Билет № 32
1). Surface wave - it is normally expected that radio waves will travel a straight line but in certain conditions, the waves will bend and follow the surface of the earth giving increased ranges. The two primary factors that cause this are diffraction and surface attenuation.
2). Attenuation - the term attenuation refers to the loss of power or signal strength suffered by radio waves pass they pass through matter or over a surface.
The following general rules are explained in later chapters:
Surface attenuation increases with increase in frequency.
Ionospheric attenuation increases with decrease in frequency.
Radar attenuation increases with increase in frequency
Surface waves are to a greater or lesser extent absorbed by the surface over which the radio waves are passing. The ionosphere and particles in the atmosphere may to a greater or lesser extent block the passage of radio or radar energy. The processes of absorption and blocking are referred to as ATTENUATION.
3). At what Frequency operate MLS - The MLS system operates at a frequency band of 5031,0 – 5090,7 MHz on two separate channels at a mutual interval of 300 kHz. The protractor part of the MLS system provides continually information about an aircraft’s position relative to the runway both in the vertical and horizontal plane. The rangefinder part enables to measure the distance between an aircraft and the reference points in the approach process. The angular information for the approach course, descent, flare and go-around is determined by measuring the interval between two passages of an oscillating plane lobe through an onboard MLS antenna.
Билет №33
1). Skip Distance and Dead Space.
Skip Distance - is the distance between the transmitter and the point where the first sky wave return arrives. For a given frequency this distance varies with the time of the day.
Dead Space - is the area between the limit of the surface wave and the point of reception of the first sky wave. Dead space occurs mainly in the HF band. With increase in frequency, skip distance increases and surface wave range decreases. Dead space therefore increases with increases in frequency.
2). SATCOM (Satellite Communication System) - uses satellites as replay stations to transmit over long distances, instead of HF frequencies which are susceptible to atmospheric interference. SATCOM supports a wide range of services such as flight deck voice communications, passenger telephone/FAX and ACARS.
The satellite and ground station relay a wide range of data to and from the aircraft and airlines, airports, air traffic control and telecommunications via the public network. The satellite service, which is available to marine and land users as well as aviation, provides coverage by means of geostationary satellite between latitudes 80°N and 80°S. SATCOM will become increasingly important as ADS becomes effective. ADS is a system that uses satellite communication data links to allow air traffic control to monitor the position of aircraft by interrogating the on-board navigation systems such as GNSS.
3). At what Frequency operate AWR. Commercial AWR systems operate in two frequency ranges in the SHF band:
(G band) 4000 to 8000 MHz, example 5.44 GHz.
(I band) 8000 to 12500 MHz, example 9.33GHz.