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S057 05/03/
THE MANCHESTER METROPOLITAN UNIVERSITY
FACULTY OF SCIENCE AND ENGINEERING
DEPARTMENT OF ENGINEERING AND TECHNOLOGY
SESSION 2002/
Examination for the BEng (HONS) ELECTRICAL AND ELECTRONIC ENGINEERING (FULL-TIME/PART-TIME) BEng (HONS) COMMUNICATION AND ELECTRONIC ENGINEERING BEng (HONS) COMPUTER AND ELECTRONIC ENGINEERING BEng (HONS) ELECTRONIC ENGINEERING (PART-TIME) YEAR TWO
UNIT 64EE2105/64EE2071 : COMMUNICATION ENGINEERING
Tuesday 20 May 2003
9.30 am to 11.30 am
Instructions to Candidates
Answer THREE questions.
ALL questions carry equal marks.
- (a) Explain briefly what is meant by each of the following communication system terms:
05/03/04 continued
(i) Modem (ii) Bit Error Rate (iii) Atmospheric noise (iv) Circuit noise (v) Baseband communication (vi) Broadband communication [12]
(b) A communication system is shown in block diagram form below.
The following powers were measured at various points in the system and the results are given in the Table below.
Measured power in Watts P 1 = 0.05 W P 2 = 25 W P 3 = 0.01 W P 4 = 100 W
(i) Calculate the gain in dB of each individual stage (i.e. Gtx , Gchannel and Grx ) [6]
(ii) Also calculate the overall gain in dB of the system from the input to the transmitter stage to the output from the receiver stage. [2]
P (^1) Transmitter Amplifier gain Gtx
Physical channel gain Gchannel
Receiver Amplifier gain G (^) rx
P 2 P 3 P 4
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- (a) State two independent factors that determine overall signal impairment over a physical channel. [2]
(b) With the aid of suitable diagrams, describe the physical structure and operating principle of the following types of communication media.
(i) Twisted pair wire (ii) Co-axial cable (iii) Optical fibre [12]
(c) An optical fibre data link uses an LED transmitter that launches -15 dBm of optical power into the multimode fibre chosen for the link. The fibre link is to extend to 6 km without repeaters, with a fibre cable loss of 3 dB/km. The fibre cable must be spliced at 1.5 km intervals, with an average loss of 0.3 dB per splice and, in addition, there is a connector loss at the receiver of 0.8 dB. The p-i-n photodiode receiver to be used has a sensitivity of -40 dBm at the wavelength of operation.
Perform an optical power budget for the link and hence calculate the safety margin. [6]
S057 05/03/
- A TV link operates via a satellite that behaves effectively as a frequency converter with a gain of 90 dB (excluding the aerials) and having a common receive/transmit aerial of 30 dB gain.
The satellite is at a distance of 41,000 km from both the transmitting and receiving earth stations. The system operates with uplink and downlink frequencies of 6GHz and 3.75GHz respectively.
Each earth station has an aerial of 60dB gain, and the signal power at the earth transmitting station (i.e. prior to the transmitting aerial gain) is 400W.
(Assume the Aerial Receiving Aperture = A = G λ 2 / 4 π and the speed of propagation of the wave is c = 3 x 10^8 m/s )
Determine:
(i) the power density in (W/m^2 ) incident on the satellite receiving aerial; [6]
(ii) the Effective Isotropic radiated power (EIRP) in Watts radiated from the satellite transmitting aerial; [7]
(iii) the Signal to Noise ratio in dB at the earth station (i.e. after the aerial has amplified the incoming signal) if the combined noise power at this point in the system is 100nW. [7]
END
