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Flashcards
LF
30-300 kHz ==> 1-10 km ==> ground waves => NDB
MF
Medium Frequency 300 kHz - 3 MHz ==> 100m - 1 km ==> ground waves => NDB
HF
3-30 MHz ==> 10-100 m ==> Sky waves => HF Radiotelefony
VHF
30-300 MHz ==> 1-10 m ==> Direct Waves => VHF, VDF, VR ILS, Marker Beacons
UHF
300-3000 MHz ==> 1-100 cm ==> Direct Waves => DME, ILS Glideslope
Oscillation
A cycle is a periodically changing signal = called oscillation
The amplitude of an oscillation corresponds to the:
max. signal strength
Which is the correct definition of theunit Hertz
The number of oscillation per second
Which of the definition below describes the components of a radio waves correctly?
Modulation/ Demodulation
packing and unpacking of information onto the radio waves is called modulation/demodulation =>
baseband
teh frequency spectrum of the information
After modulation process, teh nformation appears on both sides next to the carrier freuquency (HF) ==> how called
LSB = Lower side band => the part below the carrier frequency USB=Upper side band = the part above the carrier frequency
The notification uses three symbols; They are?
First symbol: Type of modulation ( amplitude or frequency)
Second symbol: nature of the signal (analog or digital)
Third symbol: nature of the information
A1A
switched on/off => simplicity and limited transport => used together with N0N modulation for NDB
A2A
a single morse audio tone => advantage: the simplicity receiver design => Disadvantage: broader switch
A3E
the carrier is modulated by speech => greater amount of information transferred per time => disadvantage: the broader bandwidth ==> VHF Communications
SSB is used for
Single Side band Modulation is used for HF communication
SSB
Single Side Band Modulation => the information packed onto the carrier is available through each side band ===> the necessary bandwidth can be reduced ====> Used for HF communication
FM for what
Frequency Modulation ==> F3E => For FM-Radio ==> robustness against disturbance
Fm in aviation only for
transort navigation signal (VOR)
Phase modulation for what
GPS
Pulse modulation What and for what?
the carrier is pulsed first => radar systems transmit a short pulse of radio waves ==> RADAR System
Antenna
which transduce the electrical signals of the radio into electromagnetic fields and vice versa
Electrical fiel (E) exist between.......
Electrical current (I) produces a ....
Electrical fiel (E) exist between different eectrical charges
Electrical current (I) produces a magnetic field (H)
electromagnetic induction
change of magnetic flux produces a electromagnetic force = voltage ==> electric current will be induced in any closed electric circuit when exposed to an altering or changing magnetic field
the mechanical length of the antenna need to be
half the AC's wavelength => the simplest form of an antenna is a wire with a mechanical length corresponding to half a wavelength
the radiation process
how to separate the field energy from the antenna and send it into space ==> the electrical field and the magnetic field are phased shifted by 90 degrees at the antenna = >near field
When the distance to the antenna increases, the phase difference disappears and both fields are
When the distance to the antenna increases, the phase difference disappears and both fields are in-phase
Which is teh normal antenna design?
the dipole antenna => with a mechanical length of about half the wavelength of the radio wave to be transmittd
impedance
is the resistance at the feeding point of the antenna => installed in order to transport the energy from the transmitter to the antenna as efficiency as possible
voltage standing wave ratio
a measure for the amount of reflected power of the antenna => depends on the radio frequency fed to the antenna and its mechanical dimension
polarisation of the antenna
indicates the orientation in space of the electrical field component of the transmitted radio wave
polarisation of the antenna: 3 arten
1. horizontal polarisation: VOR
2. vertical polarisation: Communication
3. Circular polarisation: radio wave where the electromagnetic fields rorare in space while propagating (Verbreiten): satellite and raddar
radiation pattern of the antenna
describes in which direction the electromagnetic energy is radiated => radiation pattern of a dipole antenna develops the amx. level of radiation in the middle part of the wire and zero in the direction of the wire = 8-shaped pattern
4 weitere Arten radar
0. Dipole Antenna
1. Loop antenna for ADF => hot loop antenna
2. Parabolic antenna
3. slotted planar array antenna
4. helical antenna
loop antenna
a big cir => magnetic antenna => 8-shaped => LF and MF band ==> ADF = hot loop antenna!
parabolic antenna
a flash lamp => the electromagnetic energy from so--called horn in the centre f the antenna towards the reflector => the reflector concentrates the energy and radiates it in one direction
Helical Antenna
a special type of antenna used for circular polarization => it forces the electromagnetic energy to circle around its centre while building up radiation ==> combination with satellite
At which speed do radio waves propagate (ausbreiten)
Speed of light, the relative speed between transmitter and receiver is irrelevant
propagate
ausbreiten
