‫كتاب تجارب‬

‫معمل االتصاالت‬
 ‫أوال‪ :‬بيانات المعمل األساسية‬

‫• اسم المعمل‪ :‬معمل االتصاالت‬

‫• القسم العلمي‪ :‬قسم هندسه االتصاالت وااللكترونيات‬

‫• المشرف‪ :‬ا‪.‬د‪/‬شريف السيد كشك‬

‫• مهندس المعمل‪ :‬د‪ /‬مجدي فاضل‬

‫• أمين المعمل‪ :‬أ‪ /‬سارة محمود‬

‫• تليفون‪1277 :‬‬

‫• الموقع‪ :‬الدور الثالث‪ ،‬المعامل البحرية أمام صاالت عمارة‬

‫‪2‬‬
‫• مساحة‪ 124.75 :‬م‬
 :‫ قائمه باألجهزة والمعدات الموجودة بالمعمل‬:‫ثانيا‬
Serial number ‫العدد‬ ‫الجهاز‬
1042 2 40 HZ oscilloscope CDS
Model TP8102 7 Function generator
5052 3 Function generator
1232 7 Digital multimeter
300223 1 3/8 logic analog model
- 1 Universal counter
- 10 Micro electronic kit
2012 2 Function generator
- 1 Micro trainer model
2597 1 Transmitter model
MC188 1 Field meter model
- 1 ‫جهاز قياس هرموني متغير‬
2090 1 Power supply
1230 1 Digital storage oscilloscope
Analog digital communication
3xBue 1
computing
1008 1 ‫جهاز توليد ذبذبات‬
1082 1 Ac power supply
3230 1 Function generator
- 1 Feedback communication system
 :‫ قائمه بالتجارب التي تؤدي داخل المعمل‬:‫ثالثا‬
‫الغرض منها‬ ‫التجربة‬ ‫م‬
Understanding the principle of amplitude
modulation(AM).
1. Designing an amplitude modulator usingMC1496. AM Modulators 1
2. Measuring and adjusting an amplitude modulator
circuit
1. Understanding the principle of amplitude
demodulation.
2. Implementing an amplitude demodulator with
AM Demodulators 2
diode.
3. Implementing an amplitude demodulator with a
product detect
1. Studying the operation and characteristics of
varactor diode.
2. Understanding the operation of voltage
FM Modulators 3
controlled oscillator.
3. Implementing a frequency modulator with
voltage-controlled oscillator.
1. Studying the principle of phase-locked loop.
2. Understanding the characteristics of the
PLLLM565.
FM Demodulators 4
3. Demodulating FM signal using PLL.
4. Demodulating FM signal using FM to AM
conversion discriminator
To construct a two stage R-C Coupled amplifier, to
RC-Coupled
study the frequency response of the amplifier and to 5
Amplifier
determine the bandwidth.
The ability to diagnose and cure problems in a
systematic manner is an exceptionally valuable skill.
In PHY2028 students are given a heap of components, a Troubleshooting
6
breadboard, and measuring equipment. This virtually Amplifier
guarantees that nothing will work first time, and
students are forced to develop troubleshooting skills.
1. To construct a series-fed transistor Hartley
oscillator.
2. To change frequency determining components
oscillators-and-
and observe variations infrequency. 7
multi-viberators
3. To measure any harmonic frequencies present.
Hart- ley oscillator is used for varying frequencies over
large ranges, as in local oscillators of radio receivers.
 ‫رابعا الخدمات المجتمعية التي يؤديها المعمل‪:‬‬

‫‪ .1‬عدد المستفيدين من المعمل‪ :‬طالب قسم هندسه االتصاالت وااللكترونيات (‪4‬‬

‫دفعات)‪ ،‬طالب قسم برنامج هندسة االتصاالت (‪ 4‬دفعات)‪ ،‬طالب الدراسات‬

‫العليا‬

‫‪ .2‬الجهات التي تتعامل مع المعمل‪ :‬قسم هندسه االتصاالت وااللكترونيات‬

‫‪ .3‬الدخل السنوي‪ :‬ال يوجد‬

‫‪ .4‬الجهات الممولة ألنشطه المعمل‪ :‬قسم هندسه االتصاالت واإللكترونيات‬

‫والبرامج الخاصة‬

‫‪ .5‬المشاريع التنافسية التي يشارك فيها المعمل‪ :‬مشاريع تخرج لطالب قسم‬

‫هندسه االتصاالت وااللكترونيات دفعة سنه رابعة‬

 ‫خامسا الخدمات الطالبية‪:‬‬

‫‪ .1‬عدد المستفيدين من المعمل‪ :‬طالب قسم هندسه االتصاالت وااللكترونيات (‪4‬‬

‫دفعات)‪ ،‬طالب قسم برنامج الهندسة االتصاالت (‪ 4‬دفعات)‪ ،‬طالب الدراسات‬

‫العليا‬

‫‪ .2‬األقسام العلمية المستفيدة من المعمل‪ :‬قسم هندسه االتصاالت وااللكترونيات‬

‫(‪ 4‬دفعات)‪ ،‬قسم برنامج الهندسة االتصاالت (‪ 4‬دفعات)‬

‫‪ .3‬الفرق الدراسية التي تستخدم المعمل‪ :‬طالب قسم هندسه االتصاالت‬

‫وااللكترونيات (‪ 4‬دفعات)‪ ،‬قسم برنامج الهندسة االتصاالت (‪ 4‬دفعات)‬

‫‪ .4‬الرسائل العلمية‪ :‬رسائل علميه خاصة بالهندسة االتصاالت‬

‫‪ .5‬الدورات‪ :‬ال يوجد‬

‫‪ .6‬الدراسات العليا‪ :‬يوجد محاضرات خاصة بتدريس مواد تمهيدي ماجستير بقسم‬

‫هندسه االتصاالت وااللكترونيات خاصة بتصميم الشبكات‬

‫‪ .7‬المسابقات‪ :‬ال يوجد‬

‫‪ .8‬األنشطة‪ :‬مشاريع تخرج خاصة بطالب قسم هندسه االتصاالت وااللكترونيات‬

 EXPERIMENT 1

AM MODULATORS

1.1EDUCATIONAlOBJECTIVES:
❖ Understanding the principle of amplitude modulation(AM).

❖ Understanding the waveform and frequency spectrum of AM signal

and calculating the percent of modulation.

❖ Designing an amplitude modulator usingMC1496.

❖ Measuring and adjusting an amplitude modulator circuit

1.2REFERENCeREADINGS:
❖ Kennedy G., Electronic Communication Systems, McGraw-Hill,
Third Edition,1994,

❖ D. Roddy and J. Coolen, Electronic Communications, Prentice Hall

of India,1995.

❖ Young Paul H., Electronic Communication Techniques, Merrill

Publishing Company, Third Edition1990.
❖ Haykin Simon, Communication Systems, John Wiley, 4th Edition,
2001.

1.3 BACKGROUND INFORMATION:

Modulation is the process of impressing a low-frequency intelligence
signal onto a high-frequency carrier signal. Amplitude Modulation
(AM) is a process that a high-frequency carrier signal is modulated by
a low- frequency modulating signal (usually an audio). In amplitude
modulation the carrier amplitude varies with the modulating amplitude,
as shown in Fig.1-1.
 If the audio signal is Amcos(2πfmt) and the carrier signal is
Accos(2πfct), the amplitude-modulated signal can be expressed by

(1-1)
Where
ADC = dc level
Am = audio amplitude
Ac = carrier amplitude
fm = audio frequency
fc = carrier frequency
m = modulation Index or depth of modulation = Am /ADC

Fig.1-1 Amplitude modulation waveforms

 Rewriting Eq. (1-1), we obtain

(1-2)
The first term on the right side of Eq. (1-2) represents double sideband signal and the
second term is the carrier signal. According to Eq. (1-2), we can plot the spectrum of AM
modulated signal as shown in Fig. 3-2. In an AM transmission the carrier frequency and
amplitude always remain constant, while the side bands are constantly varying in
frequency and amplitude. Thus, the carrier contains no message or information since it
never changes. This means that the carrier power is a pure dissipation when transmitting
an AM signal. Thus, the transmitting efficiency of amplitude modulation is lower than that
of double-sideband suppressed carrier (DSB-SC) modulation, but the
amplitude demodulator circuit is simpler.

Fig.3-2 Spectrum of AM signal

The m in Eq. (3-1), called modulation index or depth of modulation, is an important
parameter. When m is a percentage, it is usually called percentage modulation. It is defined
as:

(1-3)
It is difficult to measure the ADC in a practical circuit so that the modulation index is
generally calculated by

(1-4)
Where Emax=Ac+Am and Emin=Ac-Am, as indicated in Fig. 1-1.
As mentioned above, audio signal is contained in the side bands so that the
greater the sideband signals the better the transmitting efficiency. From Eq. (1-2), we
can also find that the greater the modulation index, the greater the sideband signals and the
better the transmitting efficiency. In practice, the modulation index is usually less or equal
to 1; if m > 1, it is called over modulation.
A comparison between various balanced modulator outputs under various input
frequency conditions
In the following experiments we will implement an AM modulator using a monolithic
balanced modulator MC1496. According to different input signal frequencies, the
MC1496 may be used as a frequency multiplier, an AM modulator, or a double sideband
suppressed carrier (DSB-SC) modulator. Table 1-1 shows the summary of different input,
output signals and circuit characteristics.
Fig. 1-3 shows the internal configuration of MC1496. The differential amplifier Q5 and
Q6 is used to drive the differential amplifiers Q1Q2 andQ3Q4. The constant-current source
generator Q7 and Q8 provides the differential amplifier Q5 and Q6 with a constant
current. Overall gain of MC1496 can be controlled by externally connecting a resistor
between pins 2 and 3. For AM modulation, the modulating signal should be applied to
pins 1 and 4, and the carrier to pins 8 and 10. The bias current to pin 5 is commonly
provided by connecting a series resistor from this pin to the power supply.

Fig.3-3 MC1496 internal circuit

`
Fig. 1-4 shows an AM modulator circuit, whose carrier and audio signals are single-ended
inputs, carrier to pin 10 and audio to pin 1. The gain of entire circuit is determined by the R8
value. The R9 determines the amount of bias current. Adjusting the amount of VR1 or the
audio amplitude can change the percentage modulation.

Fig.3-4 Amplitude modulator using MC1496

1.4 EQUIPMENTREQUIRED
1. ModuleKL-92001
2. ModuleKL-93002
3. Oscilloscope
4. Spectrum Analyzer
5. RF Generator
 EXPERIMENT2
AM DEMODULATORS

2.1 EDUCATIONAl OBJECTIVES:

❖ Understanding the principle of amplitude demodulation.
❖ Implementing an amplitude demodulator with diode.
❖ Implementing an amplitude demodulator with a product detector.

2.2 REFERENCe READINGS:

▪ Kennedy G., Electronic Communication Systems, Mc GRW-Hill, Third
Edition, 1994,
▪ D. Roddy and J. Coolen, Electronic Communications, Prentice Hall of
India,1995.
▪ Young Paul H., Electronic Communication Techniques, Merrill
Publishing Company, Third Edition 1990.
• Haykin Simon, Communication Systems, John Wiley, 4th Edition, 2001.

2.3 BACKGROUNd INFORMATION:

A demodulation process is just the opposition of a modulation process. As noticed
in Chapter 3, an AM signal is a modulated signal that is high- frequency carrier
amplitude varied with low-frequency audio amplitude for transmission. To recover
the audio signal in receiver, it is necessary to extract the audio signal from an AM
signal. The process of extracting a modulating signal from a modulated signal is
called demodulation or detection. It is shown in Fig.2-1.
In general, detectors can be categorized into two types: synchronous and
asynchronous detectors. We will discuss these two types of AM detectors in the
rest of this chapter.

Fig.2-1 illustration of an amplitude demodulation

• Diode Detector
Since an AM modulated signal is the signal that the carrier amplitude varies
with the modulating amplitude, a demodulator is used to extract the original
modulating signal from the AM signal.

Fig.2-2 Block diagram of a rectified demodulator

The block diagram of diode detector, shown in Fig. 2-2, is a typical

asynchronous detector. The AM modulated signal including both positive- half
and negative-half envelope waves is applied to the input of the rectifier. The
rectified output signal is the positive half envelope plus a dc level and is fed into
a low-pass filter whose output is the original modulating signal with dc level. Then the
modulating signal will be recovered by removing the dc voltage.
Fig. 2-3 shows a practical diode detector circuit. The components R1, R2, R3,
 R4, U1 and U2 constitute two inverting amplifiers connected in cascading to
offer a proper gain for the AM signal. The amplified AM signal is rectified by D1
diode and then fed into the input of the low-pass filter constructed by C2, C3 and
R5. The output signal of low-pass filter is the positive-half envelope with a dc
level. The capacitor C4 is used to pass the ac components while blocking the dc
component.

Fig.2-3 Diode detector circuit

• Product Detector
Demodulation for AM signal can be also accomplished with the balanced
modulator discussed before. Such demodulator is called synchronous detector
or product detector. Fig. 2-4 provides the internal circuit of MC1496 balanced
modulator. See the discussion in Chapter 3 for details. If xAM(t) represents the
AM signal and xc(t) is the carrier, and are expressed by

(2-1)
 (2-2)
If these two signals are connected to the inputs of balance demodulator, then the
output of balance demodulator will be

(2-3)

Where k is the gain of balanced modulator. The first term on the right side of Eq.
(2-3) represents dc level, the second term is the modulating signal, and the third
term is the second-order harmonic signal. To recover the modulating signal, the
intelligence must be extracted from the AM signal xout(t).
 Fig. 2-4 MC 1496 internal circuit

Fig. 2-5 shows the product detector circuit. The VR1 controls the input level of
the carrier signal. The output signal from the MC1496 pin 12 is expressed by Eq.
(2-3). The low-pass filter constructed by C7, C9 and R9 is used to remove the
third term, which is the second-order harmonic signal in the AM modulated signal.
The first term of Eq. (2-3) is the dc level that can be blocked by the capacitor
C10. The amplitude demodulated output signal can be given by

(2-4)
Eq. (2-4) represents the audio signal. In other words, the product detector has
extracted the audio signal from the AM signal.
From the discussion above, we can conclude that the diode detector is an
asynchronous detector whose circuit is simple but quality is bad. The product
detector is a synchronous detector whose quality is excellent but the circuit is
more complicated and the carrier signal must exactly synchronize with the AM
signal.

Fig. 2-5 Product detector circuit

2.4 EQUIPMENT REQUIRED

1. Module KL-92001
2. Module KL-93002
3. Oscilloscope
4. RF Generator
 EXPERIMENT3
FM MODULATORS

3.1 EDUCATIONAl OBJECTIVES:

❖ Studying the operation and characteristics of varactor diode.
❖ Understanding the operation of voltage controlled oscillator.
❖ Implementing a frequency modulator with voltage-controlled oscillator.

REFERENCe READINGS:
❖ Kennedy G., Electronic Communication Systems, McGRW-Hill,
Third Edition,1994,
❖ D. Roddy and J. Coolen, Electronic Communications, Prentice Hall
of India,1995.
❖ Young Paul H., Electronic Communication Techniques, Merrill
Publishing Company, Third Edition1990.
❖ Haykin Simon, Communication Systems, John Wiley, 4th Edition,
2001.

3.2 BACKGROUNd INFORMATION:

• Principle of Frequency Modulation Operation:
Frequency modulation (FM) is a process in which the carrier frequency is
varied by the amplitude of the modulating signal (i.e., intelligence signal).
The FM signal can be expressed by the following equation:
(3-1)
If x(λ)=Amcos(2πfmλ), then

(3-2)
Where
θ (t) = instantaneous modulated frequency
fc = carrier frequency
FM = modulating frequency
β = modulation index = Am (fΔ /FM)
The frequency of FM signal xFM(t) may be expressed as

(3-3)

From Eq. (3-3) we can find that the frequency of frequency modulated
signal occurs frequency deviation from the center frequency of the carrier
when the intelligence amplitude is variation.

• Varactor Diode:
The varactor diode, sometimes called tuning diode, is the diode whose
capacitance is proportional to the amount of the reverse bias voltage across p-n
junction. Increasing the reverse bias voltage applied across the diode decreases
the capacitance due to the depletion region width becomes wider.
Conversely, when the reverse bias voltage decreased, the depletion region width
becomes narrower and the capacitance increased. When an ac voltage is applied
across the diode, the capacitance varies with the change of the amplitude.
 Fig. 3-1 Relationship between reactor diode and capacitor

A relationship between a varactor diode and a conventional capacitor is shown

in Fig. 3-1. In fact, a reverse-biased varactor diode is similar to a capacitor.
When a p and n semiconductors combined together, a small depletion region is
formed because of the diffusion of minority carriers. The positive and negative
charges occupy n and p sides of junction, respectively. This just likes a
capacitor. The amount of internal junction capacitance can be calculated by the
capacitance formula

(3-4)
Where
ε= 11.8 ε0 = dielectric constant
εo = 8.85×10-12
A= cross area of capacitor
d = width of depletion region
From the formula above, we know that the varactor capacitance is inversely
proportional to the width of depletion region (or the distance between plates) if
the area A is constant. Therefore, a small reverse voltage will produce a small
depletion region and a large capacitance. In other words, an increase in reverse
bias will result in a large depletion region and a small capacitance.

Fig.3-2 the equivalent circuit of varactor diode

A varactor diode can be considered as a capacitor and resistor connected in

series as shown in Fig. 3-2. The CJ is the junction capacitance between p and n
junctions. The Rs is the sum of bulk resistance and contact resistance,
approximately several ohms, and it is an important parameter determining the
quality of varactor diode.
Tuning ratio (TR) is defined as the ratio of the capacitance of varactor diode at
the reverse voltage V2 to that at another reverse voltage V1, and can be
expressed by

(3-5)
Where
TR = tuning ratio
CV1 = capacitance of varactor diode at V1
CV2 = capacitance of varactor diode at V2
The 1SV55 varactor diode is used in our experiments and its
major characteristics are
C3V = 42 pF (capacitance of varactor diode at 3V)
TR = 2.65 (at 3V →30V)
 • Frequency Modulator Based on MC1648VCO:

In our experiments we will implement the frequency modulator with MC1648

VCO chip shown in Fig. 3-3. Basically, this circuit is an oscillator and the
tuning circuit at input end determines its oscillating frequency. In this circuit,
capacitors C2 and C3 are the bypass capacitors for filtering noise. When
operating at a high frequency (for example 2.4 MHz), the capacitive reactance
of these two capacitors are very small and can be neglected for practical
purposes.
Therefore, an ac equivalent circuit of tuning tank, shown in Fig. 3-4, is a
parallel LC resonant circuit. The C can be considered as the capacitance of
1SV55 (Cd) and the input capacitance of MC1648 (Cin) connected in parallel.
The value of Cin is approximately 6 pF. If we neglect the spray capacitance,
the oscillating frequency can be calculated by the formula

(3-6)

Fig.3-3 MC1648 FM modulator circuit

 As mentioned above, the capacitance Cd of varactor diode D1 varies with the
amount of its reverse bias voltage. According to Eq. (3-6), we know that the
change of Cd value will cause the change of oscillating frequency. In the
circuit of Fig. 3-3, a small dc bias will produce a large Cd value and a low
frequency output. On the other hand, an increase in dc bias will result in a
small Cd value and a high frequency output. Therefore, if the dc bias is fixed
and an audio signal is applied to this input, the VCO output signal will be a
frequency- modulated signal.

Fig.3-4 AC equivalent circuit of tuning tank

• Frequency Modulator Based on LM566VCO:

The circuit of Fig. 3-5 is a frequency modulator based on voltage-controlled

oscillator (VCO) IC, LM566. If the SW1 is open, this circuit is a typical VCO
whose output frequency is determined by the values of C3 and VR1, and the
audio input voltage. If the values of C3 and VR1 are fixed, the output frequency
is directly proportional to the voltage difference between pins 8 and 5, (V8-V5).
In other words, an increase in audio input voltage (V5) causes a decrease in the
value of (V8-V5) and a decrease in the output frequency. Conversely, decreasing
the audio input voltage (V5) will cause the output frequency to increase. As
discussed above, the values of C3 and VR1 can also determine the output
frequency, which is inversely proportional to the product of VR1 and C3. That is,
the greater the VR1×C3 value the lower the output frequency.
 Fig.3-5 LM566 frequency modulator circuit

If the SW1 is closed, the voltage divider constructed by R1 and R2 provides a

dc level to the audio input (pin 5). By adjusting the VR1, we can easily tune
the VCO center frequency fo. When an audio signal is applied to the audio
input, the output frequency will generate frequency deviations around fo in the
variations of audio amplitude. Thus, a frequency-modulated signal is obtained.

3.3 EQUIPMENTREQUIRED
1. ModuleKL-92001
2. ModuleKL-93004
3. Oscilloscope
4. Spectrum Analyzer
 EXPERIMENT4
FM DEMODULATORS

4.1 EDUCATIONAl OBJECTIVES:

❖ Studying the principle of phase-locked loop.
❖ Understanding the characteristics of the PLLLM565.
❖ Demodulating FM signal using PLL.
❖ Demodulating FM signal using FM to AM conversion discriminator

4.1 REFERENCe READINGS:

❖ Kennedy G., Electronic Communication Systems, McGRW-Hill,
Third Edition,1994,
❖ D. Roddy and J. Coolen, Electronic Communications, Prentice Hall
of India,1995.
❖ Young Paul H., Electronic Communication Techniques, Merrill
Publishing Company, Third Edition1990.
❖ Haykin Simon, Communication Systems, John Wiley, 4th Edition,
2001.

4.2 BACKGROUNd INFORMATION:

Frequency demodulator, also called frequency discriminator, is a circuit,
which converts instantaneous frequency variations to linear voltage changes.
There are many types of circuit used in communication system such as FM to
AM conversion, balanced, and phase-shift discriminators and phase-locked
loop (PLL) frequency demodulator. In this experiment we will introduce the
operations of PLL frequency demodulator and FM to AM conversion
discriminator.
 • Phase-Locked Loop (PLL)operation
The PLL is an electronic feedback control system, as illustrated by the block
diagram in Fig. 4-1, of locking the output and input signals in good agreements
in both frequency and phase. In radio communication, if a carrier frequency
drifts due to transmission, the PLL in receiver circuit will track the carrier
frequency automatically.

Fig.4-1 PLL block diagram

The PLL in the following experiments is used in two different ways: (1) as a
demodulator, where it is used to follow phase or frequency modulation and (2)
to track a carrier signal which may vary in frequency with time. In general, a
PLL circuit includes the following sections:
1. Phase Detector(PD)
2. Low Pass Filter(LPF)
3. Voltage Controlled Oscillator(VCO)
The phase detector within the PLL locks at its two inputs and develops an
output that is zero if these two input frequencies are identical. If the two input
frequencies are not identical, then the output of detector, when passed through
the low-pass filter removing the ac components, is a dc level applied to the
VCO input. This action closes the feedback loop since the dc level applied to
the VCO input changes the VCO output frequency in an attempt to make it
exactly match the input frequency. If the VCO output frequency equals the
 Fig.4-2 Phase detection

A better understanding of the operation of phase detector may be obtained by

considering that the simple EXCULSIVE-OR (XOR) gate is used as a phase
detector. The XOR gate can be thought of as an inequality detector which
compares the inputs and produces a pulse output when these inputs are unequal.
The width of the output pulse is proportional to the phase error of the input
signals. As shown in Fig. 4-2, the width of the output pulse of (b) is larger than
that of (a) and is smaller than that of (c). When the output of phase detector is
applied to the input of low-pass filter, the output of low-pass filter should be a
dc level that is directly proportional to the pulse width. In other words, the
output dc level is proportional to the phase error of input signals. Fig. 4-2(d)
shows the relationship between the input phase error and the output dc level.
 Fig.4-3 Operation of frequency locking

For a further understanding of the operation of the PLL can be obtained by

considering that initially the PLL is not in lock. The VCO has an input voltage
of 2V and is running at its free-running frequency, say 1 kHz. Consider the
signals shown in Fig. 4-3. If the VCO frequency and the signal A with the
lower frequency 980Hz are applied to the inputs of the phase detector XOR,
the narrower width of output pulse will cause the low-pass filter obtaining the
smaller output voltage of 1V. This smaller voltage decreases the VCO
frequency close to the input frequency. If the VCO output frequency equals the
input frequency, lock will result. On the contrary, the higher frequency 1.2
KHz of input signal B causes the larger filter output of 3V that increases the
VCO frequency output to lock at the input frequency.

• LM565 PLL Basic Characteristics

The LM565 is a general-purpose phase-locked loop and is widely used in
frequency demodulation. In designing with the LM565, the important
parameters of interest are as follows:
1. Free-running Frequency
Fig. 4-4 shows a PLL circuit with LM565. In the absence of the input signal,
the output frequency of the VCO is called the free-running frequency fo. In
the PLL circuit of Fig. 4-4, the free-running frequency of LM565 is
determined by the timing components C2 and VR1, and can be found by

Free running frequency

Closed loop gain

where Vc = total supply voltage to the circuit = Vcc-(-Vcc) =5V-(-5V) = 10V

Fig.4-4 LM565 PLL

2. Lock Range:
Initially, the PLL is in already-locked state and the VCO is running at some
frequency. If the input frequency fi is away from the VCO frequency fo,
locking may still occur. When the input frequency reaches a specific
frequency where the PLL loses lock, the frequency difference of fi and fo is
called the lock range of the loop. The lock range of LM565 can be found by

(4-3)

3. Capture Range:
Initially, the loop is unlocked and the VCO is running at some frequency. If
the input frequency fi is close to the VCO frequency fo, unlocking may
maintain.
When the input frequency reaches a specific frequency where the PLL locks,
the frequency difference of fi and fo is called the capture range of the loop.
The capture range of LM565 can be found by

(4-4)
 Fig.4-5 Illustration of lock and capture ranges

• Frequency Demodulator Based on LM565PLL

The PLL circuit of Fig. 4-4 can be used as a frequency demodulator. When
the input signal increases in frequency, the output signal decreases in
voltage.
Inversely, if the input signal decreases in frequency, the output signal
will increase in voltage.
The VCO circuit of the LM565 is equivalent to that of the LM566. The free-
running frequency fo of the VCO is determined by the values of external
components C2 and VR1. The internal resistor 3.6 kΩ (pin7) and the external
capacitor C3 form a low-pass filter. The capacitor C4 connected between pins
7 and 8 is a frequency compensation capacitor.

• FM-to-AM Conversion Discriminator:

Fig. 4-6 shows the blocks of FM to AM discriminator. The inputs FM signal
is first converted into the AM signal by the differentiator, and then the output
AM signal is demodulated by the envelope detector to recover the original
audio signal.

Fig.4-6 Block diagram of FM-to-AM conversion discriminator

in Fig. 4-6, if input signal xFM (t) is

Then the differentiator output will be

(4-6)
From Eq. (4-6) above, the amplitude of x´FM(t) signal vary with the variation of
x(t) amplitude. Thus the x´FM(t) signal is an amplitude modulated signal. If this
AM signal passes through an envelope detector, the audio signal will be
recovered.
The circuit of Fig.4-7 is a frequency discriminator with FM-to-AM conversion
technique. The components U1, C1, C2, R1 and R2, operate as a differentiator.
The inverting amplifier U2 with a gain of - R4 /R3, and the AM peak detector
including D1, R5, R6, C4 and C5. The coupling capacitor C6 is used to block
the dc level.

Fig.4-7 FM to AM conversion discriminator circuit

 Fig.4-8 Frequency response of band pass filter

Excepting various frequency demodulators mentioned above, LC band pass

filters are popularly available in the use of frequency demodulation in
ultrahigh and microwave frequency ranges. Fig. 4-8 shows the response of
band pass filter. The linear portion on the curve where the voltage variation is
proportional to the frequency variation meets the requirement of a
discriminator.

4.3 EQUIPMENT REQUIRED

1. ModuleKL-92001
2. ModuleKL-93004
3. Oscilloscope
 EXPERIMENT5
R-C Couple
Amplifier
Aim: To construct a two stage R-C Coupled amplifier, to study the frequency
response of the amplifier and to determine the bandwidth.
Apparatus: Two identical n-p-n transistors, power supply (0-15V), signal
generator (0 – l MHz), Carbon resistors, Capacitors, a.c. milli-voltmeter and
connecting terminals.

V
Formula: Voltage Gain(G) = 0Vi
Where Vo = Output voltage Vi = Input voltage
Bandwidth of the amplifier = f2 - f1KHz

where f1 = lower half-power (cut-off) frequency f2 = upper half-power (cut-

off)frequency

Description: - D.C. power supply, the resistances R1, R2 and RE provides potential
divider biasing and stabilization network. i.e. It establishes a proper operating point
to get faithful amplification. RE reduces the variation of collector current with
temperature. The potential divider bias provides forward bias to the emitter
junction and reverse bias to the collector junction. Since the emitter is grounded, it
is common to both input and output signals. Therefore, the amplifier is common-
emitter amplifier. Capacitor Cin (= 10 uF) isolates the d.c. component and the
internal resistance of the signal generator and couples the a.c. signal voltage to the
base of the transistor. The capacitor CE connected across the emitter resistor REis of
large value (= 100 uF) offers a low reactance path to the alternating component of
emitter current and thus bypasses resistor RE at audio frequencies. Consequently,
the potential difference across REis due to the d.c. component of the current only.
The coupling capacitor Cc (= 10 μF) couples the output of the first stage of
amplifier to the input of the second stage. It blocks the d.c. voltage of the first stage
from reaching the base of the second stage. The output voltage is measured
between the collector and emitter terminals.

Fig. 1
THEORY: - When a.c. signal is applied to the base of the first transistor, it is
amplified and developed across the out of the 1 st stage. This amplified voltage is
applied to the base of next stage through the coupling capacitor C c where it is
further amplified and reappears across the output of the second stage. Thus the
successive stages amplify the signal and the overall gain is raised to the desired
level. Much higher gains can be obtained by connecting a number of amplifier
stages in succession (one after the other). Resistance-capacitance (RC) coupling is
most widely used to connect the output of first stage to the input (base) of the
second stage and so on. It is the most popular type of coupling because it is cheap
and provides a constant amplification over a wide range of frequencies. Fig. 1
shows the circuit arrangement of a two stage RC coupled CE mode transistor
amplifier where resistor R is used as a load and the capacitor C is used as a
coupling element between the two stages of the amplifier.

Frequency response curve

The curve representing the variation of gain of an amplifier with frequency is
known as frequency response curve. It is shown in Fig. 2. The voltage gains of the
amplifier increases with the frequency, f and attains a maximum value. The
maximum value of the gain remains constant over a certain frequency range and
afterwards the gain starts decreasing with the increase of the frequency. It may be
seen to be divided into three regions. 1) Low frequency range (<50 Hz) 2) Mid
frequency range (50 Hz to 20 KHz) and 3) High frequency range (> 20 kHz).
 Fig. 2

Procedure: - The circuit connections are made as shown in the Fig.1. First the signal generator is
connected directly to the a.c. milli-voltmeter by keeping signal frequency at about
500 Hz. The amplitude (voltage) of the input signal is adjusted to 0.1V or 0.05V.
This is the amplifier input (Vi). Now the signal generator is disconnected from the
a.c. milli-voltmeter and connected to the input of the of the amplifier and the a.c.
milli- voltmeter is connected to the output of the amplifier.

Set the input frequency at 10 Hz, note the output voltage (Vo) from the a.c.
milli-voltmeter keeping the input voltage, Vi constant. Vary the input frequency ‘f’
and note the output voltage. The frequency of the input signal is varied in
convenient steps
i.e. at least 5 values with equal intervals, in each range of frequency in the signal
generator, the output voltage Vo is noted in the table for each frequency. Calculate
the voltage gain, G of the amplifier for each value of the frequency, f of the input
signal, using the relation, Voltage gain, G = Vo /Vi.

To determine the bandwidth (BW) of the amplifier

Draw the frequency response curve as said above, by taking the frequency f
(or log10f) on X-axis and voltage gain on Y-axis. Note the maximum gain, Gmax
and mark the value of 0.707Gmaxonthey-axis. From that value draw a line (dashed
line) parallel to x-axis. This line cuts the curve at two points, called the half-power
points. From those two points draw two perpendicular lines on to x - axis, the feet
of two perpendiculars corresponding to two frequencies f1 and f2. These are called
as lower half- power frequency and the upper half-power frequency (or cut-off
frequency). The difference between these two frequencies f1 and f2 is the bandwidth
(BW) of the amplifier.
∴ Bandwidth of the amplifier = f2 - f1

Precautions: - 1) Before going to the experiment the input voltage V i should be

measured.
2) The input voltage should be less than 0.1V.
3) The input voltage should be maintained at constant value throughout the
experiment.
4) The connections should be tight.
 EXPERIMENT 6
Trouble shooting Amplifier

Introduction
The ability to diagnose and cure problems in a systematic manner is an exceptionally
valuable skill. In PHY2028 students are given a heap of components, a breadboard,
and measuring equipment. This virtually guarantees that nothing will work first time,
and students are forced to develop troubleshooting skills.
Students: please ensure that you can answer 'yes' to the relevant questions below
before asking a demonstrator for help.

The Method
Carry out quick and easy checks first: start with a visual inspection, then use a multi-
meter, finally an oscilloscope.

Before You Start

1. Is the circuit diagram open on the bench?

2. Do you understand how it is supposed to work?
3. Are you sure of the pin-outs and polarity of each device?

Power and Grounds

1. Is the power supply is working? Check for stable outputs with a digital
multimeter (DMM)
2. Are op-amps connected to both supply rails? Check voltages with respect to
ground at pins of each device. Do not cause short-circuits with the DMM probes
3. Is the ground rail continuous? Check voltage between power supply rail and
points on circuit that should be at ground.

Passive Components
1. Are the resistor and capacitor values correct? Check them with a
DMM/capacitance meter. If you are not confident that you can estimate the
 effects of other components for in situ measurements, carefully disconnect one
end of the component from the board. Don't simultaneously touch both probes
with your hands when making the measurement or you will get misleading
results.
2. Are potentiometers being used correctly? Check that the wiper voltage varies in
a reasonable manner as the potentiometer is adjusted. Avoid using
potentiometers as variable resistors.
3. Are switches of the correct type? Have you checked your assumptions about
which terminal is which with a DMM?

Op-Amps
If you suspect an op-amp is faulty, check it by substitution but first:

1. Is each pin of the op-amp connected?

Check visually that none of its pins have become wrapped under its body instead
of being inserted into the board.
2. Is the output finite?
If the output is within a volt or so of either power rail then either it has failed, or
there is an excessive voltage at its inputs.
3. Is the input consistent with the output?
Measure the voltage between the inverting and non-inverting inputs, it should be
within millivolts of zero.

Offset Voltages
A few millivolts of offset at the input of a system with a high DC gain can be
amplified to the point that it saturates the final stage. Many op-amps have offset
adjust facilities which can reduce the offset by something like a factor of 10.
Offsets are temperature dependent.

Instability
Instability typically appears as high-frequency 'fuzz' on the output signal
oscilloscope trace. Breadboard circuits are very prone to it because of inter-track
capacitance and long components leads. Try the following:

1. Organize the physical layout of the circuit to keep the input and output stages
separate.
 2. Decouple the breadboard power supply rails with a circa 0.1µF capacitors to
ground.
3. Work out the loop-gain (see worksheet 1) and study the op-amp manufacturer's
data-sheet.
4. Don't use op-amps with an unnecessarily good frequency response, e.g. use a
LM741 instead of an LF411 where possible.

Divide and Conquer

If you have a complex system involving several stages:

1. Divide the system into sub-circuits that can be tested individually.

If you want to do an open-loop test on a closed-loop system use a signal
generator or voltage source to inject a simulation of the closed-loop signal at
the point where you open the loop.
2. Check the signal at the input and output of each section, using an oscilloscope if
appropriate.
It is possible for a faulty section to load its predecessor in the chain.

How to Kill a Working Circuit

1. Short-circuit a supply rail to something sensitive with the DMM probes when
checking the PSU or by dropping something (e.g. a screwdriver) onto the
working circuit.
2. Apply power for an instant to only one rail of a circuit that requires two rails.
3. Make changes to the circuit without switching off the PSU first.
 EXPERIMENT7
oscillators-and-
multi-viberators
 THE OSCILLATORS AND MULTIVIBRATORS TRAINER PROVIDE THE
STUDY OF VARIOUS TYPES OF OSCILLATORS AND MULTIVIBRATORS
CIRCUITS. THE CIRCUITS ARE SCREEN-PRINTED ON THE PRINTED
CIRCUIT BOARD. THE STU- DENT’S WORKBOOK ARE WELL ORGANISED
WHERE THE STUDENTS ARE ABLE TO FOLLOW AND UNDERSTAND
EASILY.
The Oscillators and Multivibrators Trainer is designed to figure out the oscillators and
multivibrators concept of every method study in theory. This trainer is a system with
three different modules. On the panel of each module, a circuit diagram, input and
output ports and test points which necessary in monitoring waveforms and signal
levels.
The trainer offers training and experiment capabilities in two main areas: functional
tests on individual circuits and experiments on the characteristics of the circuits.
Topics covered:
HARTLEY Oscillator
Objectives of this experiment:
• To construct a series-fed transistor Hartley oscillator.
• To change frequency determining components and observe variations
infrequency.
• To measure any harmonic frequencies present. Hartley oscillator is used for
varying frequencies over large ranges, as in local oscillators of radio receivers.
COLPITTS’ OSCILLATOR

Objectives of this experiment:

• To construct a basic COLPITTS oscillator, using a transistor.
• To determine the frequency of oscillation.
• To measure any harmonic frequencies generated by it. Colpitts oscillator is used
for fixed frequency of oscillation.

CRYSTALOSCILLATOR
Objectives of this experiment:
• To construct a crystal oscillator.
• To determine the frequency of oscillator.
• To measure any harmonic frequency generated in the crystal oscillator called
 PIERCE oscillator the frequency determining L-C network is provided by a piezo
electric-quartz crystal. Inductance L is represented by the inertia of the mass of
the crystal plate when R is vibrating, capacitance C is represented by the
reciprocal of the stiffness of the crystal plate.

PHASE SHIFT OSCILLATOR

Objectives of this experiment:

• To determine the range frequency of an R-C phase shift oscillator.
• To construct RC phase shift oscillator & to compare the phase shift networks and
feedback voltages in this oscillator. R-C oscillator uses resistors and capacitors as
the frequency determining components. Each element of R-C network shifts the
phase by 60 degrees. Three such elements shift the phase by 180 degrees. A
transistor amplifier, associated with this network shifts the phase by another 180
degrees. Thus the R-C network and the transistor shifts the phase by 360 degrees in
positive feedback circuit, throwing it into oscillation. This type of oscillator is used
as a fixed frequency oscillator

WIEN-BRIDGE OSCILLATOR

Objectives of this experiment:

• To construct a wien-bridge oscillator and determine the resistor ratio required to
develop the correct de- generative feedback.
• To insert a simple automatic gain-control and ob- serve the effect on oscillator
operation.
• To vary the values of resistance and capacitance in the lead-lag network and to
observe the resultant frequency changes.
• To construct wein-bridge oscillator using RC combination, usually preferred for
low frequency application. A lead lag R-C network determines the oscillator
frequency and controls the amount of regenerative.

VOLTAGE CONTROLLED OSCILLATOR

Objectives of this experiment:

• To construct voltage controlled oscillator circuit and verify the frequency variations
 in accordance with input voltage.
• ARMSTRONG OSCILLATOR

Objectives of this experiment:

• To construct Armstrong oscillator circuit and study the characteristics of the
circuit.

MULTIVIBRATORS

Objectives of this experiment:

• The purpose of this experiment is to investigate the operation and characteristics
of the as table multivi-brator, the mono-stable multi-vibrator and bistable multi-
vibrator. A stable multi-vibrator is free running rectangular wave generator. It has
two outputs, which are 180 degrees out of phase. Monostable is a one- shot multi-
vibrator and R is triggered by sharp pulse, obtained by differentiating a square-
wave. It produces one output pulse for each input pulse. A bistable is a flip-flop
and it is stable either in ‘1’ or ‘0’ state, till it is triggered into their other state.
Output changes for every two Input triggers. It can also be used as divide-by-two
counter.

SCHMITT TRIGGER

Objectives of this experiment:

• To construct an emitter-coupled Schmitt trigger using transistors.
• To observe that this produces a rectangular wave output from a sine wave input.
To construct Schmitt trigger using op-amp.
• To observe that any increase in amplitude of input sine wave has an effect on the
width of the output waveform.
• To verify these facts, usingIC-7413.

Standard Accessories:

• Variable ±15VDC Power Supply with 240V, 50Hz input.

• 4 mm Patch Cables.
• Experiments Manual.
• Instructor’s Workbook.
• Operation Manual.