Reviewer in Satellite Communications | ECE Board Exam

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(Last Updated On: February 15, 2020)

Review Notes in Satellite Communications

This is the Reviewer 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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