Basics Transmission Flashcards
(36 cards)
What are transmissions
Electromagnetic waves propagating from a source
Can be caused by ac voltage / current through a wire
What happens if you put 2 wires next to each other
When wires are next to each other
What is the carrier wave
The number you dial into e.g. 119.875
Transport audio from
Transmitter to receiver
When does a transmission follow the curve of the earth
If it’s very long wavelength (VLF/ LF)
What is a Sky wave
MF / HF
Wave hits ionosphere which speeds up the top of the wave refracting it back down to earth
When is the ionosphere lowest
During the day the ionosphere is lower
Meaning the bounce is closer = can’t transmit a sky wave as far
Formula for line of sight range
Line of sight range = 1.23 x squareroot (height of transmitter in feet) + squareroot (height of airplane in feet)
What wavelength is skywave
MF / HF
What is VLF
3-30 KHZ
What is LF
30-300 KHZ
1000-9999m
Kilometric
What is MF
300-3000 KHZ
100-999m
Hectometric
What is HF
3-30 MHZ
10-99m
Decametric
What is VHF
30-300MHZ
1-9m
Metric
What is UHF
300-3000 MHZ
0.1 - 0.9m
Decimetric
What is SHF
3-30 GHZ
0.01-0.09m
Centimetric
What is modulation
Imposing audio onto carrier wave
What is AM
Amplitude modulation
What is FM
Frequency modulation
Does aviation use AM or FM
AM because it uses less frequency channels as FM requires +/- HZ either side of frequency
What are pulse waves used for
Digital
What is phase signal used for
GPS
What is omnidirectional antenna
Disturbs electromagnetic waves in every direction
What is a helical antenna used for
GPS
Sits near cg of aircraft so it doesn’t move much
Circular polarisation
What is the ideal length of an antenna
Wavelength
Can be 1/2 or 1/4
