01 Basic Radio Propagation Theory Flashcards
ATPL RADIO
Concerning the wave propagation in the ionosphere, we can divide the vertical extent of the ionosphere into three layers. Those three layers are:
D, E and F layers and their depth varies with time.
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The D, E and F layers of the ionosphere are the layers responsible for diffraction of radio waves turning them into sky waves. Their depth is depending on solar activity and will therefore vary with time.
Reflection from ionospheric layers is used in the following radio frequencies:
HF
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Transmissions in the high frequency (HF) band contain sky waves that are refracted by the ionosphere back towards the Earth, in addition to a surface wave part, i.e. a part that will follow the surface of the Earth. Very low frequency (VLF) transmissions will contain mainly surface waves. Very high frequency (VHF) and ultra-high frequencies (UHF) contain space waves propagating through the ionosphere.
Single Side Band (SSB) is used:
In HF two-way communication.
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Single sideband (SSB) is used in HF transmissions as a mean of reducing the transmitter power while keeping the range and reducing the bandwidth needed for the transmission (i.e. more available frequencies for a given frequency band).
What is the function of pulse P2 in modes A/C during interrogation?
To suppress responses from aircraft which are located in the direction of the side lobes of the interrogation antenna.
A reason that GPS satellites use helical antennae is:
because the signal has a circular polarization.
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The helical antenna is used for GPS receivers as it is the most suitable antenna for receiving the circular polarised signals from the satellites as the relative orientation of the transmitter (satellite) and receiver (aircraft) is constantly varying.
The superposition of two electromagnetic waves of the same or nearly the same frequency is called?
interference
An amplitude modulation is shown in figure:
a
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Amplitude modulation will have a uniform central carrier wave with varying amplitude (or wave shaped upper and lower part).
A DME that has difficulty obtaining a “lock-on”:
NOTE: PRF = pulse recurrence frequency, PPS = pulses per second
stays in search mode but reduces PRF to max. 60 PPS after 15000 pulse pairs have been transmitted
The skip distance (skip zone) of HF-transmission will increase with:
Higher frequency and higher position of the reflecting ionospheric layer
Modulation is:
Addition of a low frequency signal (tone, voice) onto high frequency carrier wave.
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Modulation is the process of superimposing one wave onto another. For radio transmissions this is superimposing the low frequency voice signal (speech or tone) onto the higher frequency carrier wave.
MF (Medium Frequency) waves appear in the frequency spectrum:
300 kHz - 3000 kHz
HF (High Frequency) waves appear in the frequency spectrum:
3 MHz - 30 MHz
The wavelength of a radio transmitted on frequency 121.95 MHz is:
2.46 m
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Wavelength (?) = speed of light (c) ÷ frequency (f) = 300 000 000 m/s ÷ 121 950 000 Hz = 2.46 m
In accordance with the International Telecommunication Union (ITU) a radio signal can be classified by three symbols. The first symbol indicates: (eg A1A)
type of modulation of the main carrier.
To establish and maintain effective HF communications the frequency used at a given range:
Should be decreased at night.
The wavelength of a radio signal transmitted at the frequency of 75 MHz is:
4 m
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Wavelength = Speed of Light ÷ Frequency
VHF (Very High Frequency) waves appear in the frequency spectrum:
30 MHz - 300 MHz
What is the Doppler effect with reference to radio signals?
It is the shift in frequency of a radio wave due to the relative movement between transmitter and receiver.
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Doppler shift is the change in frequency that occur as a result of relative movement between the transmitter and the receiver.
If the transmitter travel towards the receiver the frequency will increase and if the transmitter is travelling away from the receiver the frequency is decreasing.
An electromagnetic wave consists of an oscillating electric field (E) and an oscillating magnetic field (H). Which statement is correct?
the E and H fields are perpendicular to each other.
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An electromagnetic wave consist of two components, the electrical field (E field) and the magnetic field (H field). During propagation these two fields will be perpendicular to each other.
An electromagnetic wave has two types of energy field:
An E electrical field and an H magnetic field.
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An electromagnetic wave has two types of energy field, an E electrical field and an H magnetic field.
What is necessary to enable an antenna to transmit an electromagnetic wave?
The antenna has to be fed with alternating current of high frequency.
A loop antenna is commonly used in:
ADF receivers.
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The loop antenna gives the ADF its directional properties (although the sense antenna is also required in order to remove ambiguity to the direction).
The skip distance of HF-transmission will increase with:
higher frequency and higher position of the reflecting ionospheric layer.
How is amplitude modulation accomplished?
The information is added onto the carrier wave by altering the amplitude of the carrier wave.
The wavelength of a radio signal transmitted at the frequency of 3 GHz is:
10 cm.
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The wavelength of a radio signal transmitted at the frequency of 3 GHz is 10 cm.
Phase modulation:
is a modulation form used in GPS where the phase of the carrier wave is reversed.
The polarisation of an electromagnetic wave describes:
the orientation of the plane of oscillation of the electrical component of the wave with regard to its direction of propagation.
From which physical phenomenon do skywaves originate?
refraction
The phenomenon when a wave bends when it passes around an impenetrable obstacle is:
diffraction
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Diffraction is a term for the bending of waves that occur around obstacles.
An NDB transmits on 427 kHz, the corresponding wavelength is:
702.5 m
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Wavelength (?) = speed of light (c) ÷ frequency (f) = 300 000 000 m/s ÷ 427 000 Hz = 702.6 m
What is the wavelength of an NDB transmitting on 375 kHz?
800 m
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The calculation for wavelength is: Wavelength (λ) = speed of light (c) ÷ frequency (f) = 300 000 000 m/s ÷ 375 000 Hz = 800 m
What does the term ‘fading’ mean?
The interference of the ground wave and the sky wave.
Wavelength of frequency 117.95 MHz is:
2.54m
The term Doppler shift refers to:
The change in frequency measured at the receiver.
Which statement is true?
The lower the frequency the greater the ionospheric attenuation.
SHF (Super High Frequency) waves appear in the frequency spectrum:
3 GHz - 30 GHz
Given a wire fed with alternating current and a second wire parallel to, but remote from it. The results will be:
the first wire will radiate electromagnetic waves into space and alternating current will be induced in the second wire.
The super position of two radio waves of the same or nearly the same frequency is called:
Interference.
Due to ‘Doppler’ effect an apparent decrease in the transmitted frequency, which is proportional to the transmitter’s velocity, will occur when:
the transmitter moves away from the receiver.
Which of the following lists only includes directional antennae?
Loop antenna, parabolic antenna, slotted planar antenna, helical antenna.
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Directional antennas are the loop antenna, parabolic antenna, slotted planar array antenna and the helical antenna. The dipole and sense antenna are both omnidirectional.
With regard to radio waves propagation, a cycle is defined as:
a complete series of values of a periodical process.
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For the propagation of radio waves, one cycle is defined as a complete series of values of a periodic process.
VLF (Very Low Frequency) waves appear in the frequency spectrum:
3 kHz - 30 KHz
Single-sideband modulation (SSB) is a modulation technique where only one sideband is transmitted, SSB is used for:
HF Volmet and HF two-way communication.
Refer to the annex.
Which number in the picture indicates the skip distance?
4
The frequency which corresponds to a wavelength of 3 km is:
100 KHz
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Frequency = Speed of Light ÷ Wavelength
The term ‘phase difference’ can be defined as:
the angular difference between the corresponding points of two cycles of equal wavelength, measurable in degrees.
Modulation is:
the addition of information onto a radio wave during transmission.
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.
An AC will be induced:
In a wire, parallel to the wire fed with a AC, but remote from it.
“Hertz” (Hz) unit is defined as:
the number of oscillations per second of an electromagnetic wave.
The Doppler Navigation System is based on:
radar principles using frequency shift
The advantage of the use of slotted antennas in modern radar technology is to:
virtually eliminate lateral lobes and as a consequence concentrate more energy in the main beam
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.
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.
Refraction of an electro-magnetic radiation is:
The bending of its propagation path as it passes over or through areas of different conductivity.
A VOR and an NDB are co-located. An aircraft equipped with an RMI is flying away from the beacons on a radial of 090º through an area where magnetic variation is changing rapidly. Which statement is correct?
The ADF needle moves, the VOR needle does not
Due to the ‘Doppler’ effect, an apparent increase in the transmitted frequency will occur when:
the transmitter and receiver move towards each other.
The transmission band used by INMARSAT is:
UHF
The amplitude of a wave or of an oscillation is:
its maximum deflection.
Diffraction of an RF signal is a displacement of its propagation path due to:
Passing over obstacles with dimensions close to the wavelength.
The term “keying” means?
interrupting the carrier wave to break it into dots and dashes.
The term ‘phase’ can be defined as:
the fraction of one wavelength expressed in degrees from 000° to 360°
Which of the following is true with reference to frequency of a radio wave?
frequency is the number of cycles in one second in a radio wave expressed in Hertz (Hz).
In which one of the following circumstances is ground direction finding (VDF) likely to be used to fix an aircraft’s position?
When using the emergency VHF frequency 121.5 MHz
A radio signal loses strength as range from the transmitter increases, this is called:
attenuation
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As the range from the transmitter is increasing the energy of the signal will decrease steadily during propagation and this process is called attenuation.
The wavelength of a non-directional beacon (NDB) at a frequency of 300 kHz is:
1000 metres.
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Wavelength (λ) = speed of light (c) ÷ frequency (f) = 300 000 000 m/s ÷ 300 000 Hz = 1000 m
The frequency which corresponds to a wavelength of 12 cm is:
2500 MHz.
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Frequency (f) = speed of light (c) ÷ wavelength (?) = 300 000 000 m/s ÷ 0.12 m = 2 500 000 000 Hz = 2 500 MHz
What is the approximate speed of a radio wave?
300 000 km/s
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The approximate speed of a radio wave is 300 000 km/s.
When a transmitter is moving towards a receiver, the correct description of the Doppler effect is:
There is a decrease in apparent wavelength which is dependent on the transmitter velocity.
Which of the following statements is correct in respect of an RF signal:
The electrical component of the signal is parallel to the antenna.
In aviation electronic systems the so-called Doppler principle may be used in:
VOR, GPS and MTI and the turbulence mode of AWR.
LF (low frequency) waves appear in the frequency spectrum:
30 kHz - 300 kHz
The electromagnetic waves refracted from the E and F layers of the ionosphere are called:
sky waves
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Sky waves are refracted from the E and F layers of the ionosphere.
Diffraction is the process by which:
radio waves travel over and around obstacles.
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Diffraction is a term for the bending of waves that occur around obstacles.
In its basic type, a dipole antenna adapted for a frequency of 110 MHz will have a wire length of:
136 cm
An electromagnetic wave consists of an oscillating electric field E and an oscillating magnetic field H. Their propagation speed is:
the speed of light.
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The propagation speed for an electromagnetic wave consisting of an oscillating electric and magnetic field is the speed of light.
The wavelength of a radio signal transmitted at the frequency 118.7 MHz is:
2.53 m.
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Wavelength (λ) = speed of light (c) ÷ frequency (f) = 300 000 000 m/s ÷ 118 700 000 Hz = 2.53 m
The frequency which corresponds to a wavelength of 8.25 m is:
36.36 MHz
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Frequency = Speed of Light ÷ Wavelength
HF radio waves travel:
during daytime and night time as sky waves and the range of the ground wave is very small.
Using the attached image:
In the diagram, which refers to the propagation of HF radio waves, the letters A, B, C, D and E correctly represent:
A Sky wave B Dead space C Ground wave D Skip dist E Critical angle
EHF (Extremely High Frequency) waves appear in the frequency spectrum:
30 GHz - 300 GHz
The VHF frequency band has a wavelength limit of:
10 m to 1 m
Radio waves in the VHF and higher frequency bands propagate mainly as:
space waves.
An apparent increase in the transmitted frequency which is proportional to the transmitter velocity will occur when:
the transmitter moves towards the receiver
119.70 MHz is a typical frequency for?
Approach control
With regard to types of transmission, which of the following statements is true:
Continuous Wave transmission can be either frequency or amplitude modulated
What does ADF stand for?
Automatic Direction Finder
For what is pulse modulation used?
Radar
Which of the following terms describes the maximum deflection in an oscillation?
amplitude
The term “wavelength” can be defined as:
The distance travelled by a radio wave during one cycle of transmission.
What is the approximate speed of a radio wave?
162 000 NM/s
The process by which radio wave energy is taken up by the atmosphere is called?
absorption
The phenomenon of a change in direction of an EM-wave occurring due to a change in its speed is called?
refraction.
Which statement about VHF/UHF frequency propagation 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.
Skip distance is the:
range from the transmitter to the first sky wave
In accordance with the ITU (International Telecommunication Union) a radio signal may be classified by three symbols. The First symbol indicates (e.g. A1A):
Type of modulation of the main carrier.
The simplest type of antenna construction is a:
dipole antenna which is a wire of length equal to one half of the wavelength.
A radio wave with a horizontal magnetic component would be best received by a ………… dipole antenna.
Vertical
Radio waves travel at:
the speed of light.
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Radio waves propagate at the speed of light, 300 000 km/s (or 300 000 000 m/s).
UHF (Ultra High Frequency) waves appear in the frequency spectrum:
300 MHz - 3000 MHz
Considering LF and MF, the phenomenon called ‘fading’ can occur:
from the beginning of evening civil twilight until the end of morning civil twilight.
An aircraft at 6 400 FT will be able to receive a VOR groundstation at 100 FT above MSL at an approximate maximum range of:
113 NM
The phenomenon of a change in direction of a radio-wave occurring at an interface between two different media, so that the wave returns into the medium from which it originated, is called?
reflection.
A horizontally polarized electromagnetic wave:
Has the E field horizontal.
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.
