Transcript Telegraphy, Telephone, and Radio

► Phonograph
Demos
Needle, turntable, microscope, vinyl
record
► Regenerative Breaking with two generators.
► Microphone or Speaker and Oscilloscope
► Buzzer
► Coil inside tape player
► Electromagnet (coil) and yardstick w/ magnet
► Animal Cube Child’s Toy
► Van de Graph and radios
► Polarized Filters
► Slinky and telephone cord
► Hydrogen Fuel Cell + Solar Cell
Brief Timeline of telegraph and radio
1833: Electrical Telegraph – using electricity in wires
to transmit dots and dashes.
1835: Relay is developed
1866: First transatlantic cable is successfully laid on
ocean floor, to be used for the telegraph.
1876: First telephone (wires used to transmit voice,
not just Morse codes)
1894: First use of wireless telegraph (transmitting
Morse codes without the use of wires)
1906: First radio broadcast (transmitting voice
without wires)
Samuel Morse develops a code
comprised of dots and dashes.
Morse develops the electromagnetic
telegraph.
A weak current from
The sender activates
a relay that connects
a battery to the
sounder.
A series of Clicks and Clacks
were heard at the relay.
Sounder – Self Interrupting Circuit
Switch or Relay
Voltage Source
http://home.howstuffworks.com/doorbell2.htm
1866 – Laying the transatlantic cable
► Five
attempts to lay cable in 12 years
► 1866 cable was able to transmit eight words
a minute
http://www.cmhg.gc.ca
Alexander Graham Bell and the Telephone
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►
►
Very interested in assisting the deaf. Both his mother
and wife were deaf.
Devised hearing aides
Taught in a school for the deaf
Used the concept of Electromagnetic Induction to convert
sound waves (pressure wave) into electrical signals in 1876
A sound wave is a vibration of air molecules.
Wikipedia
Bell patents the electro-magnetic transmission of vocal
sound by undulatory electric current in 1876
http://sln.fi.edu
Microphone
http://www.acmi.net.au
Bell’s First TelephoneLiquid Transmitter
The sound wave vibrates the diaphragm
that in turn moves a rod up and down.
This changes the resistance making the
Electrical current change in response to
the sound wave.
http://www.juliantrubin.com
Another Transmitter
(The Microphone)
http://www.ctol.org.uk
G. Bell built multiple receivers
using various technologies.
http://www.samhallas.co.uk/museum/telephone.htm
It is important to note that there is no one
"inventor of the telephone" . Bell was merely the
first to patent the telephone. 16 years prior to this,
Antonio Meucci, who did not have $10 to file a
patent, demonstrated his electro-magnetic
"teletrofono" in New York in 1860.
Wikipedia
A 2002 a resolution by the U.S. House
of Representatives, gave its
endorsement of
Antonio Santi Giuseppe Meucci
as the originator of the telephone.
HR 269
The Carbon Transmitter
(microphone)
This Technology
became a basic
component of
telephones for
almost a hundred
years.
http://www.beatmag.net
http://www.exnet.btinternet.co.uk
First Telephone – The Transmitter and Receiver are the same.
http://www.exnet.btinternet.co.uk
Edison’s Recording Devices
The Phonograph in 1877 used telephone
technology to record sounds on a wax
cylinder.
The first voice recorder
Smithsonian
birminghamstories.co.uk
http://www.nps.gov
Sound waves can
be stored directly
in their analog
form by cutting
grooves on vinyl.
http://www.optics.rochester.edu
http://jvsc.jst.go.jp
Record Needle - Stylus
Contacts the recorded disc and transfers its
vibrations to the rest of the system
As the stylus rides along the
walls of the moving groove, it
vibrates back and forth. Two
transducers attached to this
stylus sense its motions and
produce electric currents that
are related to those motions. (A
coil of wire and a magnet move
relative to one another as the
stylus moves and this causes
current to flow through the
coil.) Louis A. Bloomfield
Transducer:
converts input
energy of one
form into output
energy of
another.
http://www.answers.com
So far we have:
•Using wires to transmit short and
long buzzes
•Using wires to transmit voice and
music.
Maxwell’s Equations
1. Like charges repel, unlike charges attract
2. Magnetic fields always have two poles (positive and
negative)
3. A moving/changing magnetic field produces an electric
field.
4. Moving electrical charge (current) produces a
field.
magnetic
Maxwell shows mathematically that if
charged particles are accelerated, that a
wave must be produced, and that the wave
will travel at 186,000 miles/second.
The wave has two parts – an oscillating
electric field and an oscillating magnetic
field.
An electromagnetic wave exists when the changing
magnetic field causes a changing electric field which
then causes another changing magnetic field, and so
on forever.
These oscillating fields together form an
electromagnetic wave.
An electromagnetic wave will travel at the speed of
light, 186,000 miles/sec.
In 1864 Maxwell proves that changes in either an electric field or
magnetic field will produce an electromagnetic wave; a wave that
radiates at 186,000 miles/second.
Hertz’s
Spark and Loop
Experiment
In 1888,
Heinrich Hertz
proved
Maxwell’s
theories with
this experiment.
Hertz said, “I
don’t see any
useful purpose
for this invisible
electromagnetic
energy.”
Any time charge is accelerated, an
electromagnetic wave is created.
► Van
de Graph and Radios
 Try AM and FM settings
► Polarized
Films
First wireless communications in 1895
using Morse codes
Alexander Popov sent over
a distance of 600 meters
http://en.wikipedia.org
Guglielmo Marconi sent
messages to his brother within
the grounds of his Bologna
estate.
http://www.mlahanas.de
The Coherer Tube (filled with iron
shavings) was the Receiver
When the coherer detected a radio wave, the
resistance in the tube changed causing the bell to
ring. The wave was created by a distant spark.
Guglielmo Marconi obtains a patent for
wireless telegraphy in 1896
In 1901, the letter ‘S’ is sent from Cornwall to
Newfoundland.
This proved that wireless telegraphy was possible (and
fast) over long distances.
Wireless Room on board RMS Olympic,
the sister ship to the Titanic.
Wireless technology saves 706 lives after
the Titanic sinks in 1912.
http://www.evaluationengineering.com
Dots and Dashes are digital
Voice and Music are analog
► Digital
is coding a signal using a binary
format, e.g. 0’s and 1’s, dots and dashes,
on and off
► Analog is the process of converting a signal
into a wide range of continuous values.
Digital data requires a computer to decode
(humans were the first computers).
Photographic picture is an analog
image. There are a continuous range
of hues and shades that make up the
image.
www.bbc.co.uk
A digital image is
made up of many
pixels, each pixel
having one color out
of a fixed number of
possible colors.
http://photo.net/equipment/digital/basics
Wireless transmission of Analog Data was
sought as the next big thing.
(“Human Ears Listening to the Radio” –
get rid of digital – the clicks and clacks)
► Transmitting
dots and dashes (digital)
required a human computer to decode
the message.
► Sending
Morse codes was slow
First radio broadcast of audio on
Christmas Eve in 1906
Reginald Fessenden, Canadian
Fessended commemorates this
event by playing “O Holy Night”
on the Violin
Data Transmission
Amplitude is
volume and
frequency is the
pitch.
Audio
This is
Amplitude
Modulation
(AM)
Carrier Wave’s
amplitude is
modulated
Audible range:
20 Hz - 20 kHz
Sounds travels
at 700 miles/hr.
Turned into a
Electromagnetic
Wave
http://www.answers.com
► Frequency,
f = cycles/second (hertz)
► c = 186,000 miles/sec.
► c = 300,000,000 meters/sec.
► l = wavelength (meters/cycle)
►c = f * l
This is Frequency
Modulation (FM).
This requires greater
bandwidth but it is
easier to cancel out
noise.
Turned into a
Electromagnetic
Wave
First radio stations in the US
► WWJ
in Detroit
► KDKA in Pittsburg
► In 1920, the results of
the presidential
election were
broadcasted.
► “San Jose Calling”
was the world's first
radio station with
scheduled
programming in 1910
(now known as KCBS)
► AM
Band - 520-1700 kHz
► FM Band - 87.5 to 108.0 MHz
► Stations west of the Mississippi
start with a K; east of the river
stations begin with W
Electromagnetic Spectrum
http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html
This side of line is
ionizing radiation.
Other uses of Electromagnetic waves
► Cell
phones use microwave radiation
► Radar
► Microwave Ovens
► Lasers
► Global Positioning Systems
► All radio (FM, AM, short wave, CB, Amateur)
► Wireless LANS & Bluetooth
► Remote Control Devices
► X-Rays and CAT Scans
► Magnetic Resonance Imaging (MRI)
E&M Waves can:
► Carry
Information in analog and digital form
 Radio
 Wireless pt to pt Communication
► Transmit
Energy
 Lasers
 Microwave Ovens
► Produce
images inside objects
 X-Rays, Gamma Rays
 MRI
► Produce
light (fluorescent lighting)
Microwave Ovens
Microwave Ovens use 2.45 GHz (GHz = 109
cycles per second)
How a Microwave Works
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Microwaves are absorbed by
water, fats, and sugars (the
stuff in food)
Water is a dipole molecule
with both positive and
negative sides
Water molecules constantly
flip over, trying to align
themselves with the changing
electric field of the microwave
As the water molecules flip
over they rub against each
other making heat
http://www.sciencelearn.org.nz
Transformer steps up the voltage to 2000 volts
Magnetron produces the microwave
Waveguide leads wave into oven cavity
Screen on door blocks microwaves but not visible light.
Difference between Cell Phone and
Microwave Oven

Power



Cell Phone
0.1 Watts
Microwave
1000 Watts
Modulation


Cell phone is
carrying info
Microwave is not
► Amplitude
X-Rays
Electrons are accelerated through a vacuum
tube, they slam into a target material.
Electrons in the target atoms are excited.
When the electrons relax back down into a
lower energy state, they emit X-Rays.
CAT – Computerized Axial Tomography
►A
narrow beam of X-rays is
sent through a part of the
body from many different
angles.
► A narrow beam is sent out
160 times over 1800
► Opposite the beam, a sensor
reads the absorption.
► A computer reconstructs 2-D
cross sectional images.