### SATELLITE COMMUNICATION DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
2 and 16 MARK QUESTIONS AND ANSWERS
SUBJECT CODE : EC1015
SUBJECT NAME : SATELLITE COMMUNICATION
Prepared by
S.BEEMA BEEVI (Lect/ECE)
DEV R.NEWLIN (Sr Lect/ECE)
N.I COLLEGE OF ENGG, KUMARACOIL
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGG
B.E DEGREE QUESTION BANK
EC1015-SATELLITE COMMUNICATION
PART A(2 Mark Questions)
1.What are the different applications of satellite systems?
*Largest International System(Intel sat)
*Domestic sat system in united states(Dom sat)
*U.S National Oceanography Atmospheric Administration (NOAA)
2.Mention the different services of satellite systems.
*Fixed satellite services
*Mobile satellite services
*Meteorological satellite services.
3.Define Polar-orbiting Satellites.
Polar orbiting Satellites orbit the earth in such a way as to cover the north & south
polar regions.
4.State kepeler’s first law.
It states that the path followed by the satellite around the primary will be an ellipse.
An ellipse has two focal points F1 &F2.The center of mass of the two body system,
termed the barycenter is always centered on one of the foci.
E =¥D2-b2/a
5.StateKepeler’s second law.
It states that for equal time intervals,the satellite will sweep out equal areas in its
orbital plane,focused at the barycenter.
6. State kepeler’s third law.
It states that the square of the periodic time of orbit is perpendicular to the cube of
the mean distance between the two bodies.
a3 Q2
7.Define apogee & perigee.
*The point farthest from the earth is known as apogee.
*The point closest from the earth is known as perigee.
8.What is line of apsides?
The line joining the perigee & apogee through the center of the earth.
9.Define ascending & descending node.
The point where the orbit crosses the equatorial plane going from South
North.
The point where the orbit crosses the equatorial plane going from South to North.
10.Define inclination.
The angle between the orbital plane & the earth’s equatorial plane.It is measured at
the ascending node from the equator to the orbit going from east to north.
11.Define mean anomaly & true anomaly .
Mean anomaly:It gives an average value of the angular position of the satellite with
reference to the perigee.
True anomaly : It is the angle from perigee to the satellite position ,measured at the
earth’ s center.
12.Mention the apogee &perigee height.
Ra = a(1+e)
Rp = a(1+e)
Ha = ra-rp
Hp =rp-Rp
13. Define Universal time.
It is the time used for all civil time keeping purposes & it is the time reference
which is broadcast by the national bureau of standards as a standard for setting clocks.
UT day =1/24(hours+minutes/60+seconds/3600)
UT = 360 X UT day.
14.Mention the julian dates.
JD = JD010 + day number + Utday
15.what is sideral time?
Sideral time is time measured relative to the fixed stars.It will be seen that one
complete rotation sideral time relative to the sun .This is because the earth moves in its
orbit around the sun.
16.Define Sideral day.
It is defined as one deg-A’ (ES west of satellite)
A=180deg+A’ (ES east of satellite)
For ES in northern hemisphere:
A= A’ (ES west of satellite)
A= 360- A’ (ES east of satellite)
A’ =tan-1 WDQ V- O VLQ O
23.Write short notes on attitude control system.
It is the system that achieves & maintains the required attitudes.The main functions
of attitude control system include maintaining accurate satellite position throughout the
life span of the system.
24.What is an polar antenna?
A single actuator is used which moves the antenna in a circular arc ie known as polar
mount antenna.
25.Wht is declination?
The angle of tilt is often referred to as the declination which must not be confused
with the magnetic declination used in correcting compass readings.
26.Define the terms in Eclipse.
During euinox periods,the earth the sun & the satellite are in alignment with the result
that earth’ s shadow eclipses tha satellite & the sunlight fails to reach the satellite solar
cells.The eclipse effect is noticeable for periods of about four weeks & the maximum
daily eclipse duration is about 1.20hours.
The payload refers to the equipment used to provide the service for which the satellite
has been launched.
28.What is meant by transponder?
In a communication satellite,the equipment which provides the connecting link
between the satellite’ s transmit& receive antennas is referred to as the transponder.
29.Write short notes on station keeping.
It is the process of maintenance of satellite’ s attitude against different factors that can
cause drift with time.Satellites need to have their orbits adjusted from time to time
because the satellite initially placed in the correct orbit,natural forces induce a
progressive drift.
30.What is mean by Pitch angle?
Movement of a spacecraft about an axis which is perpendicular to its longitudinal
axis.It is the deg of elevation or depression.
31.What is an propellant?
A solid or liquid substance burnt in a rocket for the purpose of producing thurst.
32. What is an Yaw?
Yaw is the rotation of a vechicle about its vertical axis.
33. What is an Zero ‘g’ ?
Zero ‘g’ is a state when the gravitational attraction is opposed by equal & opposite
inertial forces & the body experiences no mechanical stress.
34.Describe the spin stabilized satellites.
In a, spin stabilized satellites,the body of the satellite spins at about 30 to 100rpm
about the axis perpendicular to the orbital plane.The satellites are normally dual spin
satellites with a spinning section & a despun section on which antennas are
mounted.These are kept stationary w.r.to earth by counter rotating the despunsection.
35.What is meant by frequency reuse?
The carrier with opposite senses of polarization may overlap in frequency this
technique is known as frequency reuse.
36.What is meant by spot beam antenna?
A beam generated by a communication satellite antenna of sufficient size that the
angular spread of sufficient size that the angular spread of the energy in the beam is very
small with the result that a region that is only a few hundred km in diameter is
illuminated on earth.
37. What is an TWTA?
The TWTAS are widely used in transponder to provide the final output power
required to the transtube & its power supplies.
38. What is meant by Intermodulation distortion?
The AM/PM conversion is then a complicated function of carrier amplitudes,but in
addition,the nonlinear transfer characteristic introduces a more serious form of distortion
known as intermodulation distortion.
39.Define input backoff.
In order to reduce the intermodulation distortion,the operating point of the TWT
must be shifted closer to the linear portion of the curve,the reduction in input power being
referred to as i/p backoff.
40.Define diplexer.
The transmit & receives signals are separated in a device known as diplexer
41.What is an OMT?
The polarization seperation takes place in a device known as an orthocoupler or
orthogonal mode transducer.
42. What is an polarization interleaving?
Overlap occurs between channels,but these are alternating polarized left hand
circular & righthand circular to reduce interference to acceptable levels.This is referred to
as polarization interleaving.
43. What is an SCPC?
In a thin route circuit,a transponder channel(36mhz) may be occupied by a no. of
single carriers,each associated with its own voice circuit.
44.Define S/N ratio.
The S/N introduced in the preceding section is used to refer to the ratio of signal
power to noise power at the receiver output.This ratio is sometimes referred to as the post
detector.
45.What is noise weighting?
Improve the post detection signal to noise ratio is referred to as noise weighting.
46. What is an EIRP?
It is a measure of radiated or transmitted power of an antenna.It can be completed
from the antenna gain & the power fed to the antenna input.
47.Write the equations of losses for clear sky conditions.
Losses=(FSL)+(RFL)+(AML)+(AA)+(PL)
48.What is an noise power spectral density?
Noise power per unit BW is termed the NPS density.
N0 = PN/BN=KTN joules
49. What is an Intermodulation noise?
Intermodulation distortion in high power amplifier can result in signal products
which appear as noise & in fact is referred to as Intermodulation noise.
50. What are the types of antenna losses?
*sky noise
*Antenna losses
51.What is an antenna losses?
the sum of the equivalent noise temperature of all these sources.
52.Define sky noise.
It is a term used to describe the microwave radiation which is present throughtout
universe & which appears to originate from matter in any form ,at finite temperature.
53.Define noise factor.
An alternative way of representing amplifier noise is by means of its noisefactor.In
defining the NF of an amplifier,denoted by to usually taken as 290k
N0,out = FGKT0
54 What is an Apsorptive n/w?
It is one which contains resistive elements.These introduce losses by absorbing
energy from the signal& converting it to heat.Resistive attenuators, transmission lines &
waveguides are all examples of apsorptive networks.
55.Write the equation of system noise factor.
TS =Tant+ Te1+(L-1)T0/G1+L(F-1)T0/G1
56.Define saturation flux density.
The flux density required at the receiving antenna to produce saturation of
TWTA is termed the saturation flux density.
57.A satellite downlink at 12GHZ operates with a transmit power of 6w & an antenna
gain of 48.2db.Calculate the EIRP in Dbw.
EIRP = 10log6+48.2
=56Dbw.
58. Calculate the gain of a 3m parabolidal antenna operating at a frequency of
12GHZ.Assume an aperture efficiency of 0.5.
G=10log78168
=48.9Db
59.The range between a ground station & a satellite is 42000km. Calculate the free space
loss a frequency of 6GHZ.
(FSL)=32.4+20log42000+20log6000
=200.4Db.
60.An antenna has a noise temperature of 35k & its matched into a receiver which has a
noise temp of 100k. Calculate the noise power density & the noise power for a BW of
36MHZ.
N0=(35+100)X1.38X10-23
=1.86X10-21J
PN = 1.86X10-21JX36X106
=0.067PW
61.What is a single mode of operation?
A transponder channel aboard a satellite may be fully loaded by a single
transmission from an earthstation.This is referred to as a single acess mode of operation.
62.What are the methods of multiple acess techniques?
FDMA(Frequency division multiple techniques)
TDMA (Time division multiple techniques)
63.What is in CDMA?& its types?
In this method each signal is associated with a particular code that is used to
spread the signal in frequency & or time.
64.What is a thin route service?
SCPC systems are widely used on lightly loaded routes,this type of service being
referred to as a thin route service.
65. What is an important feature of Intelsat SCPC system?
The system is that each channel is voice activated.This means that on a two way
telephone conversation only one carrier is operative at any one time.
66.What is an TDMA?What are the Advantage?
Only one carrier uses the transponder at anyone time,& therefore intermodulation
products,which results from the nonlinear amplification of multiple carriers are absent.
Merits:
The transponder traveling wave tube can be operated at maximum power o/p or
saturation.
67.What is preamble?
Certain time slots at the beginning of each burst are used to carry timing
&synchronizing information.These time slots collectively are referred to as preamble.
68.Define guard time.
It is necessary to between bursts to prevent the bursts from overlapping. The guard
time will vary from burst to burst depending on the accuracy with which the various
bursts can be positioned within each frame.
69. What is meant by decoding quenching?
In certain phase detection systems the phase detector must be allowed time to
recover from one burst before the next burst is received by it.This is know as decoding
quenching.
70. What is meant by direct closed loop feedback?
The timing positions are reckoned from the last bit of the unique word in the
preamble .The loop method is also known as direct closed loop feedback.
71. What is meant by feedback closed loop control?
The synchronization information is transmitted back to an earth station from a
distant,that is termed feedback closed loop control.
72.Define frame efficiency.
It is a measure of the fraction of frame time used for the transmission of
traffic.Frame efficiency is defined as I WUDIILF ELWV WRWDO ELWV I -overhead bits/total bits.
73. What is meant by telephone load activity factor?
The fraction of time a transmission channel is active is known as the telephone
74. What is meant by digital speech interpolation ?
The point is that for a significant fraction of the time the channel is available for
other transmissions,& advantages is taken of this in a form of demand assignment known
as digital speech interpolation.
75.What are the types of digital speech interpolation?
· Digital time assignment speech interpolation
· Speech predictive encoded communications
76. What is meant by freeze out?
It has assumed that a free satellite channel will be found for any incoming speech
spurt,but ofcourse there is a finite probability that all channels will be occupied & the
speech spurt lost.Losing a speech spurt in this manner is referred to as freeze out.
77.What is DSI?
The DSI gain is the ratio of the number of terrestrialchannels to number of
satellite channels.It depends on the number of satellite channels provided as well the
design objectives stated above.
78. What are the advantage of SPEC method over DSI method?
The SPEC method over DSI method is that freezout does not occur during
79.What is ratio of bit rate IF bandwidth?
Rb/BIF P
‘m’ is the roll of factor
m=1 for BPSK
M=2 for QPSK.
80.What are the demerits of conventional approach method?
*Excessive size&weight
*Power consumption.
81.Define space division multiplexing.
The satellites in Geostationary orbit can be achieved through the use of antenna
spot beams.The use of spot beam is also known as space division multiplexing.
82.Define satellite switched TDMA?
Space division multiplexing can be realized by switching the antenna
interconnections in synchronism with the TDMA frame rate,this being know as satellite
switched TDMA.
83.What is SS/TDMA?
A modern pattern is a repetitive sequence of satellite switch modes,also referred to
as SS/TDMA.
84.What is processing gain?
The jamming or interference signal energy is redused by a factor known as the
processing gain.
85.What are the applications of Radarsat?
*Shipping & fisheries
*Ocean feature mapping
*Oil pollution monitoring
*Iceberg detection
*Crop monitoring
86.What is ECEF?
The geocentric equatorial coordinate system is used with the GPS system,where it
is called the earth centered,earth fixed coordinate system.
87.What is dilution of precision?
Position calculations involve range differences,& where the ranges are nearly
equal,any error is greatly magnified in the difference.This effect,brought about as known
as a result of the satellite geometry is known as dilution of precision.
89.What is PDOP?
With the GPS system ,dilution of position is taken into account through a factor
known as the position dilution of precision.
90. What is burst code word?
It is a binary word ,a copy of which is stored at each earth station.
91.Defin SIC.
The identifies the Transmitting station.
92.What is an start of receiving frame?
At any given traffic station,detection of the unique word in the reference burst
signals the start of receiving frame.
93.What is meant by burst position acquisition & burst position synchronization?
A station just entering ,or reentering after a long delay to acquire its correct slot
position.
94.What is an single access?
A transponder channel aboard a satellite may be fully loaded by a single
transmission from earth station.
95. What is an multiple access technique?
A transponder to be loaded by a number of carriers.These may originate from a
number of earth station may transmit one or more of the carriers.This mode of operation
known as multiple access technique.
96.What are the two types of multiple access technique?
* FDMA
* TDMA
97.What is meant by frequency reuse?
The satellite as a whole to be accessed by earth stations widely separated
geographically but transmitting on the same frequency i.e. ,known as frequency reuse.
98. What is meant by space division multiple access?
The satellite as a whole to be accessed by earth stations widely separated
geographically but transmitting on the same frequency i.e. ,known as frequency
reuse.This method of access known as space division multiple access.
99.Write the equations of C/N ratio.
C/N0=(EIRP)+(G/T)-LOSSES-(K) dBHz.
100.What is an error detecting code?
A code which allows for the detection of errors is termed an error detecting code.
PART B(16 Marks Questions)
1.Describe the terms of Earth orbiting satellites.
*Apogee: The point farthest from earth.
*Perigee: The point closest approach to earth
*Ascending node: The point where the orbit crosses the equatorial plane going from
south to north.
*Descending node: The point where the orbit crosses the equatorial plane going from
north to south.
*Line of nodes: The line joining the ascending & descending node through the center of
the earth.
*Line of apsides: The line joining the perigee & apogee through the center of the earth.
*Inclination: The angle between the orbital plane & the earth’ s equatorial plane.
*Prograde orbit: An orbit in which the satellite moves in the same direction as the earth’ s
rotation.
*Retrograde orbit: An orbit in which the satellite moves in a direction counter to the
earth’ s rotation.
*Argument of perigee: The angle from ascending node to perigee, measured in the
orbital plane at the earth’ s center in the direction of satellite motion.
2.Explain the orbital plane. Draw it neat sketch
i) Diagram:
ii) Explanation:
*In the orbital plane, the position vector ‘r’ & the velocity vector ‘v’ specify the motion
of satellite.
R=a(1-e2)/1+ecosv
*Mean anomaly M at time t is found
M=n (t-T)
VºM+2esinM+5/4e2sin2M.
3.Explain the Orbital perturbations.
Explanation:
*Effect of non-spherical earth
*Atmospheric drag
*Inclined orbits
*Calendars
*Universal time
*Julian dates
*Sidereal time
4.Explain the geocentric equatorial &top centric co-ordinate system.
· Diagram:
· Explanation:
5.Explain the sub satellite point
i) Diagram
ii) Explanation:
6. Explain the look angle determination. Draw it neat sketch.
i) Diagram:
ii) Explanation:
7. Explain the polar mount antenna. Draw it neat sketch.
i) Diagram:
ii) Explanation:
8. Explain the limits of visibility & sun transit outage.
i) Diagram:
ii) Explanation:
9.Explain the attitude control. Draw it neat sketch.
i) Diagram:
ii) Explanation:
10. Explain the Transponders system.
i) Diagram:
ii) Explanation:
*Transponder
11.Draw the neat sketch & explain the Input Demultiplexer.
i) Diagram:
ii) Explanation:
12. Draw the neat sketch & explain the Antenna subsystem.
i) Diagram:
iii) Explanation:
13. Draw the block diagram & explain the Receive only home TV systems.
i) Diagram:
ii) Explanation:
14. Explain the indoor unit& outdoor unit.
i) Diagram:
ii) Explanation:
15. Draw the block diagram & explain the Master antenna TV system.
i) Diagram:
ii) Explanation:
*Community antenna TV system
16.Explain the EIRP& Transmission losses.
*EIRP=GPs
*EIRP is often expressed in db is given by
EIRP=(Ps)+(G) Dbw.
Transmission losses:
· Free space transmission
· Feeder losses
· Antenna misalignment losses
· Fixed atmospheric & ionospheric losses
17.Draw the block diagram& Explain the System noise temperature.
i) Block) Diagram
ii) Explanation:
*System noise
*Antenna noise
*Amplifier noise temperature
*Noise factor
*Noise temperature of absorptive networks.
18. Explain the carrier to noise ratio of uplink & downlink frequency.
19.Explain the Intermodulation noise & saturation flux density.
20. Explain the operation of FDMA system with relevant diagram.
i) Diagram
ii) Explanation
*Preassigned FDMA
*Demand assigned FDMA
21.Explain the operation of FDMA down link analysis.
i) Diagram
ii) Explanation
22.Draw the Frame format & explain the operation of TDMA system.
i) Diagram
ii) Explanation
Reference burst
*Guard time
*Carrier & bit timing recovery
*Burst code word
*Station identification code
*TTY
*Service channel
23.Draw the data format & explain the Unique word detection.
i) Diagram
ii) Explanation
*Miss probability
*False detection probability
24. Explain the Satellite switched TDMA & CDMA.Draw the neat sketch.
i) Diagram
ii) Explanation
25. Explain the Radar sat & MSAT.Mention the applications.
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