Radio waves
is an electromagnetic transmission
Categories of radio waves
Low Frequency
High Frequency
Low frequency
Long Wavelength
Low Energy
Poor Quality
KHZ
1000 cycles of radio waves
High frequency
Short Wavelength
High Energy
Good Quality
MHZ
What frequency band limit is used during flight?
VHF - Very high frequency
VHF band limit
30-300 MHZ
VHF Characteristics
- Line of sight and short range. Greatly affected by the following
-Transmission power of both aircraft and ground station
-Height of transmitter and receiver
-Obstacles at or near the transmission site
-Obstructions between aircraft and ground station
Transponder modes
Mode A
Mode C
Transponder
a device that receives a radio signal
and sends out a signal in response
Mode A
sends out the Identification (Squawk) only
Mode C
sends out the Identification (Squawk) and altitude (Pressure Altitude)
Transponder squawk
- “squawk” – assigning a transponder code
- Emergency squawk codes
- Right to left
- 0 - 7
Emergency locator transmitter (ELT)
- self-contained
- self-powered
- Automatic on impact (5G’s)
- Battery should be enough to power it for at least 48 hours
- Batteries should be changed or recharged at 50 percent of the battery’s useful life
ELT distress frequencies
121.5 MHz (civilian)
406 MHz for new ELTS
243 MHz (military)
Flaws of Transponder
- FRUIT (False Replies Unsynchronized with Interrogator Transmissions)
- Garble
- FRUIT (False Replies Unsynchronized with Interrogator Transmissions)
Aircraft is in range of two ground interrogators they may reply to both. The received replies may be for the wrong station.
- Garble
Two aircrafts within 1.7NM may produce overlapping replies to the ground interrogator
Mode S
Selected Altitude
Track
Ground Speed
Magnetic Heading
Vertical Rate
TCAS
