Recent questions tagged analog-communication

Description : Define the following terms related to antennas; (i) Antenna resistance (ii) Directivity (iii) Antenna gain (iv) Power density

Last Answer : Antenna Resistance - The resistance of an antenna has two components: 1. Its radiation resistance due to conversion of power into electromagnetic waves 2. The resistance due to actual losses in the ... the transmitter power divided by the surface area of a sphere (4πR2) at that distance.

Description : Draw practical set-up and explain the procedure to measure selectivity of radio receiver.

Last Answer : Procedure to measure selectivity of radio receiver: Throughout the measurement the receiver is kept tuned to desired frequency 950 Khz. Now the generator output frequency is deviated below ... the generator output voltage is adjusted to get a standard 50 miliwatt receiver output power.

Description : Draw and label the circuit diagram of ratio detector 

Last Answer : Draw and label the circuit diagram of ratio detector  

Description : Draw the structure and state applications of: i) Ferrite loop (rod) antenna ii) Horn antenna

Last Answer : Horn antenna: Application:- i) Used at microwave frequency. ii) Used in satellite tracking.  Ferrite loop antenna: Application:- In Am radio receiver to receive MW and SW band signals. In FM radio receiver

Description : Calculate the characteristics impedance for a transmission line having L=0.5 mH/Km, C=0.08 µF and negligible R and G.

Last Answer : L=0.5 mH/Km C=0.08 µF

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

Last 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.  

Description : Explain the working of amplitude limiter in FM receiver with circuit diagram.

Last Answer : Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy  Circuit Diagram:

Description : Explain duct propagation with neat sketch.

Last Answer : Duct propagation is a special type and used for very high microwave frequencies. New phenomenon which occurs in super-refraction, also known as ducting. As the height above earth increases, ... in the standard atmosphere. The Duct propagation is used for very high frequencies in GHz range.

Description : A superheterodyne radio receiver with an IF of 455KHZ is turned to 1000KHZ. Find: (i) Image frequency (ii) Local oscillator frequency

Last Answer : Given Intermediate Frequency fi=455KHz Signal frequency =fs=1000KHz Local oscillator frequency fo=fs+fi  Fo=1000KHz+455KHz  =1455KHz Image frequency is the input frequency which produces the same intermediate frequency fsi=fs+2fi  =1000KHz+2*455KHz  =1910KHz 

Description : Draw circuit diagram of transistor reactance modulator. Explain its working.

Last Answer : Explanation- A reactance modulator is illustrated in figure. It is basically a standard commonemitter class A amplifier. Resistors R1 and R2 from a voltage divider to bias ... frequency, whereas a lower capacitance increases the frequency. The circuit produces direct frequency modulations.

Description : Define and explain the term beam width related to antenna with a sketch.

Last Answer : Definition: The beam width of an antenna is described as the angles created by comparing the half power point (3dB) on the main radiation lobe to its maximum power point. As an example the beam width ... max voltage at center of lobe (these point are known as half power points.) Sketch-  

Description : State and explain the concept of transmission bandwidth.

Last 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

Description : Define critical frequency w.r. to wave propagation.

Last Answer : Define critical frequency w.r. to wave propagation.

Description : Define VSWR with refernce to standing waves.

Last Answer : Voltage Standing Wave Ratio: The voltage standing wave ratio (VSWR) is the ratio of max voltage to min voltage. VSWR= VMAX /VMIN

Description : State two disadvantages of TRF receiver over superheterodyne receiver.

Last Answer : Disadvantages of TRF Receiver: 1. Instability due to oscillatory nature of RF amplifier. 2. Variation in bandwidth over tuning range. 3. Insufficient selectivity at high frequencies 4. Poor adjacent channel rejection capability 

Description : Define sensitivity with graph.

Last Answer : Define sensitivity with graph.

Description : Compare between simplex and full duplex communication on the basis of: 1) Definition 2) Sketch

Last Answer : Compare between simplex and full duplex communication on the basis of: 1) Definition 2) Sketch

Description : Explain operation of balanced slope detector with „s‟ curve.

Last Answer : Diagram: Explanation:   Curve:  

Description : Draw block diagram of FM receiver and explain the use of limiter circuit.

Last Answer : Diagram Explanation Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy.

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

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

Description : Explain “BALUN” with neat sketch

Last Answer : Diagram- Explaination

Description : Explain working of envelope detector with suitable diagram and waveform.

Last Answer : Envelope Detector: An Envelope Detector is an electronic circuit that takes a high frequency signal as input and provides an output which is as envelopes of the original signal. The capacitor ... decreases the responsiveness thus, real-world designs must be optimized for the application.

Description : Draw construction of Yagi-Uda antenna and explain.

Last Answer : Explanation A Yagi-Uda antenna, commonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line, usually half-wave dipoles made of ... receiver with a transmission line and additional parasitic elements called reflector and one or more directors.

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.

Last Answer : Solution :

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

Last 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.

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

Last 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.

Description : Write one application of following antenna i. Rectangular antenna ii. Dish antenna iii. Yagi-Uda antenna iv. Horn antenna 

Last Answer : i. Rectangular antenna is used in direction finding in portable recievers. ii. Dish antenna is used to transmit and receive signal from satellite. iii. Yagi-Uda antenna is used in HF and VHF range as a TV receiving antenna. iv. Horn antenna is used in satellite tracking.

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

Last 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. 

Description : a) For a transmission line, Find SWR and reflection coefficient R if, i. There is no reflected voltage. ii. Reflected voltage and incident voltage is equal. iii. If reflected voltage=20V and incident voltage=10V. iv. If reflected voltage=10V and incident voltage =20V.

Last Answer : reflection coefficient R=Vr/Vi i. There is no reflected voltage. i.e,Vr=0 R=0 SWR= 1+R/1-R=1 ii. Reflected voltage and incident voltage is equal. Vr=Vi; R=1 SWR= 1+R/1-R=1+1/1-1=infinity iii. If reflected ... and incident voltage =20V. Vr=10 and Vi=20 R=10/20=0.5 SWR= 1+R/1-R=1+.5/1-.5=3 

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.

Last 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.

Description : Define PAM, PWM, and PPM. Draw waveforms.

Last Answer : Pulse amplitude modulation is defined as a process of varying the amplitude of the carrier pulse in accordance to the modulating signal variations. Pulse width modulation is defined as a ... of varying the position of the carrier pulse, in accordance to the modulating signal variations.

Description : Explain isotropic radiator with neat sketch. 

Last Answer : An isotropic radiator is a point source that radiates equally in all the directions. It is a hypothetical antenna used as a reference to describe real antenna. The radiation is represented by a sphere with center coincides with location of isotropic radiator.

Description : A telephone cable has following primary constants per loop kilometer ,R=30Ω, L=20mH,C=0.06µF,G=0.If the applied signal has an angular frequency of 5000 rad/sec.., Determine (i) Characteristics impedence (ii) Attenuation constant

Last Answer : A telephone cable has following primary constants per loop kilometer ,R=30Ω, L=20mH,C=0.06µF,G=0.If the applied signal has an angular frequency of 5000 rad/sec.., Determine (i) Characteristics impedence (ii) Attenuation constant

Description : Explain ground wave propogation with neat sketch. 

Last 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 

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

Last 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

Description : Define the transmission line? Draw it‟s general equivalent circuit.

Last Answer : Transmission line: A conductor or conductors designed to carry electricity or an electrical signal over large distances with minimum losses and distortion.  Equivalent circuit:

Description : Draw and explain block diagram of electronic communication system.

Last Answer : Block diagram of electronic communication system. Explanation Transducer: A transducer is usually required to convert the output of a source into an electrical signal that is suitable for ... etc. Output Transducer: The output transducer converts electrical signal in to sound signal.  

Description : Explain how modulation reduces height of antenna and avoid mixing of signals.

Last Answer : Modulation reduces antenna height: For the transmission of radio signals, the antenna height must be multiple of λ/4 ,where λ is the wavelength . λ = c /f where c : is the ... will occupy different slots in the frequency domain (different channels). Thus, modulation avoids mixing of signals.

Description : Draw radiation pattern for following antenna i) Yagi-Uda antenna ii) Loop antenna iii) Dish antenna iv) Horn antenna

Last Answer : Type of antenna Radiation Patteren  Yagi-Uda antenna Loop antenna Dish antenna Horn antenna 

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

Last 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

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

Last 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

Description : State the types of electromagnetic polarization? Define any one of it.

Last Answer : Transverse electromagnetic wave:- The polarization of a plane EM wave is simply the orientation of the electric field vector with respect to the surface (i.e. looking at the horizon) If ... the field strength varies with change in polarization the wave is said to have an elliptical polarization 

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

Last 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.

Description : What is stub? What do you mean by single stub matching.

Last Answer : Stub is a 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. Single Stub Matching : ... The single stub match is perhaps the most widely used matching circuit and can match any load.  

Description : State the process FM detection? State it‟s any two types.

Last Answer : FM detection: In any radio that is designed to receive frequency modulated signals there is some form of FM demodulator or detector. This circuit takes in frequency modulated RF signals and takes the ... 3. Ratio Detector 4. Phase Discriminator 5. FM Detector using Phase Locked Loop (PLL)

Description : State the IF frequency and bandwidth of FM receiver.

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

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

Last 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.

Description : State the frequency range for audio frequency and voice frequency.

Last 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.

Description : Explain loop antenna with neat sketch. Draw radiation pattern. State its advantages and applications.

Last Answer : Loop antenna:-The single turn coil carrying RF current through it having length less than the wavelength.   Advantages:- 1. highly directive 2. Small size Applications:- 1. For direction finding 2. In portable receivers 3. In navigation 

Description : Describe the functions of mixer and local oscillator in radio receiver

Last Answer : Frequency Mixer:- The function of frequency mixer is to heterodyne signal frequency fs and local oscillator frequency fo. At the output, it produces the difference frequency known as ... local oscillator frequency fo is then mixed with incoming frequency to give intermediate frequency.