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Question 189-1 : Concerning the wave propagation in the ionosphere we denote three layers those three layers are ? [ Question security ]

D e and f layers and their depth varies with time

. 2551.the ionosphere is the ionized component of the earth's upper atmosphere from 60 to 400 km above the surface which is vertically structured in three regions or layers d e and f exemple 289 D, e and f layers and their depth varies with time.

Question 189-2 : Radio waves travel at ?

The speed of light

exemple 293 The speed of light.

Question 189-3 : In accordance with the itu international telecommunication union a radio signal may be classified by three symbols third symbol indicates . e g a1a ?

Nature of information to be transmitted

Admin .radio signal may be classified by three symbols in accordance with the itu . first symbol indicates the type of modulation of the main carrier . second symbol indicates the nature of the signal modulating the main carrier . third symbol indicates the nature of the information to be transmitted .for information only . you do not have to know that for the exam .a1a telegraphy on off keying without modulation by an audio frequency .a double sideband.1 single channel containing quantized or digital information without the use of a modulating sub carrier.a telegraphy for aural reception exemple 297 Nature of information to be transmitted.

Question 189-4 : In accordance with the itu international telecommunication union a radio signal may be classified by three symbols second symbol indicates . e g a1a ?

Nature of signal s modulating the main carrier

Admin .a radio signal may be classified by three symbols in accordance with the itu radio regulation volume 1 e g a1a . first symbol indicates the type of modulation of the main carrier . second symbol indicates the nature of the signal modulating the main carrier . third symbol indicates the nature of the information to be transmitted exemple 301 Nature of signal(s) modulating the main carrier.

Question 189-5 : In accordance with the itu international telecommunication union a radio signal may be classified by three symbols first symbol indicates . e g a1a ?

Type of modulation of the main carrier

Admin .radio signal may be classified by three symbols in accordance with the itu . first symbol indicates the type of modulation of the main carrier . second symbol indicates the nature of the signal modulating the main carrier . third symbol indicates the nature of the information to be transmitted .for information only . you do not have to know that for the exam .a1a telegraphy on off keying without modulation by an audio frequency .a double sideband.1 single channel containing quantized or digital information without the use of a modulating sub carrier.a telegraphy for aural reception exemple 305 Type of modulation of the main carrier.

Question 189-6 : Vhf very high frequency waves appear in the frequency spectrum ?

30 mhz 300 mhz

. 1682 exemple 309 30 mhz - 300 mhz

Question 189-7 : With regard to radio waves propagation a cycle is defined as ?

A complete series of values of a periodical process

.this is the official easa definition a cycle is any complete round or series of occurrences that repeats or is repeated . 2549 exemple 313 A complete series of values of a periodical process.

Question 189-8 : Vlf very low frequency waves appear in the frequency spectrum ?

3 khz 30 khz

Admin . 1682 exemple 317 3 khz - 30 khz

Question 189-9 : Lf low frequency waves appear in the frequency spectrum ?

30 khz 300 khz

Admin . 1682 exemple 321 30 khz - 300 khz

Question 189-10 : Mf medium frequency waves appear in the frequency spectrum ?

300 khz 3000 khz

Admin . 1682 exemple 325 300 khz - 3000 khz

Question 189-11 : Hf high frequency waves appear in the frequency spectrum ?

3 mhz 30 mhz

Admin . 1682 exemple 329 3 mhz - 30 mhz

Question 189-12 : Uhf ultra high frequency waves appear in the frequency spectrum ?

300 mhz 3000 mhz

Admin . 1682 exemple 333 300 mhz - 3000 mhz

Question 189-13 : Shf super high frequency waves appear in the frequency spectrum ?

3 ghz 30 ghz

Admin . 1682 exemple 337 3 ghz - 30 ghz

Question 189-14 : Ehf extremely high frequency waves appear in the frequency spectrum ?

30 ghz 300 ghz

Admin . 1682 exemple 341 30 ghz - 300 ghz

Question 189-15 : Frequency is defined as the ?

Number of cycles occurring in one second in a radio wave expressed in hertz hz

.a cycle is any complete round or series of occurrences that repeats or is repeated . 2549.the frequency is the number of cycles occurring in one second in a radio wave expressed in hertz hz exemple 345 Number of cycles occurring in one second in a radio wave expressed in hertz (hz).

Question 189-16 : Which statement about vhf/uhf frequencies is correct ?

For both vhf/uhf propagation the space wave is the only propagation path of practical use there is no sky wave under normal conditions

Admin .radio waves in vhf uhf shf and ehf propagate as space waves .radio waves in vlf lf mf and hf propagate as surface/ground waves and sky waves exemple 349 For both vhf/uhf propagation, the space wave is the only propagation path of practical use. there is no sky wave under normal conditions.

Question 189-17 : Diffraction is the process by which ?

Radio wave travel over and around obstacles

.diffraction is the phenomenon by which wave energy bends around an object exemple 353 Radio wave travel over and around obstacles.

Question 189-18 : Antennas .an ac will be induced ?

In a wire parallel to a wire fed with an ac but remote from it

Admin .inductive coupling refers to the phenomenon that exists when a magnetic field created by an electrical current induces an effect on something else when this happens the two then become mutually reactive or coupled by the inductive effects of the magnetic field for example when an electrical current passes through a wire the electromagnetic field created can induce an electrical current in another wire causing the two to be inductively coupled the principles and effects of inductive coupling find use in devices such as transformers and electric motors .the effects of inductive coupling can be used in one of three primary ways first the inducing field can create a specifically desired electrical current such as in transformers second the inducing field can create a specifically desired mechanical effect such as in electric motors finally the inducing field can create a resonance which itself can create specifically desired electrical currents such as in radio transmission and reception and non contact charging devices .in transformers an electrical current conducts through a wire wound around a core of some type called the primary winding this wire is intentionally placed near another wire wound around the same core called the secondary winding .the electromagnetic field created by passing current through the primary winding then induces an electrical current in the secondary winding .resonant devices work in a way similar to transformers though without the paired windings in these devices a standing electromagnetic field is created when this field encounters an antenna the effect of inductive coupling causes the antenna to resonate which in turn induces an electrical current at its feed point in the case of a radio the induced current is amplified and heard over the radio in a charging device the induced current is directly applied to a battery's terminals to recharge it exemple 357 In a wire, parallel to a wire fed with an ac, but remote from it.

Question 189-19 : In aviation the reflection on ionosphere layers phenomenon is used in the following frequencies ?

Hf

Admin .hf radio communications is dependent for most of its applications on the use of the ionosphere this region in the atmosphere enables radio communications signals to be reflected or more correctly refracted back to earth so that they can travel over great distances around the globe ionospheric propagation is normally though of as an hf propagation mode although it use can extend above and below the hf portion of the spectrum on many occasions .once a signal passes through the d region it travels on and reaches first the e and next the f regions at the altitude where these regions are found the air density is very much less and this means that when the free electrons are excited by radio signals and vibrate far fewer collisions occur as a result the way in which these regions act is somewhat different the electrons are again set in motion by the radio signal but they tend to re radiate it as the signal is travelling in an area where the density of electrons is increasing the further it progresses into the region the signal is refracted away from the area of higher electron density in the case of hf signals this refraction is often sufficient to bend them back to earth in effect it appears that the region has 'reflected' the signal .the tendency for this 'reflection' is dependent upon the frequency and the angle of incidence exemple 361 Hf.

Question 189-20 : The wavelength of a radio signal transmitted at the frequency 118 7 mhz is ?

2 53 m

Admin .wavelength meters = speed of light / frequency.wavelength = 300 000 000 / 118 700 000 = 2 53 m exemple 365 2.53 m.

Question 189-21 : In the propagation of mf waves the phenomenon of fading is particularly found ?

At night due to the combination of the sky and ground waves

.fading when a receiver picks up the sky signal and the surface signal the signals will interfere with each other causing the signals to be cancelled out exemple 369 At night, due to the combination of the sky and ground waves.

Question 189-22 : A radio signal looses strength as range from the transmitter increases this is called ?

Attenuation

Admin .attenuation as any radio wave travels away from the transmitter it becomes weaker looses power or is attenuated this results from the rf signal inducing currents into the surface of the earth a good conducting surface such as water will give the signal back with little loss of energy a poor conductive surface such as a hot desert will simply absorb the energy the degree of surface attenuation also varies directly with frequency .there are two main reasons for attenuation . the spreading of available rf energy over a greater area . rf energy is absorbed by the earth atmosphere or ionized layers exemple 373 Attenuation.

Question 189-23 : Skip distance is the ?

Range from the transmitter to the first sky wave

Admin .skip distance is the distance between the transmitter and the point on the surface of the earth where the first sky return arrives exemple 377 Range from the transmitter to the first sky wave.

Question 189-24 : The wavelength of a radio transmitted on frequency 121 95 mhz is ?

2 46 m

.wavelength meters = speed of light / frequency.wavelength = 300 000 000 / 121 950 000 = 2 46 m exemple 381 2.46 m.

Question 189-25 : What describes polarization ?

Orientation of the plane of oscillation of the electrical component of the electromagnetic wave

. polarisation electromagnetic radiation is comprised of the e and h fields which stand for electric and magnetic respectively .the electric field arises from voltage and the magnetic on from current the two act at rightangles to each other . 2552.a wave's polarisation is noted with reference to the electrical field so a vertically polarised wave has a vertical electrical field wich will come from a vertical aerial for efficiency the receiver must have the same orientation . 2553.the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization state the following figures show some examples of the evolution of the electric field vector black with time the vertical axes at a particular point in space along with its x and y components red/left and blue/right and the path traced by the tip of the vector in the plane purple the same evolution would occur when looking at the electric field at a particular time while evolving the point in space along the direction opposite to propagation . in linear polarisation the plane of oscillation is fixed in space whereas in circular or eliptical polarisation the plane is rotating exemple 385 Orientation of the plane of oscillation of the electrical component of the electromagnetic wave.

Question 189-26 : On which bearings errors caused by the shoreline/coastal effect reach their maximum ?

Bearings 000° 030° degrees to the coastline

Coastal refraction or shoreline effect .low frequency radio waves will refract or bend near a shoreline especially if they are close to parallel to it .least when bearings normal to coastline . radio waves passing the coastline at small angles suffer refraction due to different conducting and reflecting properties over land and sea a false bearing indication is obtained at aircraft flying over sea and taking bearings from ndb located over land the effect is less for an ndb on coast than one inland and on a bearing 90° to coastline then at an oblique angle hence given the choice use beacon at coast and rely on bearings perpendicular to the coastline . 2554 exemple 389 Bearings 000°-030° degrees to the coastline.

Question 189-27 : The doppler effect onto the radio signals is ?

The shift of frequency of the wave due to the relative movement between the transmitter and the receiver

exemple 393 The shift of frequency of the wave due to the relative movement between the transmitter and the receiver.

Question 189-28 : The d layer and e layer of the atmosphere are part of the ?

Ionosphere

. 2551.the ionosphere is the ionized component of the earth's upper atmosphere from 60 to 400 km above the surface which is vertically structured in three regions or layers d e and f exemple 397 Ionosphere.

Question 189-29 : When raising the frequency of an electromagnetic wave the ?

Wavelength decreases

.the relationship between wavelength and frequency is .wavelength = speed of light / frequency.if frequency increases wavelength decreases exemple 401 Wavelength decreases.

Question 189-30 : The phenomenon when a wave bends when it passes around an impenetrable obstacle is ?

Diffraction

Admin .diffraction is the phenomenon by which wave energy bends around an object exemple 405 Diffraction.

Question 189-31 : The phenomenon of a change in direction of an radio wave em wave occurring due to a change in its speed is called ?

Refraction

.refraction is the process by which a signal's propagation path bends and the signal changes its speed as it moves from one medium to another different density of the mediums generally the rf energy travels in straight line = following great circle paths however in some cases when there is a change in certain factors the signal's path may change direction the actual extent of the signal's path change varies significantly with the change of the environment .there are 3 main types of refraction .a coastal = the path of rf signal may change as it crosses a coastline .b atmospheric especially low altitude = changes in the path of rf signal may be caused by the changes in temperature pressure or humidity .c ionospheric = paths of rf signals may change as they pass through ionized layers exemple 409 Refraction.

Question 189-32 : A reason that gps satellites use helical antennae is ?

That the signal has a circular polarization

.helix antennas also commonly called helical antennas have a very distinctive shape as can be seen in the following picture . 2555.a helical antenna is an antenna consisting of a conducting wire wound in the form of a helix in most cases helical antennas are mounted over a ground plane exemple 413 That the signal has a circular polarization.

Question 189-33 : The mix of an electromagnetic wave with another is called ?

Interference

.interference is a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude interference usually refers to the interaction of waves that are correlated or coherent with each other either because they come from the same source or because they have the same or nearly the same frequency .this question exists also with this statement superposition of two em waves of the same or nearly the same frequency is called interference exemple 417 Interference.

Question 189-34 : Speed of a radio wave ?

300 000 km/s

exemple 421 300 000 km/s.

Question 189-35 : For long range ndb's the most common type is ?

Lf non a1a

Admin .non a2a bfo off for a2a idents 15 w power 10 25nm range .non a1a bfo on for a1a idents lf non a1a is used for long range exemple 425 Lf, non a1a.

Question 189-36 : Mountain effect occurring for instance with ndbs is caused by what physical phenomenon ?

Reflection

.mountain effect mountain areas can cause reflections and to a lesser extent diffractions and lead to the error direction reading by adf .this effect similar to night effect is obtained in mountainous areas where the energy received from an ndb consists of two or more waves one of them direct and others by reflection from the mountains bearing indications are found to change rapidly until the affected area is passed .for information night effect radio waves take two paths to the radio compass receiver the first and normal path is along the earth's surface if only these waves were received the compass would point directly to the ndb the second path is via one or more wave refracting layers above the earth the ionosphere returning to earth to mix with direct waves complete changes in the nature of the waves take place on this path and produce errors in direction

Question 189-37 : Which physical effects affecting wave propagation as shown in the figure . 2556 ?

A = refraction b = absorption c = reflection

exemple 433 A = refraction b = absorption c = reflection

Question 189-38 : Which letter in the figure below indicates the 'skip zone' . 2557 ?

C

.read carefully skip zone not 'distance' .skip zone dead space is the distance between the limit of the surface wave and the sky wave exemple 437 C.

Question 189-39 : Which letter in the figure below indicates the 'skip distance' . 2557 ?

D

.read carefully skip distance not 'zone' .skip distance is the distance between the transmitter and the point on the surface of the earth where the first sky return arrives .it is the range from the transmitter to the first sky wave

Question 189-40 : You are flying over sea parallel to the coastline an ndb is situated 10 nm inland in which sectors in the diagram does the shoreline/coastal effect reach its minimum . 2558 ?

Sectors a + b

.coastal refraction or shoreline effect .low frequency radio waves will refract or bend near a shoreline especially if they are close to parallel to it .least when bearings normal perpendicular to coastline .radio waves passing the coastline at small angles suffer refraction due to different conducting and reflecting properties over land and sea a false bearing indication is obtained at aircraft flying over sea and taking bearings from ndb located over land the effect is less for an ndb on coast than one inland and on a bearing 90° to coastline then at an oblique angle hence given the choice use beacon at coast and rely on bearings perpendicular to the coastline


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