Radio waves in the vhf and higher frequency bands propagate mainly as ? [ Multiple protocol ]

Question 177-1 : Space waves sky waves ground waves refracted waves

exemple 277 Space waves. — Ecqb04 november 2017 Space waves.

From which physical phenomenon do sky waves originate ?

Question 177-2 : Refraction diffraction absorption reflection

The skip zone is defined as ?

Question 177-3 : The area where neither the ground waves nor the sky waves are received the distance between the transmitter and the point on the surface of the earth where the first sky return arrives the area covered by the sky waves the area covered by the space waves

exemple 285 The area, where neither the ground waves nor the sky waves are received. — Ecqb04 november 2017 The area, where neither the ground waves nor the sky waves are received.

The amplitude of an electromagnetic wave is defined as the ?

Question 177-4 : Maximum deflection in an oscillation or wave physical length of an oscillation number of cycles occurring in one second in a radio wave expressed in hertz hz wavelength

exemple 289 Maximum deflection in an oscillation or wave. — . 2549.amplitude maximum deflection in an oscillation Maximum deflection in an oscillation or wave.

The definition of frequency modulation is ?

Question 177-5 : The information is carried by a modification of the frequency of the carrier the alteration of the amplitude of a wave the inversion of the phase of a carrier wave the information is carried by a change in the amplitude of the carrier

exemple 293 The information is carried by a modification of the frequency of the carrier. — Admin .frequency modulation the information that is impressed onto the carrier wave by altering the frequency of the carrier . 2560 The information is carried by a modification of the frequency of the carrier.

Frequency modulation consists of ?

Question 177-6 : A lf wave on an hf carrier wave a hf wave on an lf carrier wave an agreement between receiver and transmitter a system for interference elimination

exemple 297 A lf wave on an hf carrier wave. — Admin .frequency modulation the information that is impressed onto the carrier wave by altering the frequency of the carrier . 2560 A lf wave on an hf carrier wave.

Modulation is ?

Question 177-7 : The addition of information onto a radio wave during transmission the amplification of the received radio wave in the detector the separation of information from the radio wave during receiving the transformation of the radio wave into a digital signal

exemple 301 The addition of information onto a radio wave during transmission. — .modulation is addition of information onto a radio wave during transmission .the goal is to modify the radio frequency signal in order to superimpose audio and/or data signal a low frequency signal will be modulated by changing one ore more of its parameters amplitude frequency phase and then added onto a carrier wave which consists of a high frequency this process is known as 'modulation' and is necessary for transporting information via cable or through the air The addition of information onto a radio wave during transmission.

Skip distances are increased at night as ?

Question 177-8 : D layer disappears at night and the e and f layers are used instead d layer descends at a lower level reflection occurs earlier f layers disappears at night and the e layers is used instead the ionosphere becomes more ionized at night reflection will be stronger

exemple 305 D-layer disappears at night and the e and f-layers are used instead. — Ecqb04 november 2017 ..skip distance is the distance between the transmitter and the point on the surface of the earth where the first sky return arrives . 2551.skip distance will increase for a higher position of the reflecting ionospheric layer at night d layer disappears e layers almost disappears and therefore refraction occurs at a higher level the skip distance is increased D-layer disappears at night and the e and f-layers are used instead.

Which letter in the figure below indicates the 'ground wave' . 2561 ?

Question 177-9 : A b d c

A skip zone can be fin at letter s . 2561 ?

Question 177-10 : B and d a c and d d

The vhf omnirange vor uses the following wavelengths ?

Question 177-11 : Metric decimetric hectometric centimetric

exemple 317 Metric. — Vor beacons operate at shorter ranges and are free from most of the errors that afflict ndbs .they use line of sight frequencies in the vhf band wavelenght from 10 m to 1 m refer f between 108 mhz and 117 975 mhz it means from 10m to 1 m .wave lenght in m = propagation speed c in ms/s ÷ frequency f in hz .wave lenght in m = 300 000 000 ÷ frequency between 108 000 000 and 117 975 000 hz .result will be around 3 metres .between 108 mhz and 112 mhz the band is shared with ils so vor frequencies are only allocated at even 100 khz spacing.from 112 mhz to 117 975 mhz the band belongs to vor alone and spacing is reduced to 50 khz thus 108 2 mhz and 113 35 mhz would be vor frequencies and 108 1 mhz would not .within the vor ils shared frequency range the allocated frequencies are as follows .vor = even 100 khz numerals.108 00 108 05 108 20 108 25 to 111 80 111 85.ils = odd 100 khz numerals.108 10 108 15 108 30 108 35 t0 111 90 111 95 Metric.

Single side band ssb is used ?

Question 177-12 : In hf two way communication with transmissions of the meteorological aerodrome report metar in vhf transmissions to reduce transmission power in hf one way communication

exemple 321 In hf two-way communication. — 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 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 for our uses hf transmissions are single side band ssb In hf two-way communication.

What is meant by keying in a1a modulation ?

Question 177-13 : Interrupting the carrier wave to break it into dots and dashes interrupting the modulating signal to break it into dots and dashes changing the amplitude of the carrier wave to add information adding information on the carrier wave by use of a modulating signal

exemple 325 Interrupting the carrier wave to break it into dots and dashes. — Radio signals have only one carrier wave the carrier wave is used to carry the information .a1a is an abbreviation for the following .a = double side band .1 = a single channel containing quantized or digital information without the use of a modulating sub carrier .a = telegraphy for aural reception .a1a is the part of the emission of an interrupted unmodulated carrier wave which requires the beat frequency oscillator bfo to be on for aural reception keying is adding readable data to a carrier wave this readable data is usually formed in morse code Interrupting the carrier wave to break it into dots and dashes.

Which of the following summaries lists only directional antennas ?

Question 177-14 : Loop antenna parabolic antenna slotted planar array antenna dipole antenna loop antenna parabolic antenna slotted planar array antenna dipole antenna sense antenna parabolic antenna helical antenna sense antenna parabolic antenna slotted planar array antenna helical antenna

exemple 329 Loop antenna, parabolic antenna, slotted planar array antenna. — Refet to figures .a directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources in other words directional antennas send and receive signals in one direction only usually in a tightly focused very narrow beam directional antennas come in a variety of shapes sizes and designs that fluctuate widely according to their intended purpose common designs include slotted planar array antennasloop antennasparabolic or ‘dish’ antennashelical antennas can be directional or omnidirectional note in some authorities the helical antenna is also shown in the correct option as a directional antenna these authorities spain greece Loop antenna, parabolic antenna, slotted planar array antenna.

In aviation electronic systems the so called doppler principle may be used in ?

Question 177-15 : Vor gps and mti and the turbulence mode of awr vor dme and gps vor dme and ils vor mti and the mapping mode of awr

exemple 333 Vor, gps and mti and the turbulence mode of awr. — Refer to figure .the doppler effect is where waves electromagnetic in all these cases have a slightly higher detected frequency when the transmitter and receiver are coming together but a lower frequency when moving apart see the above annex it occurs for em waves and sound waves it is a measurable difference as we often know the precise frequency that we should be picking up and so small variations from that can tell us if a transmitter or a reflector is moving towards or away from us and at what speed .vors use this principle in doppler vors dvors which are the modern versions of vor beacons the variphase signal of the vor is transmitted by a ring of antennas in a circle and the signal transfers to each consecutive antenna so the transmission point of the signal effectively moves round in a circle this allows an aircraft to receive a frequency modulated signal due to the doppler effect to compare phase difference with the amplitude modulated reference signal and calculate the aircraft's radial .gnss including gps systems use the doppler effect to measure an object's speed as the pseudo random noise prn signals are on an exact frequency and the receiver knows the velocities of each satellite so is able to work out the relative movement of the receiver with very small doppler changes in frequency .mti moving target indication is less common to hear about but this system allows a radar to know which objects are moving towards or away from the station due to the doppler effect of their reflected pulses it can be used to only show moving targets and remove radar clutter .airborne weather radars awrs use the doppler effect to judge the relative movements of moisture particles raindrops hail etc based on the frequency of the reflected returns if this movement is large and erratic the radar system can then show it as an area of turbulence which is useful information for the pilot ..dmes use a system of time measurement to measure distance from a ground station and the 'groundspeed' function uses the rate of change of that distance not the doppler effect .ilss use difference in depth of modulation as a method of working out how far off localiser/glideslope the aircraft is not the doppler effect .awrs have a mapping mode but this does not use any doppler measurements as the ground is supposed to stay still Vor, gps and mti and the turbulence mode of awr.

A radio signal may be classified by three symbols in accordance with the itu ?

Question 177-16 : The first symbol indicates the type of modulation of the main carrier the three symbols together indicate which device is transmitting on the carrier the second symbol indicates the nature of information to be transmitted the third symbol indicates the nature of the signal modulating the main carrier

exemple 337 The first symbol indicates the type of modulation of the main carrier — Itu is known as low speed data typically divided into 3 segments .. . the first segment a letter is the type of modulation . . . the second symbol a number is the type of modulating signal . . . the third segment a letter is the type of information that is being transmitted . ..a1a is an abbreviation for the following .. . a = double sideband amplitude modulation . ..this indicates the bandwidth of the signal .. . 1 = a single channel containing quantized or digital information without the use of a modulating subcarrier . . . a = telegraphy for aural reception The first symbol indicates the type of modulation of the main carrier

Vhf very high frequency waves occur in which frequency range ?

Question 177-17 : 30 mhz – 300 mhz 3 ghz – 30 ghz 3 mhz – 30 mhz 300 mhz – 3000 mhz

exemple 341 30 mhz – 300 mhz — Refer to figure .radio frequency rf is the lowest portion in the electromagnetic spectrum familiar as a medium of analogue and modern digital wireless communication system it spreads in the range between 3 khz and 300 ghz .all known transmission systems works in the rf spectrum range including analogue radio aircraft navigation marine radio amateur radio tv broadcasting mobile networks and satellite systems 30 mhz – 300 mhz

The skip zone is defined as ?

Question 177-18 : The area where neither the ground waves nor the sky waves are received the area where only the ground wave is receivable the area where ground and sky waves are receivable the area where only the sky wave is receivable

exemple 345 The area, where neither the ground waves nor the sky waves are received. — Refer to figure .a skip zone is a region where a radio transmission can not be received radio waves which travel near to the ground groundwave and towards the ionosphere skywaves have a skip zone the skip zone is a region between the farthest point at which the groundwave can be received and the nearest point at which the refracted skywaves can be received .the skip zone is a natural phenomenon that can never be influenced by technical means it can only be reduced by decreasing the frequency of the radio waves reducing the frequency can be done by increasing the ionospheric width The area, where neither the ground waves nor the sky waves are received.

Which failure in radio navigation is connected with 'fading' ?

Question 177-19 : Twilight/night effect static discharge mountain effect shoreline/coastal effect

exemple 349 Twilight/night effect — Adf accuracy and errors.icao requirement is an accuracy of ±6° with a signal to noise ratio no less than 3 1 .the adf is subject to a number of potential errors .static.all forms of static can affect accuracy of the adf in snow and freezing rain precipitation static reduces the accuracy and attenuation reduces the range of bearing information .thunderstorms.thunderstorms in the vicinity act as radio beacons and can cause the needle to deviate in their direction .in conditions like this and where heavy static is present vhf aids should be used in preference to adf .night effect.the principal propagation method of ndbs is the ground wave .however it is possible for weak sky waves to be returned at night when the ionosphere is less dense and attenuation is least .returning sky waves take a longer propagation path than ground waves so they are often out of phase .night effect can be detected by listening for fading on the carrier wave bfo on and by the instrument hunting it is most likely at dawn or dusk .station interference.the long ground waves of lf and mf signals mean that occasionally signals from stations on similar frequencies overlap .this will not cause errors in the daytime if the stations are only used within the protected range .at night returning sky waves can cause rogue signals at considerable range producing the same problems as night effect .coastal refraction.speed of a surface wave is affected by the surface over which it travels faster over water than land .this change of speed means the wave is refracted at low altitude as it passes over a coastline .refraction is always towards the coast .an aircraft receiving a refracted wave would give a false indication of the beacon's position .it will place the aircraft nearer to the coast than it actually is this effect is worse the further back from the coast the beacon is sited .quadrantal error.the wave front from the ndb can be distorted by the aircraft's structure as it approaches the aerial .the error is called 'quadrantal error' because the effect is worst for signals arriving from 45° and 135° left and right of the nose the four 'quadrants' .quadrantal error is small and predictable .it can be compensated during the installation of the receiver aerial and any residual errors can be shown on a quadrantal error card kept near the instrument .modern receivers completely remove it .dip.dip occurs when the receiver sense aerial is masked by the loop aerial .dip gives large bearing errors only occurs in a turn and is at its greatest when the ndb is on a relative bearing of 45° and 135° left and right of the nose .mountain effect.at low altitude multipath signals reflected from terrain can cause erroneous readingsi .this effect diminishes with height as hills are further from the line of sight and interfere less with the surface wave Twilight/night effect

The frequency of an airborne weather radar is 9 33 ghz what is the ?

Question 177-20 : 3 2 cm 32 m 3 2 m 32 cm

exemple 353 3.2 cm — Refer to figure .use the simplified standard formulae . in meters = c 300 / f inmhz .first convert 9 33 ghz to mhz as seen in the figure 1 ghz is the same as 1000 mhz .9 33 ghz is equal to 9333 mhz .filling in the formulae results in the following . = 300/ 9333 mhz = 0 032 m = 3 2 cm 3.2 cm

What is the frequency of a radio wave with a wavelength of 8 25 m ?

Question 177-21 : 36 4 mhz 24 8 khz 36 4 khz 2 48 mhz

exemple 357 36.4 mhz — Wave lenght in m = propagation speed c in ms/s ÷ frequency f in hz .propagation speed c is a costant 300 000 000 m/s or 162 000 nm/s.8 25 = 300 000 000 ÷ x.x = 300 000 000 ÷ 8 25 = 36363636 hz.in our case we must convert 36363636 hz in mhz = ± 36 4 mhz 36.4 mhz

What is the simplest type of an antenna called ?

Question 177-22 : Dipole monopole loop antenna quadrupole

exemple 361 Dipole — Refer to figures.dipole antenna .this antenna is the most widely used type of antenna it is the simplest form of an antenna a basic dipole antenna as seen in figure 1 consists of 2 conductors arranged symmetrically with one side of the balanced feedline from the transmitter or receiver attached to each .monopole antenna .this antenna has a more complicated design a monopole antenna as seen in figure 2 consists of a single conductor usually attached to the ground because of the use of only one conductor the monopole antenna has twice the gain of a similar dipole antenna .loop antenna .loop antenna as the name suggests suggest of a loop of wire loop antennas as seen in figure 3 correspond directly with the magnetic field of the radio wave which means they are insensitive to electrical noise .quadrupole antenna .as the name suggests this antenna consists of 4 parts this is the most complex form of antenna and therefore not much used as seen in figure 4 it consists of 4 monopole antennas attached in order Dipole

What type of antenna is used in a modern airborne weather radar ?

Question 177-23 : Slotted planar antenna dipole omnidirectional antenna loop antenna

exemple 365 Slotted planar antenna — Airborne weather radar is a type of radar used to provide an indication to pilots of the intensity of convective weather modern weather radars are mostly doppler radars capable of detecting the motion of rain droplets in addition to intensity of the precipitation .airborne weather radar is typically xband pulse modulated and operating in the 8 12 ghz range with a wavelenght approx 3 cm remember well 3 ghz 300ghz correspond ro a wavelenght of 10cm 1mm .the shape of the radar beam is very important in the design of a radar for purposes of airborne weather radar a narrow beam is the most desirable because it concentrates more energy on the target which means more energy will come back in the echo .flat plate antennas are better than dish antennas and larger antennas are better than smaller antennas for concentrating the beam the pulse repetition frequency prf of a radar will determine its maximum range the prf must be long enough to allow the echo pulses to return from the maximum range target .the longer the required range the lower the prf scanning speed comes into play with the prf since a high scanning speed and low prf would cause targets to be missed at least one pulse should be transmitted per a beam width of scan pulse width will determine the minimum range of the radar and also the resolution size of the target .if a target is close and the echo is reflected back to the radar while the transmitter pulse is still being transmitted then obviously that target will be missed most radars i have worked with had a pulse width of less than 4 microseconds so this isn't a problem also many radars will shorten their pulse width in map mode allowing a higher degree of resolution for ground targets such as shorelines or islands Slotted planar antenna

What happens to the amplitude and frequency of the carrier in a1a keying the ?

Question 177-24 : And the frequency both remain constant remains constant but the frequency increases increases but the frequency remains constant and the frequency both increase

exemple 369 And the frequency both remain constant. — A1a keying is known as low speed data and the carrier wave is simply switched on and off think of it like morse code as a consequence nothing changes in terms of the frequency or amplitude of the wave And the frequency both remain constant.

Which aeronautical radio frequency band uses refraction within ionospheric ?

Question 177-25 : Hf vhf uhf vlf

exemple 373 Hf — Refer to figure .long distance communication works on skywave propagation where radio waves are directed at an angle to the sky so they refract back to earth from the ionosphere by this method it is given that frequencies in the high frequency hf band can travel beyond the horizon following the curvature of the earth and can be received at long distances .because of the refraction and reflection properties of the hf band these frequencies are also good for transmission in mountainous terrains which prevent line of sight communications Hf

The skip distance of hf transmission will increase with ?

Question 177-26 : Higher frequency and higher level of the refracting ionospheric layer lower frequency and higher level of the refracting ionospheric layer higher frequency and lower level of the refracting ionospheric layer lower frequency and lower level of the refracting ionospheric layer

Refer to figure ..radio waves can propagate in many different ways the most common is as a 'space wave' this is what most people think of when it comes to radio transmission as this is line of sight meaning that the radio waves travel in straight lines only .another propagation path is via ground waves which 'cling' to the surface and follow the contours of the earth .the third method of propagation is via sky waves which are space waves that interact with the charged particles in the ionosphere when these waves reach the ionosphere the subsequent ionospheric attenuation refracts the waves changing their course until the waves are heading downwards again this is often referred to as 'reflection' by easa so do not be confused it is refraction that occurs it just looks like the reflection from afar and they use the terms almost interchangeably .the 'skip distance' is the distance away from the transmitter where the first sky wave returns to the surface after bouncing off the ionosphere this can create a dead zone of reception for some frequencies which travel as both ground and sky waves as for example the ground waves might stop at 100 nm but the sky waves only begin at 200 nm these numbers are not even close to correct .higher frequencies receive less ionospheric attenuation therefore refracting less and not bending as sharply in the ionosphere this means that higher frequency radio signals do not 'bounce' off the ionosphere at steep angles thus making the skip distance longer see the second annex above .the height of the ionosphere also makes a difference a higher ionosphere means that the signals will travel further before reaching the level where refraction begins and will travel further on the way back down also this means that a higher ionosphere contributes to a longer skip distance $exemple 377 Higher frequency and higher level of the refracting ionospheric layer.$ Higher frequency and higher level of the refracting ionospheric layer.

The advantage of slotted antennas in modern radar technology is to… ?

Question 177-27 : Greatly reduce lateral lobes consequently concentrating more energy into the main beam produce a wide beam for better target detection eliminate the need for azimuth slaving simultaneously transmit weather and mapping beams

exemple 381 Greatly reduce lateral lobes, consequently concentrating more energy into the main beam. — Refer to figures . .learning objective 062 01 02 03 01 name the common different types of directional antennas loop antenna used in old automatic direction finding adf receivers parabolic antenna used in weather radars slotted planar array used in more modern weather radars ..radars such as awrs airborne weather radars have to be able to send pulses of electromagnetic radiation in one direction all at once this is more difficult than it sounds due to the way that these waves are produced .parabolic antenna.the older method of directing this energy was by using a parabolic reflector dish which is a shape that reflects all radiation from the focal point in the middle outwards in the same direction and vice versa any radiation from that direction is reflected onto the focal point in the middle this allows for a transmitter/receiver device to be placed in the focal point facing backwards towards the dish and for its transmissions to go forwards ahead of the aircraft and receive the reflected pulses indicating the presence of weather .one of the biggest problems with the parabolic antenna is the side lobes the formation of this 'main beam' of radiation does cause some unwanted extra radiation called side lobes which send some of the energy in a different direction than intended and can cause some spurious and incorrect responses on the radar screen .slotted planar array / flat plate antenna / phased array.these types of radars use a more efficient modern technique by having a flat plate with numerous waveguide size slots cut into it it can produce a similar beam to the parabolic antenna with much smaller sidelobes the lesser side lobes means that there are less spurious returns and that there is less wasted energy meaning that less energy is needed for the same radar scan .the main beam main lobe of a slotted planar array can also be made thinner than the parabolic antenna beam which would use even less energy allowing for increased range or just lower energy consumption Greatly reduce lateral lobes, consequently concentrating more energy into the main beam.

Modulation is ?

Question 177-28 : The process of impressing and transporting information by radio waves a continuous wave which is capable of carrying audible signals without modification to allow the signal to be amplified to the required power level the process to provide a radio carrier wave for transmission

exemple 385 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 The process of impressing and transporting information by radio waves.

The unit for measuring frequency is and measures cycles ?

Question 177-29 : Hertz per second metres per minute metres per second hertz per minute

exemple 389 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 Hertz, per second

When raising the frequency of an electromagnetic wave the ?

Question 177-30 : Wavelength decreases wavelength remains the same wavelength increases wavelength and amplitude increases

exemple 393 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 Wavelength decreases

During a flight at fl210 a pilot does not receive any dme distance indication ?

Question 177-31 : Aeroplane is below the minimum altitude for line of sight propagation aeroplane is circling around the station the power of the transmitted signal is too weak to be received by the dme station altitude is too high

exemple 397 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 Aeroplane is below the minimum altitude for line of sight propagation.

Under what conditions can vhf voice communications often suffer interference ?

Question 177-32 : A temperature inversion in the atmosphere can cause 'super refraction' the interfering signal may be refracted from the ionosphere at night the interfering signal may be refracted from mountains between the transmitter and receiver the interfering signal may be refracted as a surface wave over a large expanse of water

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 $exemple 401 A temperature inversion in the atmosphere can cause 'super-refraction'.$ A temperature inversion in the atmosphere can cause 'super-refraction'.

Pulse length is expressed as ?

Question 177-33 : Time an amplitude distance a frequency

exemple 405 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 Time.

Why do vhf radio signals used for communication and navigation have a limited ?

Question 177-34 : Because of the curvature of the earth ground waves are absorbed by the earth’s surface sky waves are refracted from the d layer direct waves interfere with ionosphere waves

exemple 409 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 Because of the curvature of the earth.

According to the international telecommunication union itu code a radio signal ?

Question 177-35 : Amplitude modulated by a speech signal such as is used for vhf com a continuous wave interrupted with a keyed morse code ident as used by an ndb amplitude modulated to transmit the morse code ident as is used by a vor interrupted to transmit the morse code identification as used by an ndb

exemple 413 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 Amplitude modulated by a speech signal, such as is used for vhf-com.

What does the term antenna shadowing mean ?

Question 177-36 : The antenna is masked from the transmitter due to the aircraft attitude the antenna shielded from the sun in order to reduce the influence of the ionosphere terrain is in between the receiver and the transmitter the antenna is placed under a dome

exemple 417 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 The antenna is masked from the transmitter due to the aircraft attitude.

What is the receiver aerial location of a gnss system ?

Question 177-37 : Top of the fuselage bottom of the fuselage left wing tip top of the tail

exemple 421 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 Top of the fuselage.

The following might be caused by antenna shadowing ?

Question 177-38 : Poor radio reception of a vor ident signal while the aircraft is making an orbit 360° medium level turn a weather radar failing to show a distant turbulent cloud due to the signals being blocked by a nearer cloud an aircraft appearing as two distinct indications on a radar controller's display blocking of a vor transmission caused by buildings close to the antenna

exemple 425 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 Poor radio reception of a vor ident signal while the aircraft is making an orbit (360° medium-level turn).

What is correct regarding antenna shadowing ?

Question 177-39 : Reduced reception by an antenna when part of the airframe blocks the signal to the antenna poor reception of gps signals due to very weak signals compared to the background noise at that frequency terrain blocking the path between the transmitter and receiver/aircraft antenna protection of a radar reception antenna from the strong signals produced by a nearby transmission 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

The correct position for the gps antenna on an airplane is ?

Question 177-40 : On the top of the fuselage on the bottom of the fuselage in the nose of the aircraft in the tailplane

exemple 433 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 On the top of the fuselage.

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