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Question 191-1 : Modulation is ? [ Level reports ]

The process of impressing and transporting information by radio waves

In electronics and telecommunications modulation is the process of varying one or more properties of a periodic waveform called the carrier signal with a modulating signal that typically contains information to be transmitted .most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast .why do we need modulation .practically speaking modulation is required for .. . high range transmission. . . quality of transmission. . . to avoid the overlapping of signals . ..difference between am and fm.amplitude modulation and frequency modulation are used to transmit data using the method of modifying a carrier signal .the am technique is totally different from frequency modulation and phase modulation where the frequency of the carrier signal is varied in the first case and in the second one the phase is varied respectively .refer to annex 1.amplitude modulation.amplitude modulation is a modulation technique where the amplitude of a carrier varies depending on the information signal .am radio broadcast signals use lower carrier frequencies this helps them to travel long distances .sometimes am signals can be able to bounce off the ionosphere .the distance travelled by the am is much larger than the fm annex2 .refer to annex 2.frequency modulation.in this module the frequency of the carrier wave is modified according to the signal that carries information .the radio signals have large bandwidth than am radio signals which helps to offer much better sound quality .frequency modulation also enables to transmit stereo signals .. . . . summary. . . . . amplitude modulation am . . . frequency modulation fm . . . . . the radio wave is called a carrier wave and the frequency and phase remain the same. . . the radio wave is called a carrier wave but the amplitude and phase remain the same. . . . . has poor sound quality but can transmit longer distance. . . has higher bandwidth with better sound quality. . . . . the frequency range of am radio varies from 535 to 1705 khz. . . the frequency range of fm is 88 to 108 mhz in the higher spectrum. . . . . more susceptible to noise. . . less susceptible to noise exemple 291 The process of impressing and transporting information by radio waves.

Question 191-2 : The unit for measuring frequency is and measures cycles ?

Hertz per second

Refer to figure .frequency in physics the number of waves that pass a fixed point in unit time also the number of cycles or vibrations undergone during one unit of time by a body in periodic motion a body in periodic motion is said to have undergone one cycle or one vibration after passing through a series of events or positions and returning to its original state .usually frequency f is measured in the hertz unit hz named in honor of the 19th century german physicist heinrich rudolf hertz the hertz measurement is the number of waves that pass by cycle per second for example an 'a' note on a violin string vibrates at about 440 hz 440 vibrations per second exemple 295 Hertz, per second

Question 191-3 : When raising the frequency of an electromagnetic wave the ?

Wavelength decreases

Wavelength is the distance of one full cycle of the oscillation longer wavelength waves such as radio waves carry low energy this is why we can listen to the radio without any harmful consequences shorter wavelength waves such as x rays carry higher energy that can be hazardous to our health consequently lead aprons are worn to protect our bodies from harmful radiation when we undergo x rays this wavelength frequently relationship is characterized by .c= 1 1 c= .where.. . c is the speed of light . . . is wavelength and. . . is frequency. ..shorter wavelength means greater frequency and greater frequency means higher energy wavelengths are important in that they tell one what type of wave one is dealing with see the annex exemple 299 Wavelength decreases

Question 191-4 : During a flight at fl210 a pilot does not receive any dme distance indication from a dme station located approximately 220 nm away the reason for this is that the ?

Aeroplane is below the minimum altitude for line of sight propagation

Refer to figure .dme measures the straight line distance from the aircraft to the ground station in the order of 200 300 nm depending on the aircraft height this is called 'slant range' and is slightly more than the actual horizontal distance because of the difference in elevation between the aircraft and the station the most extreme case of 'slant range error' occurs when the aircraft passes directly over the station instead of reading zero the dme shows the altitude of the airplane above the station in nautical miles slant range error also affects groundspeed and time to station displays when you're close to the station displayed dme groundspeed drops below actual groundspeed as you approach the station and then climbs back to normal after you pass it displayed dme time to station may not count all the way down to zero as you fly over the station the dme range slant range can be calculated using the following formula slant range = 1 23 h3 + h4 .h3 = altitude of the aircraft ft .h4 = elevation of the dme station ft in our case fl210 ft correspond at 21000ft.slant range = 1 23 21000 + 0 .slant range = 1 23 x 144 9.slant range = 178 2 nmwith the aircraft at a distance of 220 nm we can say that at fl 210 it is beyond the maximum theoretical range or below the line of sight minimum altitude for this distance exemple 303 Aeroplane is below the minimum altitude for line of sight propagation.

Question 191-5 : Under what conditions can vhf voice communications often suffer interference from transmissions on the same frequency at a distance considerably greater than line of sight ?

A temperature inversion in the atmosphere can cause 'super refraction'

The most important atmospheric effects on radio wave propagation are refraction and reflection refraction can occur in the troposphere or the ionosphere .tropospheric refraction occurs because the refractive index of the atmosphere decreases as altitude increases leading to a bending of waves back toward the earth .conversely ionospheric refraction occurs because of the electrical properties of plasmas that are formed in the ionosphere as a result of ionization of the atmosphere reflection off the ionosphere is also possible if the frequency is low enough we will differentiate these two effects and refer to the former as atmospheric refraction and the latter as ionospheric propagation .the atmosphere will also attenuate radio signals due to absorption by air molecules water molecules and precipitation rain .the most important thing to note is that refractivity is inversely proportional to temperature and directly proportional to pressure and humidity hence as we go higher into the atmosphere the refractivity tends to drop somce the pressure is less and the air is more dry temperature plays a role as well and in reality temperature gradients can cause the refractivity profile to be non monotonic exemple 307 A temperature inversion in the atmosphere can cause 'super-refraction'.

Question 191-6 : Pulse length is expressed as ?

Time

Pulse length.pulse length is also known as pulse width or pulse duration as a general definition we can say that pulse length is the nominal duration of a standard pulse which is the time interval between the half amplitude points on the rise and decay points of the curve it is a measurement of how long a pulse is exemple 311 Time.

Question 191-7 : Why do vhf radio signals used for communication and navigation have a limited range ?

Because of the curvature of the earth

An aircraft uses a range of radio frequencies to navigate to its destination and communicate with air traffic control aircraft short range communication uses vhf band between 118 mhz and 137 mhz to talk with air traffic control .these vhf frequencies have a line of sight capability meaning that they travel in a straight line whilst the surface of the earth is a downward curved surface declination relative to the signal eventually at a certain distance the receiving aircraft will fall out of the line of sight of the transmitter – because the signals normally do not follow the curvature of the earth exemple 315 Because of the curvature of the earth.

Question 191-8 : According to the international telecommunication union itu code a radio signal may be classified by three symbols the abbreviation a3e is used for the type of transmission in which the carrier wave is ?

Amplitude modulated by a speech signal such as is used for vhf com

The international telecommunication union itu has designated the type of amplitude modulations .. . . designation. description. . . a3e. am speech communication as used for aeronautical vhf communications . double side band full carrier on vhf and uhf the basic amplitude modulation scheme. . . r3e. single sideband reduced carrier. . . h3e. single sideband full carrier. . . j3e. single sideband suppressed carrier on hf. . . b8e. independent sideband emission. . . c3f. vestigial sideband exemple 319 Amplitude modulated by a speech signal, such as is used for vhf-com.

Question 191-9 : What does the term antenna shadowing mean ?

The antenna is masked from the transmitter due to the aircraft attitude

Antenna shadowing.shadowing by parts of an aircraft such as a wing may prevent signals from being received if the antenna is not sited properly .to minimize the adverse effects of antenna shading it is important to place antennas on aircraft in such locations where least shading can be expected in any normal flight attitude antennas used for reception of ground based facilities should be on the underside of the aircraft while gps antennas should be on the top exemple 323 The antenna is masked from the transmitter due to the aircraft attitude.

Question 191-10 : What is the receiver aerial location of a gnss system ?

Top of the fuselage

Refer to figure . .antenna shadowing.terrain contours or obstacles close to the transmitting or receiving antenna partially block the radio signal resulting in a weaker reception for the same transmission power and distance regardless of the type of wave propagation .to minimize the adverse effects of antenna shading it is important to place antennas on aircraft in such locations where least shading can be expected in any normal flight attitude antennas used for reception of ground based facilities should be on the underside of the aircraft while gps antennas should be on the top exemple 327 Top of the fuselage.

Question 191-11 : The following might be caused by antenna shadowing ?

Poor radio reception of a vor ident signal while the aircraft is making an orbit 360° medium level turn

Antenna shadowing.shadowing by parts of an aircraft such as a wing may prevent signals from being received if the antenna is not sited properly .to minimize the adverse effects of antenna shading it is important to place antennas on aircraft in such locations where least shading can be expected in any normal flight attitude antennas used for reception of ground based facilities should be on the underside of the aircraft while gps antennas should be on the top .during 360º medium level turn the effect of the wing shadowing the aircraft antenna should be considered exemple 331 Poor radio reception of a vor ident signal while the aircraft is making an orbit (360° medium-level turn).

Question 191-12 : What is correct regarding antenna shadowing ?

Reduced reception by an antenna when part of the airframe blocks the signal to the antenna

Antenna shadowing.shadowing by parts of an aircraft such as a wing may prevent signals from being received if the antenna is not sited properly .to minimize the adverse effects of antenna shading it is important to place antennas on aircraft in such locations where least shading can be expected in any normal flight attitude antennas used for reception of ground based facilities should be on the underside of the aircraft while gps antennas should be on the top exemple 335 Reduced reception by an antenna when part of the airframe blocks the signal to the antenna.

Question 191-13 : The correct position for the gps antenna on an airplane is ?

On the top of the fuselage

Antenna shadowing.terrain contours or obstacles close to the transmitting or receiving antenna as well as aircraft parts partially block the radio signal resulting in a weaker reception for the same transmission power and distance regardless of the type of wave propagation .to minimize the adverse effects of antenna shading it is important to place antennas on aircraft in such locations where least shading can be expected in any normal flight attitude antennas used for reception of ground based facilities should be on the underside of the aircraft while gps antennas should be on the top exemple 339 On the top of the fuselage.

Question 191-14 : A student pilot has just learnt that meteorological information for aircraft en route on long haul flights is sent by radio what kind of radio receiver is needed to receive this information ?

Single sideband receiver

Refer to figure . learning objective 062 01 01 03 03 state that hf meteorological information for aircraft in flight volmet and hf two way communication use a single sideband when we want to send information via radio waves we have to modulate the carrier wave somehow this is the process of adding information to it there are a few ways to do this in the early days of radio it was done by sending pulse of the carrier wave as morse code pulse modulation these days we can modulate the amplitude of the carrier wave to carry our information or we can modulate the frequency slightly to carry information also amplitude modulation is easier to do and far easier to represent visually the peaks and troughs of our carrier wave are modified to create our information wave over the top of each peak and the same information wave under each trough the wave over the peaks is one sideband and the wave under the troughs is the other sideband two sidebands are created but when we send hf radio signals we remove one sideband to reduce the required power of the transmitter and the required bandwidth this means to accept hf radio our receiver has to be of the single sideband ssb type this question is a bit too ambiguous as it does not mention that we are picking up a hf volmet broadcast in simple terms instead it hints at the hf part as it is a long haul flight currently en route and that it is a volmet as they are trying to pick up 'meteorological information' the learning objective above is very clear on this though and once that lo is known it is obvious what the question writer is getting at exemple 343 Single sideband receiver.

Question 191-15 : Which of the following options contains the correct frequency band propagation path and frequency range for radio communications using a single side band ?

Hf 3 mhz to 30 mhz surface and sky waves

Refer to figure . learning objective 062 01 01 03 03 state that hf meteorological information for aircraft in flight volmet and hf two way communication use a single sideband . learning objective 062 01 03 04 02 state that radio waves in lf mf and hf propagate as surface/ground waves and sky waves this question contains a mixture of two different learning objectives one is to know which frequency range of radio waves use a single side band hf and the second is to know how hf waves propagate when we want to send information via radio waves we have to modulate the carrier wave somehow this is the process of adding information to it there are a few ways to do this in the early days of radio it was done by sending pulse of the carrier wave as morse code pulse modulation these days we can modulate the amplitude of the carrier wave to carry our information or we can modulate the frequency slightly to carry information also amplitude modulation is easier to do and far easier to represent visually the peaks and troughs of our carrier wave are modified to create our information wave over the top of each peak and the same information wave under each trough the wave over the peaks is one side band and the wave under the troughs is the other side band two side bands are created but when we send hf radio signals we remove one side band to reduce the required power of the transmitter and the required bandwidth this means that hf transmissions are single side band ssb also to note hf radio waves are between 3 30 mhz the range just below familiar vhf and they travel as both surface waves clinging on to the surface of the earth and sky waves bouncing off the ionosphere exemple 347 Hf, 3 mhz to 30 mhz, surface and sky waves.

Question 191-16 : International telecommunication union itu classification abbreviations used in aviation include the 1 abbreviation this designates carrier wave emissions amplitude modulated with morse code which is used by 2 ?

1 a2a 2 ndbs

Learning objective 062 01 01 03 04 state that the following abbreviations classifications according to international telecommunication union itu regulations are used for aviation applications n0n carrier without modulation as used by non directional radio beacons ndbs a1a carrier with keyed morse code modulation as used by ndbs a2a carrier with amplitude modulated morse code as used by ndbs a3e carrier with amplitude modulated speech used for communication vhf com .the itu international telecommunication union produce a classification system for each type of radio wave describing in 3 characters how a radio wave is modulated modulation is the act of putting information onto a radio wave and includes pulse modulation frequency modulation or amplitude modulation the first letter is how the wave is modulated the second character is what type of information is modulated onto the wave digital analogue etc and the third is the information output morse code voice etc .the 3 character abbreviation for an old style ndb ident is a1a these have keyed morse code modulation bfo mode must be used to here the ident and a newer ndb ident is a2a which has amplitude modulated morse code so you can listen to it in any mode the ndb carrier wave is n0n it is not modulated and carries no information .the learning objectives also state that we must know the classification for vhf communication waves which is a3e as per the above lo .this is the limit of the learning objectives on these classifications you do not need to find and memorise the table exemple 351 (1) a2a; (2) ndbs

Question 191-17 : 3 30 khz frequency band is referred to ?

Very low frequency vlf

As seen in the table below the very low frequency vlf band reaches from 3 khz to 30 khz frequency name frequency application very low frequency vlf 3 30 khz nil low frequency lf 30 300 khz ndb/adf medium frequency mf 300 3000 khz ndb/adf long range communications high frequency hf 3 30 mhz long range communications very high frequency vhf 30 300 mhz short range communication vdf vor ils localizer marker beacons ultra high frequency uhf 300 3000 mhz ils glide path dme ssr satelite communications gnss long range radars super high frequency shf 3 30 ghz radalt awr mls short range radars extremely high frequency ehf 30 300 ghz nil mnemonic to remember the frequency names . very very low frequency . lovely low frequency . maidens medium frequency . have high frequency . very very high frequency . useful ultra high frequency . sewing super high frequency . equipment extremely high frequency exemple 355 Very low frequency, vlf.

Question 191-18 : Single sideband two way communication is used in what frequency band and how can such radio waves propagate ?

Hf 3 30 mhz as ground waves and sky waves

Refer to figure .learning objective 062 01 01 03 03 state that hf meteorological information for aircraft in flight volmet and hf two way communication use a single sideband .learning objective 062 01 03 04 02 state that radio waves in lf mf and hf propagate as surface/ground waves and sky waves .this question contains a mixture of two different learning objectives one is to know which frequency range of radio waves use a single side band hf and the second is to know how hf waves propagate .when we want to send information via radio waves we have to modulate the carrier wave somehow this is the process of adding information to it .there are a few ways to do this .in the early days of radio it was done by sending pulses of the carrier wave as morse code pulse modulation .these days we can modulate the amplitude of the carrier wave to carry our information or we can modulate the frequency slightly to carry information also ..amplitude modulation is easier to do and far easier to represent visually .the peaks and troughs of our carrier wave are modified to create our information wave over the top of each peak and the same information wave under each trough .the wave over the peaks is one side band and the wave under the troughs is the other side band .two side bands are created but when we send hf radio signals we remove one side band to reduce the required power of the transmitter and the required bandwidth .this means that hf transmissions are single side band ssb ..also to note hf radio waves are between 3 30 mhz the range just below familiar vhf and they travel as both ground waves clinging on to the surface of the earth also called surface waves and sky waves bouncing off the ionosphere .this can actually cause some interference when the two meet especially at night when the ionosphere is thinner exemple 359 Hf (3-30 mhz), as ground waves and sky waves.

Question 191-19 : The pilot of an aircraft changes its heading to the right from 214º to 334º and makes a rate 1 turn the duration of this manoeuvre is ?

40 seconds

Refer to figure .note this is certainly not a suitable question for rnav so should be appealed if seen in the exam ..if the turn is unbalanced an aircraft either slips into or skids out of the turn thereby reducing the aerodynamic efficiency of the aircraft to help correct for these unwanted conditions the aircraft is flown using the balance part of the turn and balance indicator.during a balanced turn the ball remains in the centre of the balance indicator and the pilot remains upright in the seat relative to the aircraft with no tendency to lean .rate of turn is the measurement of how long it takes for an aircraft to turn measured in degrees per second this is particularly important during instrument flying where rate 1 turns are usually carried out at a rate of 3° per second this means that the aircraft turns through 180° in 1 minute or 360° in 2 minutes a steeper angle of bank is required to carry out a rate 1 turn at higher airspeeds .to solve this exercise first we need to calculate how many degrees was the turn performed and then apply the rate of turn .334º 214º = 120º at 3º/second rate 1 turn .120/3º = 40 seconds exemple 363 40 seconds.

Question 191-20 : You are trying to get a bearing on an ndb in the hf frequency range in theory how can you best receive a strong enough signal ?

Climb to increase your chance of capturing the sky wave

Refer to figures .note this is a ridiculous question and when paired to these options is very misleading and nearly unanswerable appeal this question in the exam please send us any further feedback if you do see this question as we would certainly like to see if they change the options or if they accept the appeal we believe this question has already been appealed at least once so hopefully it will soon be gone completely ndbs non directional beacons emit their signals in the mf and lf frequency bands which allows them to propagate as sky waves bouncing off the ionosphere and surface waves sticking to the ground surface waves stick to the surface of the earth in a strange fight between reflection diffraction and refraction with the charged surface of the earth they can propagate very far in the right conditions and mostly maintain their direction over the earth other than when going from land to sea where they shift direction as part of the 'coastal effect' we can go through each option now to try and work out which could be most correct 'climb to increase your chance of capturing the sky wave 'this would give us a better chance of receiving a sky wave as the angles would be shallower so more chance of the waves 'bouncing' off the ionosphere due to total internal refraction however the bouncing off the ionosphere introduces large changes of lateral direction and we would not receive an accurate bearing but we would receive a stronger bearing we would argue that this is useless as we use ndbs for navigation so wildly inaccurate bearings are just as bad as no bearing at all 'climb to increase your chance of capturing the ground wave 'ground waves run along the surface of the earth and hold their direction much better than sky waves so this is how we usually pick up long range ndb bearings however we do not believe that climbing higher will aid us to do this 'increase your distance from the ndb to better capture the ground wave 'ground waves have limited distance the closer you are to the source the better the reception therefore this is wrong 'fly towards the ndb to better capture the sky wave 'before the 'first skip' distance of the sky wave no sky wave will be present and remember we do not want to get a sky wave anyway as it often has fading or is in the wrong direction giving us a bad bearing as you can see there is no good answer here and we believe that the assumption that you have to make to answer it is misleading exemple 367 Climb to increase your chance of capturing the sky wave.

Question 191-21 : A pilot departs an aerodrome on the west coast of spain at dawn for a flight to new york half an hour after departure the vhf station for communication can no longer be received what are two of the main reasons that vhf radio range is limited to line of sight ?

Space waves have no reflection by the ionosphere no surface waves

Refer to figure . learning objective 062 01 03 04 01 state that radio waves in vhf uhf shf and ehf propagate as space waves . learning objective 062 01 03 03 01 define ‘space waves’ the electromagnetic waves travelling through the air directly from the transmitter to the receiver as the aircraft in this scenario is communicating with the ground station via vhf radio the radio signals will only propagate as space waves space waves are line of sight waves that go in straight lines only and therefore cannot go around obstacles including around the earth's horizon this means that there is a very well defined limit of how far vhf communications can be received from it is calculated with the formula range nm = 1 23 x height of transmitter ft + 1 23 x height of receiver ft as soon as the aircraft is outside of this range vhf communication will not be possible relays with other aircraft closer to land could be used but the aircraft will usually change to hf radio and datalink communications instead hf radio can travel as a sky wave which requires ionospheric refraction to 'bounce' the signal off the upper atmosphere and as a short surface/ground wave although this is not really used so can allow transmissions that can go further than the line of sight limitations of vhf vhf has a frequency too high to be affected much by ionospheric attenuation and refraction and therefore will not be able to form a sky wave its frequency is also too high to propagate for any reasonable distances as a ground wave as the attenuation due to obstacles etc is huge even hf radio struggles to propagate as ground waves for our uses so vhf is ever worse there is some diffraction of vhf radio waves around the earth's surface which extends range slightly but it is not a huge effect note the mention of dawn in the question is not necessary vhf radio is not affected by ionospheric refraction which could create a sky wave so dawn/dusk/night does not make a difference exemple 371 Space waves have no reflection by the ionosphere, no surface waves.

Question 191-22 : An aircraft is flying in the skip zone dead space the pilot wishes to establish communication with atc on an hf frequency theoretically the pilot can fly 1 in order to receive the 2 wave ?

1 higher 2 sky

Refer to figures . hf radio waves are transmitted as surface waves figure part c or sky waves figure part b surface wave propagation exists at frequencies from about 20 khz to about 50 mhz from the upper end of vlf to the lower end of vhf surface waves are created due to diffraction the portion of the wave in contact with the surface of the earth is retarded which results in bending of the wave around the surface of the earth the range of the surface waves is limited due to surface attenuation the wave induces a voltage in the earth which takes energy away from it sky wave propagation exists at frequencies between 2 mhz to 30 mhz from the upper end of mf to the whole hf range sky waves are radio waves that reach the ionosphere an electrically charged layer of the upper atmosphere and are reflected back toward the earth since sky waves are not limited by the curvature of the earth sky wave propagation can be used to communicate beyond the horizon at intercontinental distances for every frequency capable to create sky waves there is an angle between the vertical and the radio wave known as critical angle refer to figure above which total internal refraction occurs and the wave returns to the surface first returning sky wave at angles below critical radio waves pass straight through ionosphere and outer space they do not return on the surface of the earth the distance from the transmitter to the point where the first returning sky wave appears at the surface is known as the skip distance from the point where the surface wave is totally attenuated to the point where the first returning sky wave appears there will be no detectable signal this area is known as dead space exemple 375 (1) higher; (2) sky

Question 191-23 : Imagine an aircraft not equipped with automatic temperature correction what happens with the glide path ?

Colder temperature reduces your glide path angle

Temperature correction .even with no other errors at all the pressure altimeter will not indicate true altitude height amsl unless the surface temperature and lapse rate of the column of air are those assumed in the calibration in flight from high to low temperature the altimeter would read high .this means that the approach path flown by an aircraft would be shallower than expected with a lower glide path angle exemple 379 Colder temperature reduces your glide path angle.

Question 191-24 : What is the maximum theoretical range at which an aircraft flying at 3500 ft amsl can receive a vhf radio transmission from a station at 126 ft amsl ?

87 nm

Refer to figure .the space wave is the direct line of sight transmission of a radio wave through space because the earth is round vhf communications via space waves are limited by the curvature of the earth as such aircraft at higher altitude and transmission stations at higher altitude have a higher maximum theoretical communication range the equation to calculate maximum theoretical range is maximum theoretical range in nm = 1 23 x h3 + h4 where h3 is the receiver height in feeth4 is the transmitter height in feetcalculating the range for the problem in the question range = 1 23 x 3500 + 126 = 86 6 nm 87 nm exemple 383 87 nm

Question 191-25 : The frequency of the amplitude modulation and the colour of an outer marker om light is ?

400 hz blue

. 677 exemple 387 400 hz, blue.

Question 191-26 : An rmi indicates aircraft heading and bearing .to convert the rmi bearings of ndbs and vors to true bearings the correct combination for the application of magnetic variation is ?

Ndb aircraft position .vor beacon position

.application of magnetic variation is at beacon position for a vor .application of magnetic variation is at aircraft position for a ndb exemple 391 Ndb: aircraft position xsxvor: beacon position.

Question 191-27 : An aircraft is flying on the true track 090° towards a vor station located near the equator where the magnetic variation is 15°e .the variation at the aircraft position is 8°e .the aircraft is on vor radial ?

255°

.application of magnetic variation is at beacon position for a vor so flying 90° true tracks towards a vor means that we are on the 270° inbound radial .270° minus 15° east = 255° m exemple 395 255°.

Question 191-28 : Given .magnetic heading 280° .vor radial 090° .what bearing should be selected on the omni bearing selector in order to centralise the vor deviation needle with a 'to' indication ?

270°

Admin .for training purpose please use one of the following websites .luizmonteiro learning vor exemple 399 270°.

Question 191-29 : A vor is sited at position 58°00'n 073°00'w where the magnetic variation equals 32°w .an aircraft is located at position 56°00'n 073°00'w where the magnetic variation equals 28°w .the aircraft is on vor radial ?

212°

Admin .the aircraft is south of the vor and we apply the variation at the beacon it is a vor .the aircraft is on vor radial of 180 + 32 = 212° .declination west > compass best.declination east > compass least exemple 403 212°.

Question 191-30 : In order to plot a bearing from a vor station a pilot needs to know the magnetic variation ?

At the vor

Admin .the application of magnetic variation is .ndb aircraft position .vor beacon position exemple 407 At the vor.

Question 191-31 : An aircraft dme receiver does not lock on to its own transmissions reflected from the ground because ?

They are not on the receiver frequency

Admin .the interrogation and reply frequencies always differ by 63 mhz exemple 411 They are not on the receiver frequency.

Question 191-32 : A dme is located at msl an aircraft passing vertically above the station at flight level fl 360 will obtain a dme range of approximately ?

6 nm

Admin .the aircraft is directly overhead the beacon so interrogation pulses will therefore go vertically down to the beacon and the response pulses will go vertically upwards to the aircraft ..dme range = 36000ft.1 nm = 6000ft.dme range = 36000/6000 = 6 nm exemple 415 6 nm.

Question 191-33 : During a flight at fl 210 a pilot does not receive any dme distance indication from a dme station located approximately 220 nm away the reason for this is that the ?

Aircraft is below the line of sight altitude

.dme distance measuring equipment ground stations transmit within a uhf frequency band of 962 to 1213 mhz because the equipment is uhf the signals transmitted are subject to line of sight restrictions therefore its range varies in direct proportion to the altitude of receiving equipment .generally the reception range of the signals at an altitude of 1 000 feet above ground level agl is about 40 to 45 miles this distance increases with altitude .vhf transmissions follow a line of sight course . 2562 exemple 419 Aircraft is below the “line of sight” altitude.

Question 191-34 : Which of the following will give the most accurate calculation of aircraft ground speed ?

A dme station sited on the flight route

. dme distance measuring equipment .the dme receiver can express groundspeed in knots this value is accurate only if the aircraft is flying directly to or from the station because the dme measures groundspeed by comparing the time lapse between a series of pulses when accurate the groundspeed information allows the pilot to make accurate estimates of time of arrival and accurate checks of aircraft progress exemple 423 A dme station sited on the flight route.

Question 191-35 : What is the approximate angular coverage of reliable navigation information for a 3° ils glide path out to a minimum distance of 10 nm ?

1 35° above the horizontal to 5 25° above the horizontal and 8° each side of the localiser centreline

. 1680.glide slope coverage goes from 0 45 to 1 75 times the glide path angle .3° x 0 45 = 1 35°.3° x 1 75 = 5 25° exemple 427 1.35° above the horizontal to 5.25° above the horizontal and 8° each side of the localiser centreline.

Question 191-36 : A vor is sited at position a 45°00'n 010°00'e .an aircraft is located at position b 44°00'n 010°00'e .assuming that the magnetic variation at a is 10°w and at b is 15°w the aircraft is on vor radial ?

190°

Admin .the application of magnetic variation is .for a ndb aircraft position .for a vor beacon position . 2563.aircraft is south 180°t of the vor and we have to apply variation at the vor position . variation west magnetic best .180° + 10° = 190° exemple 431 190°.

Question 191-37 : A dme station is located 1000 feet above msl .an aircraft flying at fl 370 in isa conditions which is 15 nm away from the dme station will have a dme reading of ?

16 nm

Admin .pythagoras' theorem .dme range² = ground range² + height².dme² = 225 + 36.dme = sqrt 261 .dme = 16 16 nm exemple 435 16 nm.

Question 191-38 : What is the approximate maximum theoretical range at which an aircraft at fl130 could receive information from a vdf facility which is sited 1024 ft above msl ?

180 nm

.1 23* sqrt1024 + sqrt13000 = 179 6 nm . sqrt square root exemple 439 180 nm.

Question 191-39 : In isa conditions what is the maximum theoretical range at which an aircraft at fl80 can expect to obtain bearings from a ground vdf facility sited 325 ft above msl ?

134 nm

.calculate the range using the formula .1 23 x sqrttransmitter height in feet + 1 23 x sqrtreceiver height in feet .1 23* sqrt325 + sqrt8000 = 132 2 nm . sqrt square root exemple 443 134 nm.

Question 191-40 : The principle used in vor bearing measurement is ?

Phase comparison

The vor encodes azimuth direction from the station as the phase relationship of a reference and a variable signal .the omni directional signal contains a modulated continuous wave mcw and morse code station identifier and usually contains an amplitude modulated am voice channel .the conventional 30 hz reference signal is on a 9960 hz frequency modulated fm subcarrier the variable amplitude modulated am signal is conventionally derived from the lighthouse like rotation of a directional antenna array 30 times per second although older antennas were mechanically rotated current installations scan electronically to achieve an equivalent result with no moving parts when the signal is received in the aircraft the two 30 hz signals are detected and then compared to determine the phase angle between them the phase angle by which the am signal lags the fm subcarrier signal is equal to the direction from the station to the aircraft in degrees from local magnetic north and is called the 'radial ' exemple 447 Phase comparison.


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