Transcript Air Navigation_Part 1

Advanced Radio
and Radar
Part 1
Communicating
Introduction
Communication may be defined as
“the exchange of information”
and as such is a two-way process.
It’s the transmission and the receiving
that makes a communication.
Speech is one method of communication.
You need a voice to “transmit” a message
(in the form of sound energy)
and ears to “receive” the reply.
Introduction
However, using sound has drawbacks:
a. The speed of sound is quite slow - 300 m/s.
b. Sound does not travel very far,
even if you have a very loud voice.
c. Sound can be distorted by outside factors echoes, wind & other unwanted noises.
d. Sound will not travel through a vacuum –
it needs a "medium“ to transmit the energy.
Introduction
You can improve the way sound travels
by replacing air with a solid material.
The string carries the sound better than air –
you can speak quietly into one can,
and the person holding the other one
against an ear can hear you easily.
Introduction
The Speed of Sound
Is dependant upon the type and temperature
of the medium through which it moves.
At sea level in dry air at 15°C (59°F),
the speed of sound is 340 m/s (1,115 ft/s).
BUT
At sea level in dry air at 25°C (77°F),
the speed of sound is 346 m/s (1,135 ft/s).
So the higher the temperature
the faster the speed.
Introduction
The Speed of Sound
Is dependant upon the type and temperature
of the medium through which it moves.
and at 25,000 ft,
the speed is only 309 m/s (1,014 ft/s).
While at 250,000 ft,
the speed drops to 269 m/s (883 ft/s).
So the higher the altitude
the lower the speed.
Introduction
The Speed of Sound
Is dependant upon the type and temperature
of the medium through which it moves.
And finally . . . in fresh water at 20°C,
the speed is about 1,482 m/s (4,862 ft/s).
and in solid steel,
the speed is about 5,960 m/s (19,554 ft/s).
But the accepted speed is – 300 m/s
Electromagnetic Waves
While sound works well over short distances,
for long-range communications we need RADIO.
and for radio we need some form of energy.
Electricity can be ‘static’,
like the energy that makes
your hair stand on end.
Magnetism can also be ‘static’,
as it is in a common magnet.
Electromagnetic Waves
While sound works well over short distances,
for long-range communications we need RADIO.
and for radio we need some form of energy.
A changing magnetic field
will induce a changing electric field
and vice-versa — the two are linked.
These changing fields form
‘electromagnetic waves’.
Electromagnetic Waves
While sound works well over short distances,
for long-range communications we need RADIO.
When a direct electric current flows in a wire,
a magnetic field is produced outside of the wire.
+
+
DC
-
Electromagnetic Waves
When an alternating current flows in a wire,
an electromagnetic wave is produced.
As before, the current produces a magnetic field,
but it is changing strength and direction
in sympathy with the conductor’s electric current.
+
+
-
+
-
AC
+-
Electromagnetic Waves
And you can’t change a magnetising force
without generating an electric field . . . e
And you can’t change an electric field
without generating another magnetic field . . . B !
B
e
B
e
B
e
AC
Electromagnetic Waves
This process is ever lasting,
forming a perpetual, ever radiating radio wave.
Travelling at the speed of light
186,000 miles per second
or
300,000,000
meters per second !
B
e
e
B
e
B
e
e
B
B
B
e
AC
Electromagnetic Waves
This process is ever lasting,
forming a perpetual, ever radiating radio wave.
It’s the combination of the
magnetic and electric fields
that form electromagnetic ‘em’ waves.
The frequency of the alternating current
determines the frequency of the ‘em’ waves,
And the power of the alternating current
will govern the range of radiation.
Electromagnetic Radiation
A basic radio system consists of A Transmitter
and a Reciever
The link from the Tx to the Rx
is not sound energy,
but electromagnetic (em) energy, Radio Waves.
Y
Y
Tx
Rx
Transmitter
Receiver
Electromagnetic Radiation
The transmitter converts information
into ‘em’ radiation,
(Sound, Pictures or Digital Code),
and transmits in all directions from the aerial.
Transmitters come in all shapes and sizes,
from TV remote controls of 50 milliwatts,
to radio transmitter of up to 500 kilowatts.
Y
Y
Tx
Rx
Transmitter
Receiver
Electromagnetic Radiation
Electromagnetic radiation travels in waves.
Amplitude
Axis
+3
+2
+1
-1
-2
-3
Amplitude
λ
Frequency = 2 Hz
(i.e. 2 cycles per sec)
0
1
f
2
Time in seconds
(a)
distance from the Amplitude axis to a crest.
A number of Units available
Wavelength (λ) the length of one wave – crest to crest.
Measured in metres, cm or mm
Frequency (f) the number of cycles in each second.
Measured in Hertz Hz
Velocity
(v)
the speed at which the wave moves.
and has the relationship:
=f
3 x108 m/s (speed of light)
Electromagnetic Radiation
One hertz means “one cycle per second”
100 Hz means “one hundred cycles per second”,
and so on.
Commonly used multiples are KHz (kilohertz, 103 Hz),
1,000 Hz
MHz (megahertz, 106 Hz),
1,000,000 Hz
GHz (gigahertz, 109 Hz)
1,000,000,000 Hz
and THz (terahertz, 1012 Hz)
1,000,000,000,000 Hz.
Check of Understanding
Which of the following statements
is a disadvantage of using
sound for communication?
It will not travel through air
It will not travel through a vacuum
It will not travel through water
It will not travel through solid materials
Check of Understanding
What medium replaces sound
for effective long-range communication?
Potential energy
Electrical energy
Kinetic energy
Electromagnetic energy
Check of Understanding
How many Bean cans
would you need for an effective two-way
communication system?
One
Two
Three
Four
Check of Understanding
A radio communications system consists of:
A sender, receiver and
interconnecting wires.
A transmitter, loudspeaker and
interconnecting wires.
A transmitting tower and a car,
or home radio.
A transmitter and receiver.
Check of Understanding
A wave has a frequency of 5 KHz.
What does this represent?
5,000 cycles per minute
50 cycles per minute
5,000 cycles per second
50 cycles per second
Check of Understanding
The shorter the length of an aerial becomes:
The lower the optimum frequency that it will
transmit and receive.
The more efficient it is.
The higher the optimum frequency
that it will transmit and receive.
The less efficient it is.
Check of Understanding
A few more questions.
1. What is the approximate speed of sound?
2. What is the Speed of Light?
3. What is meant by Amplitude?
4. What is the rough power range of transmitters ?
Advanced Radio
and Radar
End of Presentation