4Communicating introduction 4/Communication may be defined as the “exchange of information”
5 transmitter = voice and Communicating5/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 andreceiver = ears
6Communicating6/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 drawbacksSpeed 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 vacuumit 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 30ºCso the hotter the day …the faster the speed of sound
7echoes, wind and other unwanted noises distort and mask the sound Sound limitations7/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
8Nobody’s getting served any quicker! Note:the ‘action’ or energy goes in the same direction as the propagation …ie lies in the same planenone 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 destinationthe shove/wave isn’t an object …it has no weight or mass. It’s an experience, a phenomenona longitudinal wave8/Hey!Nobody’s getting served any quicker!ticketsdirection of wave propagation
9direction of wave propagation a longitudinal waveNot from where I’m standing!9/Sound is …Woah!Did the Earth just move for you?The plane of action or energyticketsdirection of wave propagation
10echoes, wind and other unwanted noises hamper reception Sound limitations10/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 MPHechoes, wind and other unwanted noises hamper reception
11Let’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 20ºCSpeed of propagationAir compression…ie at normal UK temperaturesAir decompressionAmbient Air Pressure = 1Barinput1AmbientpressureGraphical representation of localised air pressuresound wavelongitudinal
13Propagation or velocity of sound in air …but at higher temperatures, the speed of sound increasesnb …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’
14Propagation; sound in vacuum 14/Propagation; sound in vacuumNothing to compress ?NO SOUND HEARD!Air Pressure = 0 Barinputvacuum
15Propagation; sound in vacuum 15/Propagation; sound in vacuumThat 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 BarinputvacuumAll announcements, alarms or bells will be VERY much quieter.
161483 metres per sec (3,300 mph) Propagation; sound in liquid (water?) 16/1483 metres per sec(3,300 mph)Liquids cannot compress …so transmitsthe sound very efficiently and very fast! …and over great distances…in waterLiquid (eg water or mercury?)
17Propagation; sound in solids (steel?) 17/4500 metres per secuncompressible …so transmits sound even faster and more efficiently(10,000+ mph!!)…in solid steel…or quartz crystal…or The EarthStrange but true!Solid(Rock? or Quartz Crystal? Steel?using sound through quartz crystals is extensively used inelectronics such as TV and Radar processing circuits
18Recap Speed of Sound in … 340 m/sec 1483 metres/sec 18/Propagation; soundSpeed of Sound in …Vacuum 0 mph…it doesn’t…and for not very farAir 760mphRecap340 m/secWater 3300mph…and for maybe 1000miles +1483 metres/secSteel 10,000mph4500 metres per sec
20Sound cannot travel through a vacuum!! 20/Sound cannot travel through a vacuum!!Q. So, how do these astronauts communicateby voice, outside the International Space Station… without using a radio?
21computer won’t open the pod doors, Sergei ! 21/A. By touching space-helmets!…and, surprisingly, they do this quite often toco-ordinate their workcomputer won’t open the pod doors, Sergei !Oh! oh!not so simples
23Let’s now look at how Radio Waves travel 23/Let’s now look at how Radio Waves travel
24Radio Waves Radio – uses a different energy 24/Radio – uses a different energyA radio communications system consists of a transmitter (Tx), to send the message…and a receiver (Rx) to receive the reply
25shorthand for a radio transmitter is Radio Waves25/so…shorthand for a radio transmitter isTx …remember this abbreviation!…and for a receiver it isRx …again, remember this abbreviation too!
26Radio26/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!! Radio27/Or, if you prefer to put that speed in context, it is186, 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)or300,000,000 ms-1…exactly the speed of light!!
28A typical wave can be imagined like this… Electro-magnetic energy28/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 inA typical wave can be imagined like this…
29electromagnetic 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
30Radio wave Frequencies LowFreqsplus infra red & visible light, damaging Ultra Violet, dangerous X-rays and lethal Gamma raysHighFreqsLong wavelengthShort wavelength
31Radio wave Frequencies LowFreqsplus infra red & visible light, damaging Ultra Violet, dangerous X-rays and lethal Gamma raysHighFreqsLong wavelengthShort wavelength
32From transmitter to receiver 32/A radio Tx converts information into em radiation.information could be voice, TV pictures or digital codesem radiation from the Transmitter (Tx) will then travel from the aerial or antennaA radio Rx picks up this signal via a suitable aerial and converts the em radiation back into information.simples
33Txs come in all shapes and sizes? Transmitters33/You know…Txs come in all shapes and sizes?think about it!the car alarm remote is anotherPLB…aircrew Personal Locator BeaconAny WiFi deviceWiFi 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.
34Txs come in all shapes and sizes? Transmitters34/You know…Txs come in all shapes and sizes?think about it!your television remote control is onethe car alarm remote is anothersuch 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 deviceMan-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 500,000Wattsie ½ MegawattThese very high-powered equipments are needed to make transmissions reach to all parts of the country and combat terrestrial interference and losses within the Earth’s atmosphere.
35…Radar Warning Receivers on aircraft Rx also come in all shapes and sizes…and your TVGPS satnavthink about it!Car immobiliserRWRs…Radar Warning Receivers on aircraftObviously …your personal radiohuge radio telescopes eg Jodrell Bank
36What 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.
37Magnetism can also be ‘static’, as it is in a refrigerator magnet. What is electro-magnetic energy?37/smugElectricity can be ‘static’, like the energythat can make your hair stand on end.BDinner's in the dog!magnetic field’B’electric field ‘E’Magnetism can also be ‘static’, as it is in a refrigerator magnet.
38What 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.
39What is electromagnetic energy? 39/BB+BweakBWire conductorMagnetic fieldstrong-Direct currentIf 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
40What is electromagnetic energy? 40/BB+BBWire conductor-Direct currentThis 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
41What is electromagnetic energy? 41/Let’s now look at applying analternating current (ac)to the wire
42What is electromagnetic energy? 42/-+Wire conductor+-Alternating currentNow this alternating current introduces a new complexity which results in an electromagnetic wave being transmitted--++~
43What is electromagnetic energy? 43/BBWire conductorBWave frontAlternating currentAs before, the current produces a magnetic field B as shownLet’s just slow things down~
44What is electromagnetic energy? 44/BBWire conductorBAlternating currentbut its changing strength and direction in sympathy with the conductor’s electric current.~
48What is electromagnetic energy? 48/eBeBWire conductoreBYou 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 etcWire conductorBHow long does this action continue …when the radio frequency ac power source is removed?Ans: Well … forever!-eeProvided the wave remains ‘in space’ and it isn’t weakened by air or absorbed by other physical objects.-B
50it pushes itself forever outwards …but! But! But!!Although this process is ever lastingit pushes itself forever outwardsAnd forms a perpetual, ever radiating radio wave
51What is electromagnetic energy? 51/eBeB…and the speed at which it radiates is…Wire conductoreBThe speed of light!3 x 108 m/sRF~~
52What is electromagnetic energy? 52/BeBeWire conductorBeAlternating current~
54Both fields are 90º to each other 3 x 108 ms-1BMagnetic field ‘B’eelectric fieldAnd they propel the electro-magnetic radio wave at 90º to both e and B fieldse voltsBoth fields are 90º to each otherAt exactly 3 x 108 ms-1no fasterno slower
55and the e & B fields remain …at the original frequency 3 x 108 ms-1hMagnetic field‘B’eelectric fieldand the e & B fields remain…at the original frequencye voltsBoth fields are 90º to each otherLong after they have left the solar system , the milky way and the local group of galaxies on their way to infinity!
56electromagnetic energy 56/The frequency of the radio frequency, alternating current will determine the frequency of the em waves produced
57NASA’s Pioneer 10 and 11 spacecraft were launched in 1972/73 40 years old technologyIt has a radio to keep in touch with earthThe 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.
58NASA’s Pioneer 10 and 11 spacecraft were launched in 1972/73 40 years old technologyThat radio was turned off by command from NASA in 2003These 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.
59NASA’s Pioneer 10 and 11 spacecraft were launched in 1972/73 40 years old technologyThat radio was turned off by command from NASA in 2003These 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 powerIt was 80 times the distance the Earth is from the Sun
61Extra Hi Freq MF & HF ie & Super Hi Freq EHF & SHF VHF & UHF Low High FreqsRadio & Radar RegionHighFreqs61/ieExtra Hi Freq&Super Hi FreqkHzMHzGHzATC radiosR/C modelsMobile PhonesRadarsTelevisionSat TVRadio HamsDigital & WiFiEHF& SHFMF& HFlong range radioBBC World SvcRadio HamsTelemetryMicrowave OvensRadarMissile GuidanceVHF & UHFData Links
62definitions62/We need to cover a few definitions to progress our understanding of Radio further
63definitions63/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 LambdaVelocity () – the speed with which the waves moves has the relationship:Measured in Hertz HzA number of Units availableMeasured in metres, cm or mm…in Metres per second …always3 x 108 m/sGreek letter actually pronounced “Nu”=f…but don’t worry, most people just remember it as “V”
64electromagnetic energy definitions64/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
65electromagnetic energy definitions65/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
66Speed of travel is unimaginably fast Advantages of em66/Using em energy to carry our communications information has many advantages compared with sound energySpeed 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
67A typical PC Central Processor Unit Advantages of em67/Using em energy to carry our communications information has many advantages compared with sound energySpeed of travel is unimaginably fast…the speed of light (always 3 x 108 m/s),…but let’s get that into the context of computersAnswer: 1 wavelength of 3 GHz …Which is V = 3 x 108f= 10cm or 4”3 x 109Speed of travel is unimaginably fast…the speed of light (always 3 x 108 m/s)IntelPentium3 GHz speedA 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 speedsWe 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!IntelPentium3 GHz speedA typical PC Central Processor Unit(CPU)A Radio em wave cannot get further away than 10cm or 4” before, the next cycle begins
69All of a sudden, the speed of light doesn’t seem quite so quick! 69/All of a sudden, the speed of lightdoesn’t seem quite so quick!
70Electromagnetic 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’
71Aerial Length71/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 wavelengthAs 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/secAs we knowWe need to rearrangef*= ‘ C ’ speed of light==300000,000200,000300,000,000200,000=1500 metresWavelength….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 /4orThe best aerial length would be750m375mWhich 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==300,000,000100,000,000=3 metres…best Ae length?λ/2λ/41.5 m0.75 mor
75Aerial Length75/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/2λ/41.5 m0.75 mor
76OK, 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.
7777/Marconiin 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.
78it didn’t matter. The Funds poured in 78/TeslaMarconipreviously, 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
79night 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?
8080/the Marconi radio waves , originally called Lorenzian waves, were sent in groups of short and long signals by switching the transmitter off and on. ie Morse 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 50yrsThis station also was one of the first to receive the distress signals coming from the RMS Titanic 9 years later in
82The 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. “
83The 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 hugeBritish 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
8484/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 riftfor 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!)
85Marconi died in Rome in 1937 at age 63 85/Marconi died in Rome in 1937 at age 63In 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".
8686/footnoteMarconi 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.
87Amplitude modulation87/What was needed was a means to use speech to modulate the CW rather like a tap can modulate the flow of waterThe superheterodyne principle offers a way to achieve thisThe ‘superhet’ principle involves the effect that one ‘sine wave’ has over another adjacent ‘sine wave’ … which is of a different frequencyNotice that no mention has been made of electronics…!!!This is because it is quite simply a mathematical process …
88superheterodyne Amplitude modulation 88/superheterodyneIt applies to things that rotate or vibrate or just change over a period of time …in a sinusoidal fashionthat is … Simple Harmonic Motion …or SHM which includes pendulumsegtwo car engines running at slightly different speedstwo waves in the sea meeting and interactingThis is because it is quite simply a mathematical process …Or the interaction of two ac electrical signalsof different frequencies
89superheterodyne Amplitude modulation 89/superheterodynethis 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.
91Join up the peaks and troughs and … Amplitude modulationAdding two sinewaves91/f1&f2compositethe upper sinewave has a lower frequency f1 than the next down sinewave of frequency f2Join up the peaks and troughs and …the resultant wave form shows another virtual sine wave of frequency f2 - f1
92the resultant wave is the Amplitude modulationAdding two sinewaves92/f1+f2the resultant wave is thedifference frequencyf2 - f1
93Fd difference frequency Amplitude modulationAdding two sinewaves93/f1+f2Fd difference frequency2 kHzF d=sum…this is the virtual waveform of the difference frequencySo if f1 = 250 kHz (ie 250,000 Hz)& f2 = 252 kHzThen …F (difference)F d-==252 kHz250 kHz=2 kHz
94Adding two sinewaves –the SUM freq Amplitude modulationAdding two sinewaves –the SUM freq94/f1+f2sumthe resultant wave form shows another virtual sine wave of frequency f1 + f2Fsum frequency=fSUMSo if f1 = 250 kHz& f2 = 252 kHzThen …Then …Then …fSUM502 kHz=
95Sum & Difference Frequencies Amplitude modulation95/Sum & Difference Frequencies…this applies to interaction of all sinusoidal wavesthey could be soundwavesThis effect has even resulted in old, badly designed propeller airliners shaking themselves into fatigue failure and even destruction!or wave-motion at seaor engines at slightly different speeds to each other…which creates an unpleasant ‘beat frequency’ of vibration ..which can be catastrophic!
96Sum & Difference Frequencies Amplitude modulation96/Sum & Difference Frequencies…this applies to interaction of all sinusoidal wavesthey could be soundwavesThis effect has even led to propeller airliners shaking themselves into fatigue failure and even destruction!or wave-motion at seaThis is caused by the difference in frequency between the twoor 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 modulation97/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 produceSum and Difference frequencies
99Sum & Difference Frequencies Amplitude modulation99/Sum & Difference Frequenciesamplitudelet’s look at this in a graphical wayfrequency is along the bottom of the graphThis view is called the frequency domain…and signal strength or amplitude is along the verticalSo frequency rules! OK?frequency
100We’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 wish2182kHztransmitter
101We now transmit (Tx) on an RF of, say, 2182 kHz Amplitude modulationAmplitude modulationCW101/the frequency domainWe now transmit (Tx) on an RF of, say, 2182 kHzIt’s far, far too high for you to ‘hear’ if it was soundYou wouldn’t actually hear anything on frequency …yet!Signal strengthWatts2182 kHzRadio FrequencyF0Electromagnetic spectrum
102CW We now stop transmitting That is how Morse Code could be sent Amplitude modulation102/Let’s look at this effect another way …Amplitude modulationCWWe now stop transmittingonThat is how Morse Code could be sentSignal strength…and very efficiently too!off2182 kHzRadio FrequencyF0Electromagnetic spectrum
103Amplitude modulationCW103/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 receiverwith a Beat Frequency Oscillator to be able to hear any Morse CodeCWtransmissionSignal strength2182 kHzRadio FrequencyF0Electromagnetic spectrum
104CW CW Morse Amplitude modulation Reception transmission 104/Nothing heard on frequency!CW2182kHzReceptiontransmissionSignal strengthOrdinary AM radio2182 kHzRadio FrequencyF0Electromagnetic spectrum
105BFO Now let’s look how a radio with a Beat Frequency Oscillator would receive that same transmission.
106CW CW Morse Amplitude modulation Reception Dah Dah Dit 106/Dah Dah DitCW2182 kHzReceptionAM radio with a Beat Freq OscSignal strengthBFO2182 kHzRadio FrequencyF0Electromagnetic spectrum
108Amplitude modulationCW Morse108/…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
109Amplitude modulationCW Morse109/The Beat Frequency Oscillator(BFO)generates a very small continuous, steady sinewave signal into the i.f. circuitsReceived 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 30kHzBFOi.f.31 kHz30 kHzi.f.
110Amplitude modulationCW Morse110/What do we know happens when you ‘mix’ 2 sinewave frequencies together ?Clue: they ‘Beat’ together just like two car engines at slightly differing speedsAns: We generate Sum and, more importantly here,Difference frequencies!
111CW 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 toas 1kHz pulsed tones1.531 kHz11.02.0BFO freq difference30 kHzi.f.
112CW 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 toYou hear it as higher1½ kHz pulsed tones1.01.52.031.5 kHzBFO freq difference1.530 kHzi.f.
113CW CW Morse …it’s entirely the listeners choice Amplitude modulation 113/Dah Dit Dah Dit DitCW2182 kHzReceptionAM radio with a Beat Freq Oscthe pitch of the tone / Morse you hear is dependant upon your BFO settingSignal strengthBFO??…it’s entirely the listeners choice30 kHzRadio Frequencyi.f.
114Amplitude modulationCW Morse114/…and this mode will ‘get through’ when none of the other modes canWho 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’.
115Amplitude modulation115/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 freqThis generates Amplitude Modulation of the carrier giving sum and difference frequencies-1.5 kHz+1.5 kHzWhen the tone is present, the Carrier Wave is being modulated ie diminished/ attenuated to provide power for the Sum and Difference frequencies.301.5 kHz298.5 kHzSignal strengthNotice: power is shared between the sum, difference and carrier frequencies300 kHzRadio FrequencyF0
116(MCW) Only a simple Rx required Amplitude modulation 116/Dah Dit Dah Dit DitThe pitch/tone of the Morse is set by the transmitterAmplitude Modulated Carrier WaveOnly a simple Rx required-1 kHz+1 kHz(MCW)Signal strengthToneon345 kHz345 kHzOrdinary AM radioRadio FrequencyF0
117Amplitude modulation117/-1 kHz…mainly used for Aircraft ‘Navaid’ Beacons Morse Code Identification signals+1 kHzSignal strengthToneonToneOff345 kHzRadio FrequencyF0
119Only a simple Rx required Amplitude modulation119/Modulated Carrier WaveOnly a simple Rx required-1 kHz+1 kHzPower is divided between upper, lower and carrierSignal strength…but does not carry as far as CW morse345 kHzRadio FrequencyF0
120Amplitude modulation120/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 ?
121Amplitude modulation Di Dum ………………... Di! Li Laaaaahh Blah! 121/Di Dum ………………... Di!Li LaaaaahhBlah!Carrier WaveTransmitter
122Let’s look at that in the “Frequency Domain” again Amplitude modulation122/Let’s look at that in the“Frequency Domain” again…Centred on Tx Freq ofSay, 1442kHzWhen the speaker talks …he Amplitude Modulates the strength of the carrier wave …Which needs to convey most of the tones in his voicenot at one single frequency but a broad band of frequenciesRadio Luxemburg Freq‘Difference’freqs‘Sum’freqs1442 kHzRadio FrequencyF0
124Amplitude modulation124/To recreate the original voice, in a simple superhet receiver …requires the reception of BOTH side bands to be intelligible.Carrier Wavelower sidebandupper sideband‘Difference’freqs‘Sum’freqs1442 kHzF0
125each sideband is the mirror image of the other Amplitude modulation125/The transmitted power is shared between both sidebands and the carrier.each sideband is the mirror image of the other Tx power is being wastedCarrier Wavelower sidebandupper sideband‘Difference’freqs‘Sum’freqs1442 kHzF0
126Amplitude modulationAM 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 rangeQuality or ‘fidelity’ is limited with AM due to the RF band-width available between channelsCarrier Wavelower sidebandupper sideband‘Difference’freqs‘Sum’freqs1442 kHzF0
127268.000 267.000 268.625 268.600 UHF Amplitude modulation 127/upperlowersimple Double Side-Band AMAMCranwell 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 VictorToneVHFselectUHFGuard VGuard U
128simple Double Side-Band AM Amplitude modulation128/125.05simple Double Side-Band AMCranwell Tower, ASCOT213 now on Victor, 125 decimal 05 request join downwind for Runway 26 Left hand for visual approach to land.ToneVHFselectUHFGuard VGuard U
129Modulated Carrier Wave MCW Amplitude modulation129/I think I may have microphone amplifier failure …I will try to transmit the radio failure code using 1kHz ‘tone’ dashes and my transmit switchMode now simplyModulated Carrier Wave MCW125.05MHzCranwell Tower, ASCOT213 now on Victor, 125 decimal 05 request join downwind for Runway 26 Left hand for visual approach to land.+1 kHz-1 kHzToneVHFselectUHFGuard V121.5Guard U243.0
130Amplitude modulation130/BUT those techniques still don’t give a transmitter greater range…needed for HF commsWhat if we put all transmitted power in to one or the other side band and suppressed the carrier?Carrier Waveupper sidebandlower sideband‘Difference’freqs‘Sum’freqs1442 kHzF0
131Amplitude modulation131/What if we put all transmitted power in to one or the other side band and suppressed the carrier?upper sideband onlynb…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!6742Ordinary AM radio Rx“Gbble hmblfmbgbPmmblwrbbl”6742 kHzF0
132Single Side Band Amplitude modulation upper sideband 132/upper sidebandnb…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 receiver67426742 kHzF0
133Single Side Band Amplitude modulation upper sideband 133/upper sidebandA Single Side Band (SSB) receiver overcomes this by re-synthesising the missing sideband …in the receiver6742Single side-band RxmodeCWDSBSSB USSB L6742 kHzF0
134Single Side Band fidelity too poor for entertainment radio Amplitude modulationSingle Side Band134/Missing sideband re-synthesised on reception by Single Sideband Receiver (SSB) RxMainly used at HF and MF frequencies for Global CoverageHas range Advantage over DSB modeCarrier WaveDoubles channels available.not transmitted…but no point atV/UHF freqslower sidebandupper sidebandfidelity too poor for entertainment radio‘Difference’freqs‘Sum’freqs6742 kHz
135Single 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 sidebandupper sideband6742 kHzUsed by Armies for beyond line of sight communicationsUsed extensively Military and Merchant Navy
136Single 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 Band136/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 sidebandupper sideband80008890889188006742 kHzkHzUsed by Armies for beyond line of sight communicationsUsed extensively Military and Merchant Navyupperlower
137Single 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 Band137/Link Manager from Tactical Director; ‘Alligator’ Data Link frequency now6715 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 transmittedlower sidebandupper sideband67006715671000006000kHzUsed by Armies for beyond line of sight communicationsUsed extensively Military and Merchant Navyupperlower
138… Alligator Link 11a is …and that is exactly how it got it’s name 138/The legitimate nick-name for NATOLink 11a is… AlligatorIf 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
139it controls commercial oceanic flights around the world Amplitude modulationSingle Side Band139/Largely surpassed in quality and effectiveness by Satellite Communications but SATCOM on-air time is expensiveit controls commercial oceanic flights around the world…SSB remains an extensively used prime communications method in the HF bandSSB on-air time is …free!but not necessarily the commercial services you might request
140SSB 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 flightseg Shanwick , Iceland, New York etcMilitary long range Flight Following services and VOLMET aviation weather serviceseg RAF ‘TASCOM’ and ‘RAF VOLMET’USAF ‘MAINSAIL’Long Range, Link 11a Alligator Data LinkNATO air and naval unitsetc etc etc
141SSB is big and it's important!! 141/SSB is big and it's important!!It is not used for:Entertainment Radio ChannelsBecause …audio quality or ’fidelity’ is limitedyou need an expensive, specialist SSB radio receiver which can synthesise the missing side-band
142radio modes and their uses 142/Let’s now review theAMradio modes and their uses
143CW 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 CWDSB 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.
144Amplitude 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 CWDSB 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 Modulatedmodes
145Now let us look at the Frequency Modulated mode 145/Now let us look at the Frequency Modulated mode
146Under construction Amplitude modulation 146/This single 11/2 kHztone Amplitude Modulation of the carrier generates sum and difference frequencies-1.5 kHz+1.5 kHzUnder constructionSignal strength88.90 MHzRadio FrequencyBBC radio2VHFF0
147It’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 globeIt’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 produces10 times the power
148Then there is man-made interference 148/Then there is man-made interferenceSparks from machinery such as electric motors, vehicles etc
149Amplitude modulation149/This interference shows up on the frequency domain viewSingle tone MCWThis 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 spectrumSignal strength88.00 MHzRadio FrequencyF0
150How can we get around this interference? 150/How can we get around this interference?
151Frequency Modulation151/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.
152Frequency Modulation152/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.
153FM is suitable for HiFi transmissions Frequency ModulationFM is suitable for HiFi transmissions153/Time-Line viewExample is a simple single tone…but could be voice or musicSo interference spikes are not processedinstantaneous Amplitude is key to extracting the information from the signalAmplitude Modulation of the carrierFrequency Modulation of the carrierinstantaneous Frequency is key to extracting the information from the signaltimeAmplitude is (nearly) irrelevant with FM
154FM is suitable for HiFi transmissions Frequency ModulationFM is suitable for HiFi transmissions154/Time-Line viewExample is a simple single tone…but could be voice or musicSo interference spikes are not processedinstantaneous Amplitude is key to extracting the information from the signalAmplitude Modulation of the carrierFrequency Modulation of the carrierinstantaneous Frequency is key to extracting the information from the signaltimeAmplitude is (nearly) irrelevant with FM
155Amplitude Modulation155/The process of extracting the information /sound signal from a AM signal is called …DetectiondetectorAM Received signal…after tunerback in time
156Amplitude Modulation156/The process of extracting the information /sound signal from a FM signal is called …DiscriminationdiscriminatorFM Received signal…after tunerback in time
157Need specialist Rx with a BFO. No Voice recap157/Need specialist Rx with a BFO. No Voice**CWContinuous WaveMorse only.efficientMorse dentification of Radio BeaconsInferior range to CW but simple RxMCWModulated CWRadio 5 Live at 330 kHz?AMAmplitude ModulationOr Cranwell Tower MHz or MF NAVAIDSRAF Flight Watch 6742-upper or Shanwick or Iceland or New York OCAs on 8879-upperSSBSingle Side bandFMFrequency Modulationentertainment radio, marine channels & NAVAIDSData Links, entertainment TV & radio and new inter-ship marine comms including Distress CommsDigital…the futureRadio ‘hams’ around the world still enthusiastically use this mode
158Amplitude modulation158/‘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).
159Amplitude modulation159/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”.
160160/The audio-frequency (AF) current and the radio-frequency (RF) current are mixed in the transmitter so that the carrier wave is MODULATED by the AF current, in such a way as to duplicate the pattern of sound waves fed into the microphone. A carrier wave can be modulated in one of two ways, either by amplitude modulation (AM) or by frequency modulation (FM).
161Amplitude 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
162162/Whist this system is ideal for Morse, it is not good enough for speech or music, because sound requires many more variations (or steps) to achieve an accurate reproduction. An improvement is to alter the amplitude, or ‘modulate’ the RF Radio Frequency of the carrier wave in step with the much lower AF Audio Frequency.
163Fig 1-6: AM transmitter block diagram 163/Fig 1-6: AM transmitter block diagram
164Parts 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.
165165/The modulation takes place in the power amplifier stage. If the input frequencies to the modulator are fo from the oscillator and fm from the microphone, we find that the output of the power amplifier will consist of 3 frequencies:
167Parts 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.
168The 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).
169169/For example, if the audio frequency ranged from 30 to 300 Hz* and the carrier was 1 MHz, then the frequencies in the output would look like:* This is small range would only give pretty poor quality or fidelity eg like the quality a telephone!
170SSB170/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.
171SSB171/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.
172SSB172/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.
173173/One great drawback of the simpler double sideband AM system is the need for such a large bandwidth to accommodate all radio stations including both sidebands,Another drawback is that for High Fidelity quality ~ HiFi ,approximately 20KHz is needed for each sideband. A massive chunk of the available frequencies for broadcasting for just one station.in a limited Radio Frequency spread (30 KHz to 3 MHz in Medium Frequency MF and High Frequency HF bands).this means, in reality, that the MF-AM system could not handle Hi Fi and only have 148 stations at any one time.
174174/Try tuning through an AM band radio and see how close the stations are together!
175175/Obviously, when many transmitters are crammed into a small band and overlap each other there is a big problem with signals from other transmissions breaking into the one you are using – this is known as “mutual interference”.… and we are only discussing 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.
176There are 40,000 thunderstorms per day 176/There are 40,000 thunderstorms per dayAnother 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)
177177/To overcome AM limitations of mutual interference (crowding) and lack of HiFi, the use of short-range frequency modulated systems has become necessary.
178Frequency 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.
179Global 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 150MHzGlobal 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
180Phase 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 sec3 x 1011m/secmetres per sec3 x 1010m/secmetres per sec3 x 103m/sec3 000 metres per sec3 x 108m/secClick Buttons to enter your answer
181What is the speed of light? Phase Test181/What is the speed of light?metres per sec3 x 1011m/secmetres per sec3 x 1010m/secmetres per sec3 x 108m/sec300 x 10m/sec3 000 metres per secClick to proceed
182What is the relationship between frequency (f), wavelength (λ) and velocity of light (v) is given in the formula:Phase Test182/Avelocity =frequency x wavelength(v = f x λ)Dfrequency =velocity - wavelength (f = v - λ)Bvelocity = frequency+wavelength (v = f + λ)Cvelocity =frequency – wavelength(v = f- λ)(v = f x λ)(v = f + λ)(v = f- λ)(f = v - λ)DABCClick Buttons to enter your answer
183Click Buttons to continue Phase Test183/Click Buttons to continue
184Phase Test Assessment Questions 184/Assessment Questions3. If the velocity of radio waves are 300 x 106, what would be the value of λ for a frequency of 3 x 106?a. 1000mb. 10mc. 100md. 1m4. What does the abbreviation SSB stand for:a. Single Side Band.b. Single Silicone Band.c. Ship to Shore Broadcast.d. Solo Side Band.
185Phase Test185/If the velocity of radio waves is 3 x 108 m/sec, what would be the value of for a frequency of3 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 of3 x 106 Hz ?1f23 x 1083 x 1061 x 102100m
187 1 x 102 100m f 3 x 106 Hz ? 1 2 Phase Test = 100m 187/3 x 108 m/sec =f = 3 MHzIf the velocity of radio waves is 3 x 108 m/sec, what would be the value of for a frequency of3 x 106 Hz ?= 100m1f23 x 1083 x 1061 x 102100m
188 f 1 2 Phase Test = 100m 3 x 108 3 x 106 188/50mIdeal antenna length?3 x 108 m/sec =f = 3 MHzDipole type/2= 100m1f23 x 1083 x 106/4Whip type25m
189 f 1 2 Phase Test = 100m 3 x 108 3 x 106 189/50mIdeal antenna length?3 x 108 m/sec =f = 3 MHzBut remember …a radio wave is a transverse wave so these aerials would need to be turned through 90º to work!Dipole type/2= 100m1f23 x 1083 x 106/4Electric ‘E’ wavevertically polarisedWhip type25m
190What is the speed of light? Phase Test190/Assessment QuestionsWhat is the speed of light?a.300 x 108 ms-1b.300 x 106 ms-1c.300 x 109 ms-1d.300 x 101 ms-12.The relationship between frequency (f), wavelength (λ) and velocity of light (v) is given in the formula:a.velocity = frequency x wavelength (v = f x λ)b.velocity = frequency + wavelength (v = f x λ)c.velocity = frequency - wavelength (v = f x λ)d.frequency = velocity - wavelength (v = f x λ)3. If the velocity of radio waves are 300 x 106, what would be the value of λ for a frequency of 3 x 106?a. 1000mb. 10mc. 100md. 1m4. What does the abbreviation SSB stand for:a. Single Side Band.b. Single Silicone Band.c. Ship to Shore Broadcast.d. Solo Side Band.
191What does SSB stand for? Single Side Band ? Ship to Shore Buffer ? Phase Test191/What does SSB stand for?Click on your answerSingle Side Band ?Ship to Shore Buffer ?Single Silicon Band ?Solo Side Band?
193Continuous Wave CW Only good for Morse ie On - Off Review193/Continuous Waveinterrupted -ie On - OffCWbut you can’t hear anything on frequency unless …Marconi’s first transmissionsEfficient…your Rx can generate a single tone when it receives CWOnly good for MorseOrdinary radios do not normally have this tone facility
194Review194/Continuous Waveinterrupted -ie On - OffCW
197What is the speed of light? Phase Test197/What is the speed of light?metres per secmetres per sec3 x 1010m/secmetres per sec3 x 108m/sec3 x 103m/sec3 000 metres per sec3 x 1011m/secClick to return
198What is the speed of light? Phase Test198/What is the speed of light?metres per sec3 x 1011m/secmetres per sec3 x 1010m/secmetres per sec3 x 108m/sec3 x 103m/sec3 000 metres per secClick to return
199What is the speed of light? Phase Test199/What is the speed of light?metres per sec3 x 1011m/secmetres per sec3 x 1010m/secmetres per sec3 x 103m/sec3 000 metres per sec3 x 108m/secClick to return
200What is the speed of light? Phase Test200/What is the speed of light?metres per sec300 x 109m/secmetres per sec300 x 108m/secmetres per sec300 x 106m/sec3 000metres per sec3 x 103m/secClick to return
201Relationship between , f and Phase Test201/Relationship between , f and = f (v = f x λ)Click to return
202Relationship between , f and Phase Test202/Relationship between , f and = f + Click to return
203Relationship between , f and Phase Test203/Relationship between , f and = f - Click to return
204Relationship between , f and Phase Test204/Relationship between , f and f = - Click to return