Radio Flashcards
(32 cards)
Wavelength
- Wavelength is the distance of one complete cycle of a radio wave.
- This cycle is measured in meters
- The symbol is λ
Frequency
- Frequency is the number of waves to pass a stationary point in a period of time.
- It is measured in seconds.
- The symbol is Hz
Amplitude
- Amplitude is the height or strength of the wave.
- The amplitude decreases with time and distance traveled due to attenuation.
- Again, like the stone dropped into a pond, the strength of the waves dissipates with distance.
Frequency Bands
LF (Low Freq) 30 – 300 kHz λ = 10 km – 1 km
MF (Medium Freq) 300 – 3000 kHz λ = 1 km - 100 m
HF (High Freq) 3 MHz – 30 MHz λ = 100 – 10 m
VHF (Very High) 30 MHz – 300 MHz λ = 1 – 10m
Ground Waves
- Ground Waves follow the surface of the Earth often travelling in straight lines.
- Diffraction causes them to bend around obstacles on the surface.
- This bending is enhanced by Surface Attenuation.
Surface Attenuation
- Surface attenuation is caused by the wave coming into contact with the ground. Friction with the surface gradually causes it to lose energy.
- For this reason, radio waves will travel a greater distance over water than land.
- The higher the frequency, the greater the attenuation.
- Very low frequencies are least effected by surface attenuation. Some frequencies can even travel for thousands of miles.
Sky Waves
•Sky Waves travel up into the atmosphere and are refracted off the Ionosphere.
Skip Zone
Skip Zone is the area between where the ground waves and the sky waves strike the Earth where a signal cannot be received.
Night Effect
- Sky waves are most reflected by the ionosphere at night.
* This phenomena can cause interference with lower frequency ground waves, (like those used for ADF).
In aviation, LF and MF are primarily used for navigation.
Frequency Band: 200 KHz – 415 KHz, 510 KHz – 535 KHz
HF is not widely used in aviation.
- Frequency Band: 3 MHz – 30 MHz
- As its signal travels further than VHF, it is ideal for long-range, trans-oceanic flights or flights in remote places such as northern parts of Canada.
- HF is unpredictable due to sunspots and the height of the ionosphere.
VHF is the most commonly used frequency band in aviation because VHF waves are not affected by attenuation.
- Frequency Band: 30MHz – 300 MHz
- VHF waves do not bend or bounce but continue straight into space. However, VHF waves can only be received with direct line of sight. These radio waves suffer from less interference and are more accurate.
- VHF is used primarily for communication and in VOR, navigation.
- VHF is also used for FM radio.
UHF (Ultra High Frequency)
•Frequency Band: 300 MHz – 3000 MHz
- This frequency is used in DMEs, TACANs, as well as Glideslopes.
- UHF provides a very accurate signal over a shorter range.
- UHF is more widely used in the military.
RADAR is a device which provides information on
range, position, and sometimes altitude of objects in the path of the transmitted pulse.
PSR (Primary Surveillance Radar)
- PSR makes use of reflected energy.
- It will “bounce” a signal off anything in its path, including airplanes, flocks of birds, or even stationary objects.
- PSR is short range and provides information on the immediate area surrounding the airport.
Disadvantages of PSR
- Clutter – Caused by erroneous returns reflected from precipitation, ground obstacles, buildings, mountains, etc.
- Size Variation - Variation in the size of returns. A 747 will show up differently then an ultra-light aircraft.
- Blind Spots – Blind spots and shadows due to screening by high terrain or obstacles.
SSR (Secondary Surveillance Radar)
- SSR operates in response to the high energy pulse produced by any airplane that is equipped with a transponder
- Provides the specific identity of the aircraft as well as the position.
- Its altitude can also be transmitted (if Mode C has been selected).
- Any abnormal situation affecting the airplane, such as radio failure, distress, emergency, etc can be communicated by inputting a specific code on the aircraft’s transponder.
Transponder
•A transponder sends a strong responding signal to a secondary ground radar which can send additional information such as airplane identification, altitude, etc.
•Most transponders have two modes:
Mode A - Only requests aircraft identification
Mode C - Requests altitude information
Transponder – Special Codes
Hijack
7500
Transponder – Special Codes
Communication Failure
7600
Transponder – Special Codes
Distress (MAYDAY)
7700
Transponder Settings •OFF •STANDBY(SBY) •ON •ALT •TEST(TST)
OFF – Transponder de-activated completely.
•STANDBY(SBY) – Warmed and ready for use. This is the normal position until ready for take off
•ON – Transmits the selected code in Mode A.
•ALT – Transmits in mode C (altitude reporting mode).
•TEST(TST) – Test the transponder by causing it to generate a self interrogation signal.
ELT (Emergency Locator Transmitter)
battery operated radio transmitter
emergency frequency of 121.5 MHz or 243.0 MHz.
crash activation sensor (G-switch)
Disadvantages of an ELT
1) Use VHF spectrum = subject to line of sight transmission.
2) transmission life of approximately 48 hours
3) 98% = false alarms
