Avionics Exam 2009-2010 Questions

7/29/2019 Avionics Exam 2009-2010 Questions

http://slidepdf.com/reader/full/avionics-exam-2009-2010-questions 1/7

Copyright 2010 © University of Southampton Number ofPages 7

UNIVERSITY OF SOUTHAMPTON SESA6002W1

_________________________________________________

SEMESTER 1 EXAMINATION 2009-2010

Avionics 1

Duration: 120 mins

_________________________________________________

Attempt 4 questions only out of 6.

Marks shown are for guidance only.

Numerical questions:Only University approved calculators overstamped with the

University’s dolphin logo can be used. Marks will not beawarded unless full working is shown.

Boltzmann’s constant k= 1.380653 x 10- J/K



SESA6002W12

Q.1

(i) Discuss the importance of the Nyquist samplng

theorem for sampling a signal. [7marks]

(ii) If a message of bandwidth of 20 KHz is transmittedusing pulse modulation, give the required samplingperiod and draw a sketch of the frequency spectrumgenerated. If the message is under-sampled, show theeffect of aliasing on the spectrum.

[7 marks]

(iii) If a radar has a pulse width of 1µs and a pulserepetition frequency of 5KHz determine the averagepower transmitted if the peak power is 10KW. Whatwould be an acceptable bandwidth?

[7 marks]

(iv) What effect will this bandwidth have on the signalreceived?

[4 marks]



3 SESA6002W1

Q.2

(i) An aircraft has a high PRF radar. What does this meanand what problems will arise if it is trying to observe anaircraft moving in the same direction at the same speed?

[6 marks]

(ii) A radar operating with a PRF of 6KHz observes twotargets at 30km and 30.41km from the radar. If the PRF

is changed to 6.1KHz and a single target is observed at30.41km, what are the actual distances of the targetsfrom the radar?

[10 marks]

(iii) An aircraft moving at a velocity of 100m/s has a radar at8GHz that operates with a PRF of 40KHz. Show usingdiagrams the range of target closing rates that can beidentified.

[9 marks]



SESA6002W14

Q.3

(i) What are the factors that determine the radar crosssection of an object?

[5 marks]

(ii) Show that the radar cross section σ of a body is relatedto the backscattered power from the body.

[7 marks]

(iii) Explain how the radar cross-section can be a function ofwavelength. An aircraft can have a scattering crosssection equivalent to that of an insect. Explain how this ispossible.

[6 marks]

(iv) What considerations must be taken into account toensure that an aircraft is ‘stealthy’

[7 marks]



5 SESA6002W1

Q.4(i) Describe how a radar jammer can be used to generate

false targets and how this can be countered by the radar.

[6 marks]

(ii) If a 3cm wavelength radar transmits 1KW and receives

1µW from a continuously illuminated target of 10m2 thatis 1km away determine the effective area of the antenna.

[7 marks]

(iii) If a 0.05m wavelength radar with an effective area of 1m2 has an average power of 100W, determine the maximumrange that a target with a radar cross-section of 0.5 m2 can be observed if the minimum signal energy requiredis 20db greater than the noise energy KT, where T =600K and the integration time is 0.005s.

[8 marks]

(iv) Comment on the choice of radar parameters and thepotential application of the radar.

[4 marks]



SESA6002W16

Q.5

(i) What are the main sources of external noise in areceiver?How do they change as the frequency increases?

[6 marks]

(ii) A receiver has a noise factor of 2.5dB what is the system

noise temperature and how is this related to the physicaltemperature of the device?

[6 marks]

(iii) A receiver is tuned to measure 101MHz and theIntermediate frequency is 10.8MHz. What are thepossible local oscillator and image frequencies of thisreceiver?

[7 marks]

(iv) An amplifier has a gain of 30dB and a system noisetemperature of 500K. If the input noise is 1.38*10-21 W/Hz and the input signal to noise density ratio is 10

calculate the amplifier output signal to noise ratio[6 marks]



7 SESA6002W1

Q.6(i) An antenna company has produced their latest satellite

receiving antenna for direct broadcast television.According to the company it has the followingcharacteristics “ The small high gain antenna is isotropicand so requires no pointing. Low frequencies of200GHz are used to penetrate the atmosphere toprovide all weather coverage. Spilateral technology isused to improve the signal to noise ratio within thereceiver

Comment on each of the claims of this company.[8 marks]

(ii) What are the near field and far fields of an antenna? Ifan antenna operates at 10 GHz and is 2 m in size howwill the power change as a function of distance along theboresight?

[9 marks]

(iii) Describe different types of parabolic antenna that mightbe used for a radar.

[8 marks]

END OF PAPER

Documents

Avionics Exam 2009-2010 Questions