In accordance with the ITU International Telecommunication Union a radio signal may be classified by three symbols Third symbol indicates e g A1A ?
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In accordance with the ITU International Telecommunication Union a radio signal may be classified by three symbols Second symbol indicates e g A1A ?
In accordance with the ITU International Telecommunication Union a radio signal may be classified by three symbols First symbol indicates e g A1A ?
Vhf very high frequency waves appear in frequency spectrum Type of modulation of main carrier. . 
With regard to radio waves propagation a cycle defined as A complete series of values of a periodical process. this the official easa definition a cycle any complete round or series of occurrences that repeats or repeated . 
A loop antenna a commonly used A complete series of values of a periodical process. the aircraft equipment consists of two antennas adf receiver the adf instrument two antennas are used loop antenna the sense antenna the loop antenna can sense direction of signal from station but cannot discriminate whether station in front or behind aircraft the sense antenna can discriminate direction solves ambiguity of loop antenna. 
Vlf very low frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-8
Lf low frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-9
Mf medium frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-10
Hf high frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-11
Uhf ultra high frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-12
Shf super high frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-13
Ehf extremely high frequency waves appear in frequency spectrum A complete series of values of a periodical process. . Question 173-14
Which of following term describes maximum deflection in an oscillation A complete series of values of a periodical process. img /com_en/com062 587 jpg amplitude maximum deflection in an oscilliation. Question 173-15
Frequency defined as Number of cycles occurring in one second in a radio wave expressed in hertz (hz). a cycle any complete round or series of occurrences that repeats or repeated the frequency the number of cycles occurring in one second in a radio wave expressed in hertz (hz). Question 173-16
Single sideband modulation sbb a modulation technique where only one sideband transmitted sbb used Hf volmet hf two way communication. there redundancy in double sideband transmissions in that information contained in both upper lower sidebands additionally original rf carrier wave having served its purpose to get audio information into radio frequencies now redundant so it possible to remove one of sidebands the carrier wave because remaining sideband contains all information this known as single sideband (ssb) operation when using sky wave propagation communication differing refraction occurring at different frequencies leads to an increase in distortion if bandwidth too large the ionosphere comprises electrically charged particles which cause high levels of static interference on radio waves use of ssb significantly reduces effect of this interference the mf hf frequencies used long range communication are in great demand hence use of ssb transmissions increases number of channels available the use of ssb also reduces theamount of power required. Question 173-17
Which statement about vhf/uhf frequencies correct For both vhf/uhf propagation space wave the only propagation path of practical use there no sky wave under normal conditions. radio waves in vhf uhf shf ehf propagate as space waves radio waves in vlf lf mf hf propagate as surface/ground waves sky waves. Question 173-18
Diffraction the process which Radio wave travel over around obstacles. diffraction the phenomenon which wave energy bends around an object. Question 173-19
Antennas an ac will be induced In a wire parallel to a wire fed with an ac but remote from it. inductive coupling refers to phenomenon that exists when a magnetic field created an electrical current induces an effect on something else when this happens two then become mutually reactive or coupled the inductive effects of magnetic field for example when an electrical current passes through a wire electromagnetic field created can induce an electrical current in another wire causing two to be inductively coupled the principles effects of inductive coupling find use in devices such as transformers electric motors the effects of inductive coupling can be used in one of three primary ways first inducing field can create a specifically desired electrical current such as in transformers second inducing field can create a specifically desired mechanical effect such as in electric motors finally inducing field can create a resonance which itself can create specifically desired electrical currents such as in radio transmission reception non contact charging devices in transformers an electrical current conducts through a wire wound around a core of some type called primary winding this wire intentionally placed near another wire wound around same core called secondary winding the electromagnetic field created passing current through primary winding then induces an electrical current in secondary winding resonant devices work in a way similar to transformers though without paired windings in these devices a standing electromagnetic field created when this field encounters an antenna effect of inductive coupling causes antenna to resonate which in turn induces an electrical current at its feed point in case of a radio induced current amplified heard over radio in a charging device induced current directly applied to a battery's terminals to recharge it. Question 173-20
In aviation reflection on ionosphere layers phenomenon used in following frequencies In a wire parallel to a wire fed with an ac but remote from it. hf radio communications dependent most of its applications on use of ionosphere this region in atmosphere enables radio communications signals to be reflected or more correctly refracted back to earth so that they can travel over great distances around globe ionospheric propagation normally though of as an hf propagation mode although it use can extend above below hf portion of spectrum on many occasions once a signal passes through d region it travels on reaches first e next f regions at altitude where these regions are found air density very much less this means that when free electrons are excited radio signals vibrate far fewer collisions occur as a result way in which these regions act somewhat different the electrons are again set in motion the radio signal but they tend to re radiate it as signal travelling in an area where density of electrons increasing further it progresses into region signal refracted away from area of higher electron density in case of hf signals this refraction often sufficient to bend them back to earth in effect it appears that region has 'reflecte signal the tendency this 'reflection' dependent upon frequency the angle of incidence. Question 173-21
The wavelength of a radio signal transmitted at frequency 118 7 mhz In a wire parallel to a wire fed with an ac but remote from it. wavelength meters = speed of light / frequency wavelength = 300 000 000 / 118 700 000 = 2 53 m. Question 173-22
In propagation of mf waves phenomenon of fading particularly found At night due to combination of sky ground waves. fading when a receiver picks up sky signal the surface signal signals will interfere with each other causing signals to be cancelled out. Question 173-23
A radio signal looses strength as range from transmitter increases this called At night due to combination of sky ground waves. attenuation as any radio wave travels away from transmitter it becomes weaker (looses power) or attenuated this results from rf signal inducing currents into surface of earth a good conducting surface such as water will give signal back with little loss of energy a poor conductive surface such as a hot desert will simply absorb energy the degree of surface attenuation also varies directly with frequency there are two main reasons attenuation spreading of available rf energy over a greater area rf energy absorbed the earth atmosphere or ionized layers. Question 173-24
Skip distance the Range from transmitter to first sky wave. skip distance the distance between transmitter the point on surface of earth where first sky return arrives. Question 173-25
The wavelength of a radio transmitted on frequency 121 95 mhz Range from transmitter to first sky wave. wavelength meters = speed of light / frequency wavelength = 300 000 000 / 121 950 000 = 2 46 m. Question 173-26
What describes polarization Orientation of plane of oscillation of electrical component of electromagnetic wave. polarisation electromagnetic radiation comprised of e h fields which stand electric magnetic respectively the electric field arises from voltage the magnetic on from current the two act at rightangles to each other a wave's polarisation noted with reference to electrical field so a vertically polarised wave has a vertical electrical field wich will come from a vertical aerial (for efficiency receiver must have same orientation) the shape traced out in a fixed plane the electric vector as such a plane wave passes over it a description of polarization state the following figures show some examples of evolution of electric field vector (black) with time(the vertical axes) at a particular point in space along with its x y components (red/left blue/right) the path traced the tip of vector in plane (purple) the same evolution would occur when looking at electric field at a particular time while evolving point in space along direction opposite to propagation in linear polarisation plane of oscillation fixed in space whereas in circular or eliptical polarisation plane rotating. Question 173-27
Modulation Addition of a low frequency signal (tone voice) onto high frequency carrier wave. modulation addition of information onto a radio wave during transmission the goal to modify radio frequency signal in order to superimpose audio and/or data signal a low frequency signal will be modulated changing one ore more of its parameters (amplitude frequency phase) then added onto a carrier wave which consists of a high frequency this process known as 'modulation' is necessary transporting information via cable or through air. Question 173-28
On which bearings errors caused the shoreline/coastal effect reach their maximum Bearings ° 3 ° degrees to 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 coastline at small angles suffer refraction due to different conducting reflecting properties over land sea a false bearing indication obtained at aircraft flying over sea taking bearings from ndb located over land the effect less an ndb on coast than one inland on a bearing 90° to coastline then at an oblique angle hence given choice use beacon at coast rely on bearings perpendicular to coastline . Question 173-29
The doppler effect onto radio signals The shift of frequency of wave due to relative movement between transmitter the receiver. 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 coastline at small angles suffer refraction due to different conducting reflecting properties over land sea a false bearing indication obtained at aircraft flying over sea taking bearings from ndb located over land the effect less an ndb on coast than one inland on a bearing 90° to coastline then at an oblique angle hence given choice use beacon at coast rely on bearings perpendicular to coastline . Question 173-30
The d layer and e layer of atmosphere are part of The shift of frequency of wave due to relative movement between transmitter the receiver. the ionosphere the ionized component of earth's upper atmosphere from 60 to 400 km above surface which vertically structured in three regions or layers (d e f). Question 173-31
When raising frequency of an electromagnetic wave the Wavelength decreases. the relationship between wavelength frequency is wavelength = speed of light / frequency if frequency increases wavelength decreases. Question 173-32
The phenomenon when a wave bends when it passes around an impenetrable obstacle Wavelength decreases. diffraction the phenomenon which wave energy bends around an object. Question 173-33
The phenomenon of a change in direction of an radio wave em wave occurring due to a change in its speed called Wavelength decreases. refraction the process which a signas propagation path bends the signal changes its speed as it moves from one medium to another (different density of mediums) generally rf energy travels in straight line = following great circle paths however in some cases when there a change in certain factors signas path may change direction the actual extent of signas path change varies significantly with change of environment there are 3 main types of refraction a) coastal = path of rf signal may change as it crosses a coastline b) atmospheric (especially low altitude) = changes in path of rf signal may be caused the changes in temperature pressure or humidity c) ionospheric = paths of rf signals may change as they pass through ionized layers. Question 173-34
A reason that gps satellites use helical antennae That signal has a circular polarization. helix antennas (also commonly called helical antennas ) have a very distinctive shape as can be seen in following picture a helical antenna an antenna consisting of a conducting wire wound in form of a helix in most cases helical antennas are mounted over a ground plane. Question 173-35
The mix of an electromagnetic wave with another called That signal has a circular polarization. interference a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude interference usually refers to interaction of waves that are correlated or coherent with each other either because they come from same source or because they have same or nearly same frequency this question exists also with this statement superposition of two em waves of same or nearly same frequency called? interference. Question 173-36
Speed of a radio wave That signal has a circular polarization. interference a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude interference usually refers to interaction of waves that are correlated or coherent with each other either because they come from same source or because they have same or nearly same frequency this question exists also with this statement superposition of two em waves of same or nearly same frequency called? interference. Question 173-37
For long range ndb's most common type That signal has a circular polarization. non a2a bfo off a2a idents 15 w power 10 25nm range non a1a bfo on a1a idents lf non a1a used long range. Question 173-38
Mountain effect occurring instance with ndbs caused what physical phenomenon That signal has a circular polarization. mountain effect mountain areas can cause reflections (and to a lesser extent diffractions) lead to error direction reading adf this effect similar to night effect obtained in mountainous areas where energy received from an ndb consists of two or more waves one of them direct others reflection from mountains bearing indications are found to change rapidly until affected area passed for information night effect radio waves take two paths to radio compass receiver the first normal path along earth's surface if only these waves were received compass would point directly to ndb the second path via one or more wave refracting layers above earth (the ionosphere) returning to earth to mix with direct waves complete changes in nature of waves take place on this path produce errors in direction. Question 173-39
Which physical effects affecting wave propagation as shown in figure 2556 A = refraction b = absorption c = reflection. mountain effect mountain areas can cause reflections (and to a lesser extent diffractions) lead to error direction reading adf this effect similar to night effect obtained in mountainous areas where energy received from an ndb consists of two or more waves one of them direct others reflection from mountains bearing indications are found to change rapidly until affected area passed for information night effect radio waves take two paths to radio compass receiver the first normal path along earth's surface if only these waves were received compass would point directly to ndb the second path via one or more wave refracting layers above earth (the ionosphere) returning to earth to mix with direct waves complete changes in nature of waves take place on this path produce errors in direction. Question 173-40
Which letter in figure below indicates 'skip zone' 2557 A = refraction b = absorption c = reflection. read carefully skip zone (not 'distance') skip zone (dead space) the distance between limit of surface wave the sky wave.
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