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.