Q71) Difference between Active and Passive satellite.
Answer:
- Passive satellites are simply metal coated plastic balloons.
- Active satellites consist of transmitting antennas (fr reception and transmission) and power supply
- Passive satellites are just reflectors
- Actives satellites translate the freq to desired download freq and also amplify the signal
- Passive satellites are used for military operations because of their vulnerability
- Activew satellites are widely used for communication and broadcasting
Q72) Mention different applications of a satellite.
Answer: The typical applications of a satellite are TV signal relaying, satellite radio, surveillance, navigation, satellite phone, weather information relaying, satellite images, satellite maps and so on.
Q73) Define Horizontal Polarization.
Answer: Type of linear polarization where the electric field is approximately aligned with the local horizontal plane at an on-ground transmission or reception point.
Q74) What is Linear Polarization ?
Answer: It describes awave in which the electrical field vector observed in any fixed planenormal to the direction of propogation, maintains a constant direction with time. With linear polarization, the earth station and satellite antennas of a particular earth-space link must be precisely aligned so that their reference polarization directions co-incides in order to obatin maximum reception quality.
Q75) What is Circular Polarization ?
Answer: A circular polarized wave, in which the electric field vector, observed in any fixed plane normal to the direction of propogation, rotates with time and traces a circle in the plane of observation.
Q76) What is "TVRO" in radar ?
Answer: TVRO stands for "Television Receive Only". An earth station incapable of transmitting to the satellite and intended for the individual or collective reception of television servicefrom the satellite.
Q77) What is "SCPC" ?
Answer: Single channel per carrier. In SCPC system, each communication signal is individually modulated onto its own carrier which is used to convey that signal to the end user. A number of similar carriers shares a common satellite transponder and uses a unique portion of its bandwidth. Each carrier supports a single communication channel.
Q78) What is Antenna Noise Temperature ?
Answer: A receiving antenna collects noise from radiating bodies falling within its radiation pattern. For an on-groung receiving ntenna, this includes contribution from sky and from surroundings. The combined effect of these noise sources is modelled by an equivalant noise temperature for the antenna which varies with elevation angle antenna size.
Q79) What is meant by "High Band"?
Answer: The upper part of the Ku-Band downlink frequency range from 11.7GHz to 12.75GHz.
Q80) When an Outage is said to occur?
Answer: An outage is said to ocur when the quality od a telecommunication service or communication link falls below a specified minimum value for acceptable communciation performance.
Q81) What is sun transit outrage ?
Answer:
- This phenomenon is the interference of the solar radiation with the signals from the geostationary satellites, thereby interrupting the communication between the earth and the satellite. The solar radiations act as a powerful noise source and so it appers as a noise signal in the earth station receivers, thereby partially or entirely degrading the satelite signal. The sun transit outage lasts for about 12 minutes everyday for span of about months and these periods vary from place to place.
Q82) Explain "FSS".
Answer: FSS: Fixed Satellite Service.
This refers to any satellite communication service between earth stations located at fixed geographical positions. This term, however, oftemn used to refer the "UNPLANNED" frequency bands that are not subject to the internationally agreed regulations.
Q83) What do you mean by the term " Adjacent Channel Interference" ?
Answer: It means "unwanted electric interference from signals that are immediately adjacent in frequency to the desired signal. This can arise due to any type of imperfection in the transmission channel or equipment."
Q84) Define Cross-modulation.
Answer: It is defined as the "interference caused by the modulation of one carrier affecting another signal. It is due to non-linear device operation, which can be caused by overloading an amplifier and is worsened by signal power level imbalances."
Q85) What is Cross polar ?
Answer: Cross polar is used to refer to a signal that has the opposite polarization to a given signal.
Q86) Define Cross-polar-Discrimination.
Answer: It is the ration of the signal power received by an antenna on one polarization to the signal power on the opposite polarization. This ration is usually expressed in decibel. It is a meausre of ability of the antenna to detect signal on one plolarisation nd to reject signals at the same frequency having the opposite polarization.
Q87) What is Cross-Polar-Isolation ?
Answer: It's the ratio of the signal power received by an earth station on one polarization to the signal power received on the same polarization but originating form a cross polar signal. This ratio is usually expressed in decibel. It is a measure of interference form corss polar signals into the desired signal, which occur in all practical systems.
Q88) What is BEACON ?
Answer: A highly stable radio frequency which is used by earth stations equipped with an automatic [satellite] tracking system. Beacons can be generated on Oboard the satellite or transmitted from the ground and relayed through the satellite.
Q89) What is RFL ? How does it get introduced ?
Answer: RFL is receiver feeder losses. ie. losses due to the antenna and low noise amplifier.
- These RFL occur in :
- Connecting waveguides
- Filters
- Couplers
Q90) What is zenith and nadir ?
Answer: Zenith is point in the sky or in celestial sphere directly above the observer.
Nadir is point in the sky or in celestial sphere directly below the observer.
Both are relative to the position of the observer.
Q91) What is Clarke belt ?
Answer: Clarke Belt: The circular orbit at approximately 35800 km above the equator where satellites travel at the same speed as the earth's rotation (geostationary orbit) and thus appears to be stationary to an observer on earth.
Q92) What is "EPG" ?
Answer: EPG stands for "Electronic Programme Guide".
Its a graphical user interface generated by a digital satellite receiver and displayed on the user's television screen. It provides information on the timing and content of television programmes which is conveyed in the digital signals received form the satellites. It s main purpose is to help users to rapidly identify and select programmes of interst.
Q93) What is the meaning of "Earth-Space link" ?
Answer: It means "any communication link between an earth station and a satellite [uplink or downlink]"
Q94) Define "Band Switching" ?
Answer: It is the process of selecting one of two freqeuncy band [the lower band] or [the higher band ] for reception of satellite signals.
Q95) Define beam.
Answer: A unidirectional flow of radio waves concentrated in a particular direction. A teerm commonly used to refer to an antenna's radiation pattern by analog with a light beam.
Q96) What is Bandwidth ?
Answer: The range of frequencies used for a particular radio transmission (eg: 36MHz). It is the difference between the lowest and highest transmission frequencies used by a signal.
Q97) What is Prograde and Retrograde ?
Answer: An orbit in which the orbit orientation is in same direction as compared to the earth direction it is called Prograde orbit.
Where as a orbiting which the orbit's orientation is in opposite direction as compared to the earth direction it is called Retrograde orbit
Q98) What is "Shaped Beam" ?
Answer: The radiation pattern of a satelliteantenna that has been designed so that its footprint follows the boundary of a specificed geographical area (the area of sevice provision) as closely as possible.
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