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Show that AM wave consist of two side bands and carrier. Also prove the bandwidth of AM is double of the modulating frequency.
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Description :

In a FM system, the maximum deviation is 75KHz. Find bandwidth for modulating frequency i. fm=500Hz ii. fm=5KHz iii. fm=10KHz Draw conclusion for bandwidth of FM from answer.

Answer :

Given deviation∆=75kHz i) fm=500Hz bandwidth B.W=2(∆+fm)  =2(75k+500)=151kHz  ii). fm=5KHz bandwidth B.W=2(∆+fm)  =2(75k+5k)=160KHz iii) fm=10KHz bandwidth B.W=2(∆+fm)  =2(75k+10k)=170KHz As the modulating frequency increases bandwidth also increases.

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Description :

Explain any four different frequency bands and give their two applications of each.

Answer :

Explain any four different frequency bands and give their two applications of each.

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Description :

Why should local oscillator frequency be greater than signal frequency in AM receiver? Also explain why IF has constant value?

Answer :

Reason for LO frequency to be greater than signal frequency The local oscillator frequency (f0) is made greater than signal frequency (Fs) in radio receiver: Local oscillator frequency range is 995 ... frequency of desired signal because the IF is constant and same for all the incoming RF signal.

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4 views 1 answer
Description :

Differentiate between AM and FM on the basis of: (i) Definition (ii) Bandwidth (iii) Modulation Index (iv) Application

Answer :

Compare AM and FM on the basis of i)Definition ii)Bandwidth iii) Wave propogation iv)Number of sidebands

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11 views 2 answers
Description :

For AM, fc =500kHz , fm = 5 kHz Determine: (i) Upper and lower sideband frequencies (ii) Bandwidth

Answer :

Given data fc = 500KHz , fm = 5KHz USB =fc+fm USB = 500+5  =505 KHz. LSB =fc – fm LSB = 500 – 5  =495 KHz Bandwidth = 2fm .  = 2* 5 =10 KHz

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2 views 1 answer
Description :

Communications bandwidth that has the highest capacity and is used by microwave, cable and fibre optics lines is known as: (A) hyper-link (B) broadband (C) bus width (D) carrier wave

Answer :

Answer: B 

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13 views 1 answer
Description :

Draw waveform for standing waves on an open and shorted line. Prove that impedance is inverted at every quarter wavelength interval.

Answer :

Waveform- Explanation When the transmission line is short circuited voltage is zero and current is maximum.The variation is according to the wavelength. When the ... The pattern repeats for every half wavelength. Thus impedance is inverted at every quarter wavelength interval.

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3 views 1 answer
Description :

Define: (i) Image frequency and (ii) Double spotting

Answer :

i)Image frequency:- Image Frequency is defined as the signal frequency plus twice the intermediate frequency. It is denoted as fsi = fs+2fi Where, fs = Signal Frequency fi =intermediate frequency ... It is due to the poor front end selectivity i.e., inadequate image frequency rejection.

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5 views 1 answer
Description :

State the IF frequency and bandwidth of FM receiver.

Answer :

IF for FM receiver: 10.7 MHz. Bandwidth of FM receiver:88MHz to 108 MHz

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4 views 1 answer
Description :

A super heterodyne AM receiver is tuned to a station operating at 1200 KHz .Find local oscillator frequency and image frequency.

Answer :

A super heterodyne AM receiver is tuned to a station operating at 1200 KHz Intermediate frequency is 455KHz. IF frequency=f0-fs Local oscillator frequency is f0=IF +fs=455K+1200K=1655kHz The image frequency which gives the same IF is f0+2*IF=2110KHz

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17 views 1 answer
Description :

Define: 1)Frequency 2)Bandwidth 3)Wavelength 4)Time period

Answer :

Frequency: Frequency is the number of cycles per second. Bandwidth: A range of frequencies within a given band, in particular that used for transmitting a signal. Wavelength: Wavelength can be defined as ... for one complete cycle of vibration to pass a given point.  OR Time period=1/frequency

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6 views 1 answer
Description :

Compare ground wave and space wave propagation on the basis of: (i) Frequency range (ii) Method of propagation.

Answer :

Compare ground wave and space wave propagation on the basis of: (i) Frequency range (ii) Method of propagation.

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4 views 1 answer
Description :

Define critical frequency w.r. to wave propagation.

Answer :

Define critical frequency w.r. to wave propagation.

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Description :

A 400 W carrier is amplitude modulated to a depth of 75%.Calculate the total power in AM wave. (i) Explain the types of noise in a communication system. (ii) Compare simplex and duplex mode of communication.

Answer :

(i) Noise: Noise is any spurious or undesired disturbances that mask the received signal in a communication system. a) Atmospheric Noise: Atmospheric Noise is also known as static noise which is the ... remote control ExamplesWalkytalky,telephone,mobile,Radar, FAX,Pager 4

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20 views 1 answer
Description :

Compare AM with FM with respect to following points: a) Definition. b) Modulation index. c) Bandwidth. d) Side band.

Answer :

Parameters AM FM Definition It is the process in which the amplitude of carrier signal is varied in accordance with the instantaneous value of modulating signal keeping frequency and ... frequency deviation. Side band There are two sidebands Infinite number of sideband

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55 views 1 answer
Description :

If the carrier of a 100 percent modulation modulated AM wave is suppressed, the percentage power saving will be (A) 50.55 (B) 15.55 (C) 10.66 (D) 66.66

Answer :

If the carrier of a 100 percent modulation modulated AM wave is suppressed, the percentage power saving will be 66.66

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153 views 1 answer
Description :

Ten signals, each requiring 3000 Hz, are multiplexed on to a single channel using FDM. How much minimum bandwidth is required for the multiplexed channel ? Assume that the guard bands are 300 Hz wide. (A) 30,000 (B) 32,700 (C) 33,000 (D) None of the above

Answer :

(B) 32,700

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10 views 1 answer
Description :

State the need of stub. Explain single stub and double stub matching.

Answer :

Stub:- Stub is the piece of short circuited transmission line which is used to tune out the reactance of the load when connected across the transmission line as close as possible. ... but lengths are independently adjustable. The double stub matching provides wide range of impedance matching.  

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Description :

Define stub. Explain single and double stub in brief with neat sketch.

Answer :

Stub:- Stub is the piece of short circuited transmission line which is used to tune out the reactance of the load when connected across the transmission line as close as possible ... but lengths are independently adjustable. The double stub matching provides wide range of impedance matching. 

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Description :

Differentiate between single stub and double stub

Answer :

Differentiate between single stub and double stub

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Description :

State and explain the concept of transmission bandwidth.

Answer :

Bandwidth is defined as the portion of the electromagnetic spectrum occupied by a signal We may also define the bandwidth as the frequency range over which as information signal is transmitted. Bandwidth is the ... to 15 KHZ. Therefore the bandwidth is(f2-f1) BW= f2 - f1= 15000-20=14980Hz

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Description :

Compare PAM, PWM, and PPM on the basis of i. Variable characteristics ii. Bandwidth iii. Information contained in iv. Transmitted power

Answer :

Compare PAM, PWM, and PPM on the basis of i. Variable characteristics ii. Bandwidth iii. Information contained in iv. Transmitted power

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Description :

State and explain concept of bandwidth.

Answer :

1. Bandwidth is defined as a range within a band of frequencies or wavelengths. ... For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth ... or Hertz (Hz) 2.Suppose the frequency range is f1 to f2 , then B.W= f2 - f1

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1 view 1 answer
Description :

Define selectivity and sensitivity of AM Receiver. 

Answer :

Selectivity:-It needs to accept signals of the wanted frequency and reject other unwanted frequencies. Sensitivity:-The sensitivity of a radio receiver is its ability to amplify weak signals. It is ... the receiver input terminals to give a standard output power, measured at the output terminals. 

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1 view 1 answer
Description :

Give the expression for modulation index for AM and FM.

Answer :

1.Modulation index for AM ma=Vm / Vc Where Vm is modulating voltage Vc is the carrier voltage 2.Modulation index for FM mf=δ /fm where δ is the deviation fm is the modulating frequency

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Description :

Define modulation index in AM and give its formula.

Answer :

In AM wave, the modulation index (m) is defined as the ratio of the amplitude of the modulating signal (Vm ) to the amplitude of carrier signal (Vc). m = Vm / Vc

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10 views 1 answer
Description :

Define modulation? State the desirable value of modulation index of AM.

Answer :

Modulation: It is the process in which any of these Parameters (Amplitude, Frequency, Phase) of high frequency signal (carrier signal) are varied in accordance with low frequency signal(modulating signal) For an AM, modulation index range is 0 to 1.

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Description :

Explain effect of 'm' on AM with neat waveforms.

Answer :

i)m< 1  If m < 1 or if the percentage of modulation is less than 100% the this type of modulation is known as under modulation The amplitude of modulating signal less than carrier ... greater amplitude part of its information is lost in the process of modulation which is undesirable.

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6 views 1 answer
Description :

Explain the following characteristics of AM radio receiver: (i) Sensitivity (ii) Selectivity.

Answer :

Sensitivity:- The ability to amplify the weak signals is called sensitivity. It is the function of overall receiver gain. Sensitivity of radio receiver is decided by the gain of the RF IF ... perfectly the receiver is able to select the desired carrier frequency and reject other frequencies. 

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Description :

Explain the demodulation of AM signal using diode detector.

Answer :

Simple diode detector:- Explanation:- This is essentially just a half wave rectifier which charges a capacitor to a voltage nearly to the peak voltage of the incoming AM waveform s(t). ... detector output is proportional to the signal strength. Stronger Am signal higher is the dc AGC voltage.

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Description :

Draw the block diagram of AM transmitter, explain its operation.

Answer :

AM transmitter is of two types i)High Level AM Transmitter ii)Low Level AM Transmitter i) RF crystal oscillator: It is a source of carrier signal of desired frequency. The circuit is ... AM signal is then applied to the transmitting antenna which radiates this AM signal into air or space. 

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Description :

Suppose a digitized voice channel is made by digitizing 8 kHz bandwidth analog voice signal. It is required to sample the signal at twice the highest frequency (two samples per hertz). What is the bit rate required, if it is assumed that each sample requires 8 bits? (A) 32 kbps (B) 64 kbps (C) 128 kbps (D) 256 kbps

Answer :

(C) 128 kbps

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Description :

Compare ground wave propagation. Sky wave propagation and space wave propagation.

Answer :

Sr. N o Parameter Ground Wave Propagation Sky Wave Propagation Space wave Propagation 1 Frequency Range 30 kHz to 3 MHz  3 MHz to 30 MHz frequencies above 30 MHz 2 ... These waves have line of sight propagation, ... 6 Fading Problem less Severe Less

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8 views 1 answer
Description :

Define electromagnetic wave and polarization.

Answer :

Electromagnetic wave:-An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular; by convention Polarization:-polarization" of electromagnetic waves refers to the direction of the electric field.

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6 views 1 answer
Description :

Describe the term virtual height with the help of diagram showing ionized layer and the path of wave.

Answer :

Virtual height: -The incident wave returns back to the earth due to refraction. In this process it bends down gradually and not sharply, but the incident and reflected rays follow exactly ... . It is also defined as the maximum height that the hypothetical reflected wave would have reached. 

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Description :

For transmission line, the incident voltage Ei = 6V, and Er = 3V. Calculate: (1) Reflection coefficient (2) Standing wave ratio

Answer :

(1)Reflection coefficient  (2) Standing wave ratio (1)Reflection coefficient Reflection coefficient R=Er/Ei  =3/6  R=0.5 (2) Standing wave ratio SWR=Ei+Er/Ei-Er  =6+3/6-3  SWR =3

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3 views 1 answer
Description :

List and explain the properties of quarter wave transformer.

Answer :

Properties of quarter wave transformer: 1. Impedance transfomation: it provides impedance transformation upto the highest frequencies and is compatible with transmission line. 2. Impedance inversion: if ZL is ... or step up transformer,depending on whether ZL IS greater than or less than ZO.

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1 view 1 answer
Description :

State the frequency range for audio frequency and voice frequency.

Answer :

The generally accepted standard range of audible frequencies is 20 to 20,000 Hz, The usable voice frequency band ranges from approximately 300 Hz to 3400 Hz.

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Description :

Draw amplitude modulated waveform in time domain and frequency domain with proper labeling.

Answer :

AM in Time domain  AM in frequency domain

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Description :

 A standard AM broadcast station is allowed to transmit modulating frequencies up to 5 kHz. If the AM station is transmitting on a frequency of 980 kHz, compute the maximum and minimum upper and lower sidebands and the total bandwidth occupied by the AM station : (A) 10 kHz (B) 975 kHz (C) 990 kHz (D) 20 kHz

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85 views 0 answers
Description :

A load of 200 ohm is used to match 300 ohm transmission line to achieve SWR=1. Find out the required characteristic impedance of a quarter of a quarter wave transformer connected directly to the load.

Answer :

Solution :

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8 views 1 answer
Description :

Explain virtual height with respect to wave propagation with neat sketch.

Answer :

In ionization layer the incident wave refracts and bends down gradually than sharply.   The incident and refracted rays follow paths that are exactly the same as they would have been if reflection had taken place from a surface located at a greater height called virtual height of this layer. 

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Description :

Explain ground wave propogation with neat sketch. 

Answer :

Sketch-   Explanationi) It consists of direct wave which travels near the ground from Transmitter to Receiver. ii) The electromagnetic wave leaves the transmitting antenna & remains close to earth surface ... . The ground wave is the path chosen when frequency in between 30 KHz & 3 MHz 

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5 views 1 answer
Description :

Why electromagnetic waves are said to be transverse wave ? Explain.

Answer :

The electromagnetic waves are oscillations which propagate through free space. In electromagnetic waves the direction of electric field, magnetic field & propagation are mutually perpendicular. Hence electromagnetic waves are called as transverse wave.

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6 views 1 answer
Description :

How quarter wave transformer is used for impedance matching. 

Answer :

In all applications of transmission line, it is required that the load be matched to line, Which requires tuning out the unwanted load reactance and the transformation of resulting impedance to the required value ... Step down transformer If ZL <Zo then it acts as a Step up transformer  

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7 views 1 answer
Description :

Describe the effect of ionosphere on sky wave propagation.

Answer :

The Ionosphere is the upper portion of the atmosphere. The ultra violet radiation from the sun will ionize the upper layer of the atmosphere. In this layer free electrons and positive and negative ions are ... layer. Its Frequency Range is from 3 MHz to 30 MHz Polarization: Vertical.  

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1 view 1 answer
Description :

Explain the transverse electromagnetic waves in wave propagation.

Answer :

1. The electromagnetic waves are oscillations, which propagate through free space. 2. Em wave travel in free space at the speed of light. 3. Figure shows the simple EM wave, in which the direction of ... electromagnetic waves (TEM). Diagram:- Transverse electromagnetic wave(TEM) OR

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Description :

Draw the radiation pattern for Dipole antenna: (i) Half wave dipole (ii) Folded dipole.

Answer :

The radiation pattern for Half wave dipole antenna The radiation pattern for Folded dipole antenna.

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5 views 1 answer
Description :

Explain the following in wave propagation: 1) Actual height 2) Virtual height

Answer :

1) Actual height:- The height attained by the wave during propagation through the ionosphere is known as Actual height. 2)Virtual height: -The incident wave returns back to the earth due to ... It is also defined as the maximum height that the hypothetical reflected wave would have reached.

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18 views 1 answer
Description :

Define standing wave ratio. 

Answer :

Standing wave ratio is defined as the ratio of maximum voltage (Vmax) to minimum voltage (Vmin). Standing wave ratio is also defined as the ratio of maximum current (Imax) to minimum current (Imin).

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