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Professor Miller, Manchester Metropolitan University, Electrical Engineering, Communication Engineering.2000 2001 Exam.
Typology: Exams
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Exam ination for th e BEng (H O NS) ELECTR ICA LAND ELECTR O NIC ENGINEER ING (FULL-TIME/PA R T-TIME) YEA R TW O
W ednesday 9 M ay 2001
9 .30 am to 11.30 am
Instructions to Candidates
A nsw er FO UR questions.
continued
(b ) (i) W h at is th e significance of A lternate D igit Inversion and A lternate Mark Inversion of th e b it stream prior to output to th e transm ission ch annel? (ii) A ssum ing a b inary code sequence of 101110010, apply AMI, and A D I to th e resultant b it stream. [6]
(c) (i) In a 6 ch annelPCM system each w ith a b andw idth of 3.4 k H z, calculate th e fram e length in code pulses and th e ch annelb andw idth w h en th ere are 128 quantisation levels. (ii) By w h at percentage w illth e b andw idth increase if th e system is ch anged to 256 levels? [6]
(b ) In a 100 MH z FM system th e deviation ratio is 18 w h en a b aseband of 3. 4 k H z is used. A 15 V, 500 H z test signalproduces th e m axim um frequency deviation.
Calculate:
(i) th e system m axim um frequency deviation; [3] (ii) th e frequency deviation resulting from a 10 V, 3 k H z input; [3] (iii) th e m odulation index for a 5 V, 1.7 k H z input. [4]
(b ) A n A M transm itter h as an output of 50 k W w ith a m odulation of 100% applied to th e carrier. Calculate th e output pow er after th e m odulation is reduced to 45%, one sideband is suppressed, and th e carrier is reduced by 15 dB. [10]
continued
(c) th e signal/noise ratio (in dBs) w h en th e noise pow er is 14 x 10-14^ W. [6] END
