Билет № 25

1). Amplitude - the strength or width of one wave the greater the distance from the transmitting site, the smaller this distance.

2). Describe the term Pulse modulation - pulse modulation a type of modulation in which a train of pulses is used as the carrier wave, one or more of its parameters, such as amplitude, being modulated or modified in order to carry information.

3). At what Frequency operate DME - operating frequency range of a DME according to ICAO Annex 10 is from 960 MHz to 1215 MHz. Aircraft equipped with TACAN equipment will receive distance information from a VORTAC automatically, while aircraft equipped with VOR must have a separate DME airborne unit.

Билет №26

1). Frequency - the number of cycles per second, expressed in three units—Kilohertz (KHz), which measures the number of cycles per second, Megahertz (MHz), which measures millions of cycles per second, and Gigahertz (GHz), which measure billions of cycles per second.

2). Sidebands - In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing power as a result of the modulation process. The sidebands consist of all the Fourier components of the modulated signal except the carrier. All forms of modulation produce sidebands.

3). At what Frequency operate TCAS

TCAS involves communication between all aircraft equipped with an appropriate transponder (provided the transponder is enabled and set up properly). Each TCAS-equipped aircraft interrogates all other aircraft in a determined range about their position (via the 1,030 MHz radio frequency), and all other aircraft reply to other interrogations (via 1,090 MHz). This interrogation-and-response cycle may occur several times per second.

Билет №27

1). Wavelength. The distance travelled by a radio wave in one complete cycle.

2). Refraction. When a radio wave travels obliquely from a medium of one density to another of different density, it is bent or refracted at the surface separating the two media. The refraction occurs because radio waves travel at slightly different velocities in different media. Thus at the interface between the media there is a slight change of wavelength.

The following are well-known examples of refraction:

• COASTAL REFRACTION where there is a change of direction when the radio wave crosses the coast. This is due to the different levels of attenuation and the different speed of radio waves over land and water.

• ATMOSPHERIC REFRACTION where changes in direction occur due to variations in temperature, pressure and humidity, particularly at low altitude. Normal levels of atmospheric attenuations cause the radio horizon to be different to the visual horizon.

• IONOSPHERIC REFRACTION where changes in direction occur when the radio wave passes through the ionized layers of the earth’s upper atmosphere.

3). At what Frequency operate Loran C - is acronym for ‘’Long range navigation”. LORAN C is a hyperbolic system operating at a frequency of 100 kHz. In uses the principle of differential range by pulse technique to measure the time difference between the arrival, at an aircraft’s receiver, of a series of pulses from a Master transmitter and a series of pulses from up to four Slave or Secondary transmitters; this arrangement of transmitters is known as a chain. Loran C is also used as a non-precision approach aid in the USA.

Loran C was planned to be shut down by the end of year 2000 but has now been extended until the end of 2008, and it is very likely that it will be extended for several more years beyond 2008.