Radio Navigation Flashcards
Speed of light
300,000 km/s
Relationship between frequency and wavelength
c = f x lambda
c = speed of light
f = frequency
lambda = wavelength
Radio frequency spectrum
Attenuation
Reduction in power of a radio wave.
Atmospheric attenuation is due to dust and items in the atmosphere, surface attenuation changes over different surfaces (ice caps and poles worst, sea the best).
Space waves
- Frequencies that use it
Line of Sight waves
Used in VHF (and higher freq)
Surface waves (aka ground waves)
Waves following curvature of the earth due to diffraction and attenuation.
Strongest for low frequencies (MF and above)
Skywaves
- time of day
Waves that are reflected back from the ionosphere, strongest in day (due to solar radiation).
Fading
Interference of ground and sky waves
Skip zone
HF skywaves bounce back around 600NM to 1200NM away, whilst ground waves (space & surface) only 150NM, so there is a gap in the middle where no signal is received, called the skip zone or dead zone.
Skip DISTANCE is distance from transmitter to skywave landing point.
Ionospheric refraction of different frequencies
- VHF
- HF
- LF/MF
VHF - Not refracted
HF - Refracted a bit so get a skip zone, thus used for long distance comms
LF/MF - Refracted a lot so ground waves interfere with sky waves
Propagation of:
VHF
MF
VHF: Space waves
MF: Ground & Sky waves (thus subject to fading)
Civilian VHF range
118MHz to 137 MHz
Q codes
QDM: Magnetic TO
QTE: True FROM
QDR: Magnetic FROM
QUJ: True TO
Relative Bearing Indicator (RBI)
AKA radio compass
Simply shows relative direction of an NDB signal.
Radio Magnetic Indicator (RMI)
Similar to moving card ADF but with compass card automatically turned (usually by remote compass). This is what we have on modern aircraft, possible as part of EFIS (on the ND).
Often have two arrows for two signals and can feed from ADF or VOR.
VOR Frequencies
108MHz to 117.975MHz (VHF)
108 to 112 MHz shared with ILS so 0.2MHz spacing (108.0, 108.2) and terminal VORs only (generally)
112 to 117.975 MHz at 0.05 MHz spacing more likely for en-route VORs.
Omni-bearing indicator (OBI)
AKA CDI
VOR indicator which you dial in to a radial and see deviation marks and TO/FROM indicator.
Full scale deviation is 10 degrees (can have 5 dots of 2 dots).
Can have glidescope info which gives vertical and horizontal deviation lines.
Instrument has no concept of heading or direction (i.e. compass card)!
Horizontal Situation Indicator (HSI)
Similar to RMI, both have rotating cards driven by remote compass.
Where RMI simply points to VOR, HSI has a selected radial and then deviation marks (and to/from).
Procedure turn (2)
Head out from NDB/VOR for fixed time period or until a fix position.
Turn off 45 degrees and straight for a period of time (about 1 min) then commence turning circle (in opposite direction) to regain radial.
OR turn off 80 degrees then immediate 260 degree turn in opposite direction to regain radial.
ILS localiser frequencies
108MHz to 111.95MHz
Odd 0.1MHz, and 0.05MHz above
e.g. 108.1, 108.15, 108.3, 108.35
[108.2 is VOR, 108.25 not allocated]
AMPLITUDE modulated (otherwise the two frequencies on each side wouldn’t work!)
ILS Ident
1020 Hz tone amplitude modulated onto the carrier wave.
Usually 3 letter code, can have “I” infront to identify as ILS
Deviation markings for ILS
Displayed on OBI or HSI
Localiser deviation is 2.5 deg each side (a quarter of VOR deviation).
Glidescope deviation is 0.75deg each side (so 0.15deg per dot) [0.7?]
ILS functionality
- Beam modulation
- How centreline is identified
ILS sends out 2 beams, a 90Hz AMPLITUDE modulated “yellow” beam to left of track, a 150Hz modulated “blue” beam to the right.
Indicator measures “Depth of modulation” to assess which it gets more of, with DDM = 0 (or equal DDM) being the “green” centre line.
[Glidepath uses yellow 90Hz above and blue 150Hz below glidepath]
[Change in depth of modulation linear with angular displacement]
ILS coverage
Up to 25NM away - 10 degrees either side
Up to 17NM away - 35 degrees either side