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Advanced Studies Unit 18a BTec

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

2 Advanced Studies Unit 18a BTec
Advanced Radio

3 Advanced Studies Unit 18a BTec
communicating

4 Communicating introduction
4/ Communication may be defined as the “exchange of information”

5  transmitter = voice and
Communicating 5/ 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 and receiver = ears

6 Communicating 6/ 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

7 echoes, wind and other unwanted noises distort and mask the sound
Sound limitations 7/ Sound does not travel very far in air. The air acts like a shock absorber and the sound energy is converted into infinitesimally small amounts of heat … even if you have a loud voice! However, for a whale the transmission medium is water …liquids cannot be compressed! So sound travels faster and much more efficiently in liquid and therefore, much further. Solid media even more so. echoes, wind and other unwanted noises distort and mask the sound

8 Nobody’s getting served any quicker!
Note: the ‘action’ or energy goes in the same direction as the propagation …ie lies in the same plane none of the people (the ‘medium’) moved closer to the destination after the shove had finished …but the shove/wave does move or propagate towards the destination the shove/wave isn’t an object …it has no weight or mass. It’s an experience, a phenomenon a longitudinal wave 8/ Hey! Nobody’s getting served any quicker! tickets direction of wave propagation

9 direction of wave propagation
a longitudinal wave Not from where I’m standing! 9/ Sound is … Woah! Did the Earth just move for you? The plane of action or energy tickets direction of wave propagation

10 echoes, wind and other unwanted noises hamper reception
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
11/ Let’s look at how sound travels through various media

12 …ie at normal UK temperatures
12/ Propagation or velocity of sound in air (760 mph) 340 metres per sec …in air at 20ºC Speed of propagation Air compression …ie at normal UK temperatures Air decompression Ambient Air Pressure = 1Bar input 1 Ambient pressure Graphical representation of localised air pressure sound wave longitudinal

13 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
14/ Propagation; sound in vacuum Nothing to compress ? NO SOUND HEARD! Air Pressure = 0 Bar input vacuum

15 Propagation; sound in vacuum
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?? Air Pressure = 0 Bar input vacuum All announcements, alarms or bells will be VERY much quieter.

16 1483 metres per sec (3,300 mph) Propagation; sound in liquid (water?)
16/ 1483 metres per sec (3,300 mph) Liquids cannot compress …so transmits the sound very efficiently and very fast! …and over great distances …in water Liquid (eg water or mercury?)

17 Propagation; sound in solids (steel?)
17/ 4500 metres per sec uncompressible …so transmits sound even faster and more efficiently (10,000+ mph!!) …in solid steel …or quartz crystal …or The Earth Strange 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

18 Recap Speed of Sound in … 340 m/sec 1483 metres/sec
18/ Propagation; sound Speed of Sound in … Vacuum 0 mph …it doesn’t …and for not very far Air 760mph Recap 340 m/sec Water 3300mph …and for maybe 1000miles + 1483 metres/sec Steel 10,000mph 4500 metres per sec

19 Check of understanding
19/

20 Sound cannot travel through a vacuum!!
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 computer won’t open the pod doors, Sergei !
21/ A. By touching space-helmets! …and, surprisingly, they do this quite often to co-ordinate their work computer won’t open the pod doors, Sergei ! Oh! oh! not so simples

22 Communicating 22/ radio communication

23 Let’s now look at how Radio Waves travel
23/ Let’s now look at how Radio Waves travel

24 Radio Waves Radio – uses a different energy
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 shorthand for a radio transmitter is
Radio Waves 25/ so… shorthand for a radio transmitter is Tx …remember this abbreviation! …and for a receiver it is Rx …again, remember this abbreviation too!

26 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 …exactly the speed of light!!
Radio 27/ Or, if you prefer to put that speed in context, it is 186, 000 miles per second!! remember this speed !!! 0r 669,600,00 mph! 3 x 108 metres per second (sometimes written as m/s or ms-1) or 300,000,000 ms-1 …exactly the speed of light!!

28 A typical wave can be imagined like this…
Electro-magnetic energy 28/ 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…

29 electromagnetic energy
29/ 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

30 Radio wave Frequencies
Low Freqs plus infra red & visible light, damaging Ultra Violet, dangerous X-rays and lethal Gamma rays High Freqs Long wave length Short wave length

31 Radio wave Frequencies
Low Freqs plus infra red & visible light, damaging Ultra Violet, dangerous X-rays and lethal Gamma rays High Freqs Long wave length Short wave length

32 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

33 Txs come in all shapes and sizes?
Transmitters 33/ You know… Txs come in all shapes and sizes? think about it! the car alarm remote is another PLB …aircrew Personal Locator Beacon Any WiFi device WiFi home hub? Man-made satellights? your mobile phone? 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.

34 Txs come in all shapes and sizes?
Transmitters 34/ You know… Txs come in all shapes and sizes? think about it! 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? Any WiFi device Man-made satellights? but a BBC television or a Medium Frequency (MF) radio transmitter will, on the other hand, have a power rating of up to 500,000Watts ie ½ Megawatt These 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.

35 …Radar Warning Receivers on aircraft
Rx also come in all shapes and sizes …and your TV GPS satnav think about it! Car immobiliser RWRs …Radar Warning Receivers on aircraft Obviously …your personal radio huge radio telescopes eg Jodrell Bank

36 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 Magnetism can also be ‘static’, as it is in a refrigerator magnet.
What is electro-magnetic energy? 37/ smug Electricity can be ‘static’, like the energy that can make your hair stand on end. B Dinner's in the dog! magnetic field ’B’ electric field ‘E’ Magnetism can also be ‘static’, as it is in a refrigerator magnet.

38 What is electro-magnetic energy?
38/ A changing magnetic field will induce a changing electric field and vice-versa—the two are linked. These changing fields form electromagnetic waves.

39 What is electromagnetic energy?
39/ B B + B weak B Wire conductor Magnetic field strong - Direct current 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?
40/ B B + B B Wire conductor - Direct current 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

41 What is electromagnetic energy?
41/ Let’s now look at applying an alternating current (ac) to the wire

42 What is electromagnetic energy?
42/ - + Wire conductor + - Alternating current Now this alternating current introduces a new complexity which results in an electromagnetic wave being transmitted - - + + ~

43 What is electromagnetic energy?
43/ B B Wire conductor B Wave front Alternating current As before, the current produces a magnetic field B as shown Let’s just slow things down ~

44 What is electromagnetic energy?
44/ B B Wire conductor B Alternating current but its changing strength and direction in sympathy with the conductor’s electric current. ~

45 …but

46 What is electromagnetic energy?
46/ e h e h Wire conductor e h You can’t change a magnetising force without generating an electric field ..e ~

47 … but …but!

48 What is electromagnetic energy?
48/ e B e B Wire conductor 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 ~

49 ~ e B -e -B 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? Ans: Well … forever! -e e Provided the wave remains ‘in space’ and it isn’t weakened by air or absorbed by other physical objects. -B

50 it pushes itself forever outwards
…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?
51/ e B e B …and the speed at which it radiates is… Wire conductor e B The speed of light! 3 x 108 m/s RF ~ ~

52 What is electromagnetic energy?
52/ B e B e Wire conductor B e Alternating current ~

53 B Magnetic Field ‘B’ e electric field e volts

54 Both fields are 90º to each other
3 x 108 ms-1 B Magnetic field ‘B’ e electric field And they propel the electro-magnetic radio wave at 90º to both e and B fields e volts Both fields are 90º to each other At exactly 3 x 108 ms-1 no faster no slower

55 and the e & B fields remain …at the original frequency
3 x 108 ms-1 h Magnetic field ‘B’ e electric field and the e & B fields remain …at the original frequency e volts Both fields are 90º to each other Long after they have left the solar system , the milky way and the local group of galaxies on their way to infinity!

56 electromagnetic energy
56/ The frequency of the radio frequency, alternating current will determine the frequency of the em waves produced

57 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.

58 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, 8 billion miles away. 3metres (it’s not big) …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.

59 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, 8 billion miles away. 3metres (it’s not big) 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

60 The Electromagnetic Spectrum
Low Freqs Radio & Radar Region High Freqs kHz MHz GHz ATC radios R/C models Mobile Phones Radars Television Sat TV Radio Hams Digital & WiFi long range radio BBC World Svc Radio Hams Telemetry Microwave Ovens Radar Missile Guidance The Electromagnetic Spectrum Data Links

61 Extra Hi Freq MF & HF ie & Super Hi Freq EHF & SHF VHF & UHF Low High
Freqs Radio & Radar Region High Freqs 61/ ie Extra Hi Freq & Super Hi Freq kHz MHz GHz ATC radios R/C models Mobile Phones Radars Television Sat TV Radio Hams Digital & WiFi EHF & SHF MF & HF long range radio BBC World Svc Radio Hams Telemetry Microwave Ovens Radar Missile Guidance VHF & UHF Data Links

62 definitions 62/ We need to cover a few definitions to progress our understanding of Radio further

63 definitions 63/ 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 or power axis. Wavelength () – the distance between any two identical points in a wave (ie peak to peak ~the length of one whole wave). Greek letter pronounced Lambda Velocity () – the speed with which the waves moves has the relationship: Measured in Hertz Hz A number of Units available Measured in metres, cm or mm …in Metres per second …always 3 x 108 m/s Greek letter actually pronounced “Nu” = f …but don’t worry, most people just remember it as “V”

64 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). Velocity () – the speed with which the waves moves has the relationship: This Greek letter is pronounced “Lambda” being a Greek L for “length” f = The most useful form of this expression is to calculate wavelength  for aerial selection …so, rearranging for 

65 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 Speed of travel is unimaginably fast
Advantages of em 66/ 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 108 m/s), …but let’s get that into the context of computers

67 A typical PC Central Processor Unit
Advantages of em 67/ 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 108 m/s), …but let’s get that into the context of computers Answer: 1 wavelength of 3 GHz … Which is V = 3 x 108 f = 10cm or 4” 3 x 109 Speed of travel is unimaginably fast …the speed of light (always 3 x 108 m/s) Intel Pentium 3 GHz speed A typical PC Central Processor Unit (CPU) So, 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
68/ This is a severe limiting factor for PC CPU speeds We need faster radio waves or smaller CPUs = 10cm or 4” We cant have different ‘newness’ of data from one side of a chip to the other! Intel Pentium 3 GHz speed 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!
69/ All of a sudden, the speed of light doesn’t seem quite so quick!

70 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 71/ 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    f Aerial Length * * = = = = 1500 metres eg For f = 200 kHz, &
72/ * eg For f = 200 kHz, & = 300,000,000 m/sec As we know We need to rearrange f * = ‘ C ’ speed of light = = 300000,000 200,000 300,000,000 200,000 = 1500 metres Wavelength ….nearly there!

73   /2  /4 Aerial Length = 1500 metres 750m 375m
73/ So, given that the wavelength for our 200kHz radio is … = 1500 metres  /2  /4 or The best aerial length would be 750m 375m Which would be… or

74   f Aerial Length = = = λ/2 λ/4
74/ So what aerial lengths would best suit a frequency of 100 MHz? f = = 300,000,000 100,000,000 = 3 metres …best Ae length? λ/2 λ/4 1.5 m 0.75 m or

75 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? λ = for 100 MHz? 3 metres …best Ae length? λ/2 λ/4 1.5 m 0.75 m or

76 OK, they were a few fundamentals to be going on with…
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 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.

78 it didn’t matter. The Funds poured in
78/ 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 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

79 night ranges are always greater than by day
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 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.

81 …although submarinecable messages had been exchanged for nearly 50yrs
81/ Marconi built a radio station near South Wellfleet, Massachusetts and on January 18, 1903 sent a message (in Morse) of greetings from Theodore Roosevelt, the President of the United States, to King Edward VII of the United Kingdom, marking the first transatlantic radio transmission originating in the United States. …although submarinecable messages had been exchanged for nearly 50yrs This station also was one of the first to receive the distress signals coming from the RMS Titanic 9 years later in

82 The U. S. Supreme Court stated that …
82/ In 1943, a lawsuit regarding Marconi's numerous other radio patents was finally resolved in the United States. The U. S. Supreme Court stated that … “Marconi's reputation as the man who first achieved successful radio transmission rests on his original patent, and which is not in question.” but “That reputation, however well-deserved, does not entitle him to a patent for every later improvement which he claims in the radio field. “

83 The advances were rapid
83/ The importance of radio was grasped by the military of all of the major nations …but the American Army portable radios of 1911 were: the ‘Pack Set’, carried by a "section normally composed of 10 mounted men and 4 pack mules", and the ‘Wagon Set’, whose "section is normally composed of 18 mounted men, the waggoner and engineer, who ride on the wagon, and one wagon wireless set, drawn by 4 mules" They were huge British wireless in the trenches of 1917 had advanced such that where operators with portable transmitters which proved invaluable, for "If a gas attack is coming, it is he who sends the warning to the men behind to put their gas helmets on." The advances were rapid

84 84/ A Marconi Corporation of America transmitter at Siasconsett, Massachusetts was closed down in 1914 after it handled a ‘non-neutral’ message from the British cruiser HMS Suffolk. America remained neutral until 1917, but the Suffolk incident was a major political and legal rift for the duration of WWI it became illegal for private U.S. citizens to have an operational radio transmitter or receiver …it was considered Treason. (nb an archaic draconian reaction? Well, if you try to remove your personal, encrypted laptop PC from present-day USA you will be considered to be illegally exporting armaments and charged/treated accordingly …unless the US government is provided with the ‘key’ to decrypt; it you’re in trouble. They don’t mess around with National Security!)

85 Marconi died in Rome in 1937 at age 63
85/ Marconi died in Rome in 1937 at age 63 In 1919, the british author David W. Bone wrote in his book Merchantmen-at-Arms … "If to one man we seamen owe a debt unpayable, Marconi holds the bond".

86 86/ footnote Marconi joined the Italian Fascist party in In 1930, Italian dictator Benito Mussolini appointed him President of the Royal Academy of Italy, which made Marconi a member of the Fascist Grand Council.

87 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 …

88 superheterodyne 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

89 superheterodyne 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 complex wave which has sum and difference frequencies embedded within it.

90 Amplitude modulation 90/ superheterodyne sum & difference frequencies

91 Join up the peaks and troughs and …
Amplitude modulation Adding two sinewaves 91/ f1 & f2 composite the upper sinewave has a lower frequency f1 than the next down sinewave of frequency f2 Join up the peaks and troughs and … the resultant wave form shows another virtual sine wave of frequency f2 - f1

92 the resultant wave is the
Amplitude modulation Adding two sinewaves 92/ f1 + f2 the resultant wave is the difference frequency f2 - f1

93 Fd difference frequency
Amplitude modulation Adding two sinewaves 93/ f1 + f2 Fd difference frequency 2 kHz F d = sum …this is the virtual waveform of the difference frequency So if f1 = 250 kHz (ie 250,000 Hz) & f2 = 252 kHz Then … F (difference) F d - = = 252 kHz 250 kHz = 2 kHz

94 Adding two sinewaves –the SUM freq
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 frequency = fSUM So if f1 = 250 kHz & f2 = 252 kHz Then … Then … Then … fSUM 502 kHz =

95 Sum & Difference Frequencies
Amplitude modulation 95/ Sum & Difference Frequencies …this applies to interaction of all sinusoidal waves they could be soundwaves This effect has even resulted in old, badly designed propeller airliners shaking themselves into fatigue failure and even destruction! 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!

96 Sum & Difference Frequencies
Amplitude modulation 96/ Sum & Difference Frequencies …this applies to interaction of all sinusoidal waves they could be soundwaves This effect has even led to propeller airliners shaking themselves into fatigue failure and even destruction! or wave-motion at sea This is caused by the difference in frequency between the two or engines at slightly different speeds to each other …which creates an unpleasant ‘beat frequency’ of vibration ..which can be catastrophic!

97 … which we will not go in to!
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

98 Sum & Difference Frequencies
Amplitude modulation 98/ Sum & Difference Frequencies Amplitude Modulation with regards to Radio Waves

99 Sum & Difference Frequencies
Amplitude modulation 99/ Sum & Difference Frequencies amplitude let’s look at this in a graphical way frequency is along the bottom of the graph This view is called the frequency domain …and signal strength or amplitude is along the vertical So frequency rules! OK? frequency

100 We’re now going to look, using the frequency domain, at a hypothetical radio transmitter receiver on a random frequency, say , 2182kHz or Hz if you wish 2182kHz transmitter

101 We now transmit (Tx) on an RF of, say, 2182 kHz
Amplitude modulation Amplitude modulation CW 101/ the frequency domain We now transmit (Tx) on an RF of, say, 2182 kHz It’s far, far too high for you to ‘hear’ if it was sound You wouldn’t actually hear anything on frequency …yet! Signal strength Watts 2182 kHz Radio Frequency F0 Electromagnetic spectrum

102 CW We now stop transmitting That is how Morse Code could be sent
Amplitude modulation 102/ Let’s look at this effect another way … Amplitude modulation CW We now stop transmitting on That is how Morse Code could be sent Signal strength …and very efficiently too! off 2182 kHz Radio Frequency F0 Electromagnetic spectrum

103 Amplitude modulation CW 103/ 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 specialist receiver with a Beat Frequency Oscillator to be able to hear any Morse Code CW transmission Signal strength 2182 kHz Radio Frequency F0 Electromagnetic spectrum

104 CW CW Morse Amplitude modulation Reception transmission
104/ Nothing heard on frequency! CW 2182kHz Reception transmission Signal strength Ordinary AM radio 2182 kHz Radio Frequency F0 Electromagnetic spectrum

105 BFO Now let’s look how a radio with a Beat Frequency Oscillator
would receive that same transmission.

106 CW CW Morse Amplitude modulation Reception Dah Dah Dit
106/ Dah Dah Dit CW 2182 kHz Reception AM radio with a Beat Freq Osc Signal strength BFO 2182 kHz Radio Frequency F0 Electromagnetic spectrum

107 Amplitude modulation CW Morse 107/ …but how?

108 Amplitude modulation CW Morse 108/ …basically, in all radios, most of the processing and amplification is done at a fixed, intermediate frequency (i.f.). For our example radio we will assume that, no matter what the receiver is tuned to, the received signal is converted down to an i.f based at, say, 30kHz

109 Amplitude modulation CW Morse 109/ The Beat Frequency Oscillator (BFO) generates a very small continuous, steady sinewave signal into the i.f. circuits Received signal reduced to 30kHz …but at a slightly different frequency to the intermediate frequency (i.f.) of the radio receiver. In this case signal now scaled to 30kHz BFO i.f. 31 kHz 30 kHz i.f.

110 Amplitude modulation CW Morse 110/ 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!

111 CW Morse Amplitude modulation Dah Dit Dah Dit Dit
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 31 kHz 1 1.0 2.0 BFO freq difference 30 kHz i.f.

112 CW Morse Amplitude modulation Dah Dit Dah Dit Dit
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 1.0 1.5 2.0 31.5 kHz BFO freq difference 1.5 30 kHz i.f.

113 CW CW Morse …it’s entirely the listeners choice Amplitude modulation
113/ Dah Dit Dah Dit Dit CW 2182 kHz Reception AM radio with a Beat Freq Osc the pitch of the tone / Morse you hear is dependant upon your BFO setting Signal strength BFO ?? …it’s entirely the listeners choice 30 kHz Radio Frequency i.f.

114 Amplitude modulation CW Morse 114/ …and this mode will ‘get through’ when none of the other modes can Who would use such a primitive and archaic mode of communication? …well, it’s no longer a primary, secondary or even tertiary mode for NATO military communications where Morse skills have all but disappeared …but there is a massive World-wide network of amateur radio enthusiasts known as Radio Hams who use this mode to ‘keep in touch’.

115 Amplitude modulation 115/ Now, what happens if we modulate the Carrier Wave with an amplified single tone of say 1.5 kHz? When there is no 1.5 kHz tone modulation all of the power is transmitted at the Carrier freq This generates Amplitude Modulation of the carrier giving sum and difference frequencies -1.5 kHz +1.5 kHz When the tone is present, the Carrier Wave is being modulated ie diminished/ attenuated to provide power for the Sum and Difference frequencies. 301.5 kHz 298.5 kHz Signal strength Notice: power is shared between the sum, difference and carrier frequencies 300 kHz Radio Frequency F0

116 (MCW) Only a simple Rx required Amplitude modulation
116/ Dah Dit Dah Dit Dit The pitch/tone of the Morse is set by the transmitter Amplitude Modulated Carrier Wave Only a simple Rx required -1 kHz +1 kHz (MCW) Signal strength Tone on 345 kHz 345 kHz Ordinary AM radio Radio Frequency F0

117 Amplitude modulation 117/ -1 kHz …mainly used for Aircraft ‘Navaid’ Beacons Morse Code Identification signals +1 kHz Signal strength Tone on Tone Off 345 kHz Radio Frequency F0

118 Amplitude Modulated Carrier Wave
Amplitude modulation 118/ Amplitude Modulated Carrier Wave Only a simple Rx required -1 kHz +1 kHz Signal strength Tone on 345 kHz Radio Frequency F0

119 Only a simple Rx required
Amplitude modulation 119/ Modulated Carrier Wave Only a simple Rx required -1 kHz +1 kHz Power is divided between upper, lower and carrier Signal strength …but does not carry as far as CW morse 345 kHz Radio Frequency F0

120 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 ?

121 Amplitude modulation Di Dum ………………... Di! Li Laaaaahh Blah!
121/ Di Dum ………………... Di! Li Laaaaahh Blah! Carrier Wave Transmitter

122 Let’s look at that in the “Frequency Domain” again
Amplitude modulation 122/ Let’s look at that in the “Frequency Domain” again …Centred on Tx Freq of Say, 1442kHz When the speaker talks …he Amplitude Modulates the strength of the carrier wave … Which needs to convey most of the tones in his voice not at one single frequency but a broad band of frequencies Radio Luxemburg Freq ‘Difference’ freqs ‘Sum’ freqs 1442 kHz Radio Frequency F0

123 Amplitude modulation lower sideband upper sideband ‘Difference’ freqs
123/ Carrier Wave lower sideband upper sideband ‘Difference’ freqs ‘Sum’ freqs 1442 kHz Radio Frequency F0

124 Amplitude modulation 124/ To recreate the original voice, in a simple superhet receiver …requires the reception of BOTH side bands to be intelligible. Carrier Wave lower sideband upper sideband ‘Difference’ freqs ‘Sum’ freqs 1442 kHz F0

125 each sideband is the mirror image of the other
Amplitude modulation 125/ The transmitted power is shared between both sidebands and the carrier. each sideband is the mirror image of the other  Tx power is being wasted Carrier Wave lower sideband upper sideband ‘Difference’ freqs ‘Sum’ freqs 1442 kHz F0

126 Amplitude modulation AM is OK for V/UHF Air Traffic comms as it is cheap, reliable and the equipment common and light. 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 higher quality in terms of interference and audio freq range Quality or ‘fidelity’ is limited with AM due to the RF band-width available between channels Carrier Wave lower sideband upper sideband ‘Difference’ freqs ‘Sum’ freqs 1442 kHz F0

127 268.000 267.000 268.625 268.600 UHF Amplitude modulation
127/ upper lower simple Double Side-Band AM AM Cranwell Tower, ASCOT213 on Uniform 268 decimal 625 request join downwind for Runway 26 Left hand for visual approach to land. ASCOT213 nothing heard, changing to Victor Tone VHF select UHF Guard V Guard U

128 simple Double Side-Band AM
Amplitude modulation 128/ 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. Tone VHF select UHF Guard V Guard U

129 Modulated Carrier Wave MCW
Amplitude modulation 129/ 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 Mode now simply Modulated Carrier Wave MCW 125.05 MHz Cranwell Tower, ASCOT213 now on Victor, 125 decimal 05 request join downwind for Runway 26 Left hand for visual approach to land. +1 kHz -1 kHz Tone VHF select UHF Guard V 121.5 Guard U 243.0

130 Amplitude modulation 130/ 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 side band and suppressed the carrier? Carrier Wave upper sideband lower sideband ‘Difference’ freqs ‘Sum’ freqs 1442 kHz F0

131 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 utterly garbled and not decipherable in any way! 6742 Ordinary AM radio Rx “Gbble hmblfmbgb Pmmblwrbbl” 6742 kHz F0

132 Single Side Band Amplitude modulation upper sideband
132/ upper sideband nb…the trouble is that receiving this on an ordinary domestic medium wave AM radio; the audio would be utterly garbled and not decipherable in any way! A Single Side Band (SSB) receiver overcomes this by re-synthesising the missing sideband and carrier wave …in the receiver 6742 6742 kHz F0

133 Single Side Band Amplitude modulation upper sideband
133/ upper sideband A Single Side Band (SSB) receiver overcomes this by re-synthesising the missing sideband …in the receiver 6742 Single side-band Rx mode CW DSB SSB U SSB L 6742 kHz F0

134 Single Side Band fidelity too poor for entertainment radio
Amplitude modulation Single Side Band 134/ Missing sideband re-synthesised on reception by Single Sideband Receiver (SSB) Rx Mainly used at HF and MF frequencies for Global Coverage Has range Advantage over DSB mode Carrier Wave Doubles channels available. not transmitted …but no point atV/UHF freqs lower sideband upper sideband fidelity too poor for entertainment radio ‘Difference’ freqs ‘Sum’ freqs 6742 kHz

135 Single Side Band Amplitude modulation
135/ Civil & Military long range voice comms tends to use Upper Side Band (in the HF freq band) Military Tactical Data Link tends to use Lower Side Band (in the HF freq band) lower sideband upper sideband 6742 kHz Used by Armies for beyond line of sight communications Used extensively Military and Merchant Navy

136 Single Side Band 8000 8890 8891 8800 Amplitude modulation
Shanwick this is Rafair2134 on 8891 upper, position 5630 North, Ten West at 1510, estimating Iceland boundary at… over! Single Side Band 136/ Civil & Military long range voice comms tends to use Upper Side Band (in the HF freq band) Military Tactical Data Link tends to use Lower Side Band (in the HF freq band) lower sideband upper sideband 8000 8890 8891 8800 6742 kHz kHz Used by Armies for beyond line of sight communications Used extensively Military and Merchant Navy upper lower

137 Single Side Band 6700 6715 6710 0000 6000 Amplitude modulation
Shanwick this is Rafair2134 on 8891 upper, position 5630 North, Ten West at 1510, estimating Iceland boundary at… over! Single Side Band 137/ Link Manager from Tactical Director; ‘Alligator’ Data Link frequency now 6715 lower. Civil & Military long range voice comms tends to use Upper Side Band (in the HF freq band) Military Tactical Data Link tends to use Lower Side Band (in the HF freq band) not transmitted lower sideband upper sideband 6700 6715 6710 0000 6000 kHz Used by Armies for beyond line of sight communications Used extensively Military and Merchant Navy upper lower

138 … Alligator Link 11a is …and that is exactly how it got it’s name
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

139 it controls commercial oceanic flights around the world
Amplitude modulation Single Side Band 139/ Largely surpassed in quality and effectiveness by Satellite Communications but SATCOM on-air time is expensive it controls commercial oceanic flights around the world …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

140 SSB is big and it's important!!
140/ SSB is big and it's important!! 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 eg RAF ‘TASCOM’ and ‘RAF VOLMET’ USAF ‘MAINSAIL’ Long Range, Link 11a Alligator Data Link NATO air and naval units etc etc etc

141 SSB is big and it's important!!
141/ SSB is big and it's important!! 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 side-band

142 radio modes and their uses
142/ Let’s now review the AM radio modes and their uses

143 CW Carrier Wave (Morse only – no voice). Needs a receiver BFO
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.

144 Amplitude Modulated All of these are…
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. All of these are… Amplitude Modulated modes

145 Now let us look at the Frequency Modulated mode
145/ Now let us look at the Frequency Modulated mode

146 Under construction Amplitude modulation
146/ This single 11/2 kHztone Amplitude Modulation of the carrier generates sum and difference frequencies -1.5 kHz +1.5 kHz Under construction Signal strength 88.90 MHz Radio Frequency BBC radio2 VHF F0

147 It’s all natural interference
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 It’s all natural interference …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
148/ Then there is man-made interference Sparks from machinery such as electric motors, vehicles etc

149 Amplitude modulation 149/ This interference shows up on the frequency domain view Single tone MCW This interference ruins the fidelity of the received signal and appears as crackles and bangs to the listener -1.5 kHz +1.5 kHz …as fleeting and ever changing spikes spread across the em spectrum Signal strength 88.00 MHz Radio Frequency F0

150 How can we get around this interference?
150/ How can we get around this interference?

151 Frequency Modulation 151/ 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 152/ 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.

153 FM is suitable for HiFi transmissions
Frequency Modulation FM is suitable for HiFi transmissions 153/ Time-Line view Example is a simple single tone…but could be voice or music So interference spikes are not processed instantaneous Amplitude is key to extracting the information from the signal Amplitude Modulation of the carrier Frequency Modulation of the carrier instantaneous Frequency is key to extracting the information from the signal time Amplitude is (nearly) irrelevant with FM

154 FM is suitable for HiFi transmissions
Frequency Modulation FM is suitable for HiFi transmissions 154/ Time-Line view Example is a simple single tone…but could be voice or music So interference spikes are not processed instantaneous Amplitude is key to extracting the information from the signal Amplitude Modulation of the carrier Frequency Modulation of the carrier instantaneous Frequency is key to extracting the information from the signal time Amplitude is (nearly) irrelevant with FM

155 Amplitude Modulation 155/ The process of extracting the information /sound signal from a AM signal is called … Detection detector AM Received signal …after tuner back in time

156 Amplitude Modulation 156/ The process of extracting the information /sound signal from a FM signal is called … Discrimination discriminator FM Received signal …after tuner back in time

157 Need specialist Rx with a BFO. No Voice
recap 157/ Need specialist Rx with a BFO. No Voice * * CW Continuous Wave Morse only. efficient Morse dentification of Radio Beacons Inferior range to CW but simple Rx MCW Modulated CW Radio 5 Live at 330 kHz? AM Amplitude Modulation Or Cranwell Tower MHz or MF NAVAIDS RAF Flight Watch 6742-upper or Shanwick or Iceland or New York OCAs on 8879-upper SSB Single Side band FM Frequency Modulation entertainment radio, marine channels & NAVAIDS Data Links, entertainment TV & radio and new inter-ship marine comms including Distress Comms Digital …the future Radio ‘hams’ around the world still enthusiastically use this mode

158 Amplitude modulation 158/ ‘EM’ radio energy can be made to carry speech if we combine or mix the low-frequency (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).

159 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”.

160 160/ 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).

161 Amplitude Modulation (AM)
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

162 162/ 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.

163 Fig 1-6: AM transmitter block diagram
163/ Fig 1-6: AM transmitter block diagram

164 Parts of the basic transmitter
164/ 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.

165 165/ 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:

166 Amplitude Modulated transmitter block diagram
166/ Amplitude Modulated transmitter block diagram AM transmitter block diagram

167 Parts of the basic transmitter
167/ 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.

168 The carrier minus the audio frequency band (ie speech) (fo – fm).
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).

169 169/ 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!

170 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.

171 SSB 171/ Such Single Sideband (SSB) transmissions are used for voice or data-link work and is the standard mode for long range ‘Oceanic’ communication for civilian trans-Atlantic aircraft traffic flow. eg ‘SHANWICK’ at Prestwick and the ARINC network in the USA. The RAF uses also SSB for the military world-wide ‘TASCOM’ Flight Watch service based in Harrogate and the corresponding USAF ‘MAINSALE’ network. The Upper and Lower sidebands can both be used independently.

172 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.

173 173/ 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.

174 174/ Try tuning through an AM band radio and see how close the stations are together!

175 175/ 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 There are 40,000 thunderstorms per day
176/ There are 40,000 thunderstorms per day 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)

177 177/ To overcome AM limitations of mutual interference (crowding) and lack of HiFi, the use of short-range frequency modulated systems has become necessary.

178 Frequency Modulation (FM)
178/ 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.

179 Global Maritime Distress Safety System it’s big!
179/ 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 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 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

180 Phase Test 3 x 1011 m/sec 3 x 1010 m/sec 3 x 103 m/sec 3 x 108 m/sec
180/ What is the speed of light? metres per sec 3 x 1011 m/sec metres per sec 3 x 1010 m/sec metres per sec 3 x 103 m/sec 3 000 metres per sec 3 x 108 m/sec Click Buttons to enter your answer

181 What is the speed of light?
Phase Test 181/ What is the speed of light? metres per sec 3 x 1011 m/sec metres per sec 3 x 1010 m/sec metres per sec 3 x 108 m/sec 300 x 10 m/sec 3 000 metres per sec Click to proceed

182 What is the relationship between frequency (f), wavelength (λ) and velocity of light (v) is given in the formula: Phase Test 182/ A velocity = frequency x wavelength (v = f x λ) D frequency = velocity - wavelength (f = v - λ) B velocity = frequency+wavelength (v = f + λ) C velocity = frequency – wavelength (v = f- λ) (v = f x λ) (v = f + λ) (v = f- λ) (f = v - λ) D A B C Click Buttons to enter your answer

183 Click Buttons to continue
Phase Test 183/ Click Buttons to continue

184 Phase Test Assessment Questions
184/ 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.

185 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 ? 3 MHz  = f  

186   1 x 102 100m   f   3 x 106 Hz ? 1   2  Phase Test 3 x 108
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 Hz ? 1 f 2 3 x 108 3 x 106 1 x 102 100m

187   1 x 102 100m   f   3 x 106 Hz ? 1   2  Phase Test  = 100m
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 3 x 106 Hz ? = 100m 1 f 2 3 x 108 3 x 106 1 x 102 100m

188    f  1   2 Phase Test   = 100m 3 x 108 3 x 106 
188/ 50m Ideal antenna length? 3 x 108 m/sec  = f = 3 MHz Dipole type /2 = 100m 1 f 2 3 x 108 3 x 106 /4 Whip type 25m

189    f  1   2 Phase Test   = 100m 3 x 108 3 x 106 
189/ 50m Ideal antenna length? 3 x 108 m/sec  = f = 3 MHz But remember …a radio wave is a transverse wave so these aerials would need to be turned through 90º to work! Dipole type /2 = 100m 1 f 2 3 x 108 3 x 106 /4 Electric ‘E’ wave vertically polarised Whip type 25m

190 What is the speed of light?
Phase Test 190/ 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 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.

191 What does SSB stand for? Single Side Band ? Ship to Shore Buffer ?
Phase Test 191/ What does SSB stand for? Click on your answer Single Side Band ? Ship to Shore Buffer ? Single Silicon Band ? Solo Side Band?

192 Phase Test 192/ Single Side Band Correct !

193 Continuous Wave CW Only good for Morse ie On - Off
Review 193/ Continuous Wave interrupted - ie On - Off CW but you can’t hear anything on frequency unless … Marconi’s first transmissions Efficient …your Rx can generate a single tone when it receives CW Only good for Morse Ordinary radios do not normally have this tone facility

194 Review 194/ Continuous Wave interrupted - ie On - Off CW

195 Review 195/ Single Side Band

196 end 196/ END

197 What is the speed of light?
Phase Test 197/ What is the speed of light? metres per sec metres per sec 3 x 1010 m/sec metres per sec 3 x 108 m/sec 3 x 103 m/sec 3 000 metres per sec 3 x 1011 m/sec Click to return

198 What is the speed of light?
Phase Test 198/ What is the speed of light? metres per sec 3 x 1011 m/sec metres per sec 3 x 1010 m/sec metres per sec 3 x 108 m/sec 3 x 103 m/sec 3 000 metres per sec Click to return

199 What is the speed of light?
Phase Test 199/ What is the speed of light? metres per sec 3 x 1011 m/sec metres per sec 3 x 1010 m/sec metres per sec 3 x 103 m/sec 3 000 metres per sec 3 x 108 m/sec Click to return

200 What is the speed of light?
Phase Test 200/ What is the speed of light? metres per sec 300 x 109 m/sec metres per sec 300 x 108 m/sec metres per sec 300 x 106 m/sec 3 000 metres per sec 3 x 103 m/sec Click to return

201 Relationship between , f and 
Phase Test 201/ Relationship between , f and   = f   (v = f x λ) Click to return

202 Relationship between , f and 
Phase Test 202/ Relationship between , f and   = f +  Click to return

203 Relationship between , f and 
Phase Test 203/ Relationship between , f and   = f -  Click to return

204 Relationship between , f and 
Phase Test 204/ Relationship between , f and  f =  -  Click to return

205 Phase Test 205/ No ! Return …


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