convention used left mouse click option available not recommended in this lesson
TRANSCRIPT
Advanced Studies Unit 18a BTecAdvanced Studies Unit 18a BTec
Convention usedConvention used
Left mouse click optionLeft mouse click optionavailablavailablee
not not recommendedrecommended
in this lessonin this lesson
Advanced Studies Unit 18a BTecAdvanced Studies Unit 18a BTec
Advanced RadioAdvanced Radio
Advanced Studies Unit 18a BTecAdvanced Studies Unit 18a BTec
1.1. communicatingcommunicating
44//
Communication may be defined as Communication may be defined as the the “exchange of information”“exchange of information”
CommunicatinCommunicatingg
introductiointroductionn
55//
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
CommunicatingCommunicating
transmitter = voice and
receiver = ears
66//
• Speed of travel is quite slow in air: Speed of travel is quite slow in air: 340 m/s at 20ºC 340 m/s at 20ºC or 760 or 760 mph (the speed of propagation of sound).mph (the speed of propagation of sound). * *
• Sound will not travel through a vacuumSound will not travel through a vacuum • it needs a substance or “it needs a substance or “mediummedium” (normally air) to transmit the ” (normally air) to transmit the
energy.energy. • ……although the medium can also be although the medium can also be liquidliquid (eg water or (eg water or
mercury?) or a mercury?) or a solidsolid (eg bar of steel or a quartz crystal) (eg bar of steel or a quartz crystal)
CommunicatinCommunicatingg
Up until the Invention of the Guttenberg Up until the Invention of the Guttenberg Printing Press in 1436 we used sound in Printing Press in 1436 we used sound in
the form of speech to communicate widely.the form of speech to communicate widely.
…but sound has its drawbacks
* speed 350 m/s or 780 mph at 30ºC
so the hotter the day …the faster the speed of sound
88//a longitudinal wave
direction of wave propagation
tickets
Note:1. the ‘action’ or energy goes in the same direction as
the propagation …ie lies in the same planelies 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 doesdoes 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
Hey!Nobody’s getting
served any quicker!
99//a longitudinal wave
direction of wave propagation
tickets
The plane of action or energy
Woah!Did the
Earth just move for
you?
Not from where I’m standing!
Sound is …Sound is …
1010//Sound limitationsSound limitations
• sound does not travel very far in air , even if you sound does not travel very far in air , even if you have a loud voice. It becomes ‘attenuated’ or have a loud voice. It becomes ‘attenuated’ or weakened by theweakened by the spongy airspongy air
• ……but sound can travel for but sound can travel for thousandsthousands of kilometers of kilometers through the sea and through the earth’s solid through the sea and through the earth’s solid surface …and at 1000s of MPHsurface …and at 1000s of MPH
• echoes, wind and other unwanted noises hamper echoes, wind and other unwanted noises hamper receptionreception
1111//
Let’s look at Let’s look at howhow sound sound travels through various travels through various
mediamedia
1212//
sound wave
longitudinal
Air compressionAir decompression
Ambient Air Pressure =
1Bar
1
Propagation or velocity of sound in Propagation or velocity of sound in air
Graphical representation of localised air
pressure
(760 mph)
340 metres per sec
input
Speed of propagation …in air at 20ºC
……ie at normal ie at normal UK temperaturesUK temperatures
AmbientAmbient
pressurepressure
Propagation or velocity of sound in Propagation or velocity of sound in air
……but at higher temperatures, the but at higher temperatures, the speed of sound increasesspeed 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’
1414//
Nothing to compress ?
vacuuvacuumm
Air Pressure = 0 Bar
0
Propagation; sound in Propagation; sound in vacuum
input
NO SOUND HEARD!
NO SOUND HEARD!
1515//
vacuuvacuumm
Air Pressure = 0 Bar
0
Propagation; sound in Propagation; sound in vacuum
input
That is why,( if you have ever noticed it), that audio, alarms and That is why,( if you have ever noticed it), that audio, alarms and announcements in an aeroplane on the ground are ‘too loud’ for announcements in an aeroplane on the ground are ‘too loud’ for comfort.comfort.
Why is that do you think?
If the aeroplane lost cabin pressure at altitude how will an If the aeroplane lost cabin pressure at altitude how will an alarm audio sound to the passengers and crew who are not alarm audio sound to the passengers and crew who are not on intercom?? on intercom??
All announcements, alarms or bells will be VERY All announcements, alarms or bells will be VERY much quieter.much quieter.
1616//
Liquids cannot compress …so transmits
the sound very efficientlyvery efficiently and very very fast!fast! …and over great distancesgreat distances
Propagation; sound in liquid (Propagation; sound in liquid (water?)?)
Liquid (eg water or mercury?)
14831483 metres per sec
(3,3003,300 mph)…in
water
1717//
uncompressible …so transmits sound even faster and more efficiently
using soundsound through quartz crystals is extensively used in electronics such as TV and Radar processing circuits
Propagation; sound in Propagation; sound in solids (steel?) (steel?)
Solid (Rock? or Quartz Crystal? Steel?
45004500 metres per sec
(10,00010,000+ mph!!)…in solid steelsolid steel
Strange but true!
…or quartz crystalquartz crystal…or The EarthThe Earth
1818//
Propagation; soundPropagation; sound
Air 760mph
Water 3300mph
Steel 10,000mph
Speed of Sound in …Speed of Sound in …
RecapRecap
…and for not very far
…and for maybe 1000miles +
Vacuum 0 mph
…it doesn’t
45004500 metres per sec
340340 m/sec
14831483 metres/sec
Check of understandingCheck of understanding 1919//
2020//
QQ. So, how do these astronauts communicate
by voice, outside the International Space Station
… without using a radio?
Sound Sound cannot travel cannot travel through a through a vacuum!!vacuum!!
2121//
A. By touching space-helmets!
…and, surprisingly, they do this quite often to
co-ordinate their work
computer won’t computer won’t open the pod open the pod
doors, Sergei !doors, Sergei !
Oh! oh!Oh! oh!not so not so
simplessimples
radio communicationradio communication
CommunicatingCommunicating2222//
2323//
Let’s now look at how Radio Waves travelLet’s now look at how Radio Waves travel
Radio WavesRadio Waves
2424//Radio WavesRadio Waves
• Radio – uses a different energy Radio – uses a different energy
• A radio communications system consists of a transmitter (Tx), A radio communications system consists of a transmitter (Tx), to send the message to send the message
• ……and a receiver (Rx) to receive the reply and a receiver (Rx) to receive the reply
2525//Radio WavesRadio Waves
soso……
shorthand for a radio transmitter isshorthand for a radio transmitter is
TxTx …remember this abbreviation! …remember this abbreviation!
……and for a receiver it isand for a receiver it is
RxRx …again, remember this abbreviation too! …again, remember this abbreviation too!
2626//RadioRadio
• The link between the Tx and Rx this time is not sound energy, The link between the Tx and Rx this time is not sound energy, but electro-magnetic (em) energy, (radio waves)but electro-magnetic (em) energy, (radio waves)
• light and radio waves can travel very well through air, but more light and radio waves can travel very well through air, but more perfectlyperfectly through a vacuum – and they travel at the same through a vacuum – and they travel at the same extremely high speedextremely high speed
• ……the speed of lightthe speed of light
• ……no matter what the speed of the transmitter or receiver isno matter what the speed of the transmitter or receiver is
2727//RadioRadio
……exactly the speed of exactly the speed of light!!light!!
3 x 103 x 1088 metres per metres per secondsecond (sometimes written as m/s or ms-1)
Or, if you prefer to put that Or, if you prefer to put that speed in context, it isspeed in context, it is
186, 000 miles per second!!186, 000 miles per second!!
remember
this
speed !!
!
300,000,000 ms-1
or
0r 669,600,00 mph!
2828//
Electro-magnetic radiation travels in waves in a similar Electro-magnetic radiation travels in waves in a similar
fashion to ripples on a pond.fashion to ripples on a pond.
The waves travel in all directions from their source The waves travel in all directions from their source
rather like the pattern produced when a stone is rather like the pattern produced when a stone is
dropped indropped in
A typical wave can be imagined like this…A typical wave can be imagined like this…
Electro-magnetic energyElectro-magnetic energy
2929//electromagnetic energyelectromagnetic energy
it would seem that there is no theoretical it would seem that there is no theoretical limit to the frequency of em waves, limit to the frequency of em waves, neither lower nor upper.neither lower nor upper.
the expression “the expression “electro-magnetic spectrumelectro-magnetic spectrum” ” has been coined to embrace all radiations of this has been coined to embrace all radiations of this type, which include heat and light. type, which include heat and light.
… …but we will only concern ourselves with but we will only concern ourselves with the Radio & Radar regionthe Radio & Radar region
HighFreqs
LowFreqs
plus infra red & visible light,
damaging Ultra
Violet, dangerous X-
rays and lethal Gamma rays
Radio wave Frequencies
Long wavelengthShort wavelength
HighFreqs
LowFreqs
plus infra red & visible light,
damaging Ultra
Violet, dangerous X-
rays and lethal Gamma rays
Radio wave Frequencies
Long wavelengthShort wavelength
3232//From transmitter to From transmitter to receiverreceiver
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
3333//TransmittersTransmitters
You know…
TxsTxs come in all shapes and sizes?
think about it!think about it!
PLB
…aircrew Personal
Locator Beacon
the car alarm remote is another
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 Wattscouple hundreds of Watts for a ‘freesat’ satellight.
your mobile
phone?
WiFi home hub?
AnyAny WiFi device
Man-made satellights?
3434//TransmittersTransmitters
You know…
TxsTxs come in all shapes and sizes?think about it!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
500,000500,000Watts
ie ½ Megawatt½ MegawattThese very high-powered equipments are needed to make transmissions reach to all parts of the country and combat terrestrial interference and losses within the Earth’s atmosphere.
your television
remote control is
one
the car alarm remote is another
such devices will have a very small power output of about ½ Watt to a couple hundreds of Watts for a satellite.
your mobile
phone?
WiFi home hub?
AnyAny WiFi device
Man-made satellights?
ReceiversReceivers
Rx also come in all shapes and sizesRx also come in all shapes and sizes
think about it!think about it!
Obviously …
Obviously …
your personal
your personal
radioradio
……and your TV
and your TVGPS satnavGPS satnav
Car Car
immobiliser immobiliser
huge radio telescopes
huge radio telescopes
eg eg JJodrell Bankodrell Bank
RWRsRWRs……RRadar adar WWarning arning RReceivers eceivers on aircrafton aircraft
3636//What is What is eelectro-lectro-mmagnetagnetiic c energy? energy?
When an alternating electric current flows in a wire, both electricelectric and magneticmagnetic fieldsfields are produced surrounding the outside of the wire.
The frequencyfrequency of the alternating current will determine the frequencyfrequency of the of the eemm waves 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 eemm waves and, as we’ve seen, the expression ““electromagnetic spectrumelectromagnetic spectrum”” has been coined to embrace all radiations of this type, which include heat and light.
Electricity can be ‘static’, like the energyElectricity can be ‘static’, like the energy
that can make your hair stand on end. that can make your hair stand on end.
Magnetism can also be ‘static’, as it is in a refrigerator magnet.
3737//
electric fieldelectric field ‘E’‘E’
BB
magnetic fieldmagnetic field
’’B’B’
What is What is eelectro-lectro-mmagnetagnetiic c energy? energy?
3838//
A changing A changing magneticmagnetic field will induce a changing field will induce a changing electric electric field and field and vicevice--versaversa——the two are linkedthe two are linked..
These changing fields form These changing fields form electroelectromagneticmagnetic waves. waves.
What is What is eelectro-lectro-mmagnetagnetiic c energy? energy?
3939//What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
---
+
-Direct current
DCDC
+ -
BBBBBB
BB
• 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 BB and it flows along the direction of the red arrows.
strongstrong
weakweak
Magnetic Magnetic fieldfield
4040//What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
---
++
--Direct current
DCDC
++ --
BBBBBB
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.
Let’s now look at applying anLet’s now look at applying an
aalternating lternating ccurrent (ac)urrent (ac)
to the wireto the wire
What is electromagnetic What is electromagnetic energy? energy?
4141//
4242//
• Now this alternating current introduces a new complexity which Now this alternating current introduces a new complexity which results in an electromagnetic wave being transmittedresults in an electromagnetic wave being transmitted
What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
+
-+
-
Alternating current
+- +-
4343//
As before, the current produces a magnetic field B as shown
What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
Alternating current
Let’s just slow things
down
BB
BB
BB
Wave
fro
nt
Wave
fro
nt
4444//
but its changing strength and direction in sympathy with the conductor’s electric current.
What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
Alternating current
BB
BB
BB
……butbut
4646//
• You can’t change a magnetising force without
generating an electric field ..ee
What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
eehh
ee
eehh
hh
…… but …but!but …but!
4848//What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
eeBB
ee
eeBB
BB
…again at right angles to the
electric field that caused it
• You can’t change an electricelectric fieldfield without
generating anotheranother magnetic B fieldB field
chickenchicken andand egg egg andand chickenchicken andand egg, egg, andand chickenchicken andand egg, egg, andand chickenchicken andand egg etcegg etc
BB
ee
--BB
--ee
magnetic magnetic fieldfield
Wire conductor
~
AnsAns:: Well … Well … forever!forever!
Provided the wave remains Provided the wave remains ‘‘in space’in space’ and it isn’t and it isn’t weakened by air or weakened by air or
absorbed by other physical absorbed by other physical objects. objects.
electric fieldelectric field
How long does this How long does this action continue action continue ……when the radio when the radio
frequency ac power frequency ac power source is removed?source is removed?
……but! but! But! But! But!!But!!
Although this process is ever lastingAlthough this process is ever lasting
it pushes itself forever it pushes itself forever outwardsoutwards
And forms a perpetual, ever radiating And forms a perpetual, ever radiating radio waveradio wave
5151//What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
eeBB
ee
eeBB
BB
…and the speed at which it radiates is…
~RFRF
The speed of light!
3 x 103 x 1088 m/s m/s
5252//What is electromagnetic What is electromagnetic energy? energy?
Wire conductor
~
Alternating current
ee
BB
ee
ee
BB
BB
ee
BB Magnetic Field Magnetic Field ‘B’‘B’
electric field
electric field e voltse volts
ee
BB Magnetic field Magnetic field ‘B’‘B’
electric field
electric field e voltse volts
Both fields are Both fields are 90º to each 90º to each
otherother
At exactly 3 x 10At exactly 3 x 1088 ms ms-1-1
And they propel the electro-And they propel the electro-magnetic radio wave at 90º magnetic radio wave at 90º
to both to both ee and and BB fields fields
no fasterno faster
no slower no slower
3 x 10
3 x 1088
ms
ms -1-1
ee
hh Magnetic fieldMagnetic field
‘‘B’B’
electric field
electric field e voltse volts
Both fields are Both fields are 90º to each 90º to each
otherother
……at the original frequencyat the original frequencyand the and the ee & & BB fields remain fields remain
3 x 10
3 x 1088
ms
ms -1-1
Long after they have left the solar system , Long after they have left the solar system , the milky way and the local group of galaxies the milky way and the local group of galaxies
on their way to infinity!on their way to infinity!
5656//electromagnetic energyelectromagnetic energy
• The frequency of the radio frequency, alternating The frequency of the radio frequency, alternating current will determine the frequency of the em current will determine the frequency of the em waves produced waves produced
NASA’s NASA’s Pioneer 10Pioneer 10 and and 11 11 spacecraft were launched in spacecraft were launched in 1972/731972/73
40 years old 40 years old technology technology
It has a radio to keep in touch It has a radio to keep in touch with earth with earth
The power supply for the whole space The power supply for the whole space craft is 2 nuclear generators on the end craft is 2 nuclear generators on the end of the arms shown. Originally giving a of the arms shown. Originally giving a barely 140 Watts, when it sped past barely 140 Watts, when it sped past Saturn the power decayed to 100W.Saturn the power decayed to 100W.
The radio which has been sending a signal back The radio which has been sending a signal back to earth has a power of a mere to earth has a power of a mere 40W 40W barely barely enough for a domestic light bulb.enough for a domestic light bulb.
NASA’s NASA’s Pioneer 10Pioneer 10 and and 11 11 spacecraft were launched in spacecraft were launched in 1972/731972/73
3metres3metres
(it’s not (it’s not big)big)
40 years old 40 years old technology technology
That radio was turned off by That radio was turned off by command from NASA in 2003command from NASA in 2003
These spacecraft were, however,These spacecraft were, however,
8 billion miles8 billion miles away. away.
……and transmitting 40W at a frequency of 2 GHz and transmitting 40W at a frequency of 2 GHz
(your microwave operates at 3 GHz and blasts out (your microwave operates at 3 GHz and blasts out 800w)800w)
It took It took 12 hours12 hours for the radio signal wave front to for the radio signal wave front to reach the spacecraft and reach the spacecraft and anotheranother 12 hr12 hr for the for the return signal to reach Earth.return signal to reach Earth.
NASA’s NASA’s Pioneer 10Pioneer 10 and and 11 11 spacecraft were launched in spacecraft were launched in 1972/731972/73
3metres3metres
(it’s not (it’s not big)big)
40 years old 40 years old technology technology
That radio was turned off by That radio was turned off by command from NASA in 2003command from NASA in 2003
These spacecraft are, however,These spacecraft are, however,
8 billion miles8 billion miles away. away.
it appears that it appears that radio wavesradio waves are very robust and can are very robust and can go a go a long long long long way for very little powerway for very little power
It was 80 times the distance the Earth is from It was 80 times the distance the Earth is from the Sunthe Sun
Low
Freqs
kHz MHz GHz
long long range range radioradio
BBC BBC World World SvcSvc
Radio Radio HamsHams
ATC radiosATC radios
R/C modelsR/C models
Mobile Mobile PhonesPhones
RadarsRadars
TelevisionTelevision
Sat TVSat TV
Radio HamsRadio Hams
Digital & WiFiDigital & WiFi
TelemetryTelemetry
Microwave Microwave OvensOvens
RadarRadar
Missile Missile GuidanceGuidance
Data LinksData Links
The Electromagnetic Spectrum
Radio & Radar RegionRadio & Radar RegionHigh
Freqs
Low
Freqs
kHz MHz GHz
long long range range radioradio
BBC BBC World World SvcSvc
Radio Radio HamsHams
ATC radiosATC radios
R/C modelsR/C models
Mobile Mobile PhonesPhones
RadarsRadars
TelevisionTelevision
Sat TVSat TV
Radio HamsRadio Hams
Digital & WiFiDigital & WiFi
TelemetryTelemetry
Microwave Microwave OvensOvens
RadarRadar
Missile Missile GuidanceGuidance
Data LinksData Links
Radio & Radar RegionRadio & Radar RegionHigh
Freqs
MFMF & & HFHF VHF VHF
& & UHFUHF
EHFEHF & &
SHFSHF
ieie
EExtra xtra HHi i FFreqreq &&
SSuper uper HHi i FFreqreq
6161//
definitionsdefinitions
We need to cover a few definitions to We need to cover a few definitions to progress our understanding of Radio progress our understanding of Radio furtherfurther
6262//
• FrequencyFrequency (ff) – the number of complete vibrations or fluctuations each second (ie cycles per sec).
• AmplitudeAmplitude (aa) – the height of the wave-crest on the field strength or power axis.
• Wavelength (Wavelength () – the distance between any two ) – the distance between any two identical points in a wave (ie peak to peak ~the identical points in a wave (ie peak to peak ~the length of one whole wave). Greek letter length of one whole wave). Greek letter pronounced pronounced LambdaLambda
• VelocityVelocity () – the speed with which the waves moves has the relationship:
6363//
Greek letter actually
pronounced
“NuNu”
…but don’t worry, most people just
remember it as “VV””
=ff
definitionsdefinitions
Measured in Measured in Hertz HzHertz Hz
A number of A number of Units availableUnits available
Measured in Measured in metres, cm or metres, cm or
mmmm
……in Metres per in Metres per second …second …
alwaysalways
3 x 103 x 108 m/s8 m/s
• FrequencyFrequency (ff) – the number of complete vibrations or fluctuations each second (ie cycles per sec).
• AmplitudeAmplitude (aa) – the height of the wave-crest on the field strength axis.
• WavelengthWavelength () – the distance between any two identical points in a wave (ie peak to peak ~the length of one whole wave).
• Velocity Velocity () – the speed with which the waves moves has the relationship:
6464//electromagnetic energyelectromagnetic energydefinitionsdefinitions
This Greek This Greek letter is letter is
pronounced pronounced “Lambda” “Lambda” being a being a
Greek L for Greek L for ““length”length”
The most useful form The most useful form of this expression is to of this expression is to
calculate wavelength calculate wavelength for aerial selectionfor aerial selection
……so, rearranging for so, rearranging for =f
• FrequencyFrequency (ff) – the number of complete vibrations or fluctuations each second (ie cycles per sec).
• AmplitudeAmplitude (aa) – the height of the wave-crest on the field strength axis.
• WavelengthWavelength () – the distance between any two identical points in a wave (ie peak to peak ~the length of one whole wave).
• Velocity Velocity () – the speed with which the waves moves has the relationship:
6565//electromagnetic energyelectromagnetic energydefinitionsdefinitions
=f
6666//
Advantages of emAdvantages of em
Using em energy to carry our communications Using em energy to carry our communications information has many advantages compared information has many advantages compared with sound energywith sound energy
Speed of travel is Speed of travel is unimaginablyunimaginably fast fast
… …the speed of light the speed of light ((alwaysalways 3 x 10 3 x 1088 m/s),
……but let’s get that into the context of but let’s get that into the context of computerscomputers
6767//
Advantages of emAdvantages of em
Using Using emem energy to carry our energy to carry our communications information has many communications information has many advantages compared with sound energyadvantages compared with sound energy
Speed of travel is Speed of travel is unimaginablyunimaginably fast fast
… …the speed of light the speed of light ((alwaysalways 3 x 10 3 x 1088 m/s),
……but let’s get that into the context of but let’s get that into the context of computerscomputers
Speed of travel is Speed of travel is unimaginablyunimaginably fast fast……the speed of light (always the speed of light (always 3 x 103 x 1088 m/s) m/s)
Intel
Pentium
3 GHz speed A typical PC Central
Processor Unit
(CPU)
So, how far can our radio wave travel in the So, how far can our radio wave travel in the time for 1 cycle of this ‘chip’?time for 1 cycle of this ‘chip’?
Answer: 1 wavelength of 3 GHzAnswer: 1 wavelength of 3 GHz … …
Which is Which is VV = = 3 x 103 x 1088
ff 3 x 103 x 1099 = 10cm or = 10cm or 4”4”
6868//
Advantages of emAdvantages of em
Intel
Pentium
3 GHz speed A typical PC Central
Processor Unit
(CPU)
A Radio em wave cannot get further away than A Radio em wave cannot get further away than 10cm or 4” before, the next cycle begins10cm or 4” before, the next cycle begins
= 10cm or = 10cm or 4”4”
This is a severe limiting factor for This is a severe limiting factor for PC CPU speeds PC CPU speeds
We need faster radio We need faster radio waves or smaller waves or smaller
CPUsCPUs
We cant have We cant have different ‘newness’ different ‘newness’ of data from one of data from one
side of a chip to the side of a chip to the other!other!
All of a sudden, the All of a sudden, the speed of lightspeed of light doesn’t seem quite so quick!doesn’t seem quite so quick!
6969//
7070//Electromagnetic wavesElectromagnetic waves
• Em waves will travel through a vacuum and so can be Em waves will travel through a vacuum and so can be used for communication in space.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’
7171//
Aerial LengthAerial Lengthaerials used for transmission or reception operate aerials used for transmission or reception operate
best with certain wavelengths.best with certain wavelengths.
the length of the aerial dictates the frequency it will receive most readily.
aerial lengthsaerial lengths ofof /22 andand /44 are particularly efficient…are particularly efficient… ie ie halfhalf and and quarterquarter of wavelengthof wavelength
As we know the As we know the velocityvelocity of the waves, we can now of the waves, we can now calculatecalculate the best the best aerial lengthaerial length for a for a particular particular frequencyfrequency by finding the by finding the wavelengthwavelength of the wave. of the wave.
7272//
• eg For f = 200 kHz,
= f
& =300,000,000 m/sec*
* = ‘ C ’ speed of light=300,000,000
200,000
= 1500 metres
Aerial LengthAerial Length
As we know
Wavelength
We need to rearrange
300000,000200,000
….nearly there!
7373//
Aerial LengthAerial Length
= 1500 metres
So, given that the wavelength for our
200kHz200kHz radio is …
The best aerial length would be /2
or /4
Which would be… 750m 375mor
7474//
Aerial LengthAerial Length
• So what aerial lengths would best suit a frequency of 100 MHz?
= f = 300,000,000100,000,000
3 metres=
…best Ae length? λ/2 λ/41.5 m 0.75
mor
7575//
Aerial LengthAerial Length
3 metres=
…best Ae length? λ/2 λ/41.5 m 0.75
mor
λ
Notice – the Notice – the higherhigher the frequency, the frequency, the the shortershorter the aerial required. the aerial required.
What does this tell us about the What does this tell us about the operating frequency of a car-mounted operating frequency of a car-mounted radio aerial compared to a hand held radio aerial compared to a hand held
mobile phone? mobile phone?
for 100 MHz?
OK, they were a few fundamentals to be OK, they were a few fundamentals to be going on with…going on with…
Let’s look back in time to see how ‘radios’ Let’s look back in time to see how ‘radios’ got started.got started.
7676//
7777//
in 1901 the Italian born inventor, entrepreneur and businessman … Gulielmo Marconi claimed his system was the ‘first to transmit and ‘first to transmit and receive long range radio signals from Cornwallreceive long range radio signals from Cornwall toto Newfoundland’Newfoundland’ (not yet part of Canada at that time).
Marconi
this has since been disputed for a number of robust scientific reasons but, as a publicity stunt, it worked. What is not disputed What is not disputed is the fact that his system was the most effective in The World at is the fact that his system was the most effective in The World at that time.that time.
7878//
previously, in 1899 in the USA, the Marconi instruments were tested and they found his wireless system “… the principle component of “… the principle component of which was discovered some twenty years ago, and this was the only which was discovered some twenty years ago, and this was the only electrical device contained in the apparatus electrical device contained in the apparatus that is at all newthat is at all new""
also, Nikola TeslaNikola Tesla, a rival in transatlantic transmission, stated after being told of Marconi's 1901 transmission that : "Marconi is a good Marconi is a good fellow. Let him continue. He is using 17 of my patents.fellow. Let him continue. He is using 17 of my patents.““
it didn’t matter. The Funds poured init didn’t matter. The Funds poured in
Marconi
Tesla
7979//
Marconi, stung by criticisms and incredulity, prepared a better organized and documented test.in February 19021902, 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!it was at night! During the daytimedaytime, signals had onlyonly 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?so what about his first 1901 test?
8080//
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 CodeMorse 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.
8787//Amplitude Amplitude
modulationmodulation
What was needed was a means to use speech to modulate the CW rather like a tap can modulate the flow of water
The superhetsuperheterodyne principle offers a way to achieve this
The ‘superhet’‘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 mathematicalmathematical process …
8888//Amplitude Amplitude
modulationmodulation
This is because it is quite simply a mathematicalmathematical process …
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
two car enginestwo car engines running at slightly different speeds
egeg
two waves in the seatwo waves in the sea meeting and interacting
Or the interaction of Or the interaction of two ac electrical signalstwo ac electrical signals
of different frequencies of different frequencies
superheterodynsuperheterodynee
8989//Amplitude Amplitude
modulationmodulation
this principle which demonstrate that if you ‘mixmix’ or ‘modulatemodulate’ 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
complex wave which has sumsum and differencedifference frequencies embedded within it.
superheterodynsuperheterodynee
9090//Amplitude Amplitude
modulationmodulation
sumsum && differencedifference
frequenciesfrequencies
superheterodynsuperheterodynee
9191//Amplitude Amplitude
modulationmodulation
the upper sinewave has a lower frequency
f1 than the next down sinewave of
frequency f2
f1
f2
&
Adding two sinewaves
the resultant wave form shows another virtual sine
wave of frequency f2 - f1
Join up the peaks and troughs and …
composite
9292//Amplitude Amplitude
modulationmodulation
f1
f2
+
Adding two sinewaves
the resultant wave is the
differencedifference frequencyfrequency
ff2 2 - f- f11
9393//Amplitude Amplitude
modulationmodulation
f1
f2
+
Adding two sinewaves
sum
……this is the virtual waveform of thethis is the virtual waveform of the difference difference frequencyfrequency
So if ff11 = 250250 kHz kHz (ie 250,000 Hz250,000 Hz) & ff22 = 252252 kHzkHz Then …Then …
F F (difference)(difference) == F F dd ==252 kHz252 kHz -- 250 kHz250 kHz == 2 kHz2 kHz
Fd d
differ
ence
frequ
ency
F F dd== 2 kHz2 kHz
9494//Amplitude Amplitude
modulationmodulation
f1
f2
+
Adding two sinewaves –the SUM SUM freqfreq
sum
the resultant wave form shows another
virtual sine wave of frequency ff11 ++ ff22== ffSUMSUM
So if ff11 = 250250
kHzkHz & f f22 = 252252
kHzkHzThen …Then …
Then …Then …Then …Then …
ffSUMSUM == 502502 kHz kHz
Fsumsum frequency
9595//Amplitude Amplitude
modulationmodulation
……this applies to interaction of this applies to interaction of allall sinusoidal sinusoidal waveswaves
they could be soundwaves
oror wave-motion at sea
oror engines at slightly different speeds to each other
…which creates an unpleasant ‘‘beat beat frequency’frequency’ of vibration ..which can be catastrophic!
Sum & Difference Sum & Difference FrequenciesFrequencies
This effect has This effect has even resulted in even resulted in
old, badly old, badly designed propeller designed propeller airliners shaking airliners shaking themselves into themselves into
fatigue failure and fatigue failure and even destruction! even destruction!
9696//Amplitude Amplitude
modulationmodulation
……this applies to interaction of this applies to interaction of allall sinusoidal sinusoidal waveswaves
they could be soundwaves
oror wave-motion at sea
oror engines at slightly different speeds to each other
…which creates an unpleasant ‘‘beat beat frequency’frequency’ of vibration ..which can be catastrophic!
Sum & Difference Sum & Difference FrequenciesFrequencies
This effect has This effect has even led to even led to
propeller airliners propeller airliners shaking shaking
themselves into themselves into fatigue failure and fatigue failure and even destruction! even destruction!
This is caused This is caused by the by the
difference in difference in frequency frequency
between the between the twotwo
Amplitude Amplitude modulationmodulation
……it is entirely a physical example of a simple, it is entirely a physical example of a simple, mathematical, mathematical, trigonometricaltrigonometrical relationship. relationship.
… … which we will not go in to! which we will not go in to!
This ‘beating together’ phenomenon This ‘beating together’ phenomenon also applies to electrical currents & also applies to electrical currents & radio wavesradio waves
but just take on board; but just take on board; 2 frequencies 2 frequencies beating together do produce beating together do produce
SumSum and and Difference Difference frequenciesfrequencies
9797//
9898//Amplitude Amplitude
modulationmodulation Sum & Sum &
Difference Difference FrequenciesFrequencies
AAmplitude mplitude MModulation with regards to odulation with regards to
Radio WavesRadio Waves
9999//Amplitude Amplitude
modulationmodulation Sum & Sum &
Difference Difference FrequenciesFrequencies
let’s look at this in a graphical way
frequencyfrequency is along the bottom of the graph
…and signal strength or amplitudeamplitude is along the vertical
frequency
am
plit
ude
This view is
called the frequency
frequency domain
domainSo So frequency
frequency
rules! OK?
rules! OK?
We’re now going to look, using the using the
frequency domainfrequency domain, at a hypothetical radio transmitter receiver on a
random frequency, say , 2182kHz or 2182000Hz if you wish
2182kH
z
transmittertransmitter
101101//Amplitude Amplitude modulationmodulation the frequency domainthe frequency domain
Radio Radio FrequencyFrequency
2182 kHzFF00
Sig
nal st
rength
Sig
nal st
rength
Watt
sW
att
s
We now transmit (Tx) on We now transmit (Tx) on an RF of, say, an RF of, say, 21822182 kHz kHz
You You wouldn’t wouldn’t actually actually
hear hear anything anything
on on frequency frequency …yet!…yet!
It’s far, far It’s far, far
too high for too high for
you to ‘hear’ you to ‘hear’
if it was if it was
soundsound
Electromagnetic spectrum
Amplitude Amplitude modulationmodulation CWCW
102102//Amplitude Amplitude modulationmodulation Let’s look at this effect another way Let’s look at this effect another way ……
Radio Radio FrequencyFrequency
2182 kHzFF00
Sig
nal st
rength
Sig
nal st
rength
We now stop We now stop transmitting transmitting
That is how That is how Morse Code Morse Code
could be sentcould be sent
……and very and very efficiently too!efficiently too!
on
off
Electromagnetic spectrum
Amplitude Amplitude modulationmodulation CWCW
… … but you’ll need a but you’ll need a
specialist receiver specialist receiver
with a with a Beat Beat Frequency OscillatorFrequency Oscillator to be able to hear any to be able to hear any Morse CodeMorse Code
103103//
Let’s look at this effect another way Let’s look at this effect another way ……
Radio Radio FrequencyFrequency
2182 kHzFF00
Sig
nal st
rength
Sig
nal st
rength
This is interrupted This is interrupted CContinuousontinuous WWaveave ((i-i-CWCW)) but very often but very often
referred to as just…referred to as just…
CWCW transmissiontransmission
Electromagnetic spectrum
Amplitude Amplitude modulationmodulation CWCW
104104//
Radio Radio FrequencyFrequency
2182 kHzFF00
Sig
nal st
rength
Sig
nal st
rength CWCW transmissiontransmission
Electromagnetic spectrum
ReceptionReception2182kH
z
Nothing heard on
frequency!
Ordinary AM radioOrdinary AM radio
Amplitude Amplitude modulationmodulation CW CW MorseMorse
Now let’s look how a radio with aNow let’s look how a radio with a BBeateat FFrequencyrequency
OOscillatorscillator
BFOBFOwould receive that same transmission.would receive that same transmission.
106106//
Radio Radio FrequencyFrequency
2182 kHzFF00
Sig
nal st
rength
Sig
nal st
rength CWCW
Electromagnetic spectrum
ReceptionReception2182
kHz
Dah Dah Dit
AM radio with a Beat Freq
OscBFO
Amplitude Amplitude modulationmodulation CW CW MorseMorse
……but but how?how?
Amplitude Amplitude modulationmodulation CW CW MorseMorse
107107//
……basically, in all basically, in all
radios, most of the radios, most of the
processing and processing and
amplification is done amplification is done
at a fixed, at a fixed,
iintermediate ntermediate
ffrequency requency (i.f.)(i.f.)..For our example radio For our example radio
we will assume that, no we will assume that, no
matter what the receiver matter what the receiver
is tuned to, the received is tuned to, the received
signal is converted down signal is converted down
to an to an i.fi.f based at, say, based at, say,
30kHz30kHz
Amplitude Amplitude modulationmodulation CW CW MorseMorse
108108//
The Beat Frequency OscillatorThe Beat Frequency Oscillator
((BFOBFO))
generates a very small generates a very small
continuous, steady continuous, steady
sinewave signalsinewave signal into the into the i.f.i.f. circuits circuits
……but at abut at a slightlyslightly different frequencydifferent frequency to the intermediateto the intermediate frequency (frequency (i.f.i.f.) of ) of the radio receiver. the radio receiver. In this case signal In this case signal now scaled to
now scaled to 3030kHzkHz
30 kHz
i.f.
BFOBFOi.f.
Received signal Received signal reduced to 30kHz
reduced to 30kHz
Amplitude Amplitude modulationmodulation CW CW MorseMorse
31 kHz
109109//
What do we know happens What do we know happens when you ‘mix’ 2 sinewave when you ‘mix’ 2 sinewave
frequencies together ?frequencies together ?
Ans: We generate Sum and, more importantly here,
DifferencDifference frequencies!
Clue: they ‘Clue: they ‘BeatBeat’ together just like two ’ together just like two car engines at slightly differing speedscar engines at slightly differing speeds
Amplitude Amplitude modulationmodulation CW CW MorseMorse
110110//
……but what the difference is but what the difference is depends on where the listener depends on where the listener
moves the BFO moves the BFO (Beat Freq Osc)(Beat Freq Osc) knob knob toto
BFO freq differenceBFO freq difference0
1.0
1.5
2.0
30 kHz
31 31 kHz
11
Dah Dit Dah Dit Dit
as 1kHz pulsed tonesas 1kHz pulsed tones
i.f.
Amplitude Amplitude modulationmodulation CW CW MorseMorse
111111//
0
1.0
1.5
2.0
……but what the difference is but what the difference is depends on where the listener depends on where the listener
moves the BFO moves the BFO (Beat Freq Osc)(Beat Freq Osc) knob knob toto
BFO freq differenceBFO freq difference
30 kHz
31.5 31.5 kHz
1.1.55
Dah Dit Dah Dit Dit
You hear it as You hear it as higherhigher 1½ kHz pulsed1½ kHz pulsed tonestones
i.f.
Amplitude Amplitude modulationmodulation CW CW MorseMorse
112112//
113113//
Radio Radio FrequencyFrequency
30 kHz
Sig
nal st
rength
Sig
nal st
rength CWCW ReceptionReception218
2 kHz
Dah Dit Dah Dit Dit
AM radio with a Beat Freq
OscBFO
i.f.
????
the pitch of the tone / the pitch of the tone / Morse you hear is Morse you hear is dependant upon your BFO dependant upon your BFO setting setting
……it’s entirely the it’s entirely the listeners choicelisteners choice
Amplitude Amplitude modulationmodulation CW CW MorseMorse
Amplitude Amplitude modulationmodulation CW CW MorseMorse
Who would use such a Who would use such a
primitive and archaic mode primitive and archaic mode
of communication?of communication?
……well, it’s no longer a primary, well, it’s no longer a primary, secondary or even tertiary mode for
secondary or even tertiary mode for NATO military communications NATO military communications where Morse skills have all but where Morse skills have all but disappeareddisappeared
……but there is a massive World-
but there is a massive World-
wide network of amateur radio
wide network of amateur radio
enthusiasts known as enthusiasts known as Radio Radio
Hams Hams who use this mode to who use this mode to
‘keep in touch’.‘keep in touch’.
……and this mode will ‘get and this mode will ‘get through’ when none of the through’ when none of the
other modes canother modes can
114114//
115115//Amplitude Amplitude modulationmodulation
Radio Radio FrequencyFrequency
300 kHz
FF00
Sig
nal st
rength
Sig
nal st
rength
Now, what happens if we Now, what happens if we modulatemodulate the Carrier Wave the Carrier Wave with an amplified single with an amplified single tone of say tone of say 1.51.5 kHz? kHz?
This generates This generates AAmplitude mplitude
MModulation of the odulation of the ccarrier arrier
giving giving sumsum and and
differencedifference frequenciesfrequencies
Notice: power is Notice: power is shared between the shared between the
sumsum, , differencedifference
and and carriercarrier frequenciesfrequencies
When there is no When there is no 1.5 kHz tone 1.5 kHz tone
modulation all modulation all of the power is of the power is transmitted at transmitted at
the the CCarrier freq arrier freq
When the tone is When the tone is present, the present, the Carrier Wave is Carrier Wave is being modulated being modulated ie diminished/ ie diminished/ attenuated to attenuated to provide power for provide power for the Sum and the Sum and Difference Difference frequencies.frequencies.
301.5301.5 kHz298.5298.5 kHz
-1.5 -1.5 kHzkHz
+1.5 +1.5 kHzkHz
116116//Amplitude Amplitude modulationmodulation
Radio Radio FrequencyFrequency
345 kHz
FF00
Sig
nal st
rength
Sig
nal st
rength
-1 -1 kHzkHz
+1 +1 kHzkHz
AmplitudeAmplitude Modulated Modulated
Carrier WaveCarrier Wave Only a simple Rx Only a simple Rx requiredrequired
Tone
on
Ordinary AM radioOrdinary AM radio
(MCW)(MCW)
345 kHz
Dah Dit Dah Dit Dit
The pitch/tone of The pitch/tone of the Morse is set the Morse is set
by the by the transmittertransmitter
117117//Amplitude Amplitude modulationmodulation
Radio Radio FrequencyFrequency
345 kHz
FF00
Sig
nal st
rength
Sig
nal st
rength
-1 -1 kHzkHz
+1 +1 kHzkHz
……mainly used for mainly used for Aircraft ‘Aircraft ‘NavaidNavaid’ ’ Beacons Morse Beacons Morse
Code Code Identification Identification
signalssignals
Tone
on
Tone
OffOff
118118//Amplitude Amplitude modulationmodulation
Radio Radio FrequencyFrequency
345 kHz
FF00
Sig
nal st
rength
Sig
nal st
rength
-1 -1 kHzkHz
+1 +1 kHzkHz
Amplitude Amplitude Modulated Modulated Carrier WaveCarrier Wave Only a simple Rx Only a simple Rx
requiredrequired
Tone
on
119119//Amplitude Amplitude modulationmodulation
Radio Radio FrequencyFrequency
345 kHz
FF00
Sig
nal st
rength
Sig
nal st
rength
-1 -1 kHzkHz
+1 +1 kHzkHz
Modulated Carrier Modulated Carrier WaveWave
Only a simple Rx Only a simple Rx requiredrequired
……but does but does not carry as not carry as far as CW far as CW
morsemorse
Power is divided
between upper, lower and carrier
120120//
but instead of using a single but instead of using a single tonetone to to
‘modulate’‘modulate’ the carrier wave … the carrier wave …
……what if we used voice or music what if we used voice or music to to AAmplitudemplitude MMoodulatedulate the Carrier the Carrier WaveWave over a over a bandband of frequencies ? of frequencies ?
Amplitude Amplitude modulationmodulation
121121//
Carr
ier
Wave
Blah!
Di Dum ………………...
Di!Li Laaaaahh
Transmitte
r
Amplitude Amplitude modulationmodulation
122122//Amplitude Amplitude modulationmodulation Let’s look at that in the Let’s look at that in the
““Frequency Domain” againFrequency Domain” again
Radio Radio FrequencyFrequency
1442 kHzFF00
……Centred on Tx Freq of Centred on Tx Freq of Say, 1442kHzSay, 1442kHz
When the speaker talks When the speaker talks …he …he Amplitude Amplitude ModulatesModulates the strength the strength of the carrier wave …of the carrier wave …
not at not at oneone single single frequency but a broad frequency but a broad
bandband of frequenciesof frequencies
Which needs to Which needs to convey most of the convey most of the
tonestones in his voice in his voice
‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
Radio Luxembur
g Freq
123123//Amplitude Amplitude modulationmodulation
Radio Radio FrequencyFrequency
1442 kHz
FF00
‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
Carr
ier
Carr
ier
Wave
Wave
upperupper sidebandsideband
lower lower sidebandsideband
124124//Amplitude Amplitude modulationmodulation
1442 kHz
FF00
‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
Carr
ier
Carr
ier
Wave
Wave
upperupper sidebandsideband
lower lower sidebandsideband
To recreate the original To recreate the original voice, in a simple voice, in a simple superhetsuperhet receiver … receiver …requires the reception of requires the reception of BOTHBOTH side bands to be side bands to be intelligible.intelligible.
125125//Amplitude Amplitude modulationmodulation
1442 kHz
FF00
‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
Carr
ier
Carr
ier
Wave
Wave
upperupper sidebandsideband
lower lower sidebandsideband
The transmitted power is The transmitted power is shared between both shared between both sidebands sidebands andand the carrier. the carrier.
Tx power is Tx power is being wastedbeing wasted
each sideband is each sideband is the mirror image of the mirror image of
the otherthe other
126126//Amplitude Amplitude modulationmodulation
1442 kHz
FF00
‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
Carr
ier
Carr
ier
Wave
Wave
upperupper sidebandsideband
lower lower sidebandsideband
AMAM is OK for V/UHF Air is OK for V/UHF Air Traffic comms as it is Traffic comms as it is cheap, reliable and the cheap, reliable and the equipment common and equipment common and light.light.
Quality or ‘fidelity’ is Quality or ‘fidelity’ is limited with AM due to the limited with AM due to the RF band-width available RF band-width available between channelsbetween channels
Hi Fidelity requirements for modern Hi Fidelity requirements for modern radio entertainment has been radio entertainment has been addressed with the advent of addressed with the advent of
FFrequency requency MModulation and then odulation and then more recently, more recently, DigitalDigital Radios Radios
allowing, far higher quality in terms allowing, far higher quality in terms of interference and audio freq rangeof interference and audio freq range
Amplitude Amplitude modulationmodulation
Cranwell Tower, ASCOT213 on
Uniform 268 decimal 625268 decimal 625 request join downwind for
Runway 26 Left hand for visual approach to land.
267.000VHF
UHFGuard V
Guard U
Tone
ASCOT213 nothing heard, changing to
Victor
select
268.000268.600268.625
simple Double Side-Band simple Double Side-Band
AMAM
upper
lower
AM
268.625127127//
Cranwell Tower, ASCOT213 now
on Victor, 125 decimal 05125 decimal 05 request join downwind for
Runway 26 Left hand for visual approach to land.
VHFUHF
Guard V
Guard U
Tone
select
268.625268.050168.050135.050125.050
Amplitude Amplitude modulationmodulation
simple Double Side-Band simple Double Side-Band
AMAM
268.625125.05128128//
Cranwell Tower, ASCOT213 now
on Victor, 125 decimal 05125 decimal 05 request join downwind for
Runway 26 Left hand for visual approach to land.
VHF
UHF
Guard V
Guard U
Tone
select
268.625268.050168.050135.050125.050
Amplitude Amplitude modulationmodulation
Mode now simplyMode now simply
Modulated Carrier Wave Modulated Carrier Wave
MCWMCW
I think I may have microphone
amplifier failure …I will try to
transmit the radio failure code using
1kHz ‘tone’ dashes and my transmit switch
125.05
+1 kHz
-1 kHz
MHz
121.5
243.0
129129//
130130//Amplitude Amplitude modulationmodulation
1442 kHz
FF00
‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
Carr
ier
Carr
ier
Wave
Wave
upperupper sidebandsideband
lower lower sidebandsideband
BUTBUT those techniques still don’t give a those techniques still don’t give a transmitter greater range…needed for transmitter greater range…needed for HF commsHF comms
What if we put all transmitted power in to What if we put all transmitted power in to oneone or the or the
other other side bandside band and suppressed the carrier? and suppressed the carrier?
131131//Amplitude Amplitude modulationmodulation
6742 kHz
FF00
upperupper sideband sideband
onlyonly
What if we put all transmitted power in to What if we put all transmitted power in to oneone or the or the
other other side bandside band and suppressed the carrier? and suppressed the carrier?
nb…the trouble is that nb…the trouble is that receiving SSB on an receiving SSB on an ordinary domestic ordinary domestic medium wave AM medium wave AM
radio; the audio would radio; the audio would
be utterly be utterly garbledgarbled and not decipherable in and not decipherable in
any way! any way!
“Gbble hmblfmbgb Pmmblwrbbl”
Ordinary AM radio RxOrdinary AM radio Rx6742
132132//Amplitude Amplitude modulationmodulation
6742 kHzFF00
upperupper sidebandsideband
A A SSingle ingle SSide ide BBand and
(SSB) (SSB) receiverreceiver overcomes this by overcomes this by
re-synthesising re-synthesising the missing the missing sideband and sideband and carrier wave …carrier wave …in the receiverin the receiver
nb…the trouble is that nb…the trouble is that receiving this on an receiving this on an ordinary domestic ordinary domestic medium wave AM medium wave AM
radio; the audio would radio; the audio would
be utterly be utterly garbledgarbled and not decipherable in and not decipherable in
any way! any way!
Single Side Single Side BandBand
6742
133133//Amplitude Amplitude modulationmodulation
6742 kHzFF00
upperupper sidebandsideband
A A SSingle ingle SSide ide BBand and
(SSB) (SSB) receiverreceiver overcomes this by overcomes this by
re-synthesising re-synthesising the missing the missing sideband …in sideband …in the receiverthe receiver
Single Side Single Side BandBand
Single Single side-band side-band RxRx CW DSB
SSB UU
SSB LL
mode
6742
134134//Amplitude Amplitude modulationmodulation
6742 kHz‘Sum’Sum’
freqsfreqs
‘‘DifferenceDifference’’
freqsfreqs
CCarr
ier
arr
ier
Wave
Wave
upperupper sidebandsideband
lower lower sidebandsideband
Missing sideband re-synthesised Missing sideband re-synthesised on on receptionreception by Single Sideband by Single Sideband
Receiver (SSB) RxReceiver (SSB) Rx
Has range Advantage over DSB mode
Doubles channels available.
fidelityfidelity too poor too poor
for for entertainment entertainment radioradio
Mainly used atMainly used at HFHF
and and MFMF frequencies frequencies for Global Coveragefor Global Coverage
not not
transmittetransmitte
dd
……but no but no point point
atV/UHF atV/UHF freqsfreqs
Single Side Single Side BandBand
135135//Amplitude Amplitude modulationmodulation
6742 kHz
upperupper sidebandsideband
lower lower sidebandsideband
Civil & Military long Civil & Military long range voice comms range voice comms tends to use Upper tends to use Upper Side BandSide Band
(in the HF freq (in the HF freq bandband))
Used extensively Used extensively Military and Military and Merchant NavyMerchant Navy
Used by Used by ArmiesArmies for for beyond line of sight beyond line of sight communicationscommunications
Military Tactical Data Military Tactical Data Link tends to use Link tends to use Lower Side BandLower Side Band
(in the HF freq band)(in the HF freq band)
Single Side Single Side BandBand
136136//Amplitude Amplitude modulationmodulation
6742 kHz
upperupper sidebandsideband
lower lower sidebandsideband
Civil & Military long Civil & Military long range voice comms range voice comms tends to use Upper tends to use Upper Side BandSide Band
(in the HF freq (in the HF freq bandband))
Used extensively Used extensively Military and Military and Merchant NavyMerchant Navy
Used by Armies Used by Armies for beyond line for beyond line of sight of sight communicationscommunications
Military Tactical Data Military Tactical Data Link tends to use Link tends to use Lower Side BandLower Side Band
(in the HF freq band)(in the HF freq band)
Shanwick this is Rafair2134 on 88918891 upperupper, position 5630 North, Ten West at 1510, estimating Iceland boundary at… over!
8000880088908891
upper
lower
kHzkHz
Single Side Single Side BandBand
137137//Amplitude Amplitude modulationmodulation
upperupper sidebandsideband
lower lower sidebandsideband
Civil & Military long Civil & Military long range voice comms range voice comms tends to use Upper tends to use Upper Side BandSide Band
(in the HF freq (in the HF freq bandband))
Used extensively Used extensively Military and Military and Merchant NavyMerchant Navy
Used by Armies Used by Armies for beyond line for beyond line of sight of sight communicationscommunications
Military Tactical Data Military Tactical Data Link tends to use Link tends to use Lower Side BandLower Side Band
(in the HF freq band)(in the HF freq band)
Shanwick this is Rafair2134 on 88918891 upperupper, position 5630 North, Ten West at 1510, estimating Iceland boundary at… over!
0000
upper
lower
6000670067106715
Link Manager from Tactical Director; ‘Alligator’ Data Link frequency now 6715 lower.6715 lower.
kHzkHz
not not transmittetransmitte
dd
Single Side Single Side BandBand
The legitimate nick-name for NATO
Link 11aLink 11a is
If you actually listen to the audio that the If you actually listen to the audio that the link data makes it’s an awful croaking link data makes it’s an awful croaking
scraping sound…scraping sound…
……just like an Alligator’s mating calljust like an Alligator’s mating call
……and that is exactly how it and that is exactly how it got it’s namegot it’s name
… … AlligatorAlligator
138138//
139139//
Largely surpassed in quality and effectiveness by SatSatellite ellite ComCommunicationsmunications but SATCOM on-airon-air time is expensive
…SSBSSB remains an extensively used prime communications method in the HF band
SSB onon-airair time is …free!
but not necessarily the commercial services you might request
Amplitude Amplitude modulationmodulation Single Side Single Side
BandBand
SSBSSB
It is used for:
Procedural control of military & Procedural control of military & commercial aircraft on long commercial aircraft on long range trans-oceanic flightsrange trans-oceanic flights
Military long range Flight Military long range Flight Following servicesFollowing services and VOLMET VOLMET aviation weather servicesaviation weather services
eg Shanwick , Iceland, New York
etc
eg RAF ‘TASCOM’ and ‘RAF VOLMET’
USAF ‘MAINSAIL’
Long Range, Link 11a Alligator Long Range, Link 11a Alligator Data LinkData Link
NATO air and naval units
etc etc etcetc etc etc
140140//
SSBSSB
It is not used for:
Entertainment Radio Channels Entertainment Radio Channels
Because …
you need an expensive, you need an expensive, specialist SSB radio specialist SSB radio receiver which can receiver which can
synthesise the missing synthesise the missing side-bandside-band
audio quality or ’fidelity’ is audio quality or ’fidelity’ is limitedlimited
141141//
Let’s now review the
AMAM
radio modes and their uses
142142//
• CWCW Carrier WaveCarrier Wave (Morse only – no voice). (Morse only – no voice). Needs a receiver BFO. Pitch of Needs a receiver BFO. Pitch of
received tones set by the listener using BFO. Generally in HF band. received tones set by the listener using BFO. Generally in HF band.
Ideal for very long range comms. Used by, mainly “Hams” now, but Ideal for very long range comms. Used by, mainly “Hams” now, but
still some Military & Commercial operational messages. Can ‘still some Military & Commercial operational messages. Can ‘get get
throughthrough’’
• MCWMCW Modulated Carrier WaveModulated Carrier Wave (Morse and data - no voice) (Morse and data - no voice) …s…simple basic radio imple basic radio
receiver required. Ideal for NAVAID ident letter codes and ‘distress receiver required. Ideal for NAVAID ident letter codes and ‘distress
tones’ in MF, HF, VHF and UHF. Not as range efficient as CW tones’ in MF, HF, VHF and UHF. Not as range efficient as CW
• DSBDSB Double Side BandDouble Side Band (Voice, line-of-sight tactical Digital Data-Link (Voice, line-of-sight tactical Digital Data-Link (in UHF band)(in UHF band) and and
NAVAID beacon data)NAVAID beacon data) -operational or entertainment, ranging from MF -operational or entertainment, ranging from MF
(Medium Wave) broadcasters through to VHF commercial stations to (Medium Wave) broadcasters through to VHF commercial stations to
Air Traffic and Citizen Band radios. Limited quality/fidelity due to Air Traffic and Citizen Band radios. Limited quality/fidelity due to
channel spacing.channel spacing.
• SSBSSB Single Side BandSingle Side Band (long range voice and ‘beyond the horizon’ tactical Digital Data-(long range voice and ‘beyond the horizon’ tactical Digital Data-
Link in, mainly, HF band.)Link in, mainly, HF band.) Used by commercial Oceanic Control agencies, Used by commercial Oceanic Control agencies,
commercial and very long range military Ship to Shore connections, commercial and very long range military Ship to Shore connections,
RAF, USAF and commercial Flight Watch services. RAF, USAF and commercial Flight Watch services.
• CWCW Carrier WaveCarrier Wave (Morse only – no voice). (Morse only – no voice). Needs a receiver BFO. Pitch of Needs a receiver BFO. Pitch of
received tones set by the listener using BFO. Generally in HF band. received tones set by the listener using BFO. Generally in HF band.
Ideal for very long range comms. Used by, mainly, “Hams”, now but Ideal for very long range comms. Used by, mainly, “Hams”, now but
still some Military & Commercial operational messages.still some Military & Commercial operational messages.
• MCWMCW Modulated Carrier WaveModulated Carrier Wave (Morse and data - no voice) (Morse and data - no voice) …s…simple basic imple basic
radio receiver required. Ideal for NAVAID ident letter codes and radio receiver required. Ideal for NAVAID ident letter codes and
‘distress tones’ in MF, HF, VHF and UHF. Not as range efficient as ‘distress tones’ in MF, HF, VHF and UHF. Not as range efficient as
CW CW
• DSBDSB Double Side BandDouble Side Band (Voice, line-of-sight tactical Digital Data-Link (Voice, line-of-sight tactical Digital Data-Link (in UHF band)(in UHF band)
and NAVAID beacon data)and NAVAID beacon data) -operational or entertainment, ranging from MF -operational or entertainment, ranging from MF
(Medium Wave) broadcasters through VHF commercial stations and (Medium Wave) broadcasters through VHF commercial stations and
Taxis to Air Traffic and Citizen Band radios. If analogue, then limited Taxis to Air Traffic and Citizen Band radios. If analogue, then limited
quality/fidelity due to channel spacing.quality/fidelity due to channel spacing.
• SSBSSB Single Side BandSingle Side Band (long range voice and ‘beyond the horizon’ tactical Digital (long range voice and ‘beyond the horizon’ tactical Digital
Data-Link in, mainly, HF band.)Data-Link in, mainly, HF band.) Used by commercial Oceanic Control Used by commercial Oceanic Control
agencies, commercial and very long range military Ship to Shore agencies, commercial and very long range military Ship to Shore
connections, RAF, USAF and commercial Flight Watch services. connections, RAF, USAF and commercial Flight Watch services.
All of these All of these
are…are…
AAmplitude mplitude
MModulatedodulated
modesmodes
Now let us look at
Now let us look at
the the FFrequency requency
MModulated mode
odulated mode
145145//
146146//
Radio Radio FrequencyFrequency
88.90 MHz
FF00
Sig
nal st
rength
Sig
nal st
rength
This single 1This single 111//22 kHztone kHztone AAmplitude mplitude MModulation of odulation of
the the ccarrier generates arrier generates
sumsum and and differencedifference frequenciesfrequencies
-1.5 -1.5 kHzkHz
+1.5 +1.5 kHzkHz
Amplitude Amplitude modulationmodulation
BBC radio2
VHF
Under
Under
constr
uction
constr
uction
It is now accepted that there are around 100 to It is now accepted that there are around 100 to 200 thunderstorms per day across the globe…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 globeproducing 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
It’s all natural It’s all natural
interferenceinterference
147147//
Sparks from machinery such as Sparks from machinery such as electric motors, vehicles etcelectric motors, vehicles etc
Then there is man-made Then there is man-made interference interference
148148//
149149//
Radio Radio FrequencyFrequency
88.00 MHz
FF00
Sig
nal st
rength
Sig
nal st
rength
This interference shows This interference shows up on the frequency up on the frequency domain view domain view
-1.5 -1.5 kHzkHz
+1.5 +1.5 kHzkHz
……as fleeting and as fleeting and ever changing ever changing spikes spread spikes spread across the em across the em spectrumspectrum
Single tone Single tone
MCWMCW
Amplitude Amplitude modulationmodulation
This interference ruins This interference ruins the fidelity of the the fidelity of the
received signal and received signal and appears as crackles and appears as crackles and
bangs to the listenerbangs to the listener
How can we get How can we get around this around this
interference?interference?
150150//
With radio Frequency Modulation With radio Frequency Modulation (FM); audio or information is (FM); audio or information is
conveyed over a carrier wave by conveyed over a carrier wave by varying its instantaneous varying its instantaneous
frequencyfrequency. This contrasts with . This contrasts with amplitude modulation, in which amplitude modulation, in which the the amplitudeamplitude of the carrier is of the carrier is
varied while its frequency varied while its frequency remains constant. remains constant.
Frequency ModulationFrequency Modulation151151//
With radio Frequency Modulation With radio Frequency Modulation (FM); audio or information is (FM); audio or information is
conveyed over a carrier wave by conveyed over a carrier wave by varying its instantaneous varying its instantaneous
frequencyfrequency. This contrasts with . This contrasts with amplitude modulation, in which amplitude modulation, in which the the amplitudeamplitude of the carrier is of the carrier is
varied while its frequency varied while its frequency remains constant. remains constant.
Frequency ModulationFrequency Modulation152152//
Frequency ModulationFrequency Modulation
Time-Line view
time
Example is a simple Example is a simple single tone…but single tone…but could be voice or could be voice or
musicmusic
AAmplitude mplitude MModulation of the odulation of the carriercarrierFFrequency requency MModulation of the odulation of the carriercarrier
instantaneous instantaneous AmplitudeAmplitude is key is key to extracting the to extracting the information from information from
the signalthe signal
instantaneous instantaneous FrequencyFrequency is key is key to extracting the to extracting the information from information from
the signalthe signal
Amplitude is Amplitude is (nearly) irrelevant (nearly) irrelevant with FMwith FM
So interference So interference spikes are not spikes are not
processedprocessed
FM FM is is suitable for HiFi suitable for HiFi transmissionstransmissions
153153//
Frequency ModulationFrequency Modulation
Time-Line view
time
Example is a simple Example is a simple single tone…but single tone…but could be voice or could be voice or
musicmusic
AAmplitude mplitude MModulation of the odulation of the carriercarrierFFrequency requency MModulation of the odulation of the carriercarrier
instantaneous instantaneous Amplitude is key Amplitude is key to extracting the to extracting the information from information from
the signalthe signal
instantaneous instantaneous Frequency is key Frequency is key to extracting the to extracting the information from information from
the signalthe signal
Amplitude is Amplitude is (nearly) irrelevant (nearly) irrelevant with FMwith FM
So interference So interference spikes are not spikes are not
processedprocessed
FM FM is is suitable for HiFi suitable for HiFi transmissionstransmissions
154154//
Amplitude ModulationAmplitude Modulation
The process of The process of extracting the extracting the
information /sound information /sound signal from a signal from a AMAM signal is called …signal is called …
back in time
…after tuner
DetectionDetection
AMAM Received signalReceived signal
detector
155155//
Amplitude ModulationAmplitude Modulation
The process of The process of extracting the extracting the
information /sound information /sound signal from a signal from a FMFM signal is called …signal is called …
back in time
…after tuner
DiscriminatioDiscriminationn
FMFM Received signalReceived signal
discriminator
156156//
157157//recarecappCWCW
MCWMCW
AMAM
SSBSSB
FMFM
DigitaDigitall
Continuous Continuous WaveWave
Modulated Modulated CWCW
Amplitude Amplitude ModulationModulation
Single Side bandSingle Side band
Frequency Frequency ModulationModulation
Morse only.Morse only. efficientefficientNeed specialist Need specialist Rx with a BFO. Rx with a BFO.
No VoiceNo VoiceMorse dentification of Morse dentification of Radio BeaconsRadio Beacons
Inferior range to Inferior range to CW but simple CW but simple RxRx
****
Radio ‘hams’ around the world still Radio ‘hams’ around the world still enthusiastically use this modeenthusiastically use this mode
……the futurethe future
Radio 5 Live at 330 Radio 5 Live at 330 kHz?kHz?OrOr Cranwell Tower 125.05 MHz or MF NAVAIDSCranwell Tower 125.05 MHz or MF NAVAIDS
RAF Flight Watch 6742-upper RAF Flight Watch 6742-upper or Shanwick or Iceland or New or Shanwick or Iceland or New York OCAs on 8879-upperYork OCAs on 8879-upper
Data Links, entertainment TV & radio and new Data Links, entertainment TV & radio and new inter-ship marine comms including Distress inter-ship marine comms including Distress CommsComms
entertainmententertainment radio, marine channels & radio, marine channels & NAVAIDSNAVAIDS
158158//
‘‘EM’ radio energy can be made to EM’ radio energy can be made to carry speech if we carry speech if we combinecombine or or mix mix
the low-frequency (the low-frequency (AAudioudio FFrequencyrequency)currents produced by )currents produced by
speaking into a microphone, with the speaking into a microphone, with the high-frequency currents (high-frequency currents (CWCW) that ) that
produce radio waves. This produce radio waves. This combination process is called combination process is called amplitude modulation (amplitude modulation (AMAM). ).
Amplitude Amplitude modulationmodulation
159159//
It is an electronic circuit called an It is an electronic circuit called an
oscillatoroscillator which produces the which produces the
continuous high-frequency (continuous high-frequency (RRadio adio
FFrequency) current which has a fixed requency) current which has a fixed frequency chosen from the frequency chosen from the EM spectrumEM spectrum. . This fixed-frequency alternating current This fixed-frequency alternating current
produces the em “produces the em “ccarrier arrier wwaveave”.”.
Amplitude Amplitude modulationmodulation
160160//
The audio-frequency (AF) current and the radio-frequency (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).
161161//
Amplitude Modulation Amplitude Modulation (AM) (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
162162//
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 ‘modulatemodulate’ the RF Radio Frequency of the
carrier wave in step with the much lower AF Audio Frequency.
163163//Fig 1-6: AM transmitter block Fig 1-6: AM transmitter block diagram diagram
• Fig 1-6: AM transmitter block diagram
164164//Parts of the basic Parts of the basic transmittertransmitter
• Master Oscillator. This generates a sinusoidal voltage (the carrier) at the required RF frequency (fo). Oscillators are often crystal-controlled 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.
165165//
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:
166166//Amplitude ModulatedAmplitude Modulatedtransmitter block diagram transmitter block diagram
AM transmitter block diagram
167167//Parts of the basic Parts of the basic transmittertransmitter
• Master Oscillator. This generates a sinusoidal voltage (the carrier) at the required RF frequency (fo). Oscillators are often crystal-controlled 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.
168168//
• 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).
169169//
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!
170170//
Transmitting only one sideband …by by suppressingsuppressing the Carrier the Carrier Wave Wave and the other duplicate sidebandand the other duplicate sideband mea means all of the ns all of the output power can be applied to the remaining sidebandoutput 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.
SSB SSB
It is only used in the long wave
frequency band of 2 to 30Mhz.
172172//
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.
SSB SSB
173173//
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.
174174//
Try tuning through an AM band radio and see how close the stations are together!
175175//
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 MonoMono systems. For stereo transmissions the problem would be doubled. As a result there are nono StereoStereo AM transmissions in the MF and HF broadcast frequencies.
176176//
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)fidelity)
There are 40,000 thunderstorms per day
177177//
To overcome AMAM limitations of mutual interferencemutual interference (crowding) and
lack of HiFilack of HiFi, the use of short-range ffrequency requency mmodulatedodulated systems has become necessary.
178178//Frequency Modulation (FM)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.
179179//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. The emergency services, such as Coastguard and Lifeboats, used FM radios using VHF freqs above Civil Air Traffic (AM) …around 150MHz
Emergency and maritime agencies, plus boat and ship owners have now been 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 banished from FM VHF and must use a much more sophisticated and secure system ; system ; GMDSSGMDSS, a digital system using Digital Selective Calling , a digital system using Digital Selective Calling (DSC)(DSC), , whereby every ‘participant’ or vessel has a unique ‘digital address number’ or whereby every ‘participant’ or vessel has a unique ‘digital address number’ or Maritime Mobile Address Identity (MMAI) which allows one-to-one conversations 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 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 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 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 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 DSCday basis. We will not, currently, look any further at GMDSS or DSC
GGlobal lobal MMaritimearitime DDistress istress SSafety afety SSystem ystem it’s big!it’s big!
180180//Phase TestPhase TestWhat is the speed of light?
3 x 1033
m/sec
3 000 metres per
sec
300 000 000 000 metres per sec
3 x 101111
m/sec
30 000 000 000 metres per sec
3 x 101010
m/sec
300 000 000 metres per sec
3 x 1088
m/sec
Click Buttons to enter your answer
181181//Phase TestPhase Test
300 x 1010
m/sec
3 000 metres per sec
300 000 000 000 metres per sec
3 x 101111
m/sec
30 000 000 000 metres per sec
3 x 101010
m/sec
Click to proceed
What is the speed of light?
300 000 000 metres per
sec
3 x 1088
m/sec
182182//Phase TestPhase Test
(v = f x λ) (v = f + λ) (v = f- λ)
(f = v - λ)
D
frequency frequency =
velocity -
wavelength (f = v - λ)
A
velocityvelocity =
frequency x wavelength
(v = f x λ)B
velocityvelocity = frequency+waveleng
th (v = f + λ)
Cvelocityvelocity =
frequency – wavelength
(v = f- λ)
Click Buttons to enter your answer
What is the relationship What is the relationship
between between frequencyfrequency ( (ff), ),
wavelengthwavelength ( (λλ) and ) and velocityvelocity
of light (of light (vv) is given in the ) is given in the formula:formula:
A B C D
183183//Phase TestPhase Test
Click Buttons to continue
184184//Phase Phase TestTest
Assessment Questions3. 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.
185185//
• If the velocity of radio waves is 3 x 108 8 m/sec,
what would be the value of for a frequency of
3 x 1066 Hz ?
Phase TestPhase Test
3 MHz = f
186186//
• If the velocity of radio waves is 3 x 108 8 m/secm/sec,
what would be the value of for a frequency of
3 x 1066 Hz ?
Phase TestPhase Test
f 3 x 1088
3 x 1066
221
1 x 101 x 1022 100100mm
187187//
• If the velocity of radio waves is 3 x 108 8 m/secm/sec,
what would be the value of for a frequency of
3 x 1066 Hz ?
Phase TestPhase Test
f 3 x 1088
3 x 1066
221
1 x 101 x 1022 100100mm
f = 3 MHz
3 x 1088 m/secm/sec
=
= = 100m100m
188188//Phase TestPhase Test
f 3 x 1088
3 x 1066
221
f = 3 MHz
3 x 1088 m/secm/sec
=
= = 100m100m
Ideal antenna length?
//44
//22
Dipole type
Whip type
50m50m
2525mm
189189//Phase TestPhase Test
f 3 x 1088
3 x 1066
221
f = 3 MHz
3 x 1088 m/secm/sec
=
= = 100m100m
Ideal antenna length?
//44
//22
Dipole type
But remember …a radio wave is a transversetransverse wave so these aerials would need to be turned through 90º to work!
Whip type
50m50m
2525mm
Electric ‘E’ waveElectric ‘E’ wave
verticallyvertically polarised polarised
190190//Phase TestPhase Test
Assessment QuestionsWhat is the speed of light?
a.300 x 108 ms-1b.300 x 106 ms-1c.300 x 109 ms-1d.300 x 101 ms-12.
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.
191191//Phase TestPhase Test
What does What does SSBSSB stand for? stand for?
Single Silicon Single Silicon
Band ?Band ?
Single Side
Single Side Band ?Band ?
Ship to Shore Buffer ?
Ship to Shore Buffer ?
Solo Side Band?Solo Side Band?
Click on Click on youryour answeranswer
192192//Phase TestPhase Test
Correct !Correct !
193193//ReviewReview
CWCW
Marconi’s first Marconi’s first
transmissionstransmissions
EfficientEfficient
Only good for Only good for
MorseMorse
but you can’t but you can’t hear hear anything on anything on frequency frequency unless …unless ……your Rx can
your Rx can generate a single generate a single tone when it
tone when it receives CWreceives CW
interrupted - ie OnOn - - OffOff
Ordinary radios do Ordinary radios do notnot normally normally have this have this
tonetone facilityfacility
194194//ReviewReview
CWCW
interrupted - ie OnOn - - OffOff
195195//ReviewReview
196196//endend
ENDEND
197197//Phase TestPhase Test
What is the speed of light?
3 x 1033
m/sec
3 000 metres per sec
30000 000000 000000 000000 metres per
sec
3 x 101111
m/sec
30 000 000 000 metres per sec
3 x 101010
m/sec
300 000 000 metres per
sec
3 x 1088
m/sec
Click to return
198198//Phase TestPhase Test
What is the speed of light?
3 x 1033
m/sec
3 000 metres per sec
300 000 000 000 metres per sec
3 x 101111
m/sec
300 000000 000000 000000 metres per sec
3 x 101010
m/sec
300 000 000 metres per
sec
3 x 1088
m/sec
Click to return
199199//Phase TestPhase Test
3 x 1033
m/sec
3 000 metres per sec
300 000 000 000 metres per sec
3 x 101111
m/sec
30 000 000 000 metres per sec
3 x 101010
m/sec
Click to return
30000 000000 000 000 metres per sec
3 x 1088
m/sec
What is the speed of light?
200200//Phase TestPhase Test
What is the speed of light?
3 x 1033
m/sec
3 000000
metres per sec
300 000 000 000 metres per sec
300 x 1099
m/sec
30 000 000 000 metres per sec
300 x 1088
m/sec
300 000 000 metres per
sec
300 x 1066
m/sec
Click to return
201201//Phase TestPhase Test
Relationship between , f and
(v = f x λ)
= f
Click to return
202202//Phase TestPhase Test
Relationship between , f and
= f ++
Click to return
203203//Phase TestPhase Test
Relationship between , f and
= f --
Click to return
204204//Phase TestPhase Test
Relationship between , f and
f = --
Click to return
205205//Phase TestPhase Test
No !No !
Return …