Exam revision Flashcards
What is a sine wave?
Electromagnetic wave shape
What is a wave length?
Length of a single wave
What is the frequency of the radio?
Number of cycles passing a given point in a second
What is amplitude?
Displacement of wave peaks of troughs from the middle value
What is amplitude used for?
Measure the strength of signal
greater the amplitude, the greater the strength
What are sidebands?
Additional frequencies which occur whenever a carrier is modulated by frequency lower than itself. In modulation, the sidebands carry the intelligence
What is a ground wave?
Part of energy from non directional antenna radio frequency that travels along earth surface
What path does ground wave follow?
Roughly parallel to earth surface
What can ground waves be broken into?
Direct (follow line from transmitter to receiver)
Surface (follow contour and curvature of earth)
Sky (refracted and reflected by ionosphere
How is the range of surface waves determined?
Rate at which signal is absorbed and weakened by surface over which it is travelling (aka attenuation)
What is the THEORETIC RANGE of VHF Signals?
Square root of (1.5 x receiver altitude in feet)
Is water a good transmission surface for ground waves?
Yes
Why do night time rated coverage of NDBs drop?
Increased sky wave interference with higher ionosphere
What is skip distance?
Distance from transmitter to point where signal returns to earth after reflecting off ionosphere
What does build up of static electricity do to radio signal?
Affects negatively
What frequency does VOR operate in?
112.00 to 118.00 VHF band
What does a VOR station produce?
30Hz reference and 30 Hz variable phase
How does VOR work with aircraft?
- VOR produces radial pattern signals
- Nav receiver compares phase of signals to figure what radial its on
- Compares computer radial to radial pilot selects with OBS and deflects CDI to indicate variation between desired and actual
How is the phase orientated with VOR?
Magnetic north
What are the errors for VOR? What are the degree of difference?
Airborne equipment error (+/- 2 degrees)
Vertical polarisation error (when VOR antenna is banked out of horizon plane)
Ground station error (transmission equipment (+/- 2 degrees)
Aggregate error (total of all errors (+/- 5 degrees)
Site/terrain error (bending or scalloping of signals due to obstacles close to site (+/- 2 degrees)
What is a doppler VOR?
Transmits FM instead of AM to almost eliminate site error effects
What does NDB do?
Transmits non directional carrier signal with audio id for morse code
What range is NDB?
MF
What instrument is in the aircraft for NDB and how does it work?
ADF
Combines signal received from two antenna and gives relative bearing to/from station OR may be overlayed on RMI to give magnetic track to/from