Air Navigation_Part 1

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16 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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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
-

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.

300 m/s.

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.


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

And finally . . .

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



These changing fields form

‘electromagnetic

waves’.

the two are linked.

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

!

AC

e

e

e

B

B

B

B

Electromagnetic Waves

AC

e

e

e

B

B

e

e

e

B

B

B

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 !

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.

Transmitter

Receiver

Tx

Y

Rx

Y

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.

Transmitter

Receiver

Tx

Y

Rx

Y

Electromagnetic Radiation

Electromagnetic radiation travels in waves.

0

1

2

Time in seconds

λ

Frequency = 2 Hz

(i.e. 2 cycles per sec)

Amplitude
(a)


distance from the Amplitude axis to a crest.

Wavelength
(
λ
)


the length of one wave


crest to crest.

Frequency
(f)

the number of cycles in each second.

Velocity
(v)

the speed at which the wave moves.

Measured in Hertz Hz

Axis

Measured in metres, cm or
mm

Amplitude

f

3

x
10
8
m/s (speed of light)



=

f



A number of Units available

+3

+2

+1

-
1

-
2

-
3

and has the relationship:

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, 10
3

Hz),

1,000 Hz

MHz

(megahertz, 10
6

Hz),

1,000,000 Hz

GHz

(gigahertz, 10
9

Hz)

1,000,000,000 Hz

and
THz

(terahertz, 10
12

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 solid materials

It will not travel through air

It will not travel through water

It will not travel through a vacuum

What medium replaces sound

for effective long
-
range communication?

Electromagnetic energy

Potential energy

Kinetic energy

Electrical energy

Check of Understanding

How many Bean cans

would
you
need for
an effective two
-
way
communication system?

Four

One

Three

Two

Check of Understanding

A radio communications system consists of:

A transmitter and receiver.

A sender, receiver and

interconnecting wires.

A transmitting tower and a car,

or home radio.

A transmitter, loudspeaker and
interconnecting wires.

Check of Understanding

50 cycles per second

5,000 cycles per minute

5,000 cycles per second

50 cycles per minute

Check of Understanding

A wave has a frequency of 5 KHz.

What does this represent?

The less efficient it is.

The lower the optimum frequency that it will
transmit and receive.

The higher the optimum frequency

that it will transmit and receive.

The more efficient it is.

Check of Understanding

The shorter the length of an aerial becomes:

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 ?

Check of Understanding

Advanced Radio

and Radar

End of Presentation