It’s 5th and final article of the exclusive AAI ATC Interview Series which primarily focuses on the preparation of the JE (ATC) Interview. The series is consisted of Five Articles which cover non-technical as well technical questions that I suppose can be asked in the ATC interview.
- Read First Article of AAI ATC Interview Series (Questions 1 to 26)
- Read 2nd article of AAI ATC Interview Series (Questions 27 to 38 )
- Read 3rd article of AAI ATC Interview Series (Questions 39 to 45)
- Read 4th article of AAI ATC Interview Series (Questions 46 to 52)
This article covers some important topics which could not be included in other articles. Some of the topics are radio wave propagation, Line of sight, antenna, duplexer etc.
Ques. 53: What is Antenna?
Ans. Antenna is an electrical device used to convert electrical signals to radio waves and vice versa. A basic antenna has two parts i.e. Transmitter and Receiver.
Ques. 54: What is Duplexer?
Ans. Duplexer is a device used in communication systems which can eliminate the need of separate transmitter and receiver antenna. It alternatively switches the single antenna between transmitter and receiver. The duplexer also prevents high-power transmitted pulses to enter the receiver as it might destroy the receiver which is highly power-sensitive device.
Ques. 55: What is ADS-B?
Ans. ADS-B is an acronym for Automatic Dependent Surveillance-Broadcast.ADS-B system uses transmissions from aircraft to provide geographical position, pressure altitude data, positional integrity measures, flight identity, 24 bit aircraft address, velocity and other data which have been determined by airborne sensors.
Ques. 56: How does Aircraft establish connection with ATC?
Ans.It is done through VHF or HF communication. Usually the communication takes place in VHF band only but in areas like oceans where it is not possible to install the navigation equipment, HF communication plays a vital role to establish connection between ATC and Aircraft.
Ques. 57: How do radio waves propagate?
Ans. Radio Waves can travel through one of these methods:
- LOS (Line of Site): Limited communication area
- Sky-wave Propagation: can cover entire globe.
- Ground-wave Propagation: range in-between Mode 1 & 2.
Ques. 58: What is Line of Sightpropagation?
Ans.It is simplest form of propagation. In LOS mode, Distance between the transmitter and receiver is dependent
on the frequency / wavelength of the signal. Line of site propagation is veryuseful at VHF and UHF Frequencies. Range of LOS communication depends on the height of Transmitter.
Ques. 59: What is critical frequency?
Ans.In Sky wave propagation, Critical frequency is the limiting frequency at or below which wave is reflected back from the ionosphere, above critical frequency the wave penetrates the ionosphere and never comes back.So for sky wave propagation the value of frequency f≤ fc .
Ques. 60: What are different frequency bands?
Ans. Frequency bands are shown in this table. Corresponding wavelength can also be calculated by the formula: wavelength= c/f
Ques. 61: In which frequency band ATC communication takes place?
Ans. VHF Band: Generally Pilot-ATC Communication takes place in this band. However sometimes HF Band is used as well for long range communication where VHF communication is not possible. You must know that with the increase in frequency, Range of communication gets decreased.
Ques. 62: What is Mach Number?
Ans. Mach number is a common term used in Aviation world that denotes the ratio of air speed to the local speed of sound, e.g. Mach 1 denotes the speed equal to the speed of sound.
Ques. 63: What is Supersonic aircraft?
Ans.A supersonic aircraft is an aircraft which can exceed the speed of sound (Mach 1.0) in level flight. (Level flight means when aircraft is moving at a fixed altitude i.e. not climbing or descending). Concorde was a supersonic aircraft.
Ques. 64: Why uplink and downlink frequencies are different for Satellite or Mobile communication?
Ans. Uplink (fu) and Downlink frequencies (fd) are different so that there is no interference. Remember that in satellite communication: fu>fd whereas in Mobile Communication fd>fu.
Reason is higher the frequency, higher will be the energy requirement.
Ques. 65: What is the speed of sound?
Ans. Speed of sound varies with the temperature. The speed is proportional to the square root of the absolute temperature, giving an increase of about 0.6 m/s per degree Celsius. Some values are: 340m/s at Sea Level (Temp. 15 C), 331m/s at 0 C.
Edit: Read latest post about important definitions and terms like ADS-B, SSR, SBAS, GBAS, Runway, Flight Level etc for ATC Interview Preparation. Link is:
Important Terms and Definitions for JE-ATC Interview
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