Analog communications lab manual

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CIRCUIT DIAGRAM:

AMPLITUDE MODULATION CIRCUIT DIAGRAM:

DEMODULATION CIRCUIT DIAGRAM:

BLOCKDIAGRAM REPRESENTATION OF AMPLITUDE MODULATION AND

DE-MODULATION

1

vcc

AMPLITUDE MODULATION &DEMODULATION

AIM: To study the function of Amplitude Modulation & Demodulation (under

modulation, perfect modulation & over modulation) and also to calculated the modulation index.

APPARATUS:

THEORY:

Amplitude Modulation is defined as a process in which the amplitude of the carrier wave c(t) is varied linearly with the instantaneous amplitude of the message signal m(t).The standard form of an amplitude modulated (AM) wave is defined by

S(t) = Ac [1 + Ka m(t)] Cos(2пfct)

S.No Name of the Equipment Qty.

1. Amplitude Modulation & Demodulation trainer kit.

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2. C.R.O (20MHz) 1

3. Function generator (1MHz). 1

4. Connecting cords & probes.

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Exp. No. : Date :

Where a Ka is a constant called the amplitude sensitivity of the modulator. The demodulation circuit is used to recover the message signal from the incoming AM wave at the receiver. An envelope detector is a simple and yet highly effective device

that is well

suited for the demodulation of AM wave, for which the percentage modulation is less than 100%.Ideally, an envelop detector produces an output signal that follows the envelop of the input signal wave form exactly; hence, the name. Some version of this circuit is used in almost all commercial AM radio receivers. The Modulation Index is defined as m = (Vmax + Vmin) / (Vmax – Vmin) Where Vmax and Vmin are the maximum and minimum amplitudes of the modulated wave.

PROCEDURE: For Modulation:

1. Refer to block diagram and Carry out the following connections.2. Keep all the switch faults in OFF position.

EXPECTED WAVEFORMS:

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3. onnect SINE OUT post of

FUNCTION GENERATOR SECTION (ACL-01) to The I/p of Balance Modulator1 (ACL-01) SIGNAL IN Post.

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4. To connect o/p of VCO (ACL-01) RF OUT post to the input of Balance Modulator 1 CARRIER IN post (ACL-01).

5. Connect the power supply with proper polarity to the kit ACL-01 & ACL-02, while connecting this; ensure that the power supply is OFF.

6. Keep switch SW1 towards 1-10 KHz position.7. Keep Out post LEVEL about 0.5Vpp; FREQ. About 1 KHz.8. Keep switch SW2 towards 500 KHz position.9. Keep RF out LEVEL about 1 Vpp; FREQ. about 450 KHz, Switch on 500 KHz.10. BALANCED MODULATOR1: CARRIER NULL completely rotated

clockwise or counter clockwise, so as “unbalance” the modulator and to obtain an AM signal with not suppressed carrier across the output; OUT LEVEL in fully clockwise.

11. Observe the AM Modulator wave.12. Move the probe from post SIG to post OUT (output of the modulator), where

Signal modulated in amplitude is detected. Note that the modulated signal Envelope corresponds to the wave form of the DSB AM modulating signal.

13. Vary the amplitude of the modulating signal and check the 3 following conditions: Modulation percentage lower than the 100%, equal to the 100%, Superior to 100% (over modulation).

14. Vary the frequency and amplitude of the modulating signal, and check the Corresponding variations of the modulated signal.

15. Vary the amplitude of the modulating signal and note that the modulated Signal can result saturation or over modulation.

For Demodulation:

1. Refer to the FIG and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect SINE OUT post of FUNCTION GENERATOR SECTION (ACL- 01)

to the I/p of Balance Modulator1 (ACL-01) SIGNAL IN Post.4. Connect o/p of VCO (ACL-01) OUT post to the input of Balance modulator

(ACL-01) CARRIER IN post.5. Connect power supply with proper polarity to the kit ACL-01 & ACL -02,

While connecting this, ensure that the power supply is OFF.6. Switch on the power supply.7. Keep switch SW1 towards 1-10KHZ position.8. Keep Sine out LEVEL about 0.5 Vpp; FREQ. About 1 KHZ.9. Keep switch SW2 towards 1500KHz position10. Keep VCO Level about 0.5Vpp; FREQ. About 550 KHz.11. BALANCED MODULATOR 1: CARRIER NULL completely rotates

clockwise or counter clockwise, so that the modulator is “unbalanced” and an AM signal with not suppressed carrier is obtained across the output: adjust OUTLEVEL to obtain an AM signal across the output whose amplitude is about 500mVpp.

12. Keep Local Oscillator (ACL-02) 1000 KHz, 1V.13. Connect local oscillator OUT post to LO IN of the mixer section.14. Connect balance modulator1 out to RF IN of mixer section in ACL-02.15. Connect mixer OUT to IF IN of 1st IF Amplifier in ACL-02.

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EXPECTED WAVEFORMS:

16. Connect IF OUT1 of 1st IF to IF IN 1 and IF OUT2 of 1st IF to IFIN 2 of 2ND IF Amplifier.

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17. Connect OUT post of 2nd IF amplifier to IN post of envelope detector.18. Connect post AGC1 to post AGC2 and jumper position19. Observe the modulated signal envelope, which corresponds to the waveform of

the modulating signal at OUT post of the balanced modulator1 of ACL-01. Connect the oscilloscope to the IN and OUT post of envelope detector and detect the AM signal and the detected one. If the central frequency of the amplifier and the carrier frequency of the AM signal and local oscillator frequency coincides, you obtain two signals similar to the ones of diagram.

20. Check that the detected signal follows the behavior of the AM signal envelope. Vary the frequency and amplitude of the modulating signal, and check the corresponding variations of the demodulated signal.

RESULT:

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8

9

CIRCUIT DIAGRAM:

FREQUENCY MODULATION:

FREQUENCY DEMODULATION:

FREQUENCY MODULATION & DEMODULATION

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Exp. No. : Date :

F.M demodulated output

AIM: To study the functioning of frequency modulation & demodulation and to

calculate the modulation Index.

APPARATUS:

THEORY:

The process, in which the frequency of the carrier is varied in accordance with the instantaneous amplitude of the modulating signal, is called “Frequency Modulation”. The FM signal is expressed as

Where Ac is amplitude of the carrier signal, fc is the carrier frequency β is the modulation index of the FM wave.

Modulator has been developed using XR-2206 integrated circuit. The IC XR-2206 is a monolithic Function generator; the output waveforms can be both amplitude and frequency modulated by an external voltage. Frequency of operation can be selected externally over a range of 0.01 MHz. The circuit is ideally suited for communications, instrumentations and function generator applications requiring sinusoidal tone, AM, FM or FSK generation. In this experiment, IC XC-2206 is connected to generate sine wave, which is used as a carrier signal. The amplitude of carrier signal is 5vPP of 100 KHz frequencies.

Demodulator had been developed using LM4565 integrated circuit. The IC LM565 is a general-purpose phase locked loop containing a stable, highly linear voltage controlled oscillator for low distortion FM demodulation. The VCO free running frequency f0 is adjusted to the center frequency of input frequency modulated signal i.e. carrier frequency which is of 100 KHz. When FM signal is connected to the demodulator input, the deviation in the input signal (FM signal) frequency which creates a DC error voltage at output of the phase comparator which is proportional to the change of frequency ζf. This error voltage pulls the VCO to the new point. This error voltage will be the demodulated version of the frequency modulated input signal.

BLOCK DIAGRAM REPRESENTATION:


1. Frequency Modulation & Demodulation trainer kit.

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2. C.R.O (20MHz) 1



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FREQUENCY MODULATION:

FREQUENCY DE-MODULATION:

12

PROCEDURE:

For Modulation:

1. Refer to the block diagram & Carry out the following connections and settings.2. Connect the power supply with proper polarity to the kit ACL-03 and switch it

on.3. Keep all Switch Faults in OFF position.4. Select Sine wave signal using jumper JP1 shorted.5. Select frequency range 1-10 KHz using JP4.6. Using pot P1 keep frequency at 1 KHz and using pot P2 keep amplitude at

0.2Vpp.7. Keep switch SW2 at 1500KHz position.8. Using pot P5 keep frequency at minimum and using pot P6 keep amplitude at

2Vpp.9. Connect the o/p of function generator OUT post to the modulation IN post of

FREQUENCY MODULATOR.10. Connect the oscilloscope to the output of the modulator FM/RF OUT.

For Demodulation:

1. Refer to the block diagram & Carry out the following connections and settings.2. Connect the power supply with proper polarity to the kit ACL-03 and ACL- 04

switch it on.3. Keep all Switch Faults in OFF position.4. Select Sine wave signal using jumper JP1 shorted.5. Select frequency range 0.1-1KHz using JP4.6. Using pot P1 keep frequency at 500Hz and using pot P2 keep amplitude at

0.1Vpp.7. Keep switch SW2 at 500 KHz position.8. Using pot P5 keep frequency at 450 KHz and using pot P6 keep amplitude at

1Vpp.9. Connect the output of function generator OUT post to the modulation IN post of

FREQUENCY MODULATOR.10. Connect the output of FREQUENCY MODULATOR FM/RF OUT post to the

input of RF IN of mixer in ACL-03.11. Using pot P8 keep Local Oscillator frequency at 1000 KHz and using pot P9

keep amplitude at 1Vpp.12. Connect the LOCAL OSCILLATOR OUT to the LO IN of the MIXER.13. Observe signal at MIXER OUT post and achieve the same signal as Frequency

modulator output by setting frequency of LOCAL OSCILLATOR.14. Connect the MIXER OUT to the LIMITER IN post with the help of shorting

links.15. Observe LIMITER OUT post where output is clear from noise and stabilize

around a value of about 1.5Vpp.16. Connect the LIMITER OUT post to the FM IN of QUADRATURE

DETECTOR.17. Connect 0° post to IN1 post of the quadrature detector (ACL-04).

EXPECTED WAVEFORMS:

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18. Connect 90° post to IN2 post of the quadrature detector (ACL-04).19. Connect the oscilloscope across post OUT of Quadrature Detector. If the central

frequency of the discriminator and the carrier frequency of the FM signal and

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local oscillator frequency coincide, you obtain demodulated signal. The fact that there is still some high-frequency ripple at the output of the Quadrature Detector block indicates that the passive low pass filter circuit at the block’s output is not sufficient to remove this unwanted high frequency component. We use the LOW PASS FILTER block to overcome this problem.

20. Connect the OUT post of PLL detector to the IN post of LOW PASS FILTER.21. The LOW - PASS FILTER block strongly attenuates the high-frequency ripple

component at the detector’s output, and also blocks the d.c. offset voltage. Consequently, the signal at the output of the LOW – PASS FILTER block should very closely resemble the original audio modulating signal.

22. Note that the demodulated signal has null continuous component. Vary the amplitude of the FM signal and check that the amplitude of the detected signal varies, too.

23. Increase the carrier frequency and note that a positive voltage is added to the detected signal. Still increasing the frequency, the detected signal presents a distortion (in this condition you operate on a non linear zone of the discriminator.)

RESULT:

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CIRCUIT DIAGRAM:

BLOCK DIAGRAM REPRESENTATION OF BALANCED MODULATOR:

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BALANCED MODULATOR

AIM: To study the following of the Balanced Modulator as a 1. Frequency Doublers

2. DSB-SC Generator.

APPARATUS:

THEORY:

Balanced modulator is used for generating DSB-SC signal. A balanced modulator consists of two standard amplitude modulators arranged in a balanced configuration so as to suppress the carrier wave. The two modulators are identical except the reversal of sign of the modulating signal applied to them.1. RF Generator:

Colpitts oscillator using FET is used here to generate RF signal of approximately 100 KHz Frequency to use as carrier signal in this experiment. Adjustments for Amplitude and Frequency are provided in panel for ease of operation.

2. AF Generator:Low Frequency signal of approximately 5KHz is generated using OP-AMP based wein bridge Oscillator. IC TL 084 is used as an active component, TL 084 is FET input general purpose quad OP-AMP integrated circuit. One of the OP-AMP has been used as amplifier to improve signal level. Facility is provided to change output voltage.

3. Regulated Power Supply:This consists of bridge rectifier, capacitor filters and three terminal regulators to provide required dc Voltage in the circuit i.e. +12v, -8v @ 150 ma each.

4. Modulator: The IC MC 1496 is used as Modulator in this experiment. MC 1496 is a

monolithic integrated circuit Balanced modulator/Demodulator, is versatile and can be used up to 200 MHz.

5. Multiplier:A balanced modulator is essentially a multiplier. The output of the MC 1496 balanced modulator is proportional to the product of the two input signals. If you apply the same sinusoidal signal to both inputs of a ballooned modulator,


1. Amplitude Modulation trainer kit. 1

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Exp. No. : Date :

EXPECTED WAVEFORMS:

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the output will be the square of the input signal AM-DSB/SC: If you use two sinusoidal signals with deferent frequencies at the two inputs of a balanced modulator (multiplier) you can produce AMDSB/SC modulation. This is generally accomplished using a high- frequency “carrier” sinusoid and a lower

frequency “modulation” waveform (such as an audio signal from microphone).

PROCEDURE:

For Modulation:

1. Refer to block diagram and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect SINE OUT post of FUNCTION GENERATOR SECTION (ACL-

01) to The I/p of Balance Modulator1 (ACL-01) SIGNAL IN Post.4. To connect o/p of VCO (ACL-01) RF OUT post to the input of Balance

Modulator 1 CARRIER IN post (ACL-01).5. Connect the power supply with proper polarity to the kit ACL-01 & ACL-

02, while connecting this; ensure that the power supply is OFF.6. Keep switch SW1 towards 1-10 KHz position.7. Keep Out post LEVEL about 0.5Vpp; FREQ. About 1 KHz.8. Keep switch SW2 towards 500 KHz position.9. Keep RF out LEVEL about 1 Vpp; FREQ. about 450 KHz, Switch on 500

KHz.10. BALANCED MODULATOR1: CARRIER NULL completely rotated

clockwise or counter clockwise, so as “unbalance” the modulator and to obtain an AM signal with not suppressed carrier across the output; OUT LEVEL in fully clockwise.

11. Observe the AM Modulator wave.12. Move the probe from post SIG to post OUT (output of the modulator),

where Signal modulated in amplitude is detected. Note that the modulated

signal Envelope corresponds to the wave form of the DSB AM modulating signal.

13. Vary the amplitude of the modulating signal and check the 3 following conditions: Modulation percentage lower than the 100%, equal to the 100% ,Superior to 100% (over modulation).

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14. Vary the frequency and amplitude of the modulating signal, and check the Corresponding variations of the modulated signal.

15. Vary the amplitude of the modulating signal and note that the modulated Signal can result saturation or over modulation.

RESULT:

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CIRCUIT DIAGRAM OF PRE-EMPHASIS AND DE- EMPHASIS:

BLOCK DIAGREM REPRESENTATION OF PRE-EMPHASIS

BLOCK DIAGREM REPRESENTATION OF DE- EMPHASIS:

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PRE-EMPHASIS AND DE-EMPHASIS

AIM: To study the functioning of pre-emphasis and de-emphasis circuits.

APPARATUS:

THEORY:

Pre-emphasis:

Frequencies contain in human speech mostly occupy the region from 100 to 10,000 Hz, but most of the power is contained in the region of 500 Hz for men and 800 Hz for women. Common voice characteristics emit low frequencies higher in amplitude than higher frequencies. The problem is that in FM system the noise output of the receiver increases linearly with the frequency, which means that the signal to noise ratio becomes poorer as the modulating frequency increases.

Also, noise can make radio reception less readable and unpleasant. This noise is greatest in frequencies above 3KHz.The high frequency noise causes interference to the already weak high frequency voice. To reduce the effect of this noise and ensure an even power spread of audio frequencies, Pre emphasis is used at the Transmitter side.

A preemphasis network in the transmitter accentuates the audio frequencies above 3 KHz, so providing the higher average deviation across the voice spectrum, thus improving the signal to noise ratio.

The preemphasis is obtained by using the simple audio filter, even simple RC filter will do the job. The preemphasis circuit produces higher output at higher frequencies because the capacitive reactance is decreased as the frequency increases.

De-emphasis:The problem in FM broadcasting is that noise and hiss tend to be more

noticeable, especially when receiving the weaker stations. To reduce this effect, the treble response of the audio signal is artificially boosted prior to transmission. This is known as pre-emphasis.


1. Frequency Modulation and Demodulation trainer kit.

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Exp. No. : Date :

TABULAR COLUMN: Vin =

Pre-emphasis: De-emphasis:

MODEL GRAPH:

The response of Pre – emphasis circuits The response of De – emphasis

circuit:

S.No.

Input frequency

(50 Hz to 20

kHz)

Output

voltage

Vo

Gain

(in dB)

S.No.

Input frequency

(50 Hz to 20

kHz)

Output

voltage

Vo

Gain

(in dB)

Frequency Frequency

Amplitude

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At the receiver side a corresponding filter or “de-emphasis” circuit is required to reduce the treble response to correct level. Since most noise and hiss tend to beat the higher frequencies, the de-emphasis removes a lot of this. Pre-emphasis and de-emphasis thus allow an improved signal to noise ratio to be achieved while maintaining the frequency response of the original audio signal. The de-emphasis stage is used after the detector stage.

PROCEDURE:

PRE-EMPHASIS:1. Refer to the block diagram & Carry out the following connections and settings.2. Connect the power supply with proper polarity to the kit ACL-03 and switch it

on.3. Keep all Switch Faults in OFF position.4. Select frequency range 1-10 KHz using JP4.5. Using pot P1 keep frequency at 1 KHz and using pot P2 keep amplitude at

0.1Vpp.6. Connect the output of function generator to the IN post of pre-emphasis circuit.7. Observe output voltage at the OUT post of pre-emphasis circuit.8. Vary the frequency in steps of 500Hz and note down the output voltage the

OUT post of pre-emphasis circuit.9. Plot the graph of output voltage v/s input frequency on graph paper.10. From the response you can easily understand that using the pre-emphasis

Circuit we can increase the amplitude of modulating signal at higher frequencies thus improving the Signal to Noise ratio at higher frequencies.

DE-EMPHASIS:1. Refer to the FIG and Carry out the following connections setting.2. Connect the power supply with proper polarity to the kit ACL-04 and switch it

on.3. Keep all Switch Faults in OFF position.4. Select Sine wave signal using jumper JP1 shorted.5. Select frequency range 1-10 KHz using JP4.6. Using pot P1 keep frequency at 1 KHz and using pot P2 keep amplitude at

0.1Vpp.7. Connect the output of function generator to the IN post of De-emphasis circuit.8. Observe output voltage at the OUT post of De-emphasis circuit.9. Vary the frequency in steps of 500Hz and note down the output voltage at the

OUT post of De-emphasis circuit.10. Plot the graph of output voltage v/s input frequency on graph paper.

RESULT:

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CIRCUIT DIAGRAM:

BLOCK DIAGRAM REPRESENTATION OF MIXER:

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Input signal

CHARACTERISTICS OF MIXER

AIM: To study the functioning and characteristics of mixer.

APPARATUS:

THEORY:

Mixers are used for frequency conversion and are critical components in modern radio frequency (RF) systems. A mixer converts RF power at one frequency into power at another frequency to make signal processing easier and also inexpensive. A fundamental reason for frequency conversion is to allow amplification of the received signal at a frequency other than the RF, or the audio, frequency. A receiver may require as much as 140 decibels (dB) of gain. It might not be possible to put more than 40 dB of gain into the RF section without risking instability and potential oscillations. Likewise the gain of the audio section might be limited to 60 dB because of parasitic feedback paths, and microphonics. The additional gain needed for a sensitive receiver is normally achieved in an intermediate frequency (IF) section of the receiver.

The mixer is a nonlinear device having two sets of input terminals and one set of output terminals. Mixer will have several frequencies present in its output, including the difference between the two input frequencies and other harmonic components.

To construct frequency mixer. Connect two different inputs signal at Base (IF frequency) and emitter (Local Oscillator) and the collector output is given to low pass filter to get the beat frequency and observe the wave forms.

A frequency mixer is used in very radio and television receiver, it is also used in many other electronic systems. When a sine wave drives a nonlinear circuit, we get harmonics of each sine wave plus new frequencies called the sum and difference frequencies.

Nonlinear distortion causes harmonic and inter-modulation distortion. Any device or circuit with a nonlinear input-output relation results in nonlinear distortion of the signal. In the time domino, this means that the shape of the periodic signal changes as it passes through the nonlinear circuit. In the frequency domain, the result is a change in the spectrum of the signal. If only one input sine wave is pres ent, only harmonic distortion occurs; if two or more input sine waves are involved, both harmonic and inter-modulation distortion occurs.


1. Amplitude Demodulation trainer kit. 1

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Exp. No. : Date :

EXPECTED WAVEFORMS:

.

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Two input sine waves drive a nonlinear circuit. As before, this results in all harmonics and intermodulation components. The bandpass filter then passes one of the inter-modulation components, usually the difference frequency fx – fy. In term of spectra, the frequency mixer is a circuit that produces an output spectrum with a single line at fx – fy when the input spectrum is a pair of lines at fx and fy. A low – pass filter may be used in place of a bandpass filter, provided that fx – fy is less than fx or fy.

For instance, if fx is 2MHz and f is 1.8 MHz, then.

Fx – fy = 2 MHz – 1.8MHz = 0.2 MHzIn this case, the difference is lower than either input frequency, so we can use a

low-pass filter if we wish (Low-pass filters are usually easier to build than band pass filters.).But in applications in which fx – fy is between fx and fy, we must use a band pass filter. As an example, if fx = 2MHz and fy = 0.5 MHz, then

Fx – fy = 2 MHz – 0.5 MHz = 1.5 MHz To pass only the difference frequency, we are forced to use a band pass filter.

PROCEDURE:

1. Refer to the block diagram and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect the o/p of VCO (ACL-01) OUT post to the I/p of MIXER (ACL-02)

RF IN post.4. Connect local oscillator OUT post to LO IN of the mixer section of ACL-02.5. Connect the power supply with proper polarity to the kit ACL-01 & ACL-02

while connecting this; ensure that the power supply is OFF.6. Switch on the Power supply.7. Keep switch SW2 towards 1500 KHz position8. Keep VCO (ACL-01) LEVEL about 100 mVpp ; FREQ. 550 KHz,9. Keep LOCAL OSCILLATOR (ACL-02): LEVEL about 100 mVpp; FREQ.

1450 KHz.10. Accurately adjust the above frequency until the output is crossed again by a sine

waveform.11. Assure the frequencies and check that now: mixer frequency = fLO – fRF12. The last frequency relations indicate that the two signals with different

frequency RF are converted to the same frequency IF. If they were contemporarily present, there would be interference between the two and this would make a proper reception of the signal impossible. The unwished frequency is called image frequency. To prevent this inconvenience it is necessary to prevent that the image signal reaches the input of the mixer, and this is carried out interposing selective filters between the input of the signal RF and the mixer.

RESULT:

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BLOCKDIAGRAM REPRESENTATION OF SSB MODULATION SYSYTEM:

BLOCKDIAGRAM REPRESENTATION OF SSB DE- MODULATION

SYSYTEM:

36

SINGLE SIDE BAND SYTEM

AIM: To generate SSB using phase method and demodulation

APPARATUS:

THEORY:

An SSB signal is produced by passing the DSB signal through a highly selective band pass filter. This filter selects either the upper or the lower sideband. Hence transmission bandwidth can be cut by half if one sideband is entirely suppressed. This leads to single side band modulation (SSB). In SSB modulation bandwidth saving is accompanied by a considerable increase in equipment complexity.

Single Sideband Suppressed Carrier (SSB-SC) modulation was the basis for all long distance telephone communications up until the last decade. It was called "L carrier." It consisted of groups of telephone conversations modulated on upper and/or lower sidebands of contiguous suppressed carriers. The groupings and sideband orientations (USB, LSB) supported hundreds and thousands of individual telephone conversations.

Due to the nature of-SSB, in order to properly recover the fidelity of the original audio, a pilot carrier was distributed to all locations (from a single very stable frequency source), such that, the phase relationship of the demodulated (product detection) audio to the original modulated audio was maintained.

Also, SSB was used by the U.S. Air force's Strategic Air Command (SAC) to insure reliable communications between their nuclear bombers and NORAD. In fact, before satellite communications SSB-was the only reliable form of communications with the bombers.

The main reason-SSB-is superior to-AM,-and most other forms of modulation are:(1) since the carrier is not transmitted in SSB, there is a reduction by 50% of the transmitted power. In AM out of 100% modulation: 67% of the power is comprised of the carrier; with the remaining 33% power in both sidebands. (2) Because in SSB, only one sideband is transmitted, there is a further reduction by 50% in transmitted power. (3) Finally, because only one sideband is received, the receiver's needed bandwidth is reduced by one half--thus effectively reducing the required power by the transmitter another 50%


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Exp. No. : Date :

EXPECTED WAVEFORMS:

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PROCEDURE:

For Modulation:

1. Refer to the block diagram and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect o/p of FUNCTION GENERATOR section (ACL-01) OUT post to I/p

of Balance Modulator1 (ACL-01) SIGNAL IN post.4. Connect o/p of VCO OUT post (ACL-01) to the input of Balance modulator1

CARRIER IN post (ACL-01).5. Connect power supply with proper polarity to the kit ACL-01 & ACL-02, while

connecting this, and ensure that the power supply is OFF.6. Switch on the power supply.7. Refer to the block diagram and Carry out the following connections.8. Keep all the switch faults in OFF position.9. Connect o/p of FUNCTION GENERATOR section (ACL-01) OUT post to I/p

of Balance Modulator1 (ACL-01) SIGNAL IN post.10. Connect o/p of VCO OUT post (ACL-01) to the input of Balance modulator1

CARRIER IN post (ACL-01).11. Connect power supply with proper polarity to the kit ACL-01 & ACL-02, while

connecting this, and ensure that the power supply is OFF.12. Switch on the power supply & Keep switch SW1 towards 1-10 KHz position.13. Keep sine level about 1 Vpp, Freq. about 3 KHz & Keep switch SW2 towards

500 KHz position.14. Keep LEVEL about 2Vpp; FREQ. about 452 KHz.15. Keep Balanced Modulator 1, Carrier Null in central position, so that the

modulator is “balanced” and obtain an AM signal across the output with suppressed carrier, OUT LEVEL in clockwise position

16. Connect OUT post of balanced modulator 1 to IN post of ceramic filter.17. Observe the SSB signal at the OUT post of ceramic filter. You can observe that

the filter extracts only one of the two components (sidebands) generated by balance modulator.

18. Measure the frequency fc of the carrier (post CAR.), fm of the modulating signal (post SIG.) and fssb of the SSB signal across the output of the filter (post OUT).

19. Repeat Check that: fssb = fc + fm, this means that the band extracted by the filter corresponds to the Upper Side Band.

20. the last measurements setting the frequency of the carrier to 458 KHz. You obtain: fssb = fc – fm, this means that the band extracted by the filter corresponds to the Lower Side Band.

21. Increase the frequency of the modulating signal (SINEWAVE) and check that the SSB signal attenuates and tends to a null.

39

EXPECTED WAVEFORMS:

40

For De-modulation:

1. Refer to the block diagram and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect o/p of Function Generator (ACL-01) OUT post to the i/p of Balance

Modulator1 (ACL-01) Signal in post.4. Connect o/p of VCO (ACL-01) Out post to the input of Balance modulator1

Carrier in (ACL-01) post5. Connect power supply with proper polarity to the kit ACL-01 & ACL-02, while

connecting this; ensure that the power supply is OFF.6. Switch on the power supply.7. Keep switch SW1 towards 1-10 KHz position.8. Keep sine level about VCO level about 1Vpp, Freq. about 3 KHz.9. Keep switch SW2 towards 500 KHz position.10. Keep VCO level about 1 Vpp, Freq. about 452 KHz.11. Balanced Modulator 1, Carrier null in central position, so that the modulator is

“balanced” and obtain an AM signal across the output with suppressed carrier.12. Connect OUT post of balanced modulator to IN post of ceramic filter13. Connect the OUT post of ceramic filter to IN1 post of product detector of ACL-

02.14. Connect the OUT post of VCO in ACL-01 kit to the IN2 post of Product

Detector with same carrier for SSB demodulation.15. Observe the demodulated signal at the OUT post of the product detector.16. CERAMIC FILTER OUT Post (ACL-01) i.e. output of the SSB modulator: It is

a sine wave which corresponds to the Upper Side Band, at the base of the frequency set for the carrier.

17. Out Post (ACL-02) i.e. output of the product detector, There is a sine wave with frequency equal to the one the modulating signal (post Out of Sine wave section.), to which a component with much higher frequency is filtered.

18. Increase the frequency of the modulating signal (Sine wave) and check that the detected signal attenuates and tends to a null.

19. The frequencies of the modulating signal (Sine wave) and check that the detected signal attenuates and tends to a null.

20. Disconnect VCO from the IN2 post of product detector and connect at beat frequency oscillator OUT post, in this way, you supply the product detector with a different carrier form the one used in the modulator.

RESULT:

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CIRCUIT DIAGRAM:

BLOCK DIAGRAM REPRESENTATION OF ENVELOPE DETECTOR:

44

PRACTICAL CIRCUIT FOR DIODE DETECTOR:

SIMPLE CIRCUIT REPRESENTATION OF DIODE DETECTOR:

DIODE DETECTOR CHARACTERISTICS

AIM: To study the characteristics of diode detector or envelope detector.

APPARATUS:

THEORY:

Demodulation involves two operations: (i) Rectification of the modulated wave and (ii) Elimination of RF components of the rectified modulated wave.

The diode is the most common device used in AM demodulator. Signal (AM modulated signal) is applied to anode and output is taken from cathode. Diode operates as half wave rectifier and passes only positive half cycle of the modulated wav e. Further signal is applied to a parallel combination of resistor (Rd) and capacitor (Cd) which acts as a low pass filter. This LPF allows only low frequency signal to output and it bypasses RF component to the ground.

This simple diode detector has the disadvantage that the output voltage, in addition to being proportional to the modulating signal, also has a dc component, which represents the average envelope amplitude (i.e. carrier signal) and a small RF ripple. However these unwanted components are removed in a practical detector leaving only AF signal.

In practical diode detector the cathode terminal of the diode is connected to one end of the secondary of IF transformer. The other end is grounded. Secondary is tuned with the capacitor C1. The capacitors C2 and C3 are used for RF filtering.

The modulated signal is applied at the input of IF transformer. The voltage applied is negative and hence the cathode of the diode passes is connected to the IF transformer. So the diode passes both the positive and negative half cycles. The RF filtering is done by C2 and C3. The output is taken at the volume control.

PROCEDURE:

1. Refer to the FIG and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect SINE OUT post of FUNCTION GENERATOR SECTION (ACL-01)

To the I/p of Balance Modulator1 (ACL-01) SIGNAL IN Post.



1

2. C.R.O (20MHz) 1



45

Exp. No. : Date :

EXPECTED WAVEFORMS:

46

4. Connect o/p of VCO (ACL-01) OUT post to the input of Balance modulator (ACL-01) CARRIER IN post.

5. Connect power supply with proper polarity to the kit ACL-01 & ACL -02.While connecting this; ensure that the power supply is OFF.

6. Switch on the power supply.7. Keep switch SW1 towards 1-10KHZ position.8. Keep Sine out LEVEL about 0.5 Vpp ; FREQ. About 1 KHZ.9. Keep switch SW2 towards 1500 KHz position10. Keep VCO Level about 1.5Vpp; FREQ. About 900 KHz.11. BALANCED MODULATOR 1: CARRIER NULL completely rotates

clockwise or counter clockwise, so that the modulator is “unbalanced” and an AM signal with not suppressed carrier is obtained across the output: adjust OUTLEVEL to obtain an AM signal across the output whose amplitude is about 500mVpp.

12. Keep LOCAL OSCILLATOR (ACL-02) signal at 1350 KHz, 1 v13. Keep RF Level (ACL-02) on max. Position or adjust as per input signal..14. Connect the OUT post of balance modulator1 to the IN post of output amplifier.

In which output of amplifier is directly connected to the antenna via switch ‘SW3’.

15. Connect RF IN post to OUT of Antenna.16. Connect RF OUT post to RF IN of MIXER of ACL-02CL-02.17. Connect local oscillator OUT post to LO IN of the mixer section.18. Connect mixer OUT post to IF IN of 1st IF amplifier.19. Connect IF OUT1 of 1st IF to IF IN 1 and IF OUT2 of 1st IF to IFIN 2 OF 2ND

IF Amplifier.20. Connect OUT post of 2nd IF amplifier to IN post of envelope detector.21. Connect AGC1to AGC2 and jumper position as per the diagram.22. Connect the oscilloscope to the IN and OUT post of envelope detector and

detect the AM signal and the detected one. If the central frequency of the amplifier and the carrier frequency of the AM signal and local oscillator frequency coincides, you will obtain following signals.

23. check that the detected signal follows the behavior of the AM signal envelope. Vary the frequency and amplitude of the modulating signal, and check the corresponding variations of the demodulated signal

RESULT:

47

48

49

BLOCK DIAGRAM REPRESENTATION OF SYNCHRONOUS DETECTOR:

50

SYNCHRONOUS DETECTOR CHARACTERISTICS

AIM: To study the single side band AM reception using of product or synchronous

detector detector.

APPARATUS:

THEORY:

THE RECEIVER:The receiver is of the normal superheterodyne design. The incoming signal is

amplified by the RF Amplifier and passed to the mixer. The other input to the mixer is the local oscillator, which is running at 455 KHz above the frequency to which the receiver is tuned. The mixer generates sum and difference signals and the lower of the two is the resulting IF signal occupying a range of frequencies at around 455 KHz. The audio information must now be separated from these IF frequencies.

RECOVERING THE AUDIO SIGNALS:This is achieved by a circuit called an SSB AM decoder. It does the same job as

a demodulator or detector in a DSB AM receiver. The SSB AM decoder is slightly more complicated when compared with the DSB equivalent. One way of extracting the audio signals is to use a mixer to shift the frequencies just as we have done several times already. If a mixer combined an input of (audio + 455KHz) with another input of 455 KHz the resultant outputs would be the usual 'sum' and 'difference' frequencies. The product detector and the 455 KHz input to the product detector is provided by an oscillator called a VCO.

SSB SIGNAL DEMODULATION:The SSB signal demodulation requires the presence of the carrier, which must

be locally generated in the receiver. To obtain the starting modulating signal from the modulated signal, multiply the modulating signal and the locally generated carrier and filter the result to extract the modulating signal. The circuit carrying out the multiplication of the two signals can be the same used to generate the modulation with suppressed carrier in transmission. When used as demodulator the circuit is commonly called product detector



1

2. C.R.O (20MHz) 1



51

Exp. No. : Date :

EXPECTED WAVEFORMS:

52

PROCEDURE:

1. Refer to the block diagram and Carry out the following connections.2. Keep all the switch faults in OFF position.3. Connect o/p of Function Generator (ACL-01) OUT post to the i/p of Balance

Modulator1 (ACL-01) Signal in post.4. Connect o/p of VCO (ACL-01) Out post to the input of Balance modulator1

Carrier in (ACL-01) post5. Connect power supply with proper polarity to the kit ACL-01 & ACL-02, while

connecting this; ensure that the power supply is OFF.6. Switch on the power supply.7. Keep switch SW1 towards 1-10 KHz position.8. Keep sine level about VCO level about 1Vpp, Freq. about 3 KHz.9. Keep switch SW2 towards 500 KHz position.10. Keep VCO level about 1 Vpp, Freq. about 452 KHz.11. Balanced Modulator 1, Carrier null in central position, so that the modulator is

“balanced” and obtain an AM signal across the output with suppressed carrier.12. Connect OUT post of balanced modulator to IN post of ceramic filter13. Connect the OUT post of ceramic filter to IN1 post of product detector of ACL-

02.14. Connect the OUT post of VCO in ACL-01 kit to the IN2 post of Product

Detector with same carrier for SSB demodulation.15. Observe the demodulated signal at the OUT post of the product detector.16. CERAMIC FILTER OUT Post (ACL-01) i.e. output of the SSB modulator: It is

a sine wave which corresponds to the Upper Side Band, at the base of the frequency set for the carrier.

17. Out Post (ACL-02) i.e. output of the product detector, There is a sine wave with frequency equal to the one the modulating signal (post Out of Sine wave section.), to which a component with much higher frequency is filtered.

18. Increase the frequency of the modulating signal (Sine wave) and check that the detected signal attenuates and tends to a null.

19. The frequencies of the modulating signal (Sine wave) and check that the detected signal attenuates and tends to a null.

20. Disconnect VCO from the IN2 post of product detector and connect at beat frequency oscillator OUT post, in this way, you supply the product detector with a different carrier form the one used in the modulator.

RESULT:

53

54

55

BLOCK DIAGRAM REPRESENTATION OF PHASE LOCKED LOOP:

CIRCUIT DIAGRAM:

56

PHASE LOCKED LOOP

AIM: To study FM reception using phase locked loop detector.

APPARATUS:

THEORY:

The phase locked loop detector is another demodulator that employs a phase comparator circuit. It is a very good demodulator and has an advantage that it is available as a self-contained integrated circuit, so no setting is required. You just plug it in and it works. For these reasons, it is often used in commercial broadcast receivers. It has very low of distortion. Altogether a very nice circuit.

The overall action of the circuit may, at first, seem rather pointless.As we can see in FIG.9, there is a voltage-controlled oscillator (VCO). The DC output voltage from the output of the low pass filter controls the frequency of this oscillator. Now, this DC voltage keeps the oscillator running at the same frequency as the original input signal but 90° out of phase. The question often arises why we would want the oscillator to run at the same frequency and 90° out of phase. And if we did, then why not just add a phase shifting circuit at the input to give the 90° phase shift? The answer can be got by imagining what happens when the input frequency changes – as it would with an FM signal.

If the input frequency increases and decreases, the VCO frequency is made to follow it. To do this, the input control voltage must increase and decrease. These changes in DC voltage level form the demodulated signal. The AM signal then passes through a signal buffer to prevent any loading effect from disturbing the VCO and then through an audio amplifier if necessary. The Frequency response is highly linear.

PROCEDURE:

1. Refer to the block diagram & Carry out the following connections and settings.2. Connect the power supply with proper polarity to the kit ACL-03 and ACL- 04

switch it on.3. Keep all Switch Faults in OFF position.4. Select Sine wave signal using jumper JP1 shorted.


1. Frequency Modulation and Demodulation trainer kit.

1

2. C.R.O (20MHz) 1



57

Exp. No. : Date :

5. Select frequency range 0.1-1KHz using JP4.

EXPECTED WAVEFORM:

58

6. Using pot P1 keep frequency at 500Hz and using pot P2 keep amplitude at 0.1Vpp.

7. Keep switch SW2 at 500 KHz position.8. Using pot P5 keep frequency at 450 KHz and using pot P6 keep amplitude at

1Vpp.9. Connect the output of function generator OUT post to the modulation IN post of

FREQUENCY MODULATOR.10. Connect the output of FREQUENCY MODULATOR FM/RF OUT post to the

input of RF IN of mixer in ACL-03.11. Using pot P8 keep Local Oscillator frequency at 1000 KHz and using pot P9

keep amplitude at 1Vpp.12. Connect the LOCAL OSCILLATOR OUT to the LO IN of the MIXER.13. Observe signal at MIXER OUT post and achieve the same signal as Frequency

modulator output by setting frequency of LOCAL OSCILLATOR.14. Connect the MIXER OUT to the LIMITER IN post with the help of shorting

links.15. Observe LIMITER OUT post where output is clear from noise and stabilize

around a value of about 1.5Vpp.16. Connect the LIMITER OUT post to the FM IN of RATIO DETECTOR.17. Connect the oscilloscope across post OUT of PLL Detector. If the central

frequency of the detector and the carrier frequency of the FM signal and local oscillator frequency coincide, you obtain demodulated signal. The fact that there is still some high-frequency ripple at the output of the PLL DETECTOR block indicates that the passive low pass filter circuit at the block’s output is not sufficient to remove this unwanted high-frequency component. We use the LOW PASS FILTER block to overcome this problem.

18. Connect the OUT post of PLL detector to the IN post of LOW PASS FILTER.19. The LOW - PASS FILTER block strongly attenuates the high-frequency ripple

component at the detector’s output, and also blocks the D.C. offset voltage. Consequently, the signal at the output of the LOW – PASS FILTER block should very closely resemble the original audio modulating signal

RESULT:

59

60

61

CIRCUIT DIAGRAM:

BLOCK DIAGRAM OF FREQQUENCY SYNTHESIZER

62

finFout=N.fin

FREQUENCY SYNTHESIZERAIM:

To study the operation of frequency synthesizer using PLL

APPARATUS:

THEORY:

Phase locked loop:PLL stands for ‘Phase locked loop’ and it is basically a closed loop frequency

control system, which functioning is based on phase sensitive detection of phase difference between the input and output signals of controlled oscillator.Before the input is applied the PLL is in free running state. Once the input frequency is applied the VCO frequency starts change and phase locked loop is said to be in captured mode. The VCO frequency continues to change until it equals the input frequency and PLL is then in the phase locked state. When phase locked the loop tracks any change in the input frequency through its repetitive action.Frequency synthesizer:

The frequency divider is inserted between the VCO and the phase comparator. Since the output of the divider is locked to the input frequency fin, VCO is running at multiple of the input frequency. The desired amount of multiplication can be obtained by selecting a proper divide by N network. Where N is an integer. For example fout = 5 fin a divide by N=10, 2 network is needed as shown in block diagram. This function performed by a 4 bit binary counter 7490 configured as a divide by 10, 2 circuit. In this circuit transistor Q1 used as a driver stage to increase the driving capability of LM565 as shown in above figure.To verify the operation of the circuit, we must determine the input frequency range and then adjust the free running frequency Fout of VCO by means of R1 (between 10th and 8th pin) and C1 (9th pin), so that the output frequency of the 7490 driver is midway within the predetermined input frequency range. The output of the VCO now should be 5Fin.Free running frequency (f0):

Where there is no input signal applied, it is in free running mode.

F0 = 0.3 / (RtCt) where Rt is the timing resistor and Ct is the timing capacitor


1. Frequency synthesizer trainer kit. 1

2. C.R.O (20MHz) 1



63

Exp. No. : Date :

EXPECTED WAVEFORMS:

TABULAR FORM:

S.No. fin

(KHz)

Fout = N fin

(KHz)

Divided by

10, 2

64

Lock range of PLL (fL):FL = ± 8f0/VCC where f0 is the free running frequency = 2VCC

Capture range (fC): fC =

PROCEDURE:

1. Switch on the trainer ad verify the output of the regulated power supply i.e. ± 5V. These supplies are internally connected to the circuit so no extra connections are required.2. Observe output of the square wave generator using oscilloscope and measure the range with the help of frequency counter, frequency range should be around 1KHz to 10KHz.3. Calculate the free running frequency range of the circuit (VCO output between 4th pin and ground). For different values of timing resistor R1 ( to measure Rt switch off the trainer and measure Rt value using digital multimeter between given test points). And record the frequency values in tabular 1. Fout = 0.3 / (RtCt) where Rt is the timing resistor and Ct is the timing capacitor = 0.01 μ f. 4. Connect 4th pin of LM 565 (Fout) to the driver stage and 5th pin (Phase comparator) connected to 11th pin of 7490. Output can be taken at the 11th pin of the 7490. It should be divided by the 10, 2 times of the fout.

RESULT:

65

66

67

CIRCUIT DIAGRAM:

BLOCK DIAGRAM OF AGC:

68

AGC CHARACTERISTICSAIM:

To study the characteristics of Automatic Gain Control (AGC).

APPARATUS:

THEORY:

AGC was implemented in first radios for the reason of fading propagation (defined as slowvariations in the amplitude of the received signals) which required continuing adjustments in the receiver’s gain in order to maintain a relative constant output signal.Such situation led to the design of circuits, which primary ideal function was to maintain a constant signallevel at the output, regardless of the signal’s variations at the input of the system.Now AGC circuits can be found in any device or system where wide amplitude variations in the output signal could lead to a lost of information or to an unacceptable performance of the system.

Automatic Gain Control (AGC) circuits are employed in many systems where the amplitude of an incoming signal can vary over a wide dynamic range. The role of the AGC circuit is to provide a relatively constant output amplitude so that circuits following the AGC circuit require less dynamic range. If the signal level changes are much slower than the information rate contained in the signal, then an AGC circuit can be used to provide a signal with a well defined average level to downstream circuits. Inmost system applications, the time to adjust the gain in response to an input amplitude change should remain constant, independent of the input amplitude level and hence gain setting of the amplifier.

The large dynamic range of signals that must be handled by most receivers requires gain adjustment to prevent overload or IM of the stages and to adjust the demodulator input level for optimum operation. · A simple method of gain control would involve the use of a variable attenuator between the input and the first active stage. Such an attenuator, however, would decrease the signal level, but it would also reduce the S/N of any but the weakest acceptable signal.· Gain control is generally distributed over a number of stages, so that the gain in later stages (the IF amplifiers) is reduced first, and the gain in earlier stages (RF and first IF) is reduced only for signal levels sufficiently high to assure a large S/N.


1. Automatic Gain Control trainer kit. 1

2. C.R.O (20MHz) 1



69

Exp. No. : Date :

MODEL GRAPH:

70

· If the RF gain is small is enough switching in/out an attenuator at RF only for sufficiently high signal levels. Variable gain control for the later stages can operate from low signal levels. Variable-gain amplifiers are controlled electrically, and when attenuators are used in receivers, they are often operated electrically either by variable voltages for continuous attenuators or by electric switches (relays or diodes) for fixed or stepped attenuators.

The input signal is amplified by a Variable Gain Amplifier (VGA), whose gain is controlled by an external signal VC. The output from the VGA can be further amplified by a second stage to generate and adequate level of Vo. Some the output signal’s parameters, such as amplitude, carrier frequency, index of modulation or frequency, are sensed by the detector; any undesired component is filtered out and the

The AGC circuit consists of an OP-Amp (LM358). The OP-Amp acts as an amplifier with positive feedback. The LM358 is a single supply OPAmp. Hence the input that is given to the inverting input of the OP-Amp is biased about the mean value of the supply Vcc.

The output of the OP-Amp is fed back to the non-inverting input of the OP-Amp. Also the output is fed back to the inverting input coupled with the audio input by means of an active network. The active network consists of a BJT and a P-channel JFET. The BJT acts as a switch which sources or sinks the collector current based on the base voltage.

The P-channel JFET acts as a linear resistor dependent on the gatevoltage. The resistance is directly proportional to the gate voltage, which is in-turn proportional to the collector current of the BJT. The drain current is then fed back to the inverting input of the OP-Amp coupled with the audio input.

When the input amplitude is given it is biased about the mean value of the supply. The OP-Amp amplifies the value by the ratio (1+R9/R10). The output of the OP-Amp is then given to the base of the BJT. The collector current is inversely proportional to the base voltage. Hence when the output goes high the collector current goes low. When the collector current goes low the resistance of the JFET also goes low.Hence the voltage at the inverting input also goes low. Thus the output is controlled automatically depending on the input.The output of the AGC is then given to the power amplifier via a variable resistor. First the output is coupled to the variable resistor with the help of a coupling capacitor. It is used for scaling the output.

The transfer function of the AGC gives a good idea of what the AGC does.

PROCEDURE:

1. Connect the circuit as shown in the figure.2. Connect the function generator output to the input of AGC in AGC trainer kit.3. observe the output waveform with respect to input waveform and measure the

output voltage by keeping input voltage constant.4. The x-axis is the input amplitude and the y-axis is the output voltage. The

output is linearly dependent on the input till the voltage V1. After V1 the output remains fairly constant for change in the input till V2.

5. After V2 the AGC breaks down. The AGC is demonstrated in the region between V1 and V2.

RESULT:

71

72

73

CIRCUIT DIAGRAM:

74

DIGITAL PHASE DETECTOR

AIM: To detect the phase difference between two square wave signals using digital

phase detector.

APPARATUS:

THEORY:

The phase detector compares the input frequency and the VCO frequency and generates a dc voltage that is proportional to the phase detector difference between the two frequencies. Depending on the analog or digital phase detector used, the PLL is either called an analog or digital type respectively. For simplicity, the digital phase detectors are used. Examples of digital phase detectors are Exclusive –OR phase detector and Edge – triggered phase detectorEX-OR phase detector:

The exclusive –OR phase detector that uses an exclusive –OR gates such as CMOS type IC 4070. The EX-OR phase detector is preferred when both the inputs are square waves. The output of the EX-OR gate is high only when fin and fout are applied at EX-OR inputs the output is the difference between the two inputs. In the waveforms shown below fin is lagging fout by some phase shift, the output is the phase difference betweenthe two signals.Edge triggered phase detector:

Edge triggered type of phase detector is preferred when both the inputs are pulse waveforms. This edge triggered type of phase detector is designed using by RS Flip Flop. The RS Flip Flop is formed from a pair of cross coupled NOR gates using IC such as CD 4001. The RS Flip Flop is triggered that is the output of detector changes its logic state on the positive (leading edge of the input fin and fout.


1. Digital phase detector trainer kit. 1

2. C.R.O (20MHz) 1



75

Exp. No. : Date :

CIRCUIT DIAGRAM:

EXPECTED WAVEFORMS:

76

PROCEDURE:

1. Switch on the trainer kit2. Observe the output of the square wave generator available on the trainer kit using CRO and measure the range with the help of frequency counter, the frequency range should be around 2KHz to 13KHz.3. Calculate the free running range of the VCO output i.e between 4th pin of IC PLL 565 and ground. For different values of timing resistor Rt, fout is given by

Fout = 0.3 / ( Ct * Rt ) Where Ct: timing capacitor = 0.01 μF, Rt : timing resistor4. Connect the square wave to the input of IC PLL 565 and short 4th and 5th pin of PLL. Vary the input frequency of the square wave, when the PLL is locked that

is connected to one input fout EX-OR phase detector. The other input fin of EX-OR phase detector is the coming from inbuilt of square wave generator.5. Connect the pulse generator output to the input of IC 565 PLL and short 4th & 5th

pin of PLL. Vary the input frequency of the square wave when the PLL is locked that is connected to one input of Edge triggered phase detector input i.e. fout. The other input fin of edge triggered phase detector is the pulse input coming from

the inbuilt pulse generator.6. The dc output voltage of the exclusive-OR phase detector is a function of the

phase difference between its two inputs fin and fout.

RESULT:

77

78

Date post:	17-Nov-2014
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