This is the Review Notes in Satellite Communications as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Summary of Important Satellite Communications Review Notes
Sputnik 1 is the first active satellite
Early Bird is the first commercial satellite
Moon is the first passive satellite transponder
Telstar 1 is the first satellite to receive and transmit simultaneously
A helical antenna is used for satellite tracking because of circular polarization
Repeaters inside communication satellites are known as transponders
Privacy is considered as the unsolved problem in satellite system
Nonsynchronous satellite is a satellite that rotates around the earth in a low-altitude elliptical or circular pattern
Footprint is the geographical representation of a satellite antenna radiation pattern
Spot beam – the smallest beam of a satellite antenna radiation pattern
Global beam – a satellite beam that covers almost 42.4% of the earth’s surface
The frequency range of C-band is 3.4 to 6.425 GHz
Downlink – a satellite signal transmitted from a satellite transponder to earth’s station
Satellite dish collects very weak signals from a broadcast satellite
Orthomode transducer is a device that detects both vertically and horizontally polarized signals simultaneously
LNA detects the satellite signal relayed from the feed and converts it to an electric current, amplifies and lower its frequency
Path loss is a loss of power of a satellite downlink signal due to earth’s atmosphere
Perigee – point on the satellite orbit closest to the earth
Footprint – the earth covered by a satellite radio beam
The local oscillator (mixer) frequency of the satellite with an uplink frequency in GHz band is 2225 MHz
Gallium Arsenide solar panel array are used in some advance satellites
Satellite engine uses ion propulsion system
Lithium – a satellite battery that has more power but lighter
Hydrogen battery used by older satellites
VSAT was made available in 1979
VSAT first operate at C-band
The first Philippine Mabuhay satellite have 30 channels
The first Philippine Agila 1 will have 36 transponders
The Philippine Government request 6 satellite orbital slots
105.5° East – the location of AsiaSat 1
AsiaSat 1 covers 38 countries in Asia
The owner of AsiaSat is China Great Wall Industry Corporation
200 dB is the approximate path loss from satellite-to-earth station
INTELSAT stands for International Telecommunications Satellite
14/11 GHz – the frequency of Ku band for satellite communications
A satellite cross-link means Satellite-to-satellite link
Earth station uses Cassegrain antenna
0.5 s is the delay time for satellite transmissions from earth transmitter to earth receiver
500 MHz – the bandwidth of C-band satellite frequency band in U.S.
The most common device used as an LNA is tunnel diode
The radiation pattern of earth coverage antennas have a beamwidth of approximately 17°
A mobile satellite array usually has 14 elements
Radial divider is responsible in activating and deactivating adjacent antenna elements in a mobile satellite array
Most mobile satellite array uses quarter-wavelength transformer in transforming 50 ohm to 150 ohm impedance
Shunt – the switching from one element to the other element in a typical mobile satellite array
FDMA – a method of multiple accessing where a given RF channel bandwidth is divided into smaller frequency band
0.5 s is the delay time for satellite transmissions from earth transmitter to earth receiver
As the height of a satellite orbits gets lower, the speed of the satellite increases
The main function of a communication satellite is as a repeater
The key electronic component in a communications satellite is the transponder
A circular orbit around the equator with a 24-h period is called a geostationary orbit
A satellite stays in orbit because the gravitational force and centrifugal force are balanced
The height of a satellite in a synchronous equatorial orbit is about 22,300 mi
Most satellite operate in 3 GHz to 30 GHz
The main power sources for a satellite are solar cells
The maximum height of an elliptical orbit is called the Apogee
Batteries are used to power all satellite subsystems during eclipse periods
The satellite subsystem that monitors and controls the satellite is the telemetry, tracking and command subsystem
Spin is the basic technique used to stabilize a satellite
The jet thrusters are usually fired to maintain altitude
Most commercial satellite activity occurs in C and Ku band
Multiple earth stations share a satellite on the same frequency by frequency reuse
The typical bandwidth of a satellite band is about 500 MHz
Modulator is not usually a part of a transponder
The satellite communications channels in a transponder are defined by the bandpass filter
The HPAs in most satellite are TWTs
The physical location of a satellite is determined by its latitude and longitude
The receive GCE system in an earth station performs demodulation and demultiplexing
Magnetron is not used in earth stations
The common up-converter and down-converter IF is 70 MHz
FM modulation is used on voice and video signals
QPSk modulation is normally used with digital data
Speed is not a typical output from a GPS receiver
Passive satellite – a satellite which simply reflects the signal without further amplification
Essentially a satellite transponder is a radio repeater in the sky
Geostationary – satellite that orbits in a circular pattern with an angular velocity equal to that of the earth
Domsat – satellite that provide services within a single country
The round-trip propagation delay between two earth stations through a geosynchronous satellite is 500 to 600 ms
Uplink signal – the signal path from earth station satellite
Communication satellite - designed to receive a signal from a transmitting station on the ground an retransmit it to a receiving station located elsewhere
Downlink signal – the signal path from satellite to earth-based receiver
A satellite position is measured by its elevation angle with respect to the horizon
The azimuth angle measures the satellite position clockwise from the direction of true north
Arthur Clarke incidentally propose the geostationary scheme or orbit of the satellite in 1940s
The control routine necessary to keep the satellite in position is referred to as station keeping
Satellite altitude – refers to the satellite orientation with respect to the earth
The first Intelsat satellite that was launched in 1965 was named Early Bird 1
Syncom 1 – the first satellite launched for a geosynchronous orbit but unfortunately lost during orbit injection
Communication is the most common application of satellite
Descending pass for a satellite means a pass from North to South
Geostationary stationary satellites are located 0° latitude with respect to the equator
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