Transcript Advanced Studies Unit 18a BTec Convention used in this lesson not recommended Left mouse click option available.

Advanced Studies Unit 18a BTec
Convention used
in this lesson
not recommended
Left mouse click option available
Advanced Studies Unit 18a BTec
Advanced Radio
Advanced Studies Unit 18a BTec
1.
communicating
Communicating
Communication may be defined as the
“exchange of information”
introduction
4/
5/
Communicating
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
 transmitter = voice
receiver
= ears
and
Communicating
Up until the Invention of the Guttenberg
Printing Press in 1436 we used sound in the
form of speech to communicate widely.
…but sound has its drawbacks
• Speed of travel is quite slow in air: 340 m/s at 20ºC or 760
mph (the speed of propagation of sound). *
• Sound will not travel through a vacuum
• it needs a substance or “medium” (normally air) to transmit the
energy.
• …although the medium can also be liquid (eg water or
mercury?) or a solid (eg bar of steel or a quartz crystal)
* speed 350 m/s or 780 mph at 30ºC
so the hotter the day …the faster the speed of sound
6/
Note:
a longitudinal wave
1. the ‘action’ or energy goes in the same direction as the
propagation …ie lies in the same plane
2. none of the people (the ‘medium’) moved closer to the
destination after the shove had finished
3. …but the shove/wave does move or propagate towards
the destination
4. the shove/wave isn’t an object …it has no weight or
mass. It’s an experience, a phenomenon
direction of wave propagation
8/
Hey!
Nobody’s
getting
served any
quicker!
a longitudinal wave
9/
Not from
where I’m
standing!
Sound is …
The plane of action or energy
Woah!
Did the Earth
just move for
you?
direction of wave propagation
Sound limitations
10/
• sound does not travel very far in air , even if you
have a loud voice. It becomes ‘attenuated’ or
weakened by the spongy air
• …but sound can travel for thousands of kilometers
through the sea and through the earth’s solid
surface …and at 1000s of MPH
• echoes, wind and other unwanted noises hamper
reception
11/
Let’s look at how sound
travels through various
media
Propagation or velocity of sound in air
(760 mph)
12/
340 metres per sec
Speed of propagation
Air compression
…in air
at 20ºC
…ie at normal
Air decompression
UK temperatures
Ambient Air
Pressure =
1Bar
input
1
Graphical
representation
of localised air
pressure
longitudinal
sound wave
Propagation or velocity of sound in air
…but at higher temperatures, the speed
of sound increases
nb …that’s why early in 1950’s, the ‘sub-sonic’ RAF world
speed records were conducted in the hot desert
…to delay reaching the so called ‘sound barrier’
14/
Propagation; sound in vacuum
Nothing to
compress ?
input
Air Pressure
= 0 Bar
vacuum
0
15/
Propagation; sound in vacuum
That is why,( if you have ever noticed it), that audio, alarms and
announcements in an aeroplane on the ground are ‘too loud’ for
comfort.
Why is that do you think?
If the aeroplane lost cabin pressure at altitude how will an alarm
audio sound to the passengers and crew who are not on intercom??
input
Air Pressure
= 0 Bar
vacuum
0
All announcements, alarms or bells will be VERY much
quieter.
16/
Propagation; sound in liquid (water?)
1483 metres per sec
Liquids cannot compress …so transmits
the sound very
efficiently and very fast!
…and over great distances
Liquid (eg water or mercury?)
(3,300 mph)
…in
water
Propagation; sound in solids (steel?)
17/
4500 metres per sec
uncompressible …so transmits sound even
faster and more efficiently
Strang
e but
true!
Solid
(Rock? or Quartz Crystal? Steel?
using sound through quartz crystals is extensively used in
electronics such as TV and Radar processing circuits
(10,000+ mph!!)
…in solid steel
…or quartz crystal
…or The Earth
18/
Propagation; sound
Vacuum
…it doesn’t
0 mph
Air
760mph
340 m/sec
Speed of Sound in …
…and for not very far
Recap
Water …and for maybe 1000miles +
1483 metres/sec
3300mph
Steel
10,000mph
4500 metres per sec
Check of understanding
19/
20/
Sound cannot
travel
through a
vacuum!!
Q. So, how do these astronauts communicate
by voice, outside the International Space Station
… without using a radio?
21/
A. By touching space-helmets!
…and, surprisingly, they do this quite often to
co-ordinate their work
Oh! oh!
not so
simples
computer won’t
open the pod
doors, Sergei !
Communicating
radio communication
22/
Radio Waves
Let’s now look at how Radio Waves travel
23/
Radio Waves
24/
• Radio – uses a different energy
• A radio communications system consists of a transmitter (Tx),
to send the message
• …and a receiver (Rx) to receive the reply
25/
Radio Waves
so…
shorthand for a radio transmitter is
Tx …remember this abbreviation!
…and for a receiver it is
Rx …again, remember this abbreviation too!
Radio
26/
• The link between the Tx and Rx this time is not sound energy,
but electro-magnetic (em) energy, (radio waves)
• light and radio waves can travel very well through air, but more
perfectly through a vacuum – and they travel at the same
extremely high speed
• …the speed of light
• …no matter what the speed of the transmitter or receiver is
27/
Radio
Or, if you prefer to put that
speed in context, it is
186, 000 miles per second!!
3 x 108 metres per second
or
(sometimes written as m/s or ms-1)
300,000,000 ms-1
…exactly the speed of light!!
Electro-magnetic energy
Electro-magnetic radiation travels in waves in a similar
fashion to ripples on a pond.
The waves travel in all directions from their source
rather like the pattern produced when a stone is
dropped in
A typical wave can be imagined like this…
28/
electromagnetic energy
it would seem that there is no theoretical
limit to the frequency of em waves, neither
lower nor upper.
the expression “electro-magnetic spectrum”
has been coined to embrace all radiations of this
type, which include heat and light.
…but we will only concern ourselves with the
Radio & Radar region
29/
From transmitter to receiver
32/
A radio Tx converts information into em radiation.
information could be voice, TV pictures or digital
codes
em radiation from the Transmitter (Tx) will then travel
from the aerial or antenna
A radio Rx picks up this signal via a suitable aerial and
converts the em radiation back into information.
simples
Transmitters
33/
You know…
Txs come in all shapes and sizes?
think about it!
Any WiFi device
Man-made
satellights?
such devices will have a very small power output
of about ½ Watt
( not enough to light a single Xmas tree light)
to a couple hundreds of Watts for a
‘freesat’ satellight.
Transmitters
34/
You know…
Txs come in all shapes and sizes?
think about it!
but a BBC television or a Medium Frequency (MF) radio transmitter
will, on the other
hand,
have
a power rating of up to
Any
WiFi
device
500,000Watts
Man-made
ie ½ Megawatt
satellights?
These very high-powered equipments are needed to make
transmissions
towill
all parts
thesmall
country
andoutput
combat
such reach
devices
have aof
very
power
terrestrial
within
the Earth’s
ofinterference
about ½ Wattand
to losses
a couple
hundreds
of Watts
atmosphere.
for a satellite.
Receivers
Rx also come in all shapes and sizes
think about it!
What is electro-magnetic energy?
36/
When an alternating electric current flows in a wire, both electric and
magnetic fields are produced surrounding the outside of the wire.
The frequency of the alternating current will determine the
frequency of the em waves produced, and its power rating and
frequency chosen will govern how that radiation behaves in the
Earth’s atmosphere .
There is no theoretical limit to the frequency of em waves and, as
we’ve seen, the expression “electromagnetic spectrum” has been
coined to embrace all radiations of this type, which include heat and
light.
37/
What is electro-magnetic energy?
Electricity can be ‘static’, like the energy
that can make your hair stand on end.
magnetic field
’B’
Magnetism can also be ‘static’, as it is in a refrigerator magnet.
What is electro-magnetic energy?
A changing magnetic field will induce a changing electric
field and vice-versa—the two are linked.
These changing fields form electromagnetic waves.
38/
39/
What is electromagnetic energy?
B
+
B
weak
B
B
strong
• If we apply a dc voltage from a battery or generator to
a wire conductor …we generate a magnetic field around
the wire and it is usual to show the ‘magnetic field’ as a
letter B and it flows along the direction of the red arrows.
+
-
--DC
40/
What is electromagnetic energy?
B
+
B
BB
• This isn’t a radio wave …it’s just a constant magnetic field. You
would need a magnetic compass to detect it. It quickly becomes
very weak the further from the conductor. It’s constant or ‘static’
…the magnetic field is going nowhere… and will only last as
long as there is a current flowing in the conductor.
+
-
--DC
What is electromagnetic energy?
Let’s now look at applying an
alternating current (ac)
to the wire
41/
42/
What is electromagnetic energy?
++
-
• Now this alternating current introduces a new complexity which
results in an electromagnetic wave being transmitted
-+
~
-+
43/
What is electromagnetic energy? B
B
B
As before, the current produces a magnetic field B as shown
~
Let’s just
slow things
down
What is electromagnetic energy?
44/
B
B
B
but its changing strength and direction in sympathy with the conductor’s
electric current.
~
…but
What is electromagnetic energy?
e
h
e
h
e
h
• You can’t change a magnetising force without
generating an electric field ..e
~
46/
…
but …but!
48/
What is electromagnetic energy?
e
B
e
B
e
B
• You can’t change an electric field without
generating another magnetic B field
~
…again at right
angles to the
electric field that
caused it
magnetic
field
electric field
~
chicken and egg and chicken and egg, and chicken and egg, and chicken and egg etc
Wire conductor
B
How long does this
action continue …when
the radio frequency
ac power source is
removed?
-e
e
-B
Ans: Well
… forever!
Provided the wave remains ‘in
space’ and it isn’t weakened
by air or absorbed by other
physical objects.
but! But!
…
But!!
Although this process is ever lasting
it pushes itself forever outwards
And forms a perpetual, ever radiating radio
wave
51/
What is electromagnetic energy?
e
B
e
e
B
B
…and the speed at which
it radiates is…
The speed of
light!
8
3 x 10 m/s
RF
~~
What is electromagnetic energy? B
e
B
e
B
e
~
52/
B
e
Magnetic Field
‘B’
Magnetic field
‘B’
B
e
Both fields are
90º to each
other
And they propel the electromagnetic radio wave at 90º to
both e and B fields
At exactly 3 x 108 ms-1
no faster
no slower
h
Magnetic field
‘B’
e
Both fields are
90º to each
other
and the e & B fields remain
…at the original frequency
Long after they have left the solar system , the
milky way and the local group of galaxies on their
way to infinity!
electromagnetic energy
56/
• The frequency of the radio frequency, alternating
current will determine the frequency of the em waves
produced
NASA’s Pioneer
10 and 11 spacecraft were launched in
1972/73
40 years old technology
It has a radio to keep in touch with
earth
The power supply for the whole space craft
is 2 nuclear generators on the end of the
arms shown. Originally giving a barely 140
Watts, when it sped past Saturn the power
decayed to 100W.
The radio which has been sending a signal back to
earth has a power of a mere 40W barely enough for
a domestic light bulb.
NASA’s Pioneer
10 and 11 spacecraft were launched in
1972/73
40 years old technology
That radio was turned off by
command from NASA in 2003
These spacecraft were, however,
3metres
(it’s not big)
8 billion miles away.
…and transmitting 40W at a frequency of 2 GHz
(your microwave operates at 3 GHz and blasts out 800w)
It took 12 hours for the radio signal wave front to
reach the spacecraft and another 12 hr for the
return signal to reach Earth.
NASA’s Pioneer
10 and 11 spacecraft were launched in
1972/73
40 years old technology
That radio was turned off by
command from NASA in 2003
These spacecraft are, however,
3metres
(it’s not big)
8 billion miles away.
it appears that radio waves are very robust and can go a
long long way for very little power
It was 80 times the distance the Earth is from the
Sun
Low
Radio & Radar Region High
Freqs
Freqs
kHz
long
range
radio
BBC
World
Svc
Radio
Hams
GHz
MHz
ATC radios
R/C models
Mobile Phones
Radars
Television
Telemetry
Microwave
Ovens
Sat TV
Radio Hams
Digital & WiFi
Data Links
Radar
Missile
Guidance
The Electromagnetic
Spectrum
Low
Radio & Radar Region High
61/
Freqs
Freqs
ie
kHz
long
range
MF
radio
GHz
MHz
ATC radios
EHF
&
Telemetry
Mobile Phones
&
SHF
BBC
Microwave
HF
Radars
VHF
World
Ovens
Svc
&
Television
Radar
UHF
Radio
Sat TV
Hams
R/C models
Radio Hams
Digital & WiFi
Data Links
Missile
Guidance
Extra Hi Freq
&
Super Hi Freq
definitions
62/
We need to cover a few definitions to progress
our understanding of Radio further
63/
definitions
• Frequency (f) – the number of complete vibrations or
Measured in
fluctuations each second (ie cycles per sec). Hertz Hz
• Amplitude (a) – the height of the wave-crest on the
A number of
field strength or power axis.
Units available
• Wavelength () – the distance between any two
identical points in a wave (ie peak to peak ~the length
Measured in
of one whole wave). Greek letter pronounced
Lambda
metres,
cm or mm
• Velocity () – the speed with which the waves moves
…in Metres per
has the relationship:
Greek letter
actually
pronounced
“Nu”
 =f 
second …always
3 x most
108 m/s
…but don’t worry,
people just remember
it as
“V”
electromagnetic energy
definitions
64/
• Frequency (f) – the number of complete vibrations or
fluctuations each second (ie cycles per sec).
• Amplitude (a) – the height of the wave-crest on the
field strength axis.
• Wavelength () – the distance between any two
identical points in a wave (ie peak to peak ~the length
of one whole wave).
This Greek
• Velocity () – the speed with which
has the relationship:
The most useful form of
this expression is to
calculate wavelength
for aerial selection

 =f 
letter is
the pronounced
waves moves
“Lambda”
being a Greek
L for “length”
…so, rearranging for

electromagnetic energy
definitions
65/
• Frequency (f) – the number of complete vibrations or
fluctuations each second (ie cycles per sec).
• Amplitude (a) – the height of the wave-crest on the
field strength axis.
• Wavelength () – the distance between any two
identical points in a wave (ie peak to peak ~the length
of one whole wave).
• Velocity () – the speed with which the waves moves
has the relationship:
= 
f
66/
Advantages of em
Using em energy to carry our communications
information has many advantages compared
with sound energy
Speed of travel is unimaginably fast
…the speed of light (always 3 x 10 m/s),
8
…but let’s get that into the context of
computers
67/
Advantages of em
Using em
energy
to carryofour
communications
Answer:
1 wavelength
3 GHz
…
8
information
compared
Which is Vhas
= many
3 x 10advantages
= 10cm or
with sound energy
f
3 x 109
4”
Speed of travel is
unimaginably fast
Intel
8 m/s)
Pentium(always 3 x 108
…the speed
speed of
of light
light
…the
(always 3 x 10 m/s),
3 GHz
speed
A typical PC Central
Processor Unit
…but let’s get that into the context
(CPU)of
So,computers
how far can our radio wave travel in the time
for 1 cycle of this ‘chip’?
68/
Advantages of em
This is a severe limiting factor for
PC CPU speeds
We need faster radio
waves or smaller CPUs

Intel
Pentium
3 GHz
speed
= 10cm or
4”
We cant have
different ‘newness’ of
data from one side of
a chip
to the other!
A typical
PC Central
Processor Unit
(CPU)
A Radio em wave cannot get further away than 10cm
or 4” before, the next cycle begins
69/
All of a sudden, the speed
of light
doesn’t seem quite so quick!
Electromagnetic waves
70/
• Em waves will travel through a vacuum and so can be
used for communication in space.
•
Em waves travel a very, very long way for a given
transmitter power …providing no material or ‘medium’ is
‘in the way’
71/
Aerial Length
aerials used for transmission or reception operate best
with certain wavelengths.
the length of the aerial dictates the frequency it will receive
most readily.
aerial lengths of /2 and /4 are particularly efficient… ie
half and quarter of wavelength
As we know the velocity of the waves, we can now
calculate the best aerial length for a particular
frequency by finding the wavelength of the wave.
72/
Aerial Length
• eg
For
f = 200 kHz,
As we know
=
&
We need to rearrange
=
f
=
Wavelength
….nearly there!

300,000,000
300000,000
200,000
200,000
=
*
300,000,000 m/sec
1500 metres
Aerial Length
73/
So, given that the
wavelength for our
200kHz radio is …
=
1500 metres
The best aerial length would be
Which would be…
 /2  /4
or
750m
or
375m
Aerial Length
74/
• So what aerial lengths would best suit a
frequency of 100 MHz?
300,000,000
f = 100,000,000
=
=
…best Ae
length?
λ/2
3 metres
1.5 m
or
λ/4
0.75 m
Aerial Length
75/
Notice – the higher the frequency,
the shorter the aerial required.
What does this tell us about the
operating frequency of a car-mounted
radio aerial compared to a hand held
mobile phone?
for 100 MHz?
…best Ae
length?
λ=
λ/2
3 metres
1.5 m
or
λ/4
0.75 m
76/
OK, they were a few fundamentals to be going
on with…
Let’s look back in time to see how ‘radios’
got started.
77/
Marconi
in 1901 the Italian born inventor, entrepreneur and businessman …
Gulielmo Marconi claimed his system was the ‘first to transmit and receive
long range radio signals from Cornwall to Newfoundland’ (not yet part of
Canada at that time).
this has since been disputed for a number of robust scientific reasons
but, as a publicity stunt, it worked. What is not disputed is the fact
that his system was the most effective in The World at that time.
Tesla
Marconi
previously, in 1899 in the USA, the Marconi instruments were tested and
they found his wireless system “… the principle component of which was
discovered some twenty years ago, and this was the only electrical device
contained in the apparatus that is at all new"
also, Nikola Tesla, a rival in transatlantic transmission, stated after being
told of Marconi's 1901 transmission that : "Marconi is a good fellow. Let
him continue. He is using 17 of my patents.“
it didn’t matter. The Funds poured in
78/
79/
Marconi, stung by criticisms and incredulity, prepared a better organized and
documented test.
in February 1902, the SS Philadelphia sailed west from Great Britain with Marconi
and his receiver aboard, carefully recording signals sent daily from the Cornwall
station.
The test results produced audio reception up to 3,378 kilometres (2,099 mi) nearly
the same distance as the Newfoundland test…but unlike that test, it was at night!
During the daytime, signals had only been received up to about 1,125 kilometres
(699 mi). …this is in accordance with present day theory and experience.
night ranges are always greater than by day
…so what about his first 1901 test?
80/
the Marconi radio waves , originally called Lorenzian waves, were sent in
groups of short and long signals by switching the transmitter off and on.
ie Morse Code.
His 1901 transmission consisted of 1 letter ‘S’ Morse code being endlessly
repeated. Possibly why the 1901 results may have been imagined whereas
1902 results were conclusive. No matter, he was a world-beater.
although effective, this system did depend on the operators interpreting
the Morse Code sequence– not something everybody could do.
Amplitude
modulation
87/
What was needed was a means to use speech to modulate the CW
rather like a tap can modulate the flow of water
The superheterodyne principle offers a way to achieve this
The ‘superhet’ principle involves the effect that one ‘sine wave’ has over
another adjacent ‘sine wave’ … which is of a different frequency
Notice that no mention has been made of electronics…!!!
This is because it is quite simply a mathematical process …
Amplitude
modulation
88/
superheterodyne
It applies to things that rotate or vibrate or just change over a period of
time …in a sinusoidal fashion
that is … Simple Harmonic Motion …or SHM which includes pendulums
eg
two car engines running at slightly different speeds
two waves in the sea meeting and interacting
This is because it is quite simply a mathematical process …
Or the interaction of two ac electrical signals
of different frequencies
Amplitude
modulation
89/
superheterodyne
this principle which demonstrate that if you ‘mix’ or ‘modulate’ any
sort of sinewave force (that’s the dyne bit) with another sinewave (of a
same similar …that’s the hetero bit), the result is a
has
complex wave which
sum and difference frequencies embedded within it.
Amplitude
modulation
90/
superheterodyne
&
frequencies
Amplitude
modulation
Adding two sinewaves
f1
&
f2
composite
the upper sinewave has a lower frequency f1
than the next down sinewave of frequency f2
the resultant wave form shows another virtual sine wave of
frequency f2
- f1
91/
Amplitude
modulation
Adding two sinewaves
f1
+
f2
the resultant wave is the
difference frequency
f2 - f1
92/
Amplitude
modulation
Adding two sinewaves
93/
f1
+
f2
Fd
=
2 kHz
sum
…this is the virtual waveform of the difference frequency
So if f1 = 250 kHz (ie 250,000 Hz)
F (difference) =
Fd
= 252 kHz
-
250 kHz =
& f2 = 252 kHz
2 kHz
Then …
Amplitude
modulation
Adding two sinewaves –the
SUM freq
94/
f1
+
f2
sum
the resultant wave form shows another virtual
sine wave of frequency
f1 + f2
=
fSUM
So if f1 = 250 kHz & f2 = 252 kHz
Then …
fSUM
=
502 kHz
Then …
Then …
Amplitude
modulation
95/
Sum & Difference
Frequencies
…this applies to interaction of all sinusoidal waves
they could be soundwaves
or wave-motion at sea
or engines at slightly different
speeds to each other
…which creates an
unpleasant ‘beat
frequency’ of
vibration ..which can be
catastrophic!
This effect has
even resulted in old,
badly designed
propeller airliners
shaking themselves
into fatigue failure
and even
destruction!
Amplitude
modulation
Sum & Difference
Frequencies
…this applies to interaction of all sinusoidal waves
they could be soundwaves
or wave-motion at sea
or engines at slightly different
speeds to each other
…which creates an
unpleasant ‘beat
frequency’ of
vibration ..which can be
catastrophic!
effect has
This isThis
caused
even led to
by the
propeller airliners
difference
in
shaking themselves
into fatigue failure
frequency
even
betweenand
the
destruction!
two
96/
Amplitude
modulation
97/
This ‘beating together’ phenomenon also
applies to electrical currents & radio
waves
…it is entirely a physical example of a simple,
mathematical, trigonometrical relationship.
… which we will not go in to!
but just take on board; 2 frequencies
beating together do produce
Sum and Difference frequencies
Amplitude
modulation
Sum & Difference
Frequencies
Amplitude Modulation with regards to
Radio Waves
98/
Amplitude
modulation
Sum & Difference
Frequencies
let’s look at this in a graphical way
amplitude
frequency is along the bottom of the graph
…and signal strength or amplitude is along the
vertical
frequency
99/
We’re now going to look, using the
frequency domain, at a hypothetical radio
transmitter receiver on a random
frequency, say , 2182kHz or
2182000Hz if you wish
2182
kHz
transmitter
Amplitude
modulation
CW
the frequency domain
101/
Watts
Signal strength
We now transmit (Tx) on
an RF of, say, 2182 kHz
Radio Frequency
2182
kHz
F
0
Electromagnetic
spectrum
Amplitude
modulation
CW
Signal strength
Amplitude
modulation
Let’s look at this effect another way …
Radio Frequency
We now stop
transmitting
on
That is how Morse
Code could be sent
…and very
efficiently too!
off
2182
kHz
F
0
Electromagnetic
spectrum
102/
Amplitude
modulation
CW
Let’s look at this effect another way …
This is interrupted
Continuous Wave (i-CW)
but very often
referred to as just…
… but you’ll need a
CW
Signal strength
specialist receiver
with a Beat Frequency
Oscillator to be able to
hear any Morse Code
Radio Frequency
103/
2182
kHz
F
0
Electromagnetic
spectrum
transmission
Signal strength
Amplitude
modulation
CW Morse
104/
Nothing
heard on
frequency!
CW
2182
kHz
Ordinary AM radio
Radio Frequency
2182
kHz
F
0
Electromagnetic
spectrum
Reception
transmission
Now let’s look how a radio with a
Beat Frequency Oscillator
BFO
would receive that same transmission.
Signal strength
Amplitude
modulation
CW Morse
106/
Dah Dah Dit
CW
2182
kHz
BFO
AM radio with a
Beat Freq Osc
Radio Frequency
2182
kHz
F
0
Electromagnetic
spectrum
Reception
Amplitude
modulation
CW Morse
107/
Amplitude
modulation
CW Morse
108/
Amplitude
modulation
CW Morse
109/
i.f.
30
kHz
i.f.
BFO
31 kHz
Amplitude
modulation
CW Morse
What do we know happens when
you ‘mix’ 2 sinewave frequencies
together ?
Clue: they ‘Beat’ together just like two
car engines at slightly differing speeds
Ans: We generate Sum and,
more importantly here,
Difference frequencies!
110/
Amplitude
modulation
CW Morse
111/
Dah Dit Dah
Dit Dit
…but what the difference is
depends on where the listener
moves the BFO (Beat Freq Osc) knob
to
as 1kHz pulsed tones
1.5
1.0
31 kHz
2.0
0
BFO freq difference
1
30 kHz
i.f.
Amplitude
modulation
CW Morse
112/
Dah Dit Dah
Dit Dit
…but what the difference is
depends on where the listener
moves the BFO (Beat Freq Osc) knob
to
You hear it as higher
1½ kHz pulsed tones
1.5
1.0
31.5
kHz
2.0
0
BFO freq difference
1.5
30 kHz
i.f.
Signal strength
Amplitude
modulation
CW Morse
113/
Dah Dit Dah
Dit Dit
CW
2182
kHz
BFO
AM radio with a
Beat Freq Osc
??
the pitch of the tone /
Morse you hear is
dependant upon your BFO
setting
…it’s entirely the
listeners choice
30 kHz
Radio Frequency
Reception
i.f.
Amplitude
modulation
CW Morse
114/
Amplitude
modulation
When there is no
1.5 kHz tone
modulation all of
the power is
transmitted at the
Carrier freq
-1.5
kHz
115/
Now, what happens if we
modulate the Carrier Wave with
an amplified single tone of say
1.5 kHz?
+1.5
kHz
This generates Amplitude
Modulation of the
carrier
Signal strength
giving sum and difference
When the tone is
frequencies
present, the Carrier
298.5 kHz
301.5 kHz
Wave is being
modulated ie
diminished/
Notice: power is shared
attenuated to
between the sum,
provide power for
difference and
the Sum and
300 kHz
Difference
carrier
frequencies
Radio
Frequency
F0
frequencies.
Amplitude
modulation
116/
Dah Dit Dah
Dit Dit
Amplitude
Signal strength
Modulated
Carrier Wave
(MCW)
The pitch/tone of
the Morse is set
by the
transmitter
Only a simple Rx required
-1
kHz
+1
kHz
Tone
on
345 kHz
345 kHz
Radio Frequency
F0
Ordinary AM radio
Amplitude
modulation
117/
Signal strength
-1
kHz
+1
kHz
Tone
Off
on
345 kHz
Radio Frequency
F0
…mainly used for
Aircraft ‘Navaid’
Beacons Morse
Code Identification
signals
Amplitude
modulation
118/
Amplitude
Modulated
Signal strength
Carrier Wave
Only a simple Rx required
-1
kHz
+1
kHz
Tone
on
345 kHz
Radio Frequency
F0
Amplitude
modulation
119/
Modulated Carrier
Wave
Signal strength
-1
kHz
+1
kHz
Power is
divided
between
upper, lower
and carrier
…but does not
carry as far as
CW morse
345 kHz
Radio Frequency
Only a simple Rx
required
F0
Amplitude
modulation
120/
but instead of using a single tone to ‘modulate’ the
carrier wave …
…what if we used voice or music to
Amplitude Modulate the Carrier
Wave over a band of frequencies ?
Amplitude
modulation
121/
Di Dum
Li Laaaaahh
………………... Di!
Carrier Wave
Blah!
Amplitude
modulation
122/
Let’s look at that in the
“Frequency Domain” again
…Centred on Tx Freq of
Say, 1442kHz
When the speaker talks
Which
needs to
convey
…he
Amplitude
Modulates
the
strength
the carrier
most
of the of
tones
in
wave … his voice
not at one single frequency
but a broad
frequencies
‘Difference’
‘Sum’
1442 kHz
freqs
freqs
Radio Frequency
F0
band of
Radio
Luxembur
g Freq
Amplitude
modulation
Carrier
Wave
123/
lower
sideband
upper
sideband
‘Difference’
‘Sum’
1442 kHz
freqs
freqs
Radio Frequency
F0
To recreate the original
voice, in a simple superhet
receiver …requires the
reception of BOTH side
bands to be intelligible.
Carrier
Wave
Amplitude
modulation
lower
sideband
upper
sideband
‘Difference’
‘Sum’
1442 kHz
freqs
freqs
F0
124/
The transmitted power is
shared between both
sidebands and the carrier.
 Tx power is
being wasted
lower
sideband
Carrier
Wave
Amplitude
modulation
each sideband is the
mirror image of the
other
upper
sideband
‘Difference’
‘Sum’
1442 kHz
freqs
freqs
F0
125/
AM is OK for V/UHF Air
Traffic comms as it is
cheap, reliable and the
equipment common and light.
Quality or ‘fidelity’ is limited
with AM due to the RF bandwidth available between
channels
lower
sideband
Carrier
Wave
Amplitude
modulation
126/
Hi Fidelity requirements for modern
radio entertainment has been
addressed with the advent of
Frequency Modulation and then more
recently, Digital Radios allowing, far
upper
higher quality in terms of interference
sideband and audio freq range
‘Difference’
‘Sum’
1442 kHz
freqs
freqs
F0
Amplitude
modulation
268.625
lower
upper
simple Double Side-Band
AM
AM
Cranwell Tower, ASCOT213 on
Uniform
268
decimal
ASCOT213
nothing
heard,625
request
join downwind
for Runway
changing
to Victor
26 Left hand for visual approach to
land.
267.000
268.600
268.625
268.000
Tone
VHF
select
UHF
Guard V
Guard U
127/
Amplitude
modulation
268.625
125.05
simple Double Side-Band
AM
Cranwell Tower, ASCOT213 now on
Victor, 125 decimal 05 request
join downwind for Runway 26 Left
hand for visual approach to land.
268.625
125.050
168.050
268.050
135.050
select
Tone
VHF
UHF
Guard V
Guard U
128/
Amplitude
modulation
129/
I think I may have
microphone
Modulated Carrier Wave
amplifier failure …I
will try to transmit
MCW
the radio failure
code using 1kHz
125.05 MHz
‘tone’now
dashes
Cranwell Tower, ASCOT213
on and
my transmit switch
Victor, 125 decimal 05 request
join downwind for Runway 26 Left
hand for visual approach to land.
Mode now simply
-1
kHz
+1
kHz
268.625
125.050
168.050
268.050
135.050
select
Tone
VHF
UHF
Guard V 121.5
Guard U 243.0
Amplitude
modulation
BUT those techniques still don’t give a
transmitter greater range…needed for
HF comms
What if we put all transmitted power in to one or the other
Carrier
Wave
side band and suppressed the carrier?
lower
sideband
upper
sideband
‘Difference’
‘Sum’
1442 kHz
freqs
freqs
F0
130/
Amplitude
modulation
131/
What if we put all transmitted power in to
one or the other
side band and suppressed the carrier?
upper
sideband
only
nb…the trouble is that
receiving SSB on an
ordinary domestic
medium wave AM radio;
the audio would be
6742
utterly garbled and
not decipherable in any
way!
Ordinary AM radio Rx
6742 kHz
F0
“Gbble hmblfmbgb
Pmmblwrbbl”
Amplitude
modulation
Single Side Band
132/
upper
sideband
nb…the trouble is that
receiving this on an
ordinary domestic
medium wave AM radio;
the audio would be
A Single Side Band
(SSB)
receiver
6742
overcomes this
by re-
utterly garbled and
not decipherable in any
way!
6742 kHz
F0
synthesising the
missing sideband
and carrier wave
…in the receiver
Amplitude
modulation
Single Side Band
133/
upper
sideband
A Single Side Band
6742
Single
side-band
Rx
(SSB)
mode
receiver
overcomes this by re-
CW DSB
synthesising the
missing sideband
…in the receiver
SSB U
SSB L
6742 kHz
F0
Amplitude
modulation
Single Side Band
Mainly used at
134/
Missing sideband re-synthesised
reception by Single Sideband Receiver
HF and
(SSB) Rx
MF frequencies for
Has range Advantage
over DSB mode
Doubles channels
available.
Carrier
Wave
Global Coverage
…but no point
atV/UHF
freqs
lower
sideband
on
upper
sideband
‘Difference’
‘Sum’
6742 kHz
freqs
freqs
fidelity too poor
for entertainment
radio
Amplitude
modulation
Single Side Band
135/
Civil & Military long
range voice comms
tends to use Upper
Side Band
Military Tactical Data
Link tends to use
Lower Side Band
(in the HF freq band)
(in the HF freq band)
lower
sideband
Used extensively
Military and Merchant
Navy
upper
sideband
6742 kHz
Used by Armies for
beyond line of sight
communications
Amplitude
modulation
Shanwick this is 136/
Rafair2134 on 8891
upper, position 5630
North, Ten West at
1510, estimating
Civil & MilitaryIceland
long
boundary at…
range voice comms
over!
tends to use Upper
Side Band
Single Side Band
Military Tactical Data
Link tends to use
Lower Side Band
(in the HF freq band)
(in the HF freq band)
lower
sideband
Used extensively
Military and Merchant
Navy
upper
sideband
8890
8000
8800
8891
6742
kHz
kHz
upper
lower
Used by Armies
for beyond line of
sight
communications
Amplitude
modulation
Shanwick this is 137/
Rafair2134 on 8891
upper, position 5630
North, Ten West at
1510, estimating
Civil & Military long
Iceland boundary at…
range voice comms
over!
tends to use Upper
Side Band
Single Side Band
Link Manager from Tactical
Director;
‘Alligator’
Military
Tactical
Data Data
frequency
LinkLink
tends
to use now
Lower
Side
Band
6715
lower.
(in the HF freq band)
(in the HF freq band)
lower
sideband
Used extensively
Military and Merchant
Navy
upper
sideband
6715
6700
6000
0000
6710
kHz
upper
lower
Used by Armies
for beyond line of
sight
communications
138/
The legitimate nick-name for NATO
Link 11a is
… Alligator
If you actually listen to the audio that the
link data makes it’s an awful croaking
scraping sound…
…just like an Alligator’s mating call
…and that is exactly how it got
it’s name
Amplitude
modulation
Single Side Band
Largely surpassed in quality and effectiveness by
Satellite Communications but SATCOM on-air
time is expensive
…SSB remains an extensively used
prime communications method in the HF
band
SSB on-air time is …free!
but not necessarily the
commercial services you might
request
139/
140/
SSB
It is used for:
Procedural control of military &
commercial aircraft on long range
trans-oceanic flights
eg Shanwick ,
Iceland, New York
etc
Military long range Flight
Following services and VOLMET
aviation weather services
Long Range, Link 11a Alligator
Data Link
eg RAF ‘TASCOM’ and
‘RAF VOLMET’
USAF ‘MAINSAIL’
NATO air and naval units
etc etc etc
141/
SSB
It is not used for:
Entertainment Radio Channels
Because …
audio quality or ’fidelity’ is limited
you need an expensive,
specialist SSB radio
receiver which can
synthesise the missing sideband
142/
Let’s now review the
AM
radio modes and their uses
•
CW
Carrier Wave (Morse only – no voice).
Needs a receiver BFO. Pitch of
received tones set by the listener using BFO. Generally in HF band.
Ideal for very long range comms. Used by, mainly “Hams” now, but still
some Military & Commercial operational messages. Can ‘get through’
•
MCW Modulated
Carrier Wave (Morse and data - no voice) …simple
basic radio
receiver required. Ideal for NAVAID ident letter codes and ‘distress
tones’ in MF, HF, VHF and UHF. Not as range efficient as CW
•
DSB
Double Side Band (Voice, line-of-sight tactical Digital Data-Link (in UHF band) and
NAVAID beacon data)
-operational or entertainment, ranging from MF
(Medium Wave) broadcasters through to VHF commercial stations to
Air Traffic and Citizen Band radios. Limited quality/fidelity due to
channel spacing.
•
SSB Single
Side Band (long range voice and ‘beyond the horizon’ tactical Digital Data-Link
in, mainly, HF band.)
Used by commercial Oceanic Control agencies,
commercial and very long range military Ship to Shore connections,
RAF, USAF and commercial Flight Watch services.
•
CW
Carrier Wave (Morse only – no voice).
Needs a receiver BFO. Pitch of
received tones set by the listener using BFO. Generally in HF band.
Ideal for very long range comms. Used by, mainly, “Hams”, now but still
some Military & Commercial operational messages.
•
MCW Modulated
Carrier Wave (Morse and data - no voice) …simple
basic radio
receiver required. Ideal for NAVAID ident letter codes and ‘distress
tones’ in MF, HF, VHF and UHF. Not as range efficient as CW
•
DSB
Double Side Band (Voice, line-of-sight tactical Digital Data-Link (in UHF band) and
NAVAID beacon data)
-operational or entertainment, ranging from MF
(Medium Wave) broadcasters through VHF commercial stations and
Taxis to Air Traffic and Citizen Band radios. If analogue, then limited
quality/fidelity due to channel spacing.
•
SSB Single
Side Band (long range voice and ‘beyond the horizon’ tactical Digital Data-Link
in, mainly, HF band.)
Used by commercial Oceanic Control agencies,
commercial and very long range military Ship to Shore connections,
RAF, USAF and commercial Flight Watch services.
145/
Amplitude
modulation
146/
This single 11/2 kHztone
Amplitude Modulation of the
generates sum and
difference frequencies
carrier
-1.5
kHz
Signal strength
+1.5
kHz
Radio Frequency
88.90
MHz
F0
BBC radio2
VHF
147/
It is now accepted that there are around 100 to 200
thunderstorms per day across the globe…
…recent satellite data indicates that there are around 3million flashes per day
…producing 30 flashes per second around the globe
…each producing a spike of em radio radiation
…these flashes are cloud to ground, or cloud to cloud or even weaker
ones which shoot 400 miles in to space and have names such as
sprites, elves and ‘blue jets’.
…but 10% of all flashes are the renegade ‘positive flashes’ which produces
10 times the power
148/
Then there is man-made interference
Sparks from machinery such as
electric motors, vehicles etc
Amplitude
modulation
149/
Signal strength
This interference shows up on
the frequency domain view
Radio Frequency
This interference ruins
the
of
the
-1.5 fidelity
+1.5
…as fleeting and ever
kHz
kHz
received
signal
andspikes
changing
spread across the em
appears as crackles
and
spectrum
bangs to the listener
88.00
MHz
F0
150/
How can we get around
this interference?
Frequency Modulation
With radio Frequency Modulation
(FM); audio or information is
conveyed over a carrier wave by
varying its instantaneous
frequency. This contrasts with
amplitude modulation, in which the
amplitude of the carrier is varied
while its frequency remains
constant.
151/
Frequency Modulation
With radio Frequency Modulation
(FM); audio or information is
conveyed over a carrier wave by
varying its instantaneous
frequency. This contrasts with
amplitude modulation, in which the
amplitude of the carrier is varied
while its frequency remains
constant.
152/
Frequency Modulation
FM is suitable
forview
HiFi transmissions
Time-Line
instantaneous
Amplitude is key
to extracting the
information from
the signal
instantaneous
Frequency is key
to extracting the
information from
the signal
Example
is a simple
So interference
single
tone…but
could
spikes
are not
be processed
voice or music
Amplitude Modulation
of the carrier
Frequency Modulation
of the carrier
time
Amplitude is (nearly)
irrelevant with FM
153/
Frequency Modulation
FM is suitable
forview
HiFi transmissions
Time-Line
instantaneous
Amplitude is key
to extracting the
information from
the signal
instantaneous
Frequency is key
to extracting the
information from
the signal
Example
is a simple
So interference
single
tone…but
could
spikes
are not
be processed
voice or music
Amplitude Modulation
of the carrier
Frequency Modulation
of the carrier
time
Amplitude is (nearly)
irrelevant with FM
154/
Amplitude Modulation
The process of
extracting the
information /sound
signal from a AM
signal is called …
155/
Detection
AM Received signal
…after tuner
back in time
detector
Amplitude Modulation
The process of
extracting the
information /sound
signal from a FM
signal is called …
156/
Discrimination
FM Received signal
…after tuner
back in time
discriminator
recap
CW
Continuous Wave
Modulated CW
MCW
AM
Amplitude Modulation
Single Side band
SSB
FM
157/
Frequency Modulation
Digital
Morse only.
efficient
Morse dentification of Radio
Beacons
*
Need specialist
Rx with a BFO.
No Voice
Inferior range to
CW but simple Rx
Radio 5 Live at 330 kHz?
Or Cranwell Tower 125.05 MHz or MF NAVAIDS
RAF Flight Watch 6742-upper or
Shanwick or Iceland or New
York OCAs on 8879-upper
entertainment radio, marine channels & NAVAIDS
…the future Data Links, entertainment TV & radio and new intership marine comms including Distress Comms
Radio ‘hams’ around the world still
enthusiastically use this mode
Amplitude
modulation
‘EM’ radio energy can be made to carry
speech if we combine or mix the lowfrequency (Audio Frequency)currents
produced by speaking into a microphone,
with the high-frequency currents (CW)
that produce radio waves. This
combination process is called amplitude
modulation (AM).
158/
Amplitude
modulation
159/
It is an electronic circuit called an
oscillator
which produces the continuous
high-frequency (Radio Frequency) current
which has a fixed frequency chosen from the
EM spectrum. This fixed-frequency
alternating current produces the em “carrier
wave”.
160/
The audio-frequency (AF) current and the radiofrequency (RF) current are mixed in the transmitter
so that the carrier wave is MODULATED by the AF
current, in such a way as to duplicate the pattern of
sound waves fed into the microphone. A carrier
wave can be modulated in one of two ways, either by
amplitude modulation (AM) or by frequency
modulation (FM).
161/
Amplitude Modulation
(AM)
The simplest form of transmission is basically the
way Marconi sent his first transatlantic message.
The transmitter is switched alternately “ON” and
“OFF” to interrupt the carrier wave. This
modulates the amplitude from maximum to zero ,
and then back to maximum, producing pulses of
different lengths which represent the dots and
dashes of the Morse Code
162/
Whist this system is ideal for Morse, it is not good
enough for speech or music, because sound requires
many more variations (or steps) to achieve an
accurate reproduction. An improvement is to alter
the amplitude, or ‘modulate’ the RF Radio
Frequency of the carrier wave in step with the
much lower AF Audio Frequency.
Fig 1-6: AM transmitter block
diagram
• Fig 1-6: AM transmitter block diagram
163/
Parts of the basic transmitter
164/
• Master Oscillator. This generates a sinusoidal voltage (the carrier)
at the required RF frequency (fo). Oscillators are often crystalcontrolled to ensure good frequency stability.
• Buffer Amplifier. This isolates the oscillator from the power
amplifying stage, and prevents instability occurring.
• Power Amplifier. This is used to increase the power of the signal to
the required level before radiation from the aerial (fm).
• Amplifier. This amplifies the microphone signal to the desired level
for output.
165/
The modulation takes place in the power amplifier
stage. If the input frequencies to the modulator
are fo from the oscillator and fm from the
microphone, we find that the output of the power
amplifier will consist of 3 frequencies:
Amplitude Modulated
transmitter block diagram
AM transmitter block diagram
166/
Parts of the basic transmitter
167/
• Master Oscillator. This generates a sinusoidal voltage (the carrier)
at the required RF frequency (fo). Oscillators are often crystalcontrolled to ensure good frequency stability.
•
Buffer Amplifier. This isolates the oscillator from the power
amplifying stage, and prevents instability occurring.
•
Power Amplifier. This is used to increase the power of the signal to
the required level before radiation from the aerial (fm)
•
Amplifier. This amplifies the microphone signal to the desired level
for output.
168/
• The modulation takes place in the power amplifier stage. If the input
frequencies to the modulator are fo from the oscillator and fm from
the microphone, we find that the output of the power amplifier will
consist of 3 frequencies:
• The carrier (fo).
• The carrier minus the audio frequency band (ie speech) (fo – fm).
•
The carrier plus the tone frequency band (fo + fm).
169/
For example, if the audio frequency ranged from 30 to
300 Hz* and the carrier was 1 MHz, then the
frequencies in the output would look like:
* This is small range would only give
pretty poor quality or fidelity eg like
the quality a telephone!
SSB
170/
Transmitting only one sideband …by suppressing the Carrier Wave and
the other duplicate sideband means all of the output power can be
applied to the remaining sideband – far, far more efficient; giving a
much greater range for the same Tx power available and potentially
releasing 50+% of available frequency space.
It is only used in the long wave
frequency band of 2
to 30Mhz.
SSB
172/
SSB operation, however demands a more sophisticated and expensive
transmitter.
More importantly, the receiver is expensive because the missing sideband has
to be, somehow generated, to make the resultant audio intelligible;
ie it is not possible to understand SSB voice traffic on a
simple AM receiver. It sounds completely garbled!
SSB equipment, therefore, is not used for entertainment or domestic radio
broadcasts.
173/
One great drawback of the simpler double sideband AM system
is the need for such a large bandwidth to accommodate all
radio stations including both sidebands,
Another drawback is that for High Fidelity quality ~ HiFi
,approximately 20KHz is needed for each sideband. A massive
chunk of the available frequencies for broadcasting for just
one station.
in a limited Radio Frequency spread (30 KHz to 3 MHz in
Medium Frequency MF and High Frequency HF bands).
this means, in reality, that the MF-AM system could not handle
Hi Fi and only have 148 stations at any one time.
174/
Try tuning through an AM band radio and see how close the
stations are together!
175/
Obviously, when many transmitters are crammed into a small
band and overlap each other there is a big problem with signals
from other transmissions breaking into the one you are using –
this is known as “mutual interference”.
… and we are only discussing Mono systems. For stereo
transmissions the problem would be doubled. As a result there are
no Stereo AM transmissions in the MF and HF broadcast
frequencies.
176/
Another great drawback is that random electrical ‘noise’, (some natural
generated some man-made generated ), is received and amplified the same as
any information or music sent from a transmitter. The result is distortion,
‘crackling’ and ‘fading’ which affects the quality of reception (ie fidelity)
177/
To overcome AM limitations of mutual interference (crowding) and lack
of HiFi, the use of short-range frequency modulated systems has
become necessary.
Frequency Modulation (FM)
With frequency modulation, the carrier wave has a constant amplitude
and a much higher frequency than AM signals. Modulation is achieved
by shifting the carrier frequency, f0 ,up and down slightly in step
with the audio frequency.
Although this shift is small it gives better results because it is less
prone to atmospheric or man-made noise.
178/
Try listening to an AM signal as you pass by an electric pylon or
enter a tunnel. The AM signal is distorted or lost, but an FM signal
will be largely unaffected by the same conditions. FM is used in
the range 88-108 MHz for high quality broadcasting; this
frequency range is known as the Very High Frequency (VHF) range.
179/
The emergency services, such as Coastguard and Lifeboats, used FM
radios using VHF freqs above Civil Air Traffic (AM) …around 150MHz
Global Maritime Distress Safety System it’s big!
Emergency and maritime agencies, plus boat and ship owners have now been
banished from FM VHF and must use a much more sophisticated and secure
system ; GMDSS, a digital system using Digital Selective Calling (DSC),
whereby every ‘participant’ or vessel has a unique ‘digital address number’ or
Maritime Mobile Address Identity (MMAI) which allows one-to-one conversations
in a busy radio environment. Yet to be implemented in RAF SAR helicopters who
retain the old FM VHF radios so voice co-ordination with emergency services is
therefore problematical. A huge number of people with boats will be using this
now. It’s probably the most commonly used radio system by civilians on a day to
day basis. We will not, currently, look any further at GMDSS or DSC
Phase Test
300 000 000 000
metres per sec
3x
1011
m/sec
180/
What is the speed of light?
30 000 000 000
metres per sec
3x
1010
m/sec
300 000 000
metres per sec
3 000 metres
per sec
108
3 x 103
m/sec
m/sec
3x
Click Buttons to enter
your answer
Phase Test
181/
What is the speed of light?
300 000 000 000
metres per sec
30 000 000 000
metres per sec
300 000 000
metres per sec
3x
1011
m/sec

3x
1010
m/sec

3x
108
m/sec

Click to
proceed
3 000 metres
per sec
300 x 10
m/sec

Phase Test
182/
between frequency (f),
wavelength (λ) and velocity of
A
velocity =
frequency x wavelength
(v = f x λ)
What is the relationship
light (v) is given in the
formula:
D
frequency =
B
velocity =
frequency+wavelength
(v = f + λ)
C
velocity - wavelength
(f = v
- λ)
velocity =
frequency – wavelength
(v = f- λ)
(v = f x λ)
(v = f + λ)
A
B
(v = f- λ)
C
Click Buttons to enter
your answer
(f = v - λ)
D
Phase Test
183/
Click Buttons to continue
Phase Test
Assessment Questions
3.
If the velocity of radio waves are 300 x
106, what would be the value of λ for a frequency of 3 x 106?a.
1000mb.10mc. 100md. 1m4.
What does the
abbreviation SSB stand for:a.
Single Side Band.b.
Single
Silicone Band.c. Ship to Shore Broadcast.d.
Solo Side Band.
184/
Phase Test
185/
• If the velocity  of radio waves is 3 x 108 m/sec, what
would be the value of  for a frequency of
3 x 106
Hz
?
Phase Test
186/
• If the velocity  of radio waves is 3 x 108 m/sec,
what would be the value of
 for a frequency of
3 x 106



1 x 10

2


Hz
f 
?
1
2
8
 3 x 10
3 x 106
100m 
Phase Test
187/
 = 3 x 108 m/sec
f = 3 MHz
• If the velocity  of radio waves is 3 x 108 m/sec,
what would be the value of
 for a frequency of
100m
 =3
x 106




1 x 10

2


Hz
f 
?
1
2
8
 3 x 10
3 x 106
100m 
Phase Test
 = 3 x 108 m/sec
f = 3 MHz
188/
50m
Ideal antenna
length?
Dipole
type
 = 100m




/
2
f 

/4
1
2
8
 3 x 10
3 x 106
Whip
type
25m
Phase Test
 = 3 x 108 m/sec
f = 3 MHz
189/
50m
Ideal antenna
length?
But remember …a radio wave is a
transverse wave so these aerials would
need to be turned through 90º to work!
 = 100m
 

Electric ‘E’ wave
vertically polarised

Dipole
type
/
2
f 

/4
1
2
8
 3 x 10
3 x 106
Whip type
25m
Phase Test
Assessment Questions
What is the speed of light?
a.300 x 108 ms-1b.300 x 106 ms-1c.300 x 109 ms-1d.300 x 101 ms12.
The relationship between frequency (f), wavelength (λ)
and velocity of light (v) is given in the formula:a.velocity =
frequency x wavelength (v = f x λ)b.velocity = frequency +
wavelength (v = f x λ)c.velocity = frequency - wavelength (v = f x
λ)d.frequency = velocity - wavelength (v = f x λ)3. If the velocity
of radio waves are 300 x 106, what would be the value of λ for a
frequency of 3 x 106?a. 1000mb.10mc. 100md. 1m4.
What
does the abbreviation SSB stand for:a.
Single Side Band.b.
Single Silicone Band.c.
Ship to Shore Broadcast.d.
Solo Side Band.
190/
191/
Phase Test
What does
SSB stand for?
Click on your
answer
192/
Phase Test
Correct !
193/
Review
interrupted -
CW
Ordinary radios do not
normally have this tone
facility
194/
Review
interrupted -
CW
Review
195/
196/
end
END
Phase Test
197/
What is the speed of light?
300 000 000 000
metres per sec
30 000 000 000
metres per sec
300 000 000
metres per sec
3x
1011
m/sec
3x
1010
m/sec
3 000 metres
per sec
108
3 x 103
m/sec
m/sec
3x

Click to return
Phase Test
198/
What is the speed of light?
300 000 000 000
metres per sec
30 000 000 000
metres per sec
3x
1011
m/sec
3x
1010
m/sec
300 000 000
metres per sec
3 000 metres
per sec
108
3 x 103
m/sec
m/sec
3x

Click to return
Phase Test
199/
What is the speed of light?
300 000 000 000
metres per sec
30 000 000 000
metres per sec
300 000 000
metres per sec
3x
1011
m/sec
3x
1010
m/sec
3 000 metres
per sec
108
3 x 103
m/sec
m/sec
3x

Click to return
Phase Test
200/
What is the speed of light?
300 000 000 000
metres per sec
30 000 000 000
metres per sec
300 000 000
metres per sec
300 x
109
m/sec
300 x
108
m/sec
300 x
106
m/sec
3 000
metres per sec
3 x 103
m/sec

Click to return
Phase Test
201/
Relationship between
=f

(v = f x λ)
Click to return
, f
and

Phase Test
202/
Relationship between , f and 
=f+ 

Click to return
Phase Test
203/
Relationship between , f and 
=f- 

Click to return
Phase Test
204/
Relationship between , f and 
f= 
-

Click to return
205/
Phase Test
No !
Return …