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Chaos, Communication and Consciousness Module PH19510 Lecture 5 The Telephone.

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Presentation on theme: "Chaos, Communication and Consciousness Module PH19510 Lecture 5 The Telephone."— Presentation transcript:

1 Chaos, Communication and Consciousness Module PH19510 Lecture 5 The Telephone

2 Review of Lecture 3 Dawn of the electric age Key technologies  Cells & Batteries  Electromagnet  Relay Use of standardised code

3 Lecture 4 – The Telephone The nature of sound Telephone principles The early years, Bell & Edison Automatic dialling The Thermionic Valve Multiplexing

4 Electric Universe David Bodanis £7.99 ISBN  Aventis prize for popular science How Electrons hold the universe together

5 Sound Waves Variation in pressure Amplitude (Loudness) Frequency (Pitch) Combine pure tones to form any sound (Fourier) Speed of sound  340 m/s (760mph)  Sea Level Human Ear  30Hz – 20kHz Speech  300Hz – 3.4kHz

6 The Fourier Transform Translates between Time and Frequency Easier to solve some problems in transformed domain

7 Alexander Graham Bell 1876 First Telephone Microphone  Sound  Electricity Wires  Transmit Signal Receiver  Electricity  Sound

8 Thomas Edison ( ) 1877 Phonograph 1877 Carbon granule microphone 1879 Incandescent Light

9 The Carbon Granule Microphone Carbon Granules Diaphragm transmits pressure to granules Granules Pressed together  lower resistance Resistance modulates current Battery at exchange provides power Microphone controls power

10 Telephone with Carbon Microphone Diaphragm Carbon Granules Battery Electromagnet Diaphragm MicrophoneReciever

11 Early Networks Manual switching  Operators with plug boards Bell’s patents expire 1890s 6000 telephone companies !!! (US) Post Office retains monopoly in UK 1889 Strowger invents automatic dialling

12 The Strowger Switch & Automatic Dialling Electromechanical switch 10 horizontal positions 10 vertical positions  100 lines/switch Pulse dialing  Dial phone

13 The Thermionic Valve The Diode 1904 J.Fleming Heated filament  Cathode Electrons liberated If Anode is +ve  Electrons attracted  Current Flows One way device  Anode –ve  No Flow Diode Anode (+ve) Cathode (-ve)

14 The Thermionic Valve The Triode 1907 Lee DeForest Grid between Cathode & Anode -ve voltage on grid repels electrons Control of anode current 1911 Amplification Anode (+ve) Cathode (-ve) Grid

15 Thermionic Valves Amplification from 1911 More electrodes Power Hungry Still used for  CRTs  High Power  microwaves

16 Two into one will go !! Need many circuits between exchanges & especially between cities. Can’t use 1000s of pairs of wire Multiplexing  Time Division Multiplexing (TDM)  Frequency Division Multiplexing (FDM)

17 Time Division Multiplexing (TDM) First used on telegraph Interleave messages Synchronised clocks Digital Signals FUD inarivsvete rL usa F irst u U niver s D ave L a

18 Frequency Division Multiplexing (FDM) Speech 300Hz – 3.4kHz Analogue Signals Modulation  Multiply signal with carrier  Shifts frequency of signal  Allows many signals on one wire From exchange to exchange

19 Amplitude Modulation

20 Frequency Division Multiplexing Speech Signal Modulate 60Khz Carrier 60Hz - 64kHz 64kHz - 68kHz 60kHz 64Hz f  ff 68Khz - 72kHz 72kHz - 76kHz … 300kHz 4kHz f 

21 Frequency Division Multiplexing Combine 12 speech channel to form group  Carriers 60,64,68,72…kHz  kHz Combine 5 groups to form supergroup  60 channels 312kHz – 552kHz Combine 5 supergroups  Mastergroup  300 channels

22 Review of Lecture 4 The nature of sound Telephone principles The early years, Bell & Edison Automatic dialling The Thermionic Valve Multiplexing


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