6. Maintain the records neatly.
7. Extra credits will be awarded to students who are punctual and regular.
8. Extra credits will be awarded for students who complete lab experiments
before time.
9. Get the signature for the rough record within a week. Submit the records
before 4.00pm
10. For each graph, write the scale properly.
11. Write the specifications of active components in your rough and fair
records, even if you are using it for 100 th time.
12. Submit the fair records in next class.
13. Remember it is your duty to submit and get it signed, no one will be asking
you.
14. Last date to get your fair record certified will be announced by the staff
in charge. This will not be postponed under any circumstances.
15. Everybody is expected play a part while doing experiments. Remember
you have marks for that.
16. After getting your record certificated do not waste your time in
beautification of fair record. But utilize that time by preparing for viva.
17. Sometimes for completing lab on time. Extra classes will be arranged on
Saturdays. You are expected to be present. You absence on those days will
be taken seriously.

Internal split up : Attendance , fair record , Test ,

Continuous evaluation : 30 (include performance, Rough record & viva )
 EC 16L2 COMMUNICATION LABORATORY I

1. Active Filters - Band Pass, Band reject (II order Butterworth)-Magnitude and phase
characteristics, Qfactor.
2. Amplitude modulation - frequency modulation
3. Balanced modulator
4. PLL characteristics and demodulation using PLL
5. AM generation and demodulation using OP-AMPs and IC multipliers
6. PAM .modulator and demodulator
7. PWM modulator and Demodulator
8. PPM modulator and Demodulator.

SPICE: Simulation of experiments listed above using CAD tools (It is desirable to
carry out the implementation followed by simulation)

Note : 50 % marks is earmarked for continuous evaluation, and 50 % marks for end
semester examination to be assessed by two examiners .A candidate shall secure a
minimum of 50 % marks in the aggregate and 50 % minimum in the end semester
examination for a pass.
 1. SECOND ORDER ACTIVE BAND PASS & BAND ELIMINATION
FILTERS

Aim :
To design and set up a second order active Butterworth filter for a cut- off
frequency of . KHz. For a Q factor 10 and a second order active Notch filter for a
cut off frequency of KHz.. To plot the frequency response find the bandwidth,
Components and Equipments Required:
Opamp IC 741,capacitors, resistors, function generator, CRO, dual power
supply, breadboard, connector wires

Circuit diagram

Active BPF

Active Notch filter

Ideal frequency response

Active BPF

Active Notch filter

(use semilog sheet to plot the waveforms)

Theory:
Refer standard text books for Opamps.

Design Equation
Active BPF

Af < 2 Q 2
Fc=
Assume Q , Af =1.5 , C1= C2 = ----
R1 = Q / (2 fc C Af)
R3 = Q/ (2 fc C ( 2Q 2- Af))
Rcom =R3
R2 = Q / ( Fc C)

Active Notch filter

Fo = 1 /(2 RC)
Asssume C Find R
Take Af = 1.5
Find Rf and R1.

Tabulation
For active BPF
Vin constant =
Sl No Freqency in Hz Out put Voltage in volts Gain in Db
 For active Notch filter
Vin constant =
Sl No Freqency in Hz Out put Voltage in volts Gain in Db

Details to be added :
Pin diagram of IC 741 & design parameters. Refer necessary data sheets

Procedure:
Make connections as per circuit diagram. Set up the input voltage in
function generator .Keep this constant for the entire experiment.
Vary the input frequency and note the change in output voltage for each case. Check the
condition of input voltage. Tabulate the readings find. Gain in each case. Plot the
frequency response.

Repeat the same for Active notch filter.

From the response curve find the band width, centre frequency and Q of the circuit.

Result:
A second order Active BPF and active notch filter (Butterworth) was set up and
their frequency response is plotted.
 2.AM MODULATION & DETECTION

Aim :
To design and set up an amplitude modulation circuit using collector modulation
scheme for a carrier frequency of ------KHz.
To design and set up a detector circuit to detect this AM wave.

Components and equipments required

Transistor BF 194, Diode OA 79 , IFT, resistors, capacitors, Function
generator, CRO.

Circuit diagram

Am detector
Design equation :

Assume VCC = 10 V. Ic ( from Data sheet ) Vce = 50% of Vcc .hfe = ( from data
sheet
Re = VCE /Ic
Ib =Ic / hfe
10 Ib flows through R1 and 9 Ib flows through R2
Find R1 and R2
From Equation fc= 1/(2 LC)
Assume C & find L. and tune IFT accordingly.
Or for known L design C.
C2 = 2.2 nF
C r = 0.01 F
R= 4.7 K
For by passing.

Design for Am detection

RC >>Time period of Rf
Rc= 100 T
Assume C find R or assume R find C

Waveforms

Transfer Curve of AM wave

Lead diagram of BF194 : refer data sheet

Specifications of BF 194, OA 79, IFT etc

:refer data sheets

Brief theory

Without the signal in AFT the circuit acts as a Hartley oscillator. When we apply an
AF the AF signal gets added along with Vcc and the amplitude of the output varies
according to the AF signal. The RF frequency is determined by the the value of the
inductance in primary coil of IFT and the capacitance connected in parallel to it.

Procedure

Check the inductance of primary coil of IFT using LCR meter. And tune it
to necessary value. Make connections as per circuit diagram. Before applying AF
signal check whether you are getting an
Rf signal. Note its frequency and amplitude. Give

Af . Note the AM signal . Draw the waveform. Calculate the modulation index.m

Modulation index = (Vmax V min)/ (Vmax + V min)

Result :

An Am modulator and detector circuit has been set up and the modulation index
is calculated.
RF obtained =
Modulation index =
 3.RF OSCILLATORS

Aim:
To design and set up a crystal oscillator for a frequency of _______MHz.
To design and set up a Colpitts Oscillator for a frequency of ---KHz
And plot the waveforms.

Components and Equipments required

Dc power supply, CRO, JFET BFW 10, BJT BF 194,RFC, Crystal , resistors,
capacitor, inductors.
Circuit diagram
Colpits oscillator

Vcc

Crystal oscillator
Design
For Colpits Oscillator
Assume Vcc=10 V
Ic 1mA(typical)
Hfe (find from data sheets)
Vc = 50% of Vcc,
f=
Vre = 0.1 Vcc
Re =
Rc = (Vcc Vce Vre )/Ic
Vbe+ Vre = Ib. R2
Find R2
R1 = Vcc Vr2 / 10 I b

X ce < Re /10
Find Ce
From eqn F =1 / (2 LC)
C1 =C2 = assume the value and find L

For Xtal oscillator

Assume Vcc= 10 V , Id = 2 mA
VRs = 10% of Vcc
Rs = VRS /Id
Xcs < Rs /10
Find Cs
Take Rg =1 M ohms

Lead diagram of Bf 194 and BFW 10 (refer data sheets)

Specifications ( refer data sheets)

 Theory :
Refer your circuit text books

Procedure.
For both circuits.
Make the connections as per circuit diagram. Check the Dc
conditions. After switching the power supply. Connect to oscilloscope. View thw
waveform. Measure its amplitude and frequency.

Result :

The circuits of Crystal oscillator and Colpitts oscillator are set up and
waveforms are plotted.

Sl no Type of Oscillator Theoretical frequency Obtained frequency

1 Colpitts Oscillator
2. Crystal oscillator
 4.Intermediate frequency Amplifier
Aim
To design and set up an IF amplifier for a frequency response of $53 KHz and
to plot the frequency response. To determine the lower and upper cut-off frequencies,
centre frequency and to find Q and bandwidth from the frequense response curve.

Componets and equipments required:

Transistor BF 194, IFT function generator, oscilloscope, Resistors,
capacitors,

Circuit diagram

Ideal frequency response

Lead digram of BF 194

 Specifications

Tabulations

Voltage Vin const = V

F in Khz Vout Gain in Db

Theory:

Write about If amplifiers and single tuned amplifiers.

Procedure:

Connections are made as per the circuit diagram. . Check the conditions
of amplifier . apply the input. Keep the input voltage constant. Vary the frequency. Note
output voltage and calculate gain in each case. Plot the response. (Use ordinary graph
sheets). Find Q, Band width etc.

Result :

An IF amplifier circuit was designed and set up and Fh, Fl, Fc bandwidth etc are found
after plotting the response curve..
 5. Pulse Amplitude Modulation and detection

Aim :
To design and set up a Pam modulator and detector and to plot waveforms.

Componts and equipments required :

JFET BFW 10 , Resistors Capacitors, oscilloscope, DSO , Function generator.

Circuit diagram and wave forms

PAM detector
Design
T = I/ Fc
RC > 16 T
Assume any one find other.

Specifications of BFW 10
( refer data sheet.)

Theory.

Refer text books

Procedure.

Connections are made as per circuit diagram. Give the inputs note the
waveforms, plot it. Observe the output PAM and detected one.

Result:

The circuit for Pam and its detector is set up and waveforms are noted.
 6.Frequency synthesizer using PLL

Aim
To design and set up a circuit for frequency multiplication using PLL . for a
multiplication factor K.
To find the lock and capture range and centre frequency of given PLL IC

Componts and equipments required

PLL IC 4046, power supply, resistors, breadboard, wires, resistors, capacitors

and inductors, function generator

Circuit diagram
To find Lock and capture range

Circuit for Frequency synthezer

Pin no. 14 i/p square wave.

Design

Can be changed according to the counter designed using 7490.

Theory:

Refer LIC text books

Include the block schematic
Procedure
Set up the circuit as per the circuit diagram. Obtain the lock and capture range of
the PLL. Adjust the i/p frequency. Obtain the waveforms. So that output frequency should
be in lock range. Plot the waveforms. ( for both i/p and o/p waveforms, X axis must have
same scale.)

Result.
Frequency synthesizer circuit using PLL is set up.
 7.Mixer Circuit

Aim:
To design and set up a frequency translator circuit and to measure the output for
various input frequencies .IF assumed is ----- KHz.

Components and Equipments required :

IFT, BF 194 BJT, Resistors, capacitors, DSO, Function generators, wires, bread board,
Power supply

Circuit Diagram

Ideal Frequency response

Specification and lead diagram of BF 194

Tabulation
Addition
VLO= V constant F LO = KHz constant V Rf = V Constant
Frequency Vout in V Gain in db

Subtraction
VLO= V constant F LO = KHz constant V Rf = V Constant
Frequency Vout in V Gain in db

Theory:
Refer your communication Engg Text books

Procedure.

Connect as per the circuit diagram. Keep the frequency and input voltage of the function
generator chosen as Local oscillator constant. Note the values. Note the value of input
voltage of function generator chosen as RF signal. Take two sets of readings such that in
Case 1 : F RF + F LO = IF chosen (addition). Vary the RF signal frequency note the output
voltage.(Note that the output voltage increases as the frequency increases, you will get the
maximum output voltage in this case at the above condition. The output voltage slowly
decreases after that.)
Case 2 : F RF - F LO = IF chosen (subtraction) : Reeat the same procedure. (You will find
the same)
Tabulate the readings. Plot the graph.

Result:

A mixer circuit is set up and its frequency response is plotted.

 8.Time Division Multiplexing
Aim:
To design and set up a circuit for Time Division Multiplexing and note the
waveforms

Components and Equipments Required:

74153 Mux IC, IC7490, breadboard, wires, signal generator,
Oscilloscope

Circuit diagram

Pin details of IC 74153 & 7490

Theory:

Refer text books

Procedure:
Test each ICs before wiring. . set up the circuits. Set the cock frequency at
a very low frequency. Give different types of input signals to pins 3,4,5,6, of Mux
IC74153. Note the out put waveform.

Result:
TDM circuit was set up and it waveforms are noted.
 Pulse Width Modulation and Pulse Position Modulation
Aim :
To design and set up a circuit to obtain Pulse width and Pulse Position
modulated waveforms.
Components and Equipments Required:
ICs time Ic, Lm 311 comparator, Resistors, Capacitors, Diode
1N4007,Wires, Power supply, CRO, Function generator etc.

Circuit diagram

Design condition:

Design an Astable mutivibrator using Timer IC .

RC circuit to obtain PPM design it as a differeniator.

Waveforms
Pinout of LM 311 & Timer IC

Specifications of ICs and diode 1n4007

Brief Theory:
Timer IC is wired in Astable mode. The threshold signal is compared with the
modulating signal. LM 311 is preferred because of its high slew rate. By differentiating
PWM wave form PPM wave is obtained.

Procedure.
Make connections as per circuit diagram. Check whether you are
getting the wave form of charging and discharging of capacitor. Draw the wave form.
Set the modulating signal. Give the necessary Offset voltage to modulating signals, so that
we get a compared output from LM311.Note the waveform. Draw this waveform over the
discharge wave form as shown .Observe the PWM and PPM output. Draw comparisons
and draw PPM and PWM waveforms.

Result:
The circuit for Pulse width and Pulse position Modulation was set up and the output
waveforms are plotted.
 AGC and delayed AGC

Aim:
To design and set up circuits for simple and delayed AGCs and to note the
change in output voltage when modulating voltage increases.

Components and Equipments Required

Diodes OA 79, Resistors, capacitors, Function generators, Power
supply, Bread board, wires etc

Circuit diagram

Simple AGC

Delayed AGC
Design
Let the maximum modulating signal be % KHz
Max carrier freq = 500 KHz.
R1 C1 >> time period of RF filter
R1 C1 =100T take C1= 0.01 F find R1
R1=R2 (approximate)
R1 + R2 = Xc2 find C2
Take R3 C2 =100 T >> time period of AF.
Assume C2 = 0.01 F . Find R3.
Assume C3 =0.01 F
Assume C4 = 100pF. And R4 = 10 K pot
R5 = 500 K and C5= 20 F

Ideal graph
Tabulations
Simple AGC
Input voltage Output voltage

Delayed AGC
Input voltage Output voltage

Theory:
Refer text books for communication Engineering

Procedure.

Connect as per circuit diagram. lowly increase the modulating signals. Note
the change in AGC output. Tabulate the reading. Repeat the same for delyed AGC. Plt the
graph.
Result.
Simple and Delayed AGC circuits are set uo and the variations in output when
there is change in modulating signal is noted.
 FM Modulation and Detection using PLL

Aim:
To design and set up Fm Modulation and Detection using PLL ICs.

Components and Equipments Required:

PLL IC, Capacitors, Oscilloscope, Function Generator, resistors, Bread board,

Connector wires

Circuit diagram

Waveforms
Pin details of IC 4046
(refer data sheet)

Specifications of IC4046
(refer data sheets)

Theory

Refer LIC text books

Procedure:
Find the lock& capture range of each IC and then do the connections. Give the input
modulating signal. Note it. Plot the output waveforms of each ICs

Result:
AN FM modulator & detector crcuits are set up and the waveforms are plotted.
Suggested Extra experiments.
No need to write in Fair records. But do as lab assignments

1. PWM using Timer I C only

2. Balanced modulator
3. Emitter modulation (AM)
4. AM modulation using FET.
5. Passive filters m-derived and constant K type

Do the design yourself. Can ask your teacher's help. At least do three among these.