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Flashcards
In aviation electronic system the so-called Doppler principle may be used in:
Diffraction is the process by which
radio wave travel over and around obstacles
The skip distance (Skip zone) of HF-transmission will increase with:
higher frequency and higher position of the reflecting ionospheric layer
The term Doppler shift refers to:
the change in frequency measured at the receiver
Reflection from inospheric layers is used in teh following radio frequencies.
HF
When a transmitter is moving towards a receiver, the correct descpription of Doppler effect is:
there is a decrease in apparent wavelength which is dependent on the transmitter velocity
Doppler effect?
Apparent increase of a frequency = transmitter is moving xy the receiver
Apparent decrease of a frequency = transmitter is moving xy the receiver
Apparent increase of a frequency = transmitter is moving towards the receiver
Apparent decrease of a frequency = transmitter is moving away from teh receiver
Absorption of radio wave energy
Absorption of radio wave energy is the way in which the energy is taken up by the ground or atmosphere (rain, hail, ionosphere etc.) the electromagnetic energy is then transformed to other forms of energy for example into heat
Attenuation
as any radio waves travels away from the transmitter it becomes weaker (looses power) or is attenuated. This results from the RF signal inducing currents into the surface of the earth. A good conducting surface, such as water, will give the signal back with little loss of energy. A poor conductive surface, such as a hot desert, will simply absorb teh energy. The degree of surface attenuation also varies diectly with frequency.
Interference
is a phenoenon in which two waves superimpose to form a resultant wave of greater or lower amplitude. Interference usually refers to the interaction of waves that are correlated or coherent wich wach other., either because they come from the same source or because they have the same or nearly the same frequency
Reflection
is the change in direction of a radio wave at an interference between two different media so that the radio wave returns into the media from which it originated. Reflection is observed with many types of electromagnetic wave and is important for radio transmissions VHF and radar
Redraction
is the proceeded by which a signal's propagation path bends and the signal changes its speed as it moves from one to another (different density) ==> Coastal;Atmospheric or Ionospheric
Which of teh following terms describes the maxiumim delction in an oscillation?
The term Modulation means:
Addition of a low frequency signal (tone, voice) onto high frequency carrier wave
Define the term Modulation?
teh addition of information onto a radio wave during transmission
The term Keying means:
interrupting the carrier wave to break it into dots and dashes
Single Sideband modulation SSB is a modulation technique where only one sideband is transmitted, SSB is used for
HF Volmet and HF tow-way communication
With regard to ryped of transmission, which of teh following statement is true:
Phase modulation
is a modulation form used in GPS where the phase of the carrier wave is reversed ==> for the ranging codes and navigation messages to travel from the satellite to the receiver, the y must be modulated onto a carrier frequency, by varying the phase
In order to obtain an ADF bearing on a system using sense and loop aerials, the:?
WHen has the Interference from other NDBs the greatest effect on ADF accuracy?
particularly at night
Mountain effect, occuring for instance with NDBs is caused by what physical phenomenon
reflection
Rang and Power wie stehen diese zusammen?
\(Range = {\sqrt{Power} }\)
Is the aircraft height limitting for the reception of signals from the NDB
Aircraft height is not limiting for the reception of signals from the NDB
En route sind was für NDB?
Long Range (more than 50NM), LF band, N0N and A1A
Locators?
Final approach, 10-25 NM, N0N A2A
Jolding, Approach, En-route NDB
low power => up to 50 NM, 200W, N0N A2A
Range over Water and land (NDB)?
Range over water = 3x \( {\sqrt{Power} } \)
Range over land = 2x \( {\sqrt{Power} } \)
==> for the range to be doubled, the transmitting power must be multipled by 4
NDB transmits a signal pattern in the horizontal plane which is:
omnidirectional
Concerning ADF and NDB ?
NDB is a ground equipment and ADF is an airborne equipment
the ADF indication in the cockpit is a:
relative bearing on a fixed card indicator
What actually happens in the ADF receiver when the BFO position is selected?
The BFO circuit imposes a tone onto the carrier wave to make the NDB's ident audible
With regard to the monitoring of a VOR. The monitor will remove the identification or switch off the VOR transmitter if there is a change of measured bearing greater than
1 Grad
If an aircraft flies along a VOR radial it will follow a
great circle track
Two aircraft are located on the ame radial but at (arbirary) different distances from a VOR station. Which statement is true?
Two aircraft are located on (arbitrary) different radials bu at equal distances from a VOR-station. Which statement is true?
Which of the following statements concerning the variable, or directional, signal of a conventional VOR is correct
VOR kann gestört werden durch?
a) interference from other transmitters
b) scalopping
c) uneven propagation over irregular ground surfaces
==> Failure of teh VOR station to stay within required limits can cause removal of identification and the navigation components from the carrier wave to cease
The principle used in VOR bearing measurement is:
measures the phase difference
Doppler VOR ?n
The REF signal of the DVOR is amplitude modulated, while she VAR (bearing) signal is frequency modulated => the doppler effect is created by letting the VAR signal be electronically rotated => this results in an effective FM of 30 Hz
==> the Doppler effect us used to create a signal which is received by the aircraft's VOR-receiver as a frequency modulated signal
