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1 Convention used Left mouse click option available not recommended in this lesson

2 Advanced Radio

3 1. communicating

4 Communication may be defined as the exchange of information

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 Speed of travel is quite slow in air: 340 m/s at 20ºC or 760 mph (the speed of propagation of sound). *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 vacuumSound will not travel through a vacuum it needs a substance or medium (normally air) to transmit the energy.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)…although the medium can also be liquid (eg water or mercury?) or a solid (eg bar of steel or a quartz crystal) 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 350 m/s or 780 mph at 30ºC so the hotter the day …the faster the speed of sound

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!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!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.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 soundechoes, wind and other unwanted noises distort and mask the sound

8 8/ a longitudinal wave direction of wave propagation tickets Note: 1. 1.the action or energy goes in the same direction as the propagation …ie l ll lies in the same plane 2. 2.none of the people (the medium) moved closer to the destination after the shove had finished 3. 3.…but the shove/wave d dd does move or propagate towards the destination 4. 4.the shove/wave isnt an object …it has no weight or mass. Its an experience, a phenomenon Hey! Nobodys getting served any quicker!

9 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 Im standing! Sound is …

10 10/ sound does not travel very far in air, even if you have a loud voice. It becomes attenuated or weakened by the spongy airsound 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 earths solid surface …and at 1000s of MPH…but sound can travel for thousands of kilometers through the sea and through the earths solid surface …and at 1000s of MPH echoes, wind and other unwanted noises hamper receptionechoes, wind and other unwanted noises hamper reception

11 11/ Lets look at how sound travels through various media

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

13 …but at higher temperatures, the speed of sound increases nb …thats why early in 1950s, the sub-sonic RAF world speed records were conducted in the hot desert …to delay reaching the so called sound barrier

14 14/ Nothing to compress ? Air Pressure = 0 Bar 0 input

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

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

17 17/ uncompressible …so transmits sound even faster and more efficiently sound using sound through quartz crystals is extensively used in electronics such as TV and Radar processing circuits Solid (Rock? or Quartz Crystal? Steel? metres per sec 10,000 (10,000+ mph!! ) …in s ss solid steel Strang e but true! …or q qq quartz crystal …or T TT The Earth

18 18/ Air 760mph Water 3300mph Steel 10,000mph Speed of Sound in … …and for not very far …and for maybe 1000miles + Vacuum 0 mph …it doesnt metres per sec m/sec metres/sec

19

20 20/ Q Q. So, how do these astronauts communicate by voice, outside the International Space Station … without using a radio? Sound cannot travel through a vacuum!!

21 21/ A. By touching space-helmets! …and, surprisingly, they do this quite often to co-ordinate their work computer wont open the pod doors, Sergei ! Oh! oh! not so simples

22 radio communication

23 23/ Lets now look at how Radio Waves travel

24 Radio – uses a different energyRadio – uses a different energy A radio communications system consists of a transmitter (Tx), to send the messageA radio communications system consists of a transmitter (Tx), to send the message …and a receiver (Rx) to receive the reply…and a receiver (Rx) to receive the reply

25 25/ so … shorthand for a radio transmitter is Tx …remember this abbreviation! Tx …remember this abbreviation! …and for a receiver it is Rx …again, remember this abbreviation too! Rx …again, remember this abbreviation too!

26 The link between the Tx and Rx this time is not sound energy, but electro-magnetic (em) energy, (radio waves)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 speedlight 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…the speed of light …no matter what the speed of the transmitter or receiver is…no matter what the speed of the transmitter or receiver is

27 …exactly the speed of light!! 3 x 108 m m m metres per second (sometimes written as m/s or ms -1) Or, if you prefer to put that speed 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!

28 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 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… A typical wave can be imagined like this…

29 29/ it would seem that there is no theoretical limit to the frequency of em waves, neither lower nor upper. 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. 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 …but we will only concern ourselves with the Radio & Radar region

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

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

32 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 33/ You know… Txs Txs come in all shapes and sizes? think about it! PLB …aircrew P ersonal L ocator B eacon 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) couple hundreds of Watts to a couple hundreds of Watts for a freesat satellight. your mobile phone? WiFi home hub? Any Any WiFi device Man-made satellights?

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

35 Rx also come in all shapes and sizes think about it! Obviously …your personal radio …and your TV GPS satnav Car immobiliser huge radio telescopes eg J odrell Bank RWRs … R adar W arning R eceivers on aircraft

36 36/ electric magnetic fields When an alternating electric current flows in a wire, both electric and magnetic fields are produced surrounding the outside of the wire. frequency frequency of the em waves 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 Earths atmosphere. emelectromagnetic spectrum There is no theoretical limit to the frequency of em waves and, as weve seen, the expression electromagnetic spectrum has been coined to embrace all radiations of this type, which include heat and light.

37 Electricity 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. electric field E B magnetic field B B

38 A changing magnetic field will induce a changing electric field and vice-versa the two are linked. These changing fields form electromagnetic waves. These changing fields form electromagnetic waves.

39 39/ Wire conductor Direct current DC + - B B B B BIf 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. strong weak Magnetic field

40 Wire conductor Direct current DC + - B B B B This isnt a radio wave …its just a constant magnetic field. You would need a magnetic compass to detect it. It quickly becomes very weak the further from the conductor. Its constant or static …the magnetic field is going nowhere… and will only last as long as there is a current flowing in the conductor.

41 Lets now look at applying an a lternating c urrent (ac) a lternating c urrent (ac) to the wire to the wire

42 Now this alternating current introduces a new complexity which results in an electromagnetic wave being transmittedNow this alternating current introduces a new complexity which results in an electromagnetic wave being transmitted Wire conductor ~ Alternating current

43 As before, the current produces a magnetic field B as shown Wire conductor ~ Alternating current Lets just slow things down B B B Wave front

44 but its changing strength and direction in sympathy with the conductors electric current. Wire conductor ~ Alternating current B B B

45 …but

46 eYou cant change a magnetising force without generating an electric field.. e Wire conductor ~ e h e e h h

47 … but …but!

48 Wire conductor ~ e B e e B B …again at right angles to the electric field that caused it electricfield another B fieldYou cant change an electric field without generating another magnetic B field

49 chicken and egg and chicken and egg, and chicken and egg, and chicken and egg etc B e -B-B-B-B -e-e-e-e magnetic field Wire conductor ~ Ans: Well … forever! Provided the wave remains in space and it isnt weakened by air or absorbed by other physical objects. electric field How long does this action continue …when the radio frequency ac power source is removed?

50 … but! But! But!! Although this process is ever lasting it pushes itself forever outwards And forms a perpetual, ever radiating radio wave

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

52 Wire conductor ~ Alternating current e B e e B B

53 e B Magnetic Field B electric field e volts

54 e B Magnetic field B electric field e volts Both fields are 90º to each other At exactly 3 x 10 8 ms -1 And they propel the electro- magnetic radio wave at 90º to both e and B fields no faster no slower 3 x 10 8 ms -1

55 e h Magnetic field B electric field e volts Both fields are 90º to each other …at the original frequency and the e & B fields remain 3 x 10 8 ms -1 Long after they have left the solar system, the milky way and the local group of galaxies on their way to infinity!

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

57 NASAs 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 NASAs Pioneer 10 and 11 spacecraft were launched in 1972/73 3metres (its not big) 40 years old technology That radio was turned off by command from NASA in 2003 These spacecraft were, however, 8 billion miles away. 8 billion miles away. …and transmitting 40W at a frequency of 2 GHz (your microwave operates at 3 GHz and blasts out 800w) It took 12 hours for the radio signal wave front to reach the spacecraft and another 12 hr for the return signal to reach Earth.

59 NASAs Pioneer 10 and 11 spacecraft were launched in 1972/73 3metres (its not big) 40 years old technology That radio was turned off by command from NASA in 2003 These spacecraft are, however, 8 billion miles away. 8 billion miles away. it appears that radio waves are very robust and can go a long long way for very little power It was 80 times the distance the Earth is from the Sun

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

61 Low Freqs kHz MHz GHz long range radio BBC World Svc Radio Hams ATC radios R/C models Mobile Phones RadarsTelevision Sat TV Radio Hams Digital & WiFi Telemetry Microwave Ovens Radar Missile Guidance Data Links Radio & Radar Region High Freqs MF & HF & HF VHF & UHF EHF & SHF & SHF ie E xtra H i F req & S uper H i F req S uper H i F req

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

63 Frequency fFrequency ( f ) – the number of complete vibrations or fluctuations each second (ie cycles per sec). Amplitude aAmplitude ( 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 LambdaWavelength ( ) – the distance between any two identical points in a wave (ie peak to peak ~the length of one whole wave). Greek letter pronounced Lambda VelocityVelocity ( ) – the speed with which the waves moves has the relationship: 63/ Nu Greek letter actually pronouncedNu V …but dont worry, most people just remember it asV = f 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

64 Frequency fFrequency ( f ) – the number of complete vibrations or fluctuations each second (ie cycles per sec). Amplitude aAmplitude ( a ) – 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). VelocityVelocity ( ) – the speed with which the waves moves has the relationship: This Greek letter is pronounced Lambda being a Greek L for length The most useful form of this expression is to calculate wavelength for aerial selection …so, rearranging for …so, rearranging for = f

65 Frequency fFrequency ( f ) – the number of complete vibrations or fluctuations each second (ie cycles per sec). Amplitude aAmplitude ( a ) – 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). VelocityVelocity ( ) – the speed with which the waves moves has the relationship: = f

66 66/ Using em energy to carry our communications information has many advantages compared with sound energy Speed of travel is unimaginably fast Speed of travel is unimaginably fast …the speed of light (always 3 x 10 8 …the speed of light (always 3 x 10 8 m/s), …but lets get that into the context of computers

67 Using em energy to carry our communications information has many advantages compared with sound energy Speed of travel is unimaginably fast Speed of travel is unimaginably fast …the speed of light (always 3 x 10 8 …the speed of light (always 3 x 10 8 m/s), …but lets get that into the context of computers Speed of travel is unimaginably fast …the speed of light (always 3 x 10 8 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? Answer: 1 wavelength of 3 GHz … Which is V = 3 x 10 8 f 3 x 10 9 = 10cm or 4

68 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 = 10cm or 4 This is a severe limiting factor for PC CPU speeds We need faster radio waves or smaller CPUs We cant have different newness of data from one side of a chip to the other!

69 All of a sudden, the speed of light doesnt seem quite so quick! doesnt seem quite so quick!

70 70/ Em waves will travel through a vacuum and so can be used for communication in space.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 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 lengthsof 2 and 4 are particularly efficient…ie halfand quarterof wavelength 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 72/ egFor f = 200 kHz, = f & = 300,000,000 m/sec * * = C speed of light = 300,000, ,000 = 1500 metres As we know Wavelength We need to rearrange , ,000 ….nearly there!

73 73/ = 1500 metres 200kHz So, given that the wavelength for our 200kHz radio is … The best aerial length would be /2 or /4 Which would be… 750m375m or

74 74/ So what aerial lengths would best suit a frequency of 100 MHz? = f = 300,000, ,000,000 3 metres = …best Ae length? λ/2λ/4 1.5 m0.75 m or

75 75/ 3 metres = …best Ae length? λ/2λ/4 1.5 m0.75 m or λ Notice – the higher the frequency, the shorter the aerial required. What does this tell us about the operating frequency of a car-mounted radio aerial compared to a hand held mobile phone? for 100 MHz?

76 OK, they were a few fundamentals to be going on with… Lets look back in time to see how radios got started.

77 77/ first to transmit and receive long range radio signals from Cornwall to Newfoundland 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). Marconi What is not disputed is the fact that his system was the most effective in The World 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 78/ … 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 " 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 " Nikola Tesla Marconi is a good fellow. Let him continue. He is using 17 of my patents. also, Nikola Tesla, a rival in transatlantic transmission, stated after being told of Marconi's 1901 transmission that : "Marconi is a good fellow. Let him continue. He is using 17 of my patents. it didnt matter. The Funds poured in Marconi Tesla

79 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. it was at night! daytimeonly 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? …so what about his first 1901 test?

80 80/ Morse Code 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 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 82/ Marconi's reputation as the man who first achieved successful radio transmission rests on his original patent, and which is not in question. The U. S. Supreme Court stated that … That reputation, however well- deserved, does not entitle him to a patent for every later improvement which he claims in the radio field. In 1943, a lawsuit regarding Marconi's numerous other radio patents was finally resolved in the United States. but

83 Pack Set "section normally composed of 10 mounted men and 4 pack mules" Wagon Set 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" 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" …but the American Army portable radios of 1911 were: 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 importance of radio was grasped by the military of all of the major nations They were huge The advances were rapid

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 …it was considered Treason. for the duration of WW I 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 youre in trouble. They dont mess around with National Security!)

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

86 86/ 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. footnote

87 87/ What was needed was a means to use speech to modulate the CW rather like a tap can modulate the flow of water superhet The superheterodyne principle offers a way to achieve this superhet 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…!!! mathematical This is because it is quite simply a mathematical process …

88 88/ mathematical This is because it is quite simply a mathematical 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 engines two car engines running at slightly different speeds eg two waves in the sea two waves in the sea meeting and interacting Or the interaction of two ac electrical signals of different frequencies

89 89/ mixmodulate sumdifference this principle which demonstrate that if you mix or modulate any sort of sinewave force (thats the dyne bit) with another sinewave ( of a same similar …thats the hetero bit ), the result is a complex wave which has sum and difference frequencies embedded within it.

90 90/ s u m & d i f f e r e n c e frequencies

91 91/ the upper sinewave has a lower frequency f 1 than the next down sinewave of frequency f 2 f1 f2 & Adding two sinewaves the resultant wave form shows another virtual sine wave of frequency f 2 - f 1 Join up the peaks and troughs and … composite

92 92/ f1 f2 + Adding two sinewaves the resultant wave is the difference frequency f 2 - f 1 f 2 - f 1

93 93/ f1 f2 + Adding two sinewaves sum …this is the virtual waveform of the difference frequency f kHz250,000 Hz So if f 1 = 250 kHz (ie 250,000 Hz) f kHz & f 2 = 252 kHz Then … F (difference) = F d = 252 kHz kHz = 2 kHz d Fd difference frequency F d = 2 kHz

94 94/ f1 f2 + SUM freq Adding two sinewaves –the SUM freq sum f 1 + f 2 the resultant wave form shows another virtual sine wave of frequency f 1 + f 2 = f SUM f kHz So if f 1 = 250 kHz f kHz & f 2 = 252 kHz Then … f SUM = 502 kHz sum F sum frequency

95 95/ …this applies to interaction of all sinusoidal waves they could be soundwaves or or wave-motion at sea or or engines at slightly different speeds to each other beat frequency …which creates an unpleasantbeat frequency of vibration..which can be catastrophic! Sum & Difference Frequencies This effect has even resulted in old, badly designed propeller airliners shaking themselves into fatigue failure and even destruction!

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

97 …it is entirely a physical example of a simple, mathematical, trigonometrical relationship. … which we will not go in to! This beating together phenomenon also applies to electrical currents & radio waves but just take on board; 2 frequencies beating together do produce Sum and Difference frequencies

98 98/ A mplitude M odulation with regards to Radio Waves

99 99/ lets look at this in a graphical way frequency frequency is along the bottom of the graph amplitude …and signal strength or amplitude is along the vertical frequency amplitude frequency domain This view is called the frequency domain So frequency rules! OK?

100 using the frequency domain Were 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 2182 kHz transmitter

101 101/ the frequency domain Radio Frequency 2182 kHz F0F0F0F0 Signal strength Watts We now transmit (Tx) on an RF of, say, 2182 kHz You wouldnt actually hear anything on frequency …yet! Its far, far too high for you to hear if it was sound Electromagnetic spectrum

102 102/ Lets look at this effect another way … Radio Frequency 2182 kHz F0F0F0F0 Signal strength We now stop transmitting That is how Morse Code could be sent …and very efficiently too! on off Electromagnetic spectrum

103 … but youll need a specialist receiver with a Beat Frequency Oscillator to be able to hear any Morse Code 103/ Lets look at this effect another way … Radio Frequency 2182 kHz F0F0F0F0 Signal strength This is interrupted Continuous Wave (i-CW) but very often referred to as just… CW transmission Electromagnetic spectrum

104 Radio Frequency 2182 kHz F0F0F0F0 Signal strength CW transmission Electromagnetic spectrum Reception 2182 kHz Nothing heard on frequency! Ordinary AM radio

105 Now lets look how a radio with a B eat F requency O scillator BFO would receive that same transmission.

106 Radio Frequency 2182 kHz F0F0F0F0 Signal strength CW Electromagnetic spectrum Reception 2182 kHz Dah Dah Dit AM radio with a Beat Freq Osc BFO

107 …but how?

108 …basically, in all radios, most of the processing and amplification is done at a fixed, i ntermediate f requency (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 The Beat Frequency Oscillator (BFO) generates a very small continuous, steady sinewave signal into the i.f. circuits generates a very small continuous, steady sinewave signal into the i.f. circuits …but at a slightly different frequency to the intermediate frequency (i.f.) of the radio receiver. In this case signal now scaled to 30kHz 30 kHz i.f. BFO Received signal reduced to 30kHz 31 kHz

110 What do we know happens when you mix 2 sinewave frequencies together ? Ans: We generate Sum and, more importantly here, Differenc Difference frequencies! Clue: they Beat together just like two car engines at slightly differing speeds

111 …but what the difference is depends on where the listener moves the BFO (Beat Freq Osc) knob to BFO freq difference kHz kHz1 Dah Dit Dah Dit Dit as 1kHz pulsed tones i.f.

112 …but what the difference is depends on where the listener moves the BFO (Beat Freq Osc) knob to BFO freq difference 30 kHz kHz 1.5 Dah Dit Dah Dit Dit You hear it as higher 1½ kHz pulsedtones 1½ kHz pulsed tones i.f.

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

114 Who would use such a primitive and archaic mode of communication? …well, its 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. …and this mode will get through when none of the other modes can

115 115/ Radio Frequency 300 kHz F0F0F0F0 Signal strength Now, what happens if we modulate the Carrier Wave with an amplified single tone of say 1.5 kHz? This generates Amplitude Modulation of the c arrier giving sum and difference frequencies Notice: power is shared between the sum, difference and carrier frequencies When there is no 1.5 kHz tone modulation all of the power is transmitted at the Carrier freq When the tone is present, the Carrier Wave is being modulated ie diminished/ attenuated to provide power for the Sum and Difference frequencies kHz kHz-1.5 kHz +1.5 kHz

116 116/ Radio Frequency 345 kHz F0F0F0F0 Signal strength -1 kHz +1 kHz Amplitude Modulated Carrier Wave Only a simple Rx required Tone on Ordinary AM radio (MCW) 345 kHz Dah Dit Dah Dit Dit The pitch/tone of the Morse is set by the transmitter

117 117/ Radio Frequency 345 kHz F0F0F0F0 Signal strength -1 kHz +1 kHz …mainly used for Aircraft Navaid Beacons Morse Code Identification signals Tone on ToneOff

118 118/ Radio Frequency 345 kHz F0F0F0F0 Signal strength -1 kHz +1 kHz Amplitude Modulated Carrier Wave Only a simple Rx required Tone on

119 119/ Radio Frequency 345 kHz F0F0F0F0 Signal strength -1 kHz +1 kHz Modulated Carrier Wave Only a simple Rx required …but does not carry as far as CW morse Power is divided between upper, lower and carrier

120 120/ but instead of using a single tone to modulate the carrier wave … …what if we used voice or music to A mplitude M odulate the Carrier Wave over a band of frequencies ?

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

122 122/ Lets look at that in the Frequency Domain again Radio Frequency 1442 kHz F0F0F0F0 …Centred on Tx Freq of Say, 1442kHz When the speaker talks …he Amplitude Modulates the strength of the carrier wave … not at one single frequency but a broad band of frequencies Which needs to convey most of the tones in his voice SumSumfreqsDifferencefreqs Radio Luxembur g Freq

123 123/ Radio Frequency 1442 kHz F0F0F0F0 SumSumfreqsDifferencefreqs Carrier Wave upper sideband lower sideband

124 124/ 1442 kHz F0F0F0F0 SumSumfreqsDifferencefreqs Carrier Wave upper sideband lower sideband To recreate the original voice, in a simple superhet receiver …requires the reception of BOTH side bands to be intelligible.

125 125/ 1442 kHz F0F0F0F0 SumSumfreqsDifferencefreqs Carrier Wave upper sideband lower sideband The transmitted power is shared between both sidebands and the carrier. Tx power is being wasted Tx power is being wasted each sideband is the mirror image of the other

126 126/ 1442 kHz F0F0F0F0 SumSumfreqsDifferencefreqs Carrier Wave upper sideband lower sideband AM is OK for V/UHF Air Traffic comms as it is cheap, reliable and the equipment common and light. Quality or fidelity is limited with AM due to the RF band- width available between channels Hi Fidelity requirements for modern radio entertainment has been addressed with the advent of F requency M odulation and then more recently, Digital Radios allowing, far higher quality in terms of interference and audio freq range

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

128 125 decimal 05 Cranwell Tower, ASCOT213 now on Victor, 125 decimal 05 request join downwind for Runway 26 Left hand for visual approach to land. V HF UHF Guard V Guard U Tone select simple Double Side-Band AM

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

130 130/ 1442 kHz F0F0F0F0 SumSumfreqsDifferencefreqs Carrier Wave upper sideband lower sideband BUT those techniques still dont 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?

131 131/ 6742 kHz F0F0F0F0 upper sideband only What if we put all transmitted power in to one or the other side band and suppressed the carrier? 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! Gbble hmblfmbgb Pmmblwrbbl Ordinary AM radio Rx 6742

132 132/ 6742 kHz F0F0F0F0 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! 6742

133 6742 kHz F0F0F0F0 upper sideband A S ingle S ide B and (SSB) receiver overcomes this by re- synthesising the missing sideband …in the receiver Single side-band Rx CW DSB U SSB U L SSB L mode 6742

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

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

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

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

138 The legitimate nick-name for NATO Link 11a Link 11a is If you actually listen to the audio that the link data makes its an awful croaking scraping sound… …just like an Alligators mating call …and that is exactly how it got its name … Alligator

139 139/ Sat ellite Com munications on-air Largely surpassed in quality and effectiveness by Sat ellite Com munications but SATCOM on-air time is expensive SSB … SSB remains an extensively used prime communications method in the HF band onair SSB on-air time is …free! but not necessarily the commercial services you might request

140 It is used for: Procedural control of military & commercial aircraft on long range trans-oceanic flights Military long range Flight Following servicesVOLMET aviation weather services Military long range Flight Following services and VOLMET aviation weather services eg Shanwick, Iceland, New York etc eg RAF TASCOM and RAF VOLMET USAF MAINSAIL Long Range, Link 11a Alligator Data Link NATO air and naval units etc etc etc

141 It is not used for: Entertainment Radio Channels Because … you need an expensive, specialist SSB radio receiver which can synthesise the missing side- band audio quality or fidelity is limited

142 Lets now review the AM radio modes and their uses

143 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 throughCW 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) …s imple basic radio receiver required. Ideal for NAVAID ident letter codes and distress tones in MF, HF, VHF and UHF. Not as range efficient as CWMCW Modulated Carrier Wave (Morse and data - no voice) …s imple 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.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.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 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.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) …s imple basic radio receiver required. Ideal for NAVAID ident letter codes and distress tones in MF, HF, VHF and UHF. Not as range efficient as CWMCW Modulated Carrier Wave (Morse and data - no voice) …s imple 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.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.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… A m p l i t u d e M o d u l a t e d modes modes

145 Now let us look at the F requency M odulated mode

146 Radio Frequency MHz F0F0F0F0 Signal strength This single 1 1 / 2 kHztone Amplitude Modulation of the c arrier generates sum and difference frequencies -1.5 kHz +1.5 kHz BBC radio2 VHF Under construction

147 It is now accepted that there are around 100 to 200 thunderstorms per day across the globe… …recent satellite data indicates that there are around 3million flashes per day …producing 30 flashes per second around the globe …each producing a spike of em radio radiation …these flashes are cloud to ground, or cloud to cloud or even weaker ones which shoot 400 miles in to space and have names such as sprites, elves and blue jets. …but 10% of all flashes are the renegade positive flashes which produces 10 times the power Its all natural interference

148 Sparks from machinery such as electric motors, vehicles etc Then there is man-made interference

149 Radio Frequency MHz F0F0F0F0 Signal strength This interference shows up on the frequency domain view -1.5 kHz +1.5 kHz …as fleeting and ever changing spikes spread across the em spectrum This interference ruins the fidelity of the received signal and appears as crackles and bangs to the listener

150 How can we get around this interference?

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

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

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

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

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

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

158 158/ 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).

159 159/ It is an electronic circuit called an oscillator which produces the continuous high-frequency ( R adio F requency) current which has a fixed frequency chosen from the EM spectrum. This fixed-frequency alternating current produces the em c arrier w ave.

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).

161 161/ 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/ modulate 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.

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

164 164/ 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 f o from the oscillator and fm from the microphone, we find that the output of the power amplifier will consist of 3 frequencies:

166 166/ AM transmitter block diagram

167 167/ 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.

168 168/ 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) (f o – f m ). The carrier plus the tone frequency band (f o + f m ).

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!

170 170/ by suppressing the Carrier Wave and the other duplicate sideband means all of the output power can be applied to the remaining sideband 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 30 Mhz.

171 171/ 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.

172 172/ 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. Mono no Stereo … 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.

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

177 177/ AMmutual interferencelack of HiFi f requency m odulated To overcome AM limitations of mutual interference (crowding) and lack of HiFi, the use of short-range f requency m odulated systems has become necessary.

178 178/ 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, f 0,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.

179 179/ 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 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. Its 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 G lobal M aritime D istress S afety S ystemG lobal M aritime D istress S afety S ystem its big! G lobal M aritime D istress S afety S ystem

180 180/ What is the speed of light? 3 3 x 10 3 m/sec metres per sec metres per sec 11 3 x m/sec metres per sec 10 3 x m/sec metres per sec 8 3 x 10 8 m/sec Click Buttons to enter your answer

181 181/ x 10 m/sec metres per sec metres per sec 11 3 x m/sec metres per sec 10 3 x m/sec Click to proceed What is the speed of light? metres per sec 8 3 x 10 8 m/sec

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

183 183/ Click Buttons to continue

184 184/ 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.

185 185/ 8If the velocity of radio waves is 3 x 10 8 m/sec, what would be the value of for a frequency of 6 3 x 10 6 Hz ? 3 MHz = f

186 186/ 8 m/secIf the velocity of radio waves is 3 x 10 8 m/sec, what would be the value of for a frequency of 6 3 x 10 6 Hz ? f 8 3 x x x m

187 187/ 8 m/secIf the velocity of radio waves is 3 x 10 8 m/sec, what would be the value of for a frequency of 6 3 x 10 6 Hz ? f 8 3 x x x m f = 3 MHz 8 m/sec 3 x 10 8 m/sec = = 100m

188 188/ f 8 3 x x f = 3 MHz 8 m/sec 3 x 10 8 m/sec = = 100m Ideal antenna length? /4/4/4/4 /2/2/2/2 Dipole type Whip type 50m 25 m

189 189/ f 8 3 x x f = 3 MHz 8 m/sec 3 x 10 8 m/sec = = 100m Ideal antenna length? /4/4/4/4 /2/2/2/2 Dipole type transverse But remember …a radio wave is a transverse wave so these aerials would need to be turned through 90º to work! Whip type 50m 25 m Electric E wave vertically polarised vertically polarised

190 190/ 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.

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

192 192/ Correct !

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

194 194/ CW interrupted - On - Off ie On - Off

195 195/

196 196/ END

197 197/ What is the speed of light? 3 3 x 10 3 m/sec metres per sec metres per sec 11 3 x m/sec metres per sec 10 3 x m/sec metres per sec 8 3 x 10 8 m/sec Click to return

198 198/ What is the speed of light? 3 3 x 10 3 m/sec metres per sec metres per sec 11 3 x m/sec metres per sec 10 3 x m/sec metres per sec 8 3 x 10 8 m/sec Click to return

199 199/ 3 3 x 10 3 m/sec metres per sec metres per sec 11 3 x m/sec metres per sec 10 3 x m/sec Click to return metres per sec 8 3 x 10 8 m/sec What is the speed of light?

200 200/ What is the speed of light? 3 3 x 10 3 m/sec metres per sec metres per sec x 10 9 m/sec metres per sec x 10 8 m/sec metres per sec x 10 6 m/sec Click to return

201 201/ Relationship between, f and (v = f x λ) = f Click to return

202 202/ Relationship between, f and + = f + Click to return

203 203/ Relationship between, f and - = f - Click to return

204 204/ Relationship between, f and - f = - Click to return

205 205/ No ! Return …


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