Chaos, Communication and Consciousness Module PH19510 Lecture 5 The Telephone

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

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

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

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

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

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

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

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

Telephone with Carbon Microphone Diaphragm Carbon Granules Battery Electromagnet Diaphragm MicrophoneReciever

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

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

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)

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

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

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)

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

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

Amplitude Modulation

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

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

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