% FILENAME = N28.TXT % Propagation % Release version 3, October 2001 %QUESTION 1 #28.1 A 'skip zone' is: the distance between the antenna and where the refracted wave first returns to earth the distance between the far end of the ground wave and where the refracted wave first returns to earth the distance between any two refracted waves a zone caused by lost sky waves % ans 2 %QUESTION 2 #28.2 The medium which reflects high frequency radio waves back to the earth's surface is called the: biosphere stratosphere ionosphere troposphere % ans 3 %QUESTION 3 #28.3 The highest frequency that will be reflected back to the earth at any given time is known as the: UHF MUF OWF LUF % ans 2 %QUESTION 4 #28.4 All communications frequencies throughout the spectrum are affected in varying degrees by the: atmospheric conditions ionosphere aurora borealis sun % ans 4 %QUESTION 5 #28.5 Solar cycles have an average length of: 1 year 3 years 6 years 11 years % ans 4 %QUESTION 6 #28.6 The 'skywave' is another name for the: ionospheric wave tropospheric wave ground wave inverted wave % ans 1 %QUESTION 7 #28.7 The polarisation of an electromagnetic wave is defined by the direction of: the H field propagation the E field the receiving antenna % ans 3 %QUESTION 8 #28.8 That portion of HF radiation which is directly affected by the surface of the earth is called: ionospheric wave local field wave ground wave inverted wave % ans 3 %QUESTION 9 #28.9 Radio wave energy on frequencies below 4 MHz during daylight hours is almost completely absorbed by this ionospheric layer: C D E F % ans 2 %QUESTION 10 #28.10 Because of high absorption levels at frequencies below 4 MHz during daylight hours, only high angle signals are normally reflected back by this layer: C D E F % ans 3 %QUESTION 11 #28.11 Scattered patches of high ionisation developed seasonally at the height of one of the layers is called: sporadic-E patchy random reflectors trans-equatorial ionisation % ans 1 %QUESTION 12 #28.12 For long distance propagation, the radiation angle of energy from the antenna should be: less than 30 degrees more than 30 degrees but less than forty-five more than 45 degrees but less than ninety 90 degrees % ans 1 %QUESTION 13 #28.13 The path radio waves normally follow from a transmitting antenna to a receiving antenna at VHF and higher frequencies is a: circular path going north or south from the transmitter great circle path straight line bent path via the ionosphere % ans 3 %QUESTION 14 #28.14 A radio wave may follow two or more different paths during propagation and produce slowly-changing phase differences between signals at the receiver resulting in a phenomenon called: absorption baffling fading skip % ans 3 %QUESTION 15 #28.15 The distance from the far end of the ground wave to the nearest point where the sky wave returns to the earth is called the: skip distance radiation distance skip angle skip zone % ans 4 %QUESTION 16 #28.16 High Frequency long-distance propagation is most dependent on: ionospheric reflection tropospheric reflection ground reflection inverted reflection % ans 1 %QUESTION 17 #28.17 The layer of the ionosphere mainly responsible for long distance communication is: C D E F % ans 4 %QUESTION 18 #28.18 The ionisation level of the ionosphere reaches its minimum: just after sunset just before sunrise at noon at midnight % ans 2 %QUESTION 19 #28.19 One of the ionospheric layers splits into two parts during the day called: A & B D1 & D2 E1 & E2 F1 & F2 % ans 4 %QUESTION 20 #28.20 Signal fadeouts resulting from an 'ionospheric storm' or 'sudden ionospheric disturbance' are usually attributed to: heating of the ionised layers over-use of the signal path insufficient transmitted power solar flare activity % ans 4 %QUESTION 21 #28.21 The 80 metre band is useful for working: in the summer at midday during high sunspot activity long distance during daylight hours when absorption is not significant all points on the earth's surface up to several thousand kilometres in darkness but atmospheric and man-made noises tend to be high % ans 4 %QUESTION 22 #28.22 The skip distance of radio signals is determined by the: type of transmitting antenna used power fed to the final amplifier of the transmitter only the angle of radiation from the antenna both the height of the ionosphere and the angle of radiation from the antenna % ans 4 %QUESTION 23 #28.23 Three recognised layers of the ionosphere that affect radio propagation are: A, E, F B, D, E C, E, F D, E, F % ans 4 %QUESTION 24 #28.24 Propagation on 80 metres during the summer daylight hours is limited to relatively short distances because of high absorption in the D layer the disappearance of the E layer poor refraction by the F layer pollution in the T layer % ans 1 %QUESTION 25 #28.25 The distance from the transmitter to the nearest point where the sky wave returns to the earth is called the: angle of radiation maximum usable frequency skip distance skip zone % ans 3 %QUESTION 26 #28.26 A variation in received signal strength caused by slowly changing differences in path lengths is called: absorption fading fluctuation path loss % ans 2 %QUESTION 27 #28.27 VHF and UHF bands are frequently used for satellite communication because: waves at these frequencies travel to and from the satellite relatively unaffected by the ionosphere the Doppler frequency change caused by satellite motion is much less than at HF satellites move too fast for HF waves to follow the Doppler effect would cause HF waves to be shifted into the VHF and UHF bands. % ans 1 %QUESTION 28 #28.28 The 'critical frequency' is defined as the: highest frequency to which your transmitter can be tuned lowest frequency which is reflected back to earth at vertical incidence minimum usable frequency highest frequency which will be reflected back to earth at vertical incidence % ans 4 %QUESTION 29 #28.29 The speed of a radio wave: varies indirectly to the frequency is the same as the speed of light is infinite in space is always less than half the speed of light % ans 2 %QUESTION 30 #28.30 The MUF for a given radio path is the: mean of the maximum and minimum usable frequencies maximum usable frequency minimum usable frequency mandatory usable frequency % ans 2 %QUESTION 31 #28.31 The position of the E layer in the ionosphere is: above the F layer below the F layer below the D layer sporadic % ans 2 %QUESTION 32 #28.32 A distant amplitude-modulated station is heard quite loudly but the modulation is at times severely distorted. A similar local station is not affected. The probable cause of this is: transmitter malfunction selective fading a sudden ionospheric disturbance front end overload % ans 2 %QUESTION 33 #28.33 Skip distance is a term associated with signals through the ionosphere. Skip effects are due to: reflection and refraction from the ionosphere selective fading of local signals high gain antennas being used local cloud cover % ans 1 %QUESTION 34 #28.34 The type of atmospheric layers which will best return signals to earth are: oxidised layers heavy cloud layers ionised layers sun spot layers % ans 3 %QUESTION 35 #28.35 The ionosphere: is a magnetised belt around the earth consists of magnetised particles around the earth is formed from layers of ionised gases around the earth is a spherical belt of solar radiation around the earth % ans 3 %QUESTION 36 #28.36 The skip distance of a sky wave will be greatest when the: ionosphere is most densely ionised signal given out is strongest angle of radiation is smallest polarisation is vertical % ans 3 %QUESTION 37 #28.37 If the height of the reflecting layer of the ionosphere increases, the skip distance of a high frequency transmission: stays the same decreases varies regularly becomes greater % ans 4 %QUESTION 38 #28.38 If the frequency of a transmitted signal is so high that we no longer receive a reflection from the ionosphere, the signal frequency is above the: speed of light sun spot frequency skip distance maximum usable frequency % ans 4 %QUESTION 39 #28.39 A 'line of sight' transmission between two stations uses mainly the: ionosphere troposphere sky wave ground wave % ans 4 %QUESTION 40 #28.40 The distance travelled by ground waves in air: is the same for all frequencies is less at higher frequencies is more at higher frequencies depends on the maximum usable frequency % ans 2 %QUESTION 41 #28.41 The radio wave from the transmitter to the ionosphere and back to earth is correctly known as the: sky wave skip wave surface wave F layer % ans 1 %QUESTION 42 #28.42 Reception of high frequency radio waves beyond 4000 km normally occurs by the: ground wave skip wave surface wave sky wave % ans 4 %QUESTION 43 #28.43 A 28 MHz radio signal is more likely to be heard over great distances: if the transmitter power is reduced during daylight hours only during the night at full moon % ans 2 %QUESTION 44 #28.44 The number of high frequency bands open to long distance communication at any time depends on: the highest frequency at which ionospheric reflection can occur the number of frequencies the receiver can tune the power being radiated by the transmitting station the height of the transmitting antenna % ans 1 %QUESTION 45 #28.45 Regular changes in the ionosphere occur approximately every 11: days months years centuries % ans 3 %QUESTION 46 #28.46 When a HF transmitted radio signal reaches a receiver, small changes in the ionosphere can cause: consistently stronger signals a change in the ground wave signal variations in signal strength consistently weaker signals % ans 3 %QUESTION 47 #28.47 The usual effect of ionospheric storms is to: increase the maximum usable frequency cause a fade-out of sky-wave signals produce extreme weather changes prevent communications by ground wave % ans 2 %QUESTION 48 #28.48 Changes in received signal strength when sky wave propagation is used are called: ground wave losses modulation losses fading sunspots % ans 3 %QUESTION 49 #28.49 Although high frequency signals may be received from a distant station by a sky wave at a certain time, it may not be possible to hear them an hour later. This may be due to: changes in the ionosphere shading of the earth by clouds changes in atmospheric temperature absorption of the ground wave signal % ans 1 %QUESTION 50 #28.50 VHF or UHF signals transmitted towards a tall building are often received at a more distant point in another direction because: these waves are easily bent by the ionosphere these waves are easily reflected by objects in their path you can never tell in which direction a wave is travelling tall buildings have elevators % ans 2