ANLOG communication full manual

C.M.R institute of Technology Redefining Quality education

AMPLITUDE MODULATION AND DEMODULATION

Aim:To study the ampltude modulation and demodulation.Apparatus:1.Amplitude modulation and demodulation.2.Signal generator.3.Oscilloscope4.Connecting wires..

Theory:Amplitude modulation (AM)is defined as a process in which the amplitude of the carrier wave C(t) is varied abot a mean value ,linearly with the base band signal.An AM wave may thus be described , in its most general form,as a function of time as fallows.

S(t)=Ac[1+Ka m(t)]Cos(2∏fct)Where Ka--Amplitude sensivity of the modulator

S(t)-Modulated signalAc-Carrier amplitudem(t)Message Signal

The amplitude of Ka m(t) is always less than unity,that is Ka m(t)<1 for all t

It ensures that the function 1+Ka m(t) is always positive.When the amplitude sensivity Ka of the modulator is large enough to make Ka m(t) >1for any t,the carrier wave becomes over modulated ,resulting in carrier phase reversal when ever the factor 1+Ka m(t)crosses zero.The modulated wave then exhibits envelope distortion as shown in fig below.

2-nd B.Tech analog communication lab manual1




Circuit diagram:

The absolute maximum value of Ka m(t) percentage of modulation.

Vmax-Vminpercentage of modulation = ------------------ Vmax +VminThe Carrier frequency fc is much greater than the highest frequency component W of message signal m(t),that is Fc>>WWhere W is the message band width.If the condition is vot satisfied ,and envolop cannot be visualized(and there fore detected)satisfactorly.

Procedure:1.Switch on the trainer and check the o/p of carrier generator on oscilloscope.2.Connect around 20 -20 khz with 2 volts A.F signal at AF i/pto the modulator circuit.3.Connect the carrier signal at Carrier i/p of modulator circuit.



4.Observe the Modulator output signal at AM O/P spring by making necessary changes in A.F signal.5.Vary the modulating frequency and amplitude and observe the effects on the modulated wave forms.6. The deapth of modulation can be varied using the variable knob(potentio meter)provided at A.F signal.7. The percentage of modulation or modulation factor can be calculated using the fallowing formule. Vmax-Vmin% of modulation= ------------------ Vmax +Vmin Vmax-VminModulation factor (m)= ------------------ Vmax +Vmin8.Connect the output of the modulator to the input of demodulator circuit and observe the out put which is same as input.

RESULT:Amplitude modulation and demodulation are studied

FREQUENCY MODULATION



AIM:- To study frequency modulation and demodulation and to calculate frequency deviation and frequency index.APPARATUS:-

1. frequency modulation and demodulation trainer2. CRO3. Signal generator 4. Connecting wires and probes

Frequency modulator:



FREQUENCY DEMODULATOR



THEORY:- FM is a system in which the amplitude of the modulated carrier is kept constant, while

its frequency and rate of change are varied by the modulating signal.By the definition of FM, the amount by which the carrier frequency is varied from its

unmodulated value, called the deviation , is made proportional to the instantaneous amplitude of the modulating voltage. The rate at which this frequency variation changes or takes place is equal to the modulating frequency.

FM is that form of angle modulation in which the instantaneous frequency f i(t) is varied linearly with the message signal m(t), as

fi(t) = fC+ kfm(t)The term fC represents the frequency of the unmodulated carrier , and the constant K f

represents the frequency sensitivity of the modulator expressed in Hertz per volt.Unlike AM, the spectrum of an FM signal is not related in a simple manner to that of

modulating signal, rather its analysis is much more difficult than that of an AM signal.

To tackle the spectral analysis of an FM signal:1. Consider the simplest case possible, namely, that of a single – tone modulation that

produces a narrow band FM signal.2. Consider the more general case also involving a single – tone modulation, but this time

the FM is wide band signal.In general, a sinusoidal modulating signal is defined by

m(t) = Am Cos(2∏fm t) Instantaneous frequency of the resulting FM signal equals

fi(t) = fC + Kf Am Cos(2∏fm t) = fC + ∆f Cos(2∏fm t)

Where ∆f = Kf Am, ∆f frequency deviationThe ratio of the frequency deviation to the modulation frequency is called the

modulation index (β) of the FM signal.β =Δf / fm

Depending on the value of the modulation index β, we may distinguish two cases of FM:a. If β < 1 radian, then Narrow band FM.b. If β > 1 radian, then wide Band FM. We may define an approximate rule for the transmission bandwidth of an FM signal

generated by a single – tone modulating signal of frequency fm asBT = 2Δf + 2fm = 2Δf(1+ 1 / β)

This relation is known as carson’s rule.Generation of FM signals:

There are essentially two basic methods of generating frequency modulated signals, namely , direct FM and indirect FM. In the direct method , the carrier frequency is directly varied in accordance with the input base band signal, which is readily accomplished using a voltage – controlled oscillator. In the indirect method, the modulating signal is first used to produce a narrow band FM signal, and frequency multiplication is next used to increase the frequency deviation to the desired level. The indirect method is the preferred choice for FM



when the stability of carrier frequency is of major concern as in commercial radio broad casting.

Indirect FM:A simplified block diagram of an indirect FM system is shown in fig. below

Indirect method of generating a wide band FM signal(fig)The message signal m(t) is first integrated and then used to phase – modulate a

crystal controlled oscillator; the use of crystal control provides frequency stability. To minimize the distortion inherent in the phase modulator, the maximum phase deviation or modulation index β is kept small, there by resulting in a narrow band FM signal.This signal is next multiplied in frequency by means of a frequency multiplier so as to produce the desired wide band FM signal.

A frequency multiplier consists of a nonlinear device followed by a band pass filter, as shown in fig. below.

Frequency multipler(fig)

The implication of the nonlinear device being memory less is that it has no energy – storage elements.

Demodulation of FM signals:Frequency demodulation is the process that enables us to recover the original

modulating signal from a frequency – modulated signal. Here we describe a direct method of frequency demodulation involving the use of popular device known as a frequency discriminator , whose instantaneous output amplitude is directly proportional to the instantaneous frequency of the input FM signal.Basically, the frequency discriminator consists of a slope circuit followed by an envelop detector.

Frequency Discriminator(fig)We may model the ideal frequency discriminator as a pair of slope circuits with their

complex transfer functions, followed by envelope detectors and finally a summer. This scheme is called a balanced frequency discriminator.PROCEDURE:

1. Switch on the Physitech experimental board.2. Connect Oscilloscope to the FM O/P and observe that carrier frequency at that point

without any A.F input. 3. Connect around 1 KHZ with 2 volts sine wave (A.F . Signal) to the input of the

frequency modulator ( At AF input)4. Now observe the frequency modulation output on the 1st channel of CRO and

adjust the amplitude of the AF signal to get clear frequency modulated wave form.5. Vary the modulating frequency (A.F signal) , and amplitude and observe the effects

on the modulated wave form.6. Connect the FM o/p to the FM i/p of De-modulator. 7. Vary the potentiometer provided in the demodulator section.8. Observe the output at demodulation o/p on second channel of CRO.



BALANCED MODULATOR



INTRODUCTION: The purpose of communication system is to transmit information bearing signals or baseband signals through a communication channel separating the transmitter from the receiver. The term baseband is used to designate the band of frequencies representing the original signal as delivered by a sources of information. The efficient utilization of the communication channel requires a shift of the range of baseband frequencies into other frequency ranges suitable for transmission a corresponding shift back to the original frequency range after reception. A shift of the range of frequency in a signal is accomplished by which some characteristic of a carrier is varied in accordance with a modulating wave. The base band signal is reffered to as the modulated wave. At the receiving end of the communications system, we usually require the original baseband signal or modulating wave to be restored. This is accomplished by using a process known as demodulation which is the reverse of the modulation process.

In amplitude modulation the amplitude of a sinusoidal carrier wave is varied in accordance with the baseband signal.AIM: To Study Balanced ModulatorApparatus:

1. Balanced Modulator trainer.2. Signal Generator (2)3. CRO4. BNC Probes

THEORY:In Balanced modulator, two non-linear devices are connected in the balnced mode, so

as to suppress the carrier wave.A Balanced Modulator that generates DSB(product) signal is shown in fig below.



The Balanced Modulator consists of summing devise(operational amplifiers) and two matched nonlinear elements. If x(t) is band limited to fx and if fc > 2 fx , then the band pass filter output will be the desired product signal.

Figure shows IC that have been specifically designed for use as balanced modulators. Figure is the 1496 balanced modulator which is manufactured by Motorola,National, and Signetics. This device uses a differential amplifier configuration. Its carrier suppression is rated at a minimum of -50db with a typical value -65 db at 500KHz.



The trainer contains a balanced modulator using a 1496 integrated circuit. You will verify that it does suppress the carrier and also adjust it for optimum carrier suppression.

Advantage of Balanced Modulator:

In simple non-linear circuits, the undesired non-linear terms(harmonics) are eliminated by a band pass filter. Hence, the bandpass filter must be carefully designed. But in a balanced modulator,the undesired non-linear terms are automatically balanced out and at the output we get only the desired terms, so filter design is not so stringent.Procedure:

1. Switch on the trainer.2. Connect 200Hz sine wave, and 100 KHz square wave from the Function Generators. Adjust R1 (1K linear pot). Connect your oscilloscope to the output

.3. Vary R1(1K) both clockwise and counter clockwise. Observe the output.4. Disconnect the SINE input to R1(1K). The output should not be close to zero.5. Increase the oscilloscope’s vertical input sensitivity to measure the output voltage. E out carrier only.6. Set the vertical input control to 1V/cm. Connect the SINE input to R1(1K) and adjust R1 for maximum output without producing clipping. Measure the peak side band output voltage. Epk sidebands = __________________________.

7. Calculate the carrier suppression in dB.

dB = - 20 log Epk sideband Eout carrier only

dB = - ______________________

Result :generation of ssb(sc) is studied and wave forms are observed.



PRE - EMPHASIS AND DE - EMPHASEAIM: To study the frequency response curve of Pre-Emphasis and De-Emphase.



APPARATUS:1. Physitech’s Pre-Emphasis and De-Emphasis trainer.2. Funtion generator3. CRO4. Connecting wires.

THEORY:Frequency modulation is much more immune to noise than amplitude modulation and

is significantly more immune than phase modulation. The threshold effect is more serious in FM as compared to AM, because in FM, the signal to noise ratio at the input of a detector , at which threshold effect starts, is higher , Lower the threshold level, better is the system because threshold can be avoided at a comparatively lower ratio, and a small signal is needed to avoid threshold level in the FM receivers. The process of lowering the



threshold level is known as threshold improvement , or threshold reduction. Two methods are used for the improvement of the threshold.

1. Pre – Emphasis and De- Emphasis circuits.2. FMFB ( Frequency Modulation with Feed Back)

Pre-Emphasis and De-Emphasis:

The noise triangle shows, noise has a greater effect on the higher modulating frequencies than on the lower ones. Thus, if the higher frequencies were arificially boosted at the transmitter and correspondingly cut at the receiver , an improvement in noise immunity could be expected, there by increasing the signal – to – noise ratio. This boosting of the higher modulating frequencies , in accordance with a prearranged curve, is termed pre-emphasis , and the compensation at the receiver is called de-emphasis. An example of a circuit used for each function is shown in fig. below.a . pre-emphasis b.De- emphasis

Two modulating signals having the same initial amplitude has been taken, with one them Pre-Emphasized to twice this amplitude, whereas the other is unaffected (being at a much lower frequency) . The receiver will naturally have to de-emphasize the first signal by a factor of 2, to ensure that both signals have the same amplitude in the output of the receiver . Before demodulation, i.e ., while susceptible to noise interference, the emphasized signal had twice the deviation it would have had without pre-emphasis and was thus more immune to noise. When this signal is de-emphasized, any noise side band voltage, are de-emphasized with it and therefore have a correspondingly lower amplitude than they would have had without emphasis. Their effect on the output is reduced.

The amount of pre-emphasis in U.S , FM broadcasting , and in the sound transmissions accompanying television, has been standaralized as 75µs, whereas a number of other services, notably Europeon and Australian broad casting and TV sound transmission, use 50µs. The usage of micro seconds for defining emphasis is standard. A 75µs de-emphasis corresponds to



a frequency response curve that is 3dB down of the frequency whose time constant RC is 75µs. This frequency is given by f = 1/2ПRC and is therefore 2120Hz. With 50µs de-emphasis it would be 3180Hz. Fig. below shows Pre-Emphasis and De-emphasis curves for a 75µs emphasis, as used in the united states.

If emphasis were applied to amplitude modulation, some improvement would also result, but it is not as great as in FM because the highest modulating frequencies in AM are no more affected by noise than any others. Apart from that , it would be difficult to introduce pre-emphasis and de-emphasis in existing AM services since extensive modifications would be needed, particularly in view of the huge numbers of receivers in use.PROCEDURE:

1. Swich on Physitech’s Pre-emphasis and De-Emphasis Trainer.2. Give the input from signal generator to AF I/P of pre- emphasis circuit. By

varying the amplitude knob set the input voltage to some milli volts say(4mV,6mV,etc.,)

3. Observe the output wavefrom on CRO channel – 1, by connecting either 75mH or 50mH.

4. The output of pre-emphasis circuit must below the audio frequency range.5. Connect the output of Pre-Emphasis to the I/P of De-emphasis circuit.6. Observe the De-Emphasis output at AF O/P of De-Emphasis circuit.7. Measure the output voltage in CRO for each frequency and notedown the

values.8. Calculate the attenuation and logF Values.9. Plot the graph between frequencies on X-axis and attenuation on Y-axis to show

the emphasis curve.10. Various values of R and C are available so that, the time constant is suitably

selected depending upon the application.



OBSERVATIONS:Input V I =

S.No Frequency in Hz

V Out

(Volts)Log(F) Attenuation In Db

20log(VO / Vi)

Data Specifications :BC 107 transistor

1. VCB(max) = 50V2. VCE(max) = 45V3. VEB(max) = 6V4. IC(max) = 100mA

SINGLE SIDE BAND SYSTEM TRAINER



INTRODUCTION: Education Trainer PHY – 165 is a useful educational kit for the demonstration of Single Side Band Signal generation using Phase shift method and demodulation of SSB signal using Synchronous detector (product detector) . This kit consists of wired circuitry of :

1. RF Generator2. AF Generator3. Two balanced modulators4. Synchronous Detector5. Summer6. Subtrator

Circuit description:1. RF Generator:

Colpitts oscillator using FET is used here to generate RF signal of approximately 100KHz frequency to use as carrier signal in this experiment. Phase shift networks is included in the same block to produce another carrier signal of same frequency with 900 out of phase. As individual controls are provided to vary the output voltage. Facility is provided to adjust phase of the output signal.

2. AF Generator:This is a sine co-sine generator using OP-AMP . IC TL 084 is used as an active

component. TL084 is a FET input general purpose quad OP-AMP integrated circuit. A three position switch is provided to select output frequency . An individual controls are provided to vary the output voltage. AGC control is provided to adjust the signal shape. 3.Balanced Modulator:

This has been developed using MC 1496IC. MC 1496 is a monolithic integrated circuit Balanced modulator / Demodulator, is versatile and can be used up to 200MHz. These modulators are used in this experiment to produce DSB – SC signals. Control is provided to balance the output. 4. Sychronous detector:

This base band signal m(t) can be uniquely recovered from a DSB –SC signal s(t) by first multiplying s(t) with a locally generated sine wave carrier and then low pass filtering the product. It is assumed that the local oscillator signal is exactly coherent or synchronous, in both frequency and phase with the carrier wave c(t) used in the balanced modulator to generate s(t) . This method of demodulation is known as coherent detection or synchronous detection.

In this unit IC MC 1496 is used as synchronous demodulator. The MC 1496 is a monolithic balanced modulator / balanced demodulator, is versatile and can be used up to 200MHz. On board generated carrier( which is used in the modulator ) is used as synchronous signal.

5. Summer and Subtractors:These circuits are simple summing and subtracting amplifiers using OP-AMP. IC TL 084 is used as an active component, TL084 is a FET input general purpose quad OP-AMP integrated circuit.



AIM:- To study single side band signle generation using phase shift method and demodulation using Synchronous detector .Apparatus:

1. SSB trainer Board2. Dual trace Oscilloscope3. Frequency Counter4. Patch Chords

Theory:The phase shift method makes use of two balanced modulators and two phase shift

networks as shown in fig. One of the modulators receives the carrier signal shifted by 900 and the modulating signal with 00( sine ) phase shift, whereas the other recives modulating signal shifted by 900and ( co-sine) and the carrier (RF) signal with 00 phase shift voltage.



Both modulators produce an output consisting only of sidebands. It will be shown that both upper sidebands leads the input carrier voltage by 900. One of the lower sidebands leads the reference voltage by 900 , and the other lags it by 900 . The two lower sidebands are thus out of phase, and when combined in the adder , they cancel each other. The upper sidebands are in phase at the adder and therefore they add together and gives SSB upper side band signal. When they combined in the subtrator , the upper side bands are cancel because in phase and lower side bands add together and gives SSB lower side band signal.

PROCEDURE:

1. Study the circuit operation of SSB system thoroughly.2. Observe the output of the RF generator using CRO. There are two outputs from the

RF generator, one is direct output and the another is 900 phase shift with the direct output . The output frequency is 100KHz and the amplitude is ≥0.2Vpp

( potentiometers are provided to vary the output amplitude)3. Observe the output of the AF generator using CRO. There are two outputs from the

AF generator, one is direct output and the another is 900 phase shift with the direct output. A switch is provided to select the required frequency (2K, 4K or 6KHz) . AGC potentiometer is provided to adjust the gain of the oscillator (or to set the output to good shape) And the amplitude is = 10V pp ( potentiometers are provided to vary the output amplitude)

4. Measure and record the RF signal frequency using frequency counter. 5. Set the amplitudes of the RF signals to 0.1 VPP and connect 00 phase shift signal to

one balanced modulator and 900 phase shift to another balanced modulator as shown in figure.

6. Selected the required frequency (2K,4K or 6 KHz) of the AF generator with the help of switch and adjust the AGC potentiometer until the output amplitude is = 10Vpp ( when amplitude controls are in maximum condition).

7. Measure and record the AF signals frequency using frequency using frequency counter.

8. Set the AF signal amplitudes to 8 Vpp using amplitude control and connect to the balanced modulators as shown in below figure.

9. Observe the outputs of both the balanced modulators simultaneously using Dual trace Oscilloscope, and adjust the balance control until you get the output wave forms(DSB –SC) as shown in figure.

10. To get SSB lower side band signal, connect balanced modulator outputs(DSB-SC) to subtractor.

11. Measure and record the SSB signal frequency using counter. 12. Calculate theoretical frequency of SSB(LSB) and compare it with the practical

value. LSB = RF frequency – AF frequency

13. To get SSB upper side band signal, connect the output of the balanced modulator to the summer circuit.

14. Measure and record the SSB upper side band signal frequency using counter.



15. Calculate theoretical value of the SSB(USB) frequency and compare it with practical value.

USB = RF frequency + AF frequencyEx: If RF frequency is 100KHz and AF frequency is 2KHz

Then USB = 100KHz + 2KHz = 102KHzDemodulation of SSB signal :

16. Connect SSB signal from the summer( or ) subtrator to the SSB signal input of the synchronous detector and RF signal(00) to the RF input of the synchronous detector.

17. Observe the detector output using CRO and compare it with the modulating signal (AF signal)

18. Observe the SSB signal for the different frequencies of the modulating (AF) signal.

MIXER CHARACTERISTICS



INTRODUCTION:A Mixer is a non – linear device that mixes the incoming signal of frequency (fC) with a

local oscillator voltage of frequency (f1) and generates an output voltage of an intermediate frequency (f1 – f C) . The non linear mixer circuit produces the sum and difference frequency components (f1 ± f C) along with the input frequencies and their harmonics. The desired intermediate frequency fi = (f1 - f C) is selected by a tuned circuit known as input intermediate frequency transformer(IFT). The IFT is tuned by adjusting the core of the transformer. The process is known as inductive tuning.

The mixer is also known as first detector. Some mixer circuits use separate devices for mixing and generating local oscillator voltage. Such circuits are referred as separately excited mixers. Another type of mixer circuit , known as self excited mixer utilizes a single device as mixer and local oscillator. They are also referred to as frequency converters. The frequency convertors and mixers perform the job of frequency changers.

AIM: To observer the characteristics of a Frequency Mixer and to measure its conversion

gain.

APPARATUS :1. frequency mixer trainer kit.2. Signal generator – (2) 3. CRO4. BNC Probes

THEORY:A mixer is a non-linear circuit with two input signals and one output signal. The output

signal is a distorted combination of the two input signals. Let the two input frequencies, given be Fx and Fy. Because of the nonlinear distortion, the output signal contains signal frequencies and their harmonics. In addition to the harmonics, a frequency signal with frequency = ( Fx – Fy) and also appear across output terminals.

A mixer circuit finds its application in a super heterodyne receiver in converting a RF signal into an IF signal with the help of a local Oscillator.



If RF signal frequency RF is 1000KHz, by choosing local Oscillator frequency to 1455 KHz the difference frequency becomes 455KHz, which is the intermediate frequency for Radio Receivers .

Other frequencies such as 1455 KHz , 1000KHz,2455 kHz can be filtered out with the help of low pass filterBut in out Physitech’s frequency mixer trainer we are giving low frequencies ( in the range of 60 – 100 KHz) for getting clear output without distortion.

CIRCUIT DESCRIPTION:In a transistor Mixer, one signal drives the bvase, the other signal drives the Emitter.

One of the input signals should be large enough to drive the transistor into non – linear operation. In non – linear mode of operation, the collector current contains fundamental frequency, its harmonics, sum frequency and also difference frequency . The low pass filter filters out all other frequencies except, the difference frequency component. Hence , a sinusoidal signal with frequencies is observed across the output terminalsPROCEDURE

1. Connect the circuit as shown in the circuit diagram.2. Apply 99 KHz signal to the base of the transistor and 100KHz, signal to the emitter

of the transistor. 3. Observe a sinusoidal signal with 1 KHz frequency across output terminals. 4. Vary Base signal frequency and note down O/P amplitude. The output reaches to a

maximum value at a particular frequency. Calculate coversion gain.

Conversion gain = O/P Voltage Base signal voltage

5. Plot conversion gain vs base signal frequency.OBSERVATIONS:



SL.NO Frequency (Base signal)(Hz)

Voltage(Base Signal)(V)

O/P

DATA SPECIFICATIONS:Transistor 2N2369

VCB( max) = 40VVCE( max) = 15VVEB( max) = 4VIC( max) = 500mA

PHASE LOCK LOOP USING LM 565



AIM:- To study phase lock loop and its capture range, lock range and free running VCO frequency.APPARATUS:- 1. Physitech’s Phase Lock Loop Using LM565 trainer.

2. Function generator.3. CRO 4. Connecting Wires.

THEORY: PLL has emerged as one of the fundamental building block in electronic technology. It is used for the frequency multiplication, FM steriodetector , FM demodulator , frequency shift keying decoders, local oscillator in TV and FM tuner.



The block diagram of a PLL is shown in the fig.below.

It consists of a phase detector, a LPF and a voltage controlled oscillator(VCO) connected together in the form of a feed back system. The VCO is a sinusoidal generator whose frequency is determined by a voltage applied to it from an external source. In effect, any frequency modulator may serve as a VCO.

The phase detector or comparator compares the input frequency , fin , with feedback frequency , f out , ( output frequency). The output of the phase detector is proportional to the phase difference between f in , and f out , . The output voltage of the phase detector is a DC voltage and thereforem is often refers to as error voltage . The output of the phase detector is then applied to the LPF , which removes the high frequency noise and produces a DC lend. The DC level, in term is the input to the VCO.

The output frequency of the VCO is directly proportional to the input DC level. The VCO frequency is compared with the input frequencies and adjusted until it is equal to the input frequency . In short , PLL keeps its output frequency constant at the input frequency.Thus , the PLL goes through 3 states.

1. Free running state.2. Capture range / mode3. Phase lock state.Before input is applied, the PLL is in the free running state. Once the input frequency is

applied, the VCO frequency starts to change and the PLL is said to be the capture range/mode.The VCO frequency cantinues to change (output frequency ) until it equals the input

frequency and the PLL is then in the phase locked state. When phase is locked, the loop tracks any change in the input frequency through its repetitive action.

The IC LM565 has a voltage controlled oscillator(VCO), whose frequency in the obsence of any synchoronising input, which is also called free running frequency ‘F O’ is given by

F O = in Hz



Where , R1 = external resistor C1 = external capacitorThe above said VCO output can be divided, or as it is connected to VCO input (pin4) of

phase camparator block, which compare & phase of VCO with that of external input signal. This gives a DC component output available at pin 7 and this is also fed internally to VCO voltage control.Lock Range or Tracking Range:

It is the range of frequencies in the vicinity of f O over which the VCO, once locked to the input signal, will remain locked and is given by F2 = HzCapture Range : (f C) : Is the range of frequencies in the vicinity of ‘f O’ over which the loop will acquire lock with an input signal initially starting out of lock and is given by . . FC = Where C2 is the filter capacitor in farads.PROCEDURE:

1. Connect + 5V to pin 10 of LM 565.2. Connect -5V to pin 1.3. Connect 10k resistor from pin 8 to + 5V4. Connect 0.01 µf capacitor from pin 9 to – 5V5. Short pin 4 to pin 5. 6. Without giving input measure(f O) free running frequency. 7. Connect pin 2 to oscillator or function generator through a 1µf capacitor, adjust the

amplitude aroung 2Vpp. 8. Connect 0.1 µf capacitor between pin 7 and + 5V (C2) 9. Connect output to the second channel is of CRO.10. Connect output to the second channel of the CRO.11. By varying the frequency in different steps observe that of one frequency the wave

form will be phase locked. 12. Change R-C components to shift VCO center frequency and see how lock range of

the input varies. Now compare the theoretical values and practical values using

the given formula.FM DEMODUALTION:

The IC LM 565 phase locked loop is a general purpose circuit designed for highly-linear FM demodulation. During lock, the average DC level of the phase camporator output signals is directly proportional to this frequency of the input signal. As the input frequency shifts, it is this output signal which caused the VCO to shift its frequency to match that of the input. Consequently the linearity of the phase comparator output with frequency is determined by the voltage to frequency transfer function of the VCO.

Connection diagram for this experiment is also some as fig(2) with small changes. The VCO free funning frequency FO should be adjusted to be at the center of the input signal frequency range. C1 can be any value, R1 should be with in the range of 2 to 20k ohms with an optimum value of the order of 4k ohms. The input signal can be directly coupled if the DC resistance seen from pins 2&3 are equal and there is no DC voltage difference between the pins. Pin 6 provides a DC reference voltage that is also to the DC potential of the demodulated output(pin7) . Thus if a resistance is connected between pin 1 ,6&7, the gain of the output stage



can be reduced with little change in the DC voltage level at theoutput . This allows the lock range to be decreased with little change in free running. In this way the lock range can be reduced from ± 60% of FO to approximately ± 20% of FO ( at ± 6V) .

A small capacitor (typically 1kpf) should be connected between pins 7 and 8 to eliminate the possible oscillation in the control current source. Single loop filter is formed by the capacitors C2 connected between pin 7 and + 5V supply.FREQUENCY MULTIPLICATION:

There are two methods by which frequency multiplication can be achieved by using 565 IC.

1. Locking to a harmonic of the input signal.2. Inclusion of a digital frequency divider or counter in loop between the VCO and

phase camporator. The first method is the simplest, and can be achived by setting the free running

frequency of the VCO to a multiple of the input frequency. A limitation of this method is that the lock range decreases as successively higher and weaker hormonics are used for locking. If the input frequency is to be constant with little tracking required the loop can generally be locked to any one of the first five hormonics.

For higher orders of multiplication, a large lock range is desired the second scheme is more desirable.

As shown in fig(3) the loop is broken the VCO and the phase



comporator and a ÷10 counter is inserted which is also provided on the trainer . The fundamental of the divided VCO frequency is locked to the frequency in this case so that the VCO is actually running at a multiple of the input frequency.The amount of the multiplication is determined by the frequency divider. Fig.3 Circuit Diagram for Frequency Multiplication

To setup the circuit ( fig.3) , the frequency limit of the input signal must be determined. The free running frequency FO of the VCO is their adjusted by means of R1 & C1. So that the output frequency of the divider is midway between the input frequency limits. The filter capacitor C2 should be large enough to eliminate variations in the modulated output voltage (at pin7) in order stabilize the VCO frequency. The output can now be taken as the VCO square wave output , and its fundamental will be the desired multiple of the input frequency , as long as the loop is in lock.The important Characterisitics of the 565 PLL are :

1. Operating frequency range : 0.001Hz to 500 Hz.2. Operating voltage range : ±6V to ±12V.3. Input level required for tracking 10mV (rms) minimum to 3V peak to peak

maximum. 4. Input impedance : 10kΩ typically.



5. Output sink current : 1mA, typical.6. Output source current : 10 mA typically.7. Drift in VCO center frequency ( f out) with temperature:300ppm/ oC typically. 8. Drift in VCO center frequency with supply voltage:1.5,1V maximum.9. Triangle wave amplitude : 2-4 V pp at ± 6V typically. 10. Band width adjustment range : < ± 1 to > ± 60%.

Result: study phase lock loop and its capture range, lock range and free running VCO frequency.



SYNCHRONOUS DETECTORAIM: To study about detection of AM demodulator (or) Syncronous Demodulator.APPARATUS:

1. Physitech’s Syncronous Detector trainer kit2. Function Generator 3. CRO4. Connecting Wires

THEORY: The phase and frequency of the locally generated carrier in synchronous detector is

extremely critical . Precision phase and frequency control of the local carrier needs an expensive and a complicated circuitry at the receiver. Pilot carrier is one synchronization technique.

A small amount of carrier signal known as pilot carrier is transmitted along with the modulated signal from the transmitter. This small amount of carrier signal is known as pilot carrier. This pilot carrier, separated at the receiver by an appropriate filter, is amplified, and is used to phase lock the locally generated carrier at the receiver. The phase locking provides synchronization. This system , where a weak carrier is transmitted along with AM –SC signal, is also referred to as partially suppressed carrier system, as the carrier is not totally syppressed. The process in which a large carrier is transmitted along with AM-SC signal is called amplitude modulation. The large carrier simplifies the reception system. The AM-SC with partially suppressed carrier is equivalent to an over modulated AM signal.

The base band signal m(t) can be uniquely recovered from a DSB-SC wave S(t) by first multiplying s(t) with a locally generated sinusoidal wave and then low-pass filtering the product, as in fig. below.

Coherent or synchronous detector fordemodulating DSB-SC modulated wave

It is assumed that the local oscillator signal is exactly coherent or synchronized, in both frequency and phase, with the carrier wave C(t) used in the product modulator to generate S(t) . This method of demodulation is known as Coherent of Synchronous demodulation.

The type MC1496 is a Monolithic modulator / demodulator which is designed to produce the product of a voltage and a switching signal.

It is used as a broad band double side band, suppressed carrier balanced madulator without transformer or tuned circuits. It can be used as an DSB product detecto, AM



modulator, AM demodulator, mixer frequency double & phase detector. The circuit consist of differential amplifier. This IC drives dual differential amplifier.

The ckt. of fig. shows external connections of MC 1496 which is used as an DSB ( double side band) product detector for this purpose all frequencies except the desired demodulated audio are in the spectrum and can be easily filtered at the output. As a result the usual carrier null adjustment not be included.

The modulating signal is applied to the upper differential amplifier, while the carrier signal is applied to the lower differential amplifier.

Ideally a constant amplitude carrier signal would be obtained by passing the modulating signal through limted ahead of the corresponding input terminals

However in the upper input signal is at a high enough level typically 300mV. The signal amplitude variations of upper signal do not appear in the output signal. Due to this reason the product detector of fig. can be used as AM detectors, is no significant in most application.

For this purpose, the modulating signal is applied to both the inputs at a level of about 600 mv. Here in this circuit if the input signal falls during modulation valley’s distortion is not significant in most applications.

It has an advantage of linear operation and ability to have detector stage with gain. In this Physitech’s Make Syncronous Detector Trainer Kit variable carrier signals

generator internally built ranges is of 50Hz to 150 KHz AM wave is generated internally by using IC 1496 configuration.PROCEDURE:

1. Observe the carrier signal at the terminal provided on the kit. Set it to 100 kHz(For Synchronous ckt)

2. Connect 200 Hz AF signal externally from the signal generator to the AF input Terminal provided on the kit. Adjust the amplitude pot of signal generator such that you should observe on AM wave form at the AM output terminal.

3. Connect the carrier output to the carrier input of Syncronous circuit.4. Connect the AM output to the AM input of the Syncrounous circuit.5. Observe the Syncronous Detector AF output on the Oscilloscope.

SYNCHRONOUS DETECTOR





EXPECTED WAVE FORMS:a. Carrier waveb. Sinusoidal modulating Signalc. Modulated Signald. Demodulated Signal



DIODE DETECTOR

The diode is by far the most common device used for A.M demodulation or detection. The simple diode detector has the disadvantages that demodulated output voltage in addition to being proportional to the modulating voltage, also has dc component which represents the average envelope amplitude(i.e. carrier strength ) and a small R.F ripple. The unwanted components are removed in a practical detector.

Fig(1) shows a practical diode detector. In this diode has been reversed, so that the negative envelope is demodulated. This has no effect on detection, but it does ensure that a negative AGC voltage will be available. Here tow resistors are used to ensure that there is a series dc path to ground for the diode, but at the same time a low pass filter has been added in the form of R1-C1 , this has the function of removing any RF ripple that might still be present. Capacitor C2 is a coupling capacitor, whose main function is to prevent the diode dc output from reaching the volume control R4. The combination of R3 – C3 is low pass filter designed to remove AF components, proving a dc voltage whose amplitude is proportional to the carrier strength and which may be used for automatic gain control.

It can be seen from the fig. that the dc diode load is equal to R1+R2, whereas the audio load impedance Zm is equal to R1 in series with the parallel combination of R2,R3 and R4, assuming that the capacitors have reactances which may be ignored. This will be true at medium frequencies , but at high and low audio frequencies Zm may have a reactive component, causing a phase shift and distortion as well as an uneven frequency response.

AIM:-To study the Demodulation of AM wave using diode detector.

APPARATUS: 1. Diode Detector Trainer 2. Oscilloscope 3. Connecting wires

PROCEDURE:1. Switch on the trainer and check the O/P of carrier generator on oscilloscope.2. Connect around 1KHz with 2 Volts A.F signal at AF I/P to the modulator circuit.3. Observe the modulator output signal at AM O/P Spring by making necessary changes

in A.F signal.4. Vary the modulating frequency and amplitude and observe the effects on the modulated

waveform.5. The depth of modulation can be varied using the variable knob (potentiometer)

provided at A.F. Input.6. Connect the output of the modulator to the input of demodulator circuit and observe the

demodulated output.7. Connect the output of the demodulator to the input of amplifier circuit and observe the

amplified output.



8. Now study the detector output for applied input of over modulation and undermodulation condition of the AM.

PRECATIONS:- 1. Connect the circuit as shown in the circuit diagram. 2. Apply the required voltages wherever needed. 3. Donot apply stress on the components.



EXPECTED WAVE FORMS



DIGITALL PHASE DETECTOR

INTRODUCTION:- The phase detector compares the phase of the two input signals and generates a voltage that is proportional to the phase difference between them. There are two types of phase detectors linear and digital phase detectors. Even though most of the monolithic PLL IC s use analogue phase detector, the majority of descrete phase detectors in use are of the digital type mainly because of its simplicity.

Examples of digital phase detectors are :i) Exclusive – OR phase detector.ii) Edge – triggered phase detector using flip flop.iii) Monolithic phase detectors.

The trainer consists of the following in built provisions.1) f0 – Reference square wave with 50% duty cycle with variable frequency.2) f1 – Square wave with 50% duty cycle with same frequency as f0 and variable phase

when compared with f0.3) Inbuilt wired circuits of three types of digital phase detectors

EXCLUSIVE – OR PHASE DETECTOR:- Fig . 1 shows Exclusive – OR phase detector. It is one of the simplest type of digital phase detector. The output of EX- OR circuit is high if, and only if , one of the two input signals is high.



Here we realized Ex-OR phase detector using 7486 IC. Ex – OR gate is generally used if the input signals (f1 and f0) are square waves ( signals with 50% duty cycle). Fig 2. shows the two input signals and corresponding output signal. The DC output voltage is a function of the phase error between the two inputs. One limitation of Ex – OR Phase detector is that the output depends on the duty cycle.

.



R- S FLIP FLOP PHASE DETECTOR:Fig.shows a simple set reset flip flop as a phase detecto. The signals f1 and f0 are connected to the set and reset inputs . The average or DC value of the output Q of flip flop will be proportional to the pahse difference between the two input signals. The input and output waveforms are as shown in fig.4. The RS flip flop works best even with low duty cycle (<50%)



DUAL D FLIP FLOP PAHSE DETECTOR:The dual D flip flop shown in Fig5. is less sensitive to the duty cycle of the input wave forms. D flips go high on the leading edge of the input wave forms and remain high until they are reset. The reset signal occurs when both inputs are high . When both signals are in phase and of the same frequency, both outputs will remain low and no pump signal will be applied to the low pass filter. When both signals are the same, but not necessarily in phase, the dc output voltage will be same as in the RS flip flop detector. The input and output wave forms are as shown in fig.6

Fig.5RS Flip Flop Phase Detector



IC 7486IC 7486 is a Quad 2 input exclusive – OR gate. This device contains four

independent gates each of which performs the logic exclusive – OR function



Absolute maximum ratings : 1. Supply voltage :7V2. Input voltage :7V3. Storage Temperature range : -65ºC to 150ºC.Function Table:

Y = AB + BAINPUTS OUTPUT

A B Y L L L H H L H H

LHHL

H =High Logic LevelL = Low Logic Level



SQUELCH CIRCUIT

INTRODUCTION: When no carrier present at the input of a receiver, i.e in the abcence of transmission on a given channel or between stations, a sensitive receiver will produce a disagreeable amount of loud noise. This is because AGC disappear in the abcence of any carrier. The receiver acquires its maximum sensitivity and amplifies the noise present at its input. In some circumstances this is not particularly important, but in many others it can be annoying and tiring. Systems such as those used by police, ambulance and coast radio stations, in which a receiver must be monitored at all times but transmission essporatic, are the principle beneficiaries of squelch. It enables the receiver’s output to remain in cutt off unless the carrier is present. Apart from eliminating inconvenience, such a system must naturally increase the efficiency of the operator. Sqelch is also called muting or quieting circuit.

Squelch Circuit consists of wired circuitry of 1. AM Generator2. Detector with A.F and AGC outputs.3. A.F Amplifier4. DC Amplifier.

CIRCUIT DESCRIPTION: The sqelch circuit as shown in fig(1) , consists of a dc amplifier to which AGC is applied and which operates upon the first Audio amplifier of the receiver. When the AGC is low or Zero , the dc amplifier, Q2 is in conduction and draws current so that bias voltage of Q1 drops and cutts of the A.F amplifier. Thus no signal or noise is passed. When the AGC voltage becomes sufficiently negative to cutt off Q2, this dc amplifier no longer draws current, so that the only now on Q1 is its self bias. The audio amplifier now functions as though squelch were not there. The squelch circuit is normally inserted immediately after the detector.AIM: - To study Squelch circuit.APPARATUS: 1. Squelch circuit trainer Board.

2. Dual trace Oscilloscope.3. Funtion generator4. Patching wires.

PROCEDURE:1. Study the circuit operation of squelch circuit.2. Apply the 500Hz of A.F signal to the input of AM generator marked as A.F input.

Observe the output of the AM generator using CRO. Adjust the amplitudes of A.F and A.M generators to get proper output of A.M wave form.

3. Now connect the A.M output to the input of the detector provided on board and monitor the detectors outputs of A.F and AGC . Measure the AGC output with a DC voltmeter.

4. Connect the A.F output from the detector to the input of the A.F amplifier and AGC output to the input of the DC amplifier.



5. Now you can study the effect of the squelch circuit by varying the amplitude of the A.M signal and adjust the sensitivity of squelch circuit by varying the potentiometer provided at the base of the transistor Q2.



AGC CHARACTERISTICS TRAINER

AIM : - To study the AGC characteristics of a Radio receiver.

APPARATUS : 1. AGC Characteristics Trainer2. 20 MHz Dual trace Oscilloscope3. Patch Chords.

THEORY: The main purpose of the receiver is to recreate the original message signal from the degraded version of the transmitted signal after propagation through the free space.THE SUPER HETERODYNE RECEIVER: The Basic receiver is shown in fig(1) . The first stage is a tuned RF amplifier, using two variable tuned circuits that each other and the local oscillator. The two tuned RF circuits form a band pass filter to pass the desired RF signal frequency while blocking others. This stage acts to boost the weak signal level from the antenna above the noise level to provide same signal selectivity and to prevent other channel signal to pass through.

The output signal from the amplifier is fed to one input of the mixer circuit and the local oscillator signal to the other. The local oscillator is variable tuned so as to track the incoming signal frequencies.

The mixer output (the difference frequency for down – conversion) is fed to multistage tuned. If amplifiers, which are fixed – tune and provided with sufficient selectivity to reject adjacent channel signals. The output from the IF amplifier chain is fed to the detector circuit. Where the audio signal is extracted from the IF signal or demodulated. The detector also provides signals for automatic gain control(AGC) . The AGC signal is used as a bias signal to reduce the gain of the RF and the IF amplifiers to prevent detector overload an strong signals. AGC is a system be means of which the overall gain of a radio receiver is varied automaticcly with the changing strength of the received signal, to keep the output substantially constant.

The audio signal from the detector is passed through a low pass filter to remove unwanted high frequency components and then through a volume control to audio amplifier. The audio amplifier is usually one low – level audio stage followed by a power amplifier and a speaker.

The gain required in the RF and IF amplifier chain of the receiver depends on the required input and output. The input is the minimum variable signal level to be presented at the antenna terminals. The output is the minimum signal level at the input of the detector required to make the detector perform satisfactory.

In this trainer we used Radio receiver IC 1619S which is having in built RF amplifier, local oscillator, a mixer, IF amplifiers and an AGC detector, audio amplifier to drive a speaker. The detailed pin configuration and functional diagrams are given at the end of this manual.



PROCEDURE:

1. Select carrier frequency of 1000KHz . AF frequency 1KHz and apply AM signal to the input of receiver . Set amplitude to aroung 1 mV.

2. Connect CRO at the output of the Audio amplifier.3. Tune the mixer – Local oscillator for maximum AF signal output at detector output

and measure the audio signal. 4. Increase the RF level in appropriate steps and note down corresponding output A.F

signal amplitude . 5. Plot the AF output vs RF input on graph which will be as shown in the fig.2







FREQUENCY SYSNTHESIZER USING LM 565

AIM: To study phase lock loop and its capture range, lock range and free running VCO Frequecy and constructing frequency sysnthesizer.

APPARATUS:

1. Frequency sysnthesizer trainer.2. CRO3. Connecting wires



THEORY: PLL has merged as one of the fundamental building block in electronic technology. It is used for the frequency multiplication, FM sterio detector, FM demodulator, frequency shift keying decoders , local oscillator in TV and FM tuner.

The block diagram of a PLL is shown in the fig. below.

fn

foutfout

It consists of a phase detector , a LPF and a voltage controlled oscillator (VCO) connected together in the form of a feed back system. The VCO is a sinusoidal generator whose frequency is determined by a voltage applied to it from an external source. In effect, any frequency modulator may serve as a VCO.

The phase detector or comparator compares the input frequency, fin, with feedback frequency, fout(output frequency) . The output of the phase detector is proportional to the phase difference betwwn fin and fout . The output voltage of the phase detector is a DC voltage and therefore, is often refers to as error voltage. The output of the phase detector is then applied to the LPF, which removes the high frequency noise and produces a DC lend. The DC level, in-term is the input to the VCO.

The output frequency of the VCO is directly proportional to the input DC level. The VCO frequency is compared with the input frequencies and adjusted until it is equal to the input frequency. In short , PLL keeps its output frequency constant at the input frequency.

Thus , the PLL goes through 3 states:1. free running state. 2. Capture range / mode.3. Phase lock state.

Before input is applied, the PLL is in the free funning state. Once the input frequency applied, the VCO frequency starts to change and the PLL is said to be the capture range/mode.

The VCO frequency continues to change (output frequency) until it equals the input frequency and the PLL is then in the phase locked state. When phase is locked, the loop tracks any change in the input frequency through its repetitive action.

The IC LM565 has a voltage controlled oscillator (VCO) , whose frequency in the absence of any synchronizing input , which is also called free running frequency ‘F0’ is given by


Pase detct

or

Low pass Filter

VCO


F0 = 1.2 / 4R1C1 in HzWhere , R1 = external resistor

C1 = external capacitorThe above said VCO output can be divided , or as it is connected to VCO input (pin4)

of phase comparator block, which compare & phase of VCO with that of external input signal . This gives a DC component output available at pin 7 and this is also fed internally to VCO voltage control.

LOCK RANGE OR TRACKING RANGE:

It is the range of frequencies in the vicinity of f0 over which the VCO, once locked to the input signal, will remain locked and is given by

F2 = ± 8f0 / Vcc HzCAPTURE RANGE : (fc) is the range of frequencies in the vicinity of fo over which the loop will acquire lock with an input signal initially starting out of lock and is given by …

FC = ±

Where C2 is the filter capacitor in farads.

PROCEDURE:

1. Connect + 5V to pin 10 of LM 5652. Connect -5V to pin13. Connect 1k potentiometer from pin 8 to + 5V4. Connect 0.01μf capacitor from pin 9 to - 5V5. Short pin 4 to pin 5.6. Without giving input measure (fo) free running frequency.7. Connect pin2 to oscillator or function generator through a 0.47 μf capacitor,

adjust the amplitude around 2Vpp. 8. Connect 0.1 μf capacitor between pin 7 and + 5V (C2) 9. Connect the input signal to the channel 1 of CRO.10. Connect output to the second channel of the CRO.11. By varying the frequency in different steps observe that at one frequency the

wave form will be phase locked.12. Change R-C components to shift VCO center frequency and see how lock range

of the input varies.Now compare the theoretical values and practical values using the given formula.

FREQUENCY SYSNTHESIZER



Sysnthesizer is an equipment capable of generating a very large number of extremely stable frequencies within some design range, while generally employing only one single stable source. The required frequency range in most synthesizers now a days is obtained from a variable voltage controller oscillator(VCO) , whose output is corrected by comparison with that of a reference source. This inbuilt source is virtually a direct synthesizer.

There are two methods by which frequency multiplication can be achieved by using 565 IC.

1. Locking to a harmonic of the input signal.2. Inclusion of a digital frequency divider or counter in loop between the VCO and

phase comparator.The first method is the simplest, and can be3 achieved by setting the free

runningfrequency of the VCO to a multiple of the input frequency. A limitation of this method is that the lock range decreases as successively higher and weaker harmonics are used for locking. If the input frequency is to be constant with little tracking required the loop can generally be locked to any one of the first five hormonics . For higher orders of multiplication, a large lock range is desired for which the second scheme is more desirable.

As shown in fig(3) the loop is broken between the VCO and the on the trainer . The fundamental of the divided VCO frequency is locked to the frequency in this case so that the VCO is actually running at a multiple of the input frequency . The amount of the multiplication is determined by the frequency divider.Phase comparator and a divide counter is inserted which is also provided

To setup the circuit(fig3) , the frequency limit of the input signal must be determined. The free running frequency Fo of the VCO is then adjusted by means of R & C. So that the output frequency of the divider is mid way between the input frequency limits. The filter capacitor C2 should be large enough to eliminate variations in the modulated output voltage(at pin 7) in order stabilize the VCO frequency. The output can now be taken as the VCO square wave output, and its fundamental will be the desired multiple of the input frequency, as long as the loop is in lock.

The important Characterisitics of the 565 PLL are:

1. Operating frequency range : 0.001Hz to 500KHz.2. Operating voltage range : ± 6V to ±12V.3. Input level required for tracking 10 mV(rms) minimum to 3V peak to peak

maximum.4. Input impedance : 10 KΩ typically.5. Output sink current : 1 mA, typical.6. Output source current : 10 mA typically.7. Drift in VCO center frequency (f out) with temperature : 300 ppm/º typically.8. Drift in VCO center frequency with supply voltage : 1.5 , 1V miximum.



Table showing different values of Capacitance for different frequencies.

VALUE OF ‘C’ N FROUTPUT FREQ.

F0 = Nfr

0.47μF0.1 μF

0.047 μF0.01 μF

0.0047 μF

21020100500

1 KHz1 KHz1 KHz1 KHz1 KHz

2 KHz10 KHz20 KHz100 KHz200 KHz

Reference frequency (FR) provided on board is 1 KHz. After connecting corresponding C value adjust 1k potentiometer to get locking




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