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Subelement ZLH

From Transmitter to Receiver

Section ZLH28

Propagation

A 'skip zone' is

  • the distance between the antenna and where the refracted wave first returns to earth
  • Correct Answer
    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
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The medium which reflects high frequency radio waves back to the earth's surface is called the

  • biosphere
  • stratosphere
  • Correct Answer
    ionosphere
  • troposphere
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The highest frequency that will be reflected back to the earth at any given time is known as the

  • UHF
  • Correct Answer
    MUF
  • OWF
  • LUF
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All communications frequencies throughout the spectrum are affected in varying degrees by the

  • atmospheric conditions
  • ionosphere
  • aurora borealis
  • Correct Answer
    sun
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Solar cycles have an average length of

  • 1 year
  • 3 years
  • 6 years
  • Correct Answer
    11 years
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The 'skywave' is another name for the

  • Correct Answer
    ionospheric wave
  • tropospheric wave
  • ground wave
  • inverted wave
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The polarisation of an electromagnetic wave is defined by the direction of

  • the H field
  • propagation
  • Correct Answer
    the E field
  • the receiving antenna
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That portion of HF radiation which is directly affected by the surface of the earth is called

  • ionospheric wave
  • local field wave
  • Correct Answer
    ground wave
  • inverted wave
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Radio wave energy on frequencies below 4 MHz during daylight hours is almost completely absorbed by this ionospheric layer

  • C
  • Correct Answer
    D
  • E
  • F
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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
  • Correct Answer
    E
  • F
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Scattered patches of high ionisation developed seasonally at the height of one of the layers is called

  • Correct Answer
    sporadic-E
  • patchy
  • random reflectors
  • trans-equatorial ionisation
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For long distance propagation, the radiation angle of energy from the antenna should be

  • Correct Answer
    less than 30 degrees
  • more than 30 degrees but less than forty-five
  • more than 45 degrees but less than ninety
  • 90 degrees
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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
  • Correct Answer
    straight line
  • bent path via the ionosphere
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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
  • Correct Answer
    fading
  • skip
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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
  • Correct Answer
    skip zone
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High Frequency long-distance propagation is most dependent on

  • Correct Answer
    ionospheric reflection
  • tropospheric reflection
  • ground reflection
  • inverted reflection
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The layer of the ionosphere mainly responsible for long distance communication is

  • C
  • D
  • E
  • Correct Answer
    F
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The ionisation level of the ionosphere reaches its minimum

  • just after sunset
  • Correct Answer
    just before sunrise
  • at noon
  • at midnight
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One of the ionospheric layers splits into two parts during the day called

  • A & B
  • D1 & D2
  • E1 & E2
  • Correct Answer
    F1 & F2
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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
  • Correct Answer
    solar flare activity
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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
  • Correct Answer
    up to several thousand kilometres in darkness but atmospheric and man-made noises tend to be high
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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
  • Correct Answer
    both the height of the ionosphere and the angle of radiation from the antenna
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Three recognised layers of the ionosphere that affect radio propagation are

  • A, E, F
  • B, D, E
  • C, E, F
  • Correct Answer
    D, E, F
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Propagation on 80 metres during the summer daylight hours is limited to relatively short distances because of

  • Correct Answer
    high absorption in the D layer
  • the disappearance of the E layer
  • poor refraction by the F layer
  • pollution in the T layer

The D layer is the bottom layer of the ionosphere during the daylight. It absorbs medium and high frequency waves, 10 MHz and below.

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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
  • Correct Answer
    skip distance
  • skip zone
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A variation in received signal strength caused by slowly changing differences in path lengths is called

  • absorption
  • Correct Answer
    fading
  • fluctuation
  • path loss
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VHF and UHF bands are frequently used for satellite communication because

  • Correct Answer
    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.
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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
  • Correct Answer
    highest frequency which will be reflected back to earth at vertical incidence
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The speed of a radio wave

  • varies indirectly to the frequency
  • Correct Answer
    is the same as the speed of light
  • is infinite in space
  • is always less than half the speed of light
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The MUF for a given radio path is the

  • mean of the maximum and minimum usable frequencies
  • Correct Answer
    maximum usable frequency
  • minimum usable frequency
  • mandatory usable frequency
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The position of the E layer in the ionosphere is

  • above the F layer
  • Correct Answer
    below the F layer
  • below the D layer
  • sporadic
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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
  • Correct Answer
    selective fading
  • a sudden ionospheric disturbance
  • front end overload
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Skip distance is a term associated with signals through the ionosphere. Skip effects are due to

  • Correct Answer
    reflection and refraction from the ionosphere
  • selective fading of local signals
  • high gain antennas being used
  • local cloud cover
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The type of atmospheric layers which will best return signals to earth are

  • oxidised layers
  • heavy cloud layers
  • Correct Answer
    ionised layers
  • sun spot layers
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The ionosphere

  • is a magnetised belt around the earth
  • consists of magnetised particles around the earth
  • Correct Answer
    is formed from layers of ionised gases around the earth
  • is a spherical belt of solar radiation around the earth
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The skip distance of a sky wave will be greatest when the

  • ionosphere is most densely ionised
  • signal given out is strongest
  • Correct Answer
    angle of radiation is smallest
  • polarisation is vertical
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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
  • Correct Answer
    becomes greater
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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
  • Correct Answer
    maximum usable frequency
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A 'line of sight' transmission between two stations uses mainly the

  • ionosphere
  • troposphere
  • sky wave
  • Correct Answer
    ground wave
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The distance travelled by ground waves in air

  • is the same for all frequencies
  • Correct Answer
    is less at higher frequencies
  • is more at higher frequencies
  • depends on the maximum usable frequency
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The radio wave from the transmitter to the ionosphere and back to earth is correctly known as the

  • Correct Answer
    sky wave
  • skip wave
  • surface wave
  • F layer
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Reception of high frequency radio waves beyond 4000 km normally occurs by the

  • ground wave
  • skip wave
  • surface wave
  • Correct Answer
    sky wave
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A 28 MHz radio signal is more likely to be heard over great distances

  • if the transmitter power is reduced
  • Correct Answer
    during daylight hours
  • only during the night
  • at full moon
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The number of high frequency bands open to long distance communication at any time depends on

  • Correct Answer
    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
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Regular changes in the ionosphere occur approximately every 11

  • days
  • months
  • Correct Answer
    years
  • centuries
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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
  • Correct Answer
    variations in signal strength
  • consistently weaker signals
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The usual effect of ionospheric storms is to

  • increase the maximum usable frequency
  • Correct Answer
    cause a fade-out of sky-wave signals
  • produce extreme weather changes
  • prevent communications by ground wave
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Changes in received signal strength when sky wave propagation is used are called

  • ground wave losses
  • modulation losses
  • Correct Answer
    fading
  • sunspots
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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

  • Correct Answer
    changes in the ionosphere
  • shading of the earth by clouds
  • changes in atmospheric temperature
  • absorption of the ground wave signal
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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
  • Correct Answer
    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
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