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Question 38924

posted 1 years ago

(a) A 50 m long lossless transmission line with Zo = 50 ohms operating at 50 MHz is terminated with a load ZL = 90 + j 30 ohms. If the wave velocity is u =0.8 c,where cis the speed of light in vacuum, find:
i. The reflection coefficient
ii. The input impedance
(b) The Direct Broadcast System (DBS) satellite (at a distance of 39000 km)transmits at 13 GHz in the Ku Band, with a transmit power of 200 W, with a transmit antenna gain of 35 dB and with an IF (Intermediate Frequency)bandwidth of 30 MHz. The ground receiving station dish has a gain of 32 d Band sees an average background brightness temperature of Tb = 50 K. The receiver LNB (Low Noise Block) has a noise figure of 1.8 dB. Find:
i.The EIRP (Effective Isotropic Radiated Power)
ii.The power received at the input of the LNB
iii.The signal to Noise ratio at the LNB output
iv.Comment on what would happen if both transmit and receive antennas are replaced by typical monopole antennas.
(c) A certain two-port network is measured and the following scattering matrix is obtained:
[S]=\left[\begin{array}{cc} 0.3 \angle 0^{\circ} & 0.7 \angle 90^{\circ} \\ 0.7 \angle 90^{\circ} & 0.3 \angle 0^{\circ} \end{array}\right]
From the data determine:
i.If the network is reciprocal
ii.If the network is lossless
(d) Briefly describe how the following RF systems operate:
i.Wilkinson power divider
ii.Circulator

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Question 38926

posted 1 years ago

(a) For a standard patch square phased array antenna at 15 GHz, please give the number of elements in order to provide a total directivity of 18 dBi and estimate the total array length and width in mm for half wavelength spacing.
(b) A communication system is required for satellite TV broadcasting.
i.Explain the requirements of satellite TV receiver antennas.
ii.Detail two different antenna designs that would fulfill these requirements.
ii.Comment and explain the advantages and disadvantages of the two designs that you selected, especially in relation to TV reception from an antenna perspective.

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Question 38925

posted 1 years ago

i.Define the polarization of an antenna. Then state three main types of polarizations and discuss their differences in regard to the axial ratio.
ii.State two different methods by which one patch antenna can generate a circular polarization.:=
(b) A spiral antenna has an input impedance of 60 + j5 Q, a radiation loss of-0.7 dB, a directivity of 6.5 dBi and is fed by a 50 Q cable. Calculate:
i.The antenna reflection co-efficient.
i.The total output power if the input power is 1 Watt (answer in dBm).
ii.The antenna realized gain.
(c) For a linear array of N isotropic elements placed along a line with inter-element spacing of d.
i.Write an expression for the array factor.
ii.What are the conditions for which the array has maximum and nulls?
(d) Describe the advantages of a waveguide over a transmission line.
(e) State the type of antenna deployed for the following applications and briefly explain why.
i.Cell phone handsets
ii.Global Positioning System receiver
iii.Very long-distance communications, e.g., for satellites

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Question 40893

posted 1 years ago

There is a requirement to design a digital broadcast transmission system that uses QuadratureAmplitude Modulation (QAM) and Orthogonal Frequency Division Multiplexing (OFDM).
a) Explain with the aid of diagrams how QAM encodes and decodes data and explain the difference between data rate and symbol rate.(8 marks)
b) Explain with aid of diagrams why Orthogonal Frequency Division Multiplexing (OFDM)would be a suitable modulation scheme for a digital broadcast transmission system and why the symbol duration is an important design consideration?(8 marks)
c) If the transmission system was capable of transmitting 64kbps with a symbol rate of 4ms.(Please show and explain all calculations for the following):
b. Explain and justify the QAM encoding level required to achieve the above.
Determine and justify the number of OFDM carriers.

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Question 40889

posted 1 years ago

At 50m you receive a -60 dBmW signal, at a frequency of 5GHZ. What was thetransmitted power in Watts if you ignore antenna gain and any losses.Please show all your working.(a)(10 marks)
(b)A data transmission line has the following characteristics:
Characteristic impedance: 50N
Сараcitance: 100pF/m
Attenuation (per 100m):1
1. The inductance per metre of the line
2. The attenuation coefficient at 10MHZ
3. The phase delay in degrees between two points over 5 metres at a frequency of10MHZ(6 marks)

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Question 40891

posted 1 years ago

If the Signal to Noise Ratio (SNR) of a wireless link is 20DB and the Radio Frequency(RF) bandwidth is 20kHz, using Shannon's capacity formula, determine the maximum theoretical data rate that can be transmitted.(5 marks)
b)With the aid of block diagrams explain the principle operation of (DSSS) Direct Sequence Spread Spectrum and (FHSS) Frequency Hopping Spread Spectrum transmission techniques.(12 marks)
With the aid of a diagram and a brief explanation, what is the purpose of the autocorrelation function, and how does it work in a DSSS WLAN.(8 marks)

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Question 40890

posted 1 years ago

With the aid of a diagram, show how a transmission line can be represented as anelectric circuit; and list the electrical properties of the transmission line with appropriateunits of measurement.(4 marks)
(ii) Decreases in resistance.
If a correctly terminated line has a characteristic impedance of 50 ohms and a measuredvelocity of propagation of 2.2 x 108 m/s with an attenuation of 6dB/km. If a faultdevelops, and the reflected pulses are returned non-inverted after 10us with amagnitude 0.025 of that of the transmitted pulse. Calculate the resistance and position(9 marks)of the fault
With the aid of diagrams, explain what happens when the load of a terminatedtransmission line:
(i) Increases in resistance.
When considering a pulse moving along a transmission line; with the aid of a diagram,explain the difference between a lumped and distributed system with reference to thetwo-way delay time 2·t and the rise time of the pulse.(6 marks)

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Question 40892

posted 1 years ago

Electro Magnetic Interference (EMI) is normally considered as being either conductive or radiative. For each type of interference describe ways of reducing their effects.
A carrier of frequency 800kHz is being Amplitude Modulated (AM) by a modulating signal that is a sine wave at a constant frequency of 8kHz and constant amplitude. The modulation index is less than 100%. Determine the frequency of the upper sideband and lower sideband and total bandwidth of the resultant Amplitude Modulated(3 marks)waveform.
If the carrier in part (b) has a peak-to-peak voltage of 10V and the modulating signal has a peak-to-peak voltage of 5V, determine the modulation index, the maximum and minimum voltages of the resultant Amplitude Modulated waveform and the peak amplitude of the upper and lower side bands. Hence, determine the modulating signal voltage that would result in 100% modulation.(7 marks)
Briefly describe the process by which the modulating signal would be extracted from the Amplitude Modulated waveform at a receiver. Using the signal described in part(b) and if the demodulator comprises a simple diode detector, determine a value for the demodulator's time constant and justify your choice. Hence, determine the value of capacitance required if the resistance = 2k.(9 marks)

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Question 36292

posted 1 years ago

Consider the closed-loop control system shown below:
\text { where } C(s)=K D_{c}(s) \text { and } G(s)=\frac{1}{(s+1)\left(\frac{s}{2}+1\right)\left(\frac{s}{5}+1\right)}
The design requirements are given below:
\text { 1. Stcady-state requircment: } K_{p} \geq 9 \text { ( } K_{p} \text { is a static position crror constant.) }
2. Transient requirement: phase margin > 45 deg
Problem 1. (10 points) Assuming De(s) = 1, dctcrminc K such that you can achicve thesteady-state requirement. Then, provide the Bode plot of the open-loop with the stabilitymargins (use "margin" command in MATLAB).

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Question 36295

posted 1 years ago

Problem 4. (10 points) Run step response simulations with your load and lag compensators. Provide your MATLAB code and plots.

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