Radar Principles Flashcards
What is Attenuation?
A radio wave reduces in strength with range or time from the point of transmission
What frequency experiences greater attenuation?
The Higher frequency the greater attenuation and
shorter range
What is Ducting?
Temperature Inversion
The waves “bounce” between the surface and the top of the duct due to the ratio of wavelength to duct height.
What is Attenuation?
Higher frequency, greater attenuation,
shorter range
Attenuation - strength diminishes with increasing distance but wavelength and frequency remain unchanged.
VLF
Very Low Frequency
3-30Khz
100km - 10km
LF
Low Frequency
30-300KHZ
10km-1km
MF
Medium Frequency
300Khz - 3Mhz
1km - 100m
HF
High Frequency
3 - 30Mhz
100m - 10m
VHF
Very High Frequency
30 - 30 MHz
10m - 1m
UHF
Ultra High Frequency
300Mhz - 3Ghz
1m - 10cm
SHF
Super High Frequency
3 - 30 GHz
10cm - 1cm
EHF
Extremely High Frequency
30 - 300 GHz
1cm - 1mm
What is VLF used for?
Long range communications.
Requires immense aerials and high transmitter power.
Very prone to static interference.
Very long range navigation aids.
What is LF and MF used for?
Reliable, long range communications.
Requires large aerials and high transmitter power.
Prone to static interference and night effect.
Very congested waveband.
NDB.
Some radio broadcasts
What is HF used for?
Long range communications by day and night limited
by diurnal and seasonal variation of the ionosphere.
Requires smaller aerials and transmitter power.
Suffers from static interference and fading.
Optimum operating frequency varies diurnally.
Long distance wireless telegraphy.
RTF communications.
What is VHF and UHF used for?
Line of sight communications.
Maximum range dependent upon aircraft height
and aerial height.
Small aerial and transmission power.
Free from static interference and easy to suppress
on aircraft.
Prone to ducting.
Wavebands become congested.
RTF, ILS, VOR, VDF, Surveillance Rada
What is SHF and EHF used for?
Short range communications.
Severe attenuation.
Precision, Surveillance and Airborne weather Radar.
Radio altimeter. (ASGMCS)
What is an indirect wave?
Low frequency propagation characteristics
Similar to ducting, the low frequencies will bend
around objects and be heard a great distance from the source.
The low frequency means less attenuation .
What is a Direct Wave?
Each waveband has different propagation
characteristics.
VHF and higher frequencies propagate on straight paths.
Communication distances limited by the curvature of
the Earth and aircraft height above sea level.
Antenna shadow
