Transcript telcommunication revision slides

distance = speed x time
d=vt
Speed
of
sound
340 m/s
Speed
of
light
300,000,000 m/s
transmitter
transmitter
sends signals
receiver
receiver
replays signals
microphone
energy change
microphone
Sound
electrical
loudspeaker
energy change
loudspeaker
electrical
sound
frequency
Number of waves
per second
Wavelength l
Amplitude
High frequency
Low frequency
High amplitude
Low amplitude
wave speed
v
speed = frequency x wavelength
v=fl
Radio waves
Same speed as
light
Aerial
Detects radio
waves
Tuner
Selects one
frequency
Decoder
Separates the audio
signal from the carrier
wave
Amplifier
Increases amplitude
of signal
Electricity supply
Provides energy to
amplifier
Loudspeaker
Changes electrical
signal to sound
Radio Transmission
Radio frequency wave
combined with
audio frequency wave
Radio Transmission
This is called
amplitude modulaton
Amplitude modulation
audio
radio
a.m.
Diffraction
Bending round obstacles
Diffraction
Long wavelength, low
frequency bends more
than short wavelength,
high frequency
Television
aerial
tuner
decoder
(vision)
decoder
(sound)
amplifier
amplifier
TV tube
Loudspeaker
Television
Line build-up
Lines made by electron beam
moving backwards and forwards
across screen
The lines build up to make picture
Television
Brightness variation
Light areas – many electrons
Dark areas – few electrons
Television
Image retention
25 pictures per second
Eye retains image for short time
– pictures seen as moving
smoothly
Colour television
Three electron guns
One to hit red dots
One to hit blue dots
One to hit green dots
Colour television
Colour mixing
Red + Blue = Magenta
Blue + Green = Cyan
Green + Red = Yellow
Blue+Green+Red = White
Colour television
Colour mixing
red
magenta
yellow white
green
blue
cyan
Reflection
Angle of
Angle of
=
incidence reflection
i
i=r
mirror
r
Refraction
air glass
Total Internal Reflection
Above a certain angle
(the critical angle), the
light is reflected.
i
r
Optical Fibres
Used to carry telephone signals.
Signal travels at 200,000,000 m/s
i
r
Optical Fibres
Advantages (compared to wires)
Cheaper, lighter, carry more signals
little energy loss
i
r
Satellites
The higher the satellite
The longer its period
(time for one revolution
round the Earth)
Satellites
Geostationary satellite
Takes 24 hours to make
one revolution
(stays above same point on
Earth’s surface)
Curved Reflectors
Large area collects
more energy
concentrates signal
on detector
Curved Reflectors
Curved reflector
Receiver at
the focus
Curved Reflectors
Curved reflector
transmitter at
the focus