Earth Station Communication System-Sagarmatha Earth Station
study is the outcome of the 'In-Plant Training in Satellite Communication'
held at Sagarmatha Earth Station, Balambu, Kathmandu, Nepal on May-June
2006. This study has investigated the essential field of communication
engineering i.e. Satellite Communication along with basic of communication
between ground station (Earth Station) and Satellite. In this research
program we study essential equipments needed for earth to satellite
communication. Study also reveals the latest technology in antenna propagation
used by Nepal Telecom for wireless communication. Advantages due to
utilization of latest equipments and it cost effectiveness is also studied
in this research program.
Benefit: This study reveals the importance of Earth Station in the field of Satellite
Communication. Sagarmatha Earth Station being only Earth Station of
Nepal, it has served to all the people of Nepal from the date of its
establishment. Communication between remote district like Humla, Jumla,
Mugu, Kalikot e.t.c where wired communication can never be thought of,
is made possible only via this earth station. As we have entered into
the modern era of high speed communication i.e. Optical Fibre communication
still we are not able to utilize it efficiently being a landlocked country.
So, satellite communication is only alternative for country like Nepal.
Thus, functions of this station is very promising and appreciating in
context of Nepal. As a whole, we can say this station is fully dedicated
to Nepalese welfare and development.
Satellite Communication  
First satellite was Russian satellite Sputnik launched in 1957.
Early Bird, launched in 1965
was first geostationary satellite. It was first satellite launched
by Intelsat later named as Intelsat I weighing
36kgs, 6/4 GHz transponder each 25 MHz bandwidth.
Canada was the first country to build a national
telecommunication system using GEO satellites. Anik 1A was launched in May 1974, just 2 months before the first U.S domestic
satellite WESTER 1.
The ability of satellite systems to provide
communication with mobile users had long been recognized, and
the International Maritime Satellite Organization (Inmrasat) has provided service to ships and aircraft for several decades.
LEO satellites were seen as one way to create
a satellite telephone system with worldwide coverage; numerous
proposals were floated in the 1990s, with three LEO systems eventually reaching completion by 2000(Iridium,
Globstarm and Orbcomm).
DBS-TV and GPS had revolutionized
the communication system in this 21st century.
Earth Station provides the communication pathway
between the Geo-stationary Satellite and local networks.
Signals from the all the local networks are send to the Satellite
for long distant communication and signal received from the Satellite
are send to desired location within a network is done by the Earth
Station. International Calls, International Direct Dialing, Occasional
TV Broadcasting, Internet Access, Weather Forecasting, VSAT
(Very Small Aperture Terminal) Communication are prominent
benefits of an Earth Station. Intelsat-1 to Intelsat-4, ThaiCom, Arabsat,
TelStar, Early Bird, KoreaSat are some satellites send by many countries
to guide wireless long distant communication. A signal also termed
as baseband signal or message signal is send via
antenna to the Satellite by the unique uplink frequency and signal are received from the satellite by the downlink
frequency. Figure below shows the block diagram of the systems
needed for efficient and accurate communication inside the earth station.
Figure: Schematic diagram of earth station communication.
Ku-Band Uplink Frequencies: 14 GHz – 14.5
Ku-Band Downlink Frequencies: 11.7 GHz – 12.2
C-band Uplink Frequencies: 5.925 GHz – 6.425
C-Band Downlink Frequencies: 3.7 GHz – 4.2
Up-link frequency is much higher than the down-link
frequency because while sending information from the earth to the
space, signal need to travel against the gravitational force of earth
and need to penetrate the thick layer of atmosphere. Baseband band
or Message signal is first send to the Multiplexer through a communication channel. Multiplexing is the process of combining
a number of signals into a single signal, so that it can be processed
by a single amplifier or transmitted over a single radio channel.
Multiplexing can be done at baseband or at a radio frequency. The
corresponding technique that recovers the individual signals is called
Demultiplexing. Multiplexing is a key feature of all commercial long-distance
communication systems, and is par of the multiple access capability
of all satellite communication systems.
Multiplexed signal is send to the DACCS
(Direct Access Cross Connect System) and DCME (Digital Circuit Multiplication
Equipment). In communications systems DACCS performs following
function, a digital system in which (a) access is performed by T-1
hardware architecture in private and public networks with
centralized switching and (b) cross-connection is performed by D3/D4
framing for switching digital-signal-0 (DS-0) channels to other DS-0
channels. Modern digital access and cross-connect systems are not
limited to the T-carrier system, and may accommodate high data rates
such as those of SONET. In the EIA/TIA 568-A standard,
a horizontal cross-connect is used to describe the distribution station
when such a station is separate from the main backbone, and accessed
via horizontal cabling. Digital Circuit Multiplication Equipment (DCME)
was a type of voice compression equipment that is installed at either
end of a long-distance link (typically communications satellite or
submarine communications cable). The main characteristics of DCME
are defined in ITU-T recommendation G.763. DCME consists
of a voice interpolation stage, which is a form of statistical multiplexer
applied to voice-band signals, and a low rate encoding stage which
exploits correlation between successive voice-band samples on an individual
input channel to reduce the transmitted bit-rate from that required
by PCM of equivalent quality.
Signal is then send to Modulator where signal is
converted to high frequency called IF (Intermediate Frequency) equals
170 MHz. Modulation is converting low frequency signal to high frequency
where property of modulating signal changes according to either Phase
or Frequency or Amplitude called as AM, PM or FM. Modulation helps
weaker signal to travel longer distance and also help to decrease
the length of antenna needed for propagation. Frequency is inversely
proportional to wavelength of wave and antenna length directly depends
on the wave length of the baseband signal. Conversion of any signal
to IF helps us in designing amplifiers and filters easily for small
range or frequencies.
IF signal is then converted to large frequency called
as uplink frequency order of GHz (C-Band uplink frequency is 6 GHz)
by the Up-Converters. Larger the Signal frequency
greater the signal has capacity to penetrate the thick atmospheric
layer and greater chance to travels to longer distance with minimum
attenuation. But frequencies greater than 12 GHz result in maximum
rain attenuation hence suitable frequency is chosen during satellite
Up-Converted signal is then send to SSPA
(Solid State Power Amplifier) to increase the power of signal
to prevent any kind of attenuation and errors (Bit Error Rate). Final
signal is send to the antenna via a wave guide pipe.
Wave Guide Pipe sends any signal with minimum attenuation and maximum
efficiency and it is a wired communication channel laid from SSPA
or any equipmemt directly to the antenna for distant communication. Antenna provides directivity and Impedance Matching to the signal for easy propagation
over the air. Number of environmental factors need to be considered
like Rain, Solar Flares, Snow Fall, Clouds, Auroras e.t.c for Satellite
Satellite needs numbers of sophisticated equipment
for receiving and transmitting the signal by FM technique to long distances. The payload of a satellite is
all the specialized equipment needed to perform its designed function.
A communications payload act like a communications repeater. RF
signals to the satellite are received, converted, amplified,
and transmitted back to Earth. The payload includes the antenna, wide-band
receivers, input and output multiplexers, programmable attenuation
devices, and amplifiers. Satellites designed with a single payload
are only able to operate with a single band of frequencies, either
C or Ku. Satellites with dual payloads, also known as Hybrid
Satellites, are able to operate with both C and Ku bands
(1 band per payload). Each payload has a set of components that operates
with a specific band of frequencies.
While receiving the signal passes via the same equipments
but under lower frequency than uplink frequency called download frequency.
Signal received at the antenna is send to the LNA (Low Noise
Amplifier) to remove all the noise and amplifies only the
required signal. LNA is present at the antenna itself and present
receiving end of the antenna. Received signal at the downlink frequency
(4 GHz for the C-Band Communication) is send to the Down-converter from the wave guide pipe to convert the signal to IF at the frequency
40 MHz. Intermediate Frequency is send from the Demodulator to the
Demultiplexer. Finally, baseband band signal is received with least
attenuation and least error from the demultiplexer.
on the Satellite Communication
Following are the factors affecting satellite communication:
Doppler Shift: For a stationary observer, the
frequency of a moving radio transmitter varies with the transmitter’s
velocity, relative to observer. If the true transmitter frequency
( the frequency that the transmitter would send when at rest), the
received frequency is higher when the transmitter is moving toward
the receiver and lower that the transmitter is moving away form the
receiver. The shift of frequency is called Doppler Shift.
Rage Variation: The position of satellite with
respect to earth exhibit a cyclic variation. For TDMA careful attention
must be done to the timing of the frames within the TDMA burst.
Solar Eclipse: During full solar eclipse satellite
must run on its own battery power as it receives no power from the
Sun Transit Outage: During equinox period (March
21 and September 23) earth station receive not only signal from satellite
but also the noise temperature transmitted by the sun. This added
noise temperature will cause the fade margin of the receiver to be
exceeded and outage will occur.
at Sagarmatha Earth Station
1. ARMA C400 SSPA
2. NEC UP/DOWN CONVERTER
3. STANDARD A OR B ANTENNAS
In Sagarmatha Earth Station we have two Standard ‘B’ antennas
(11m and 9m) and one Standard ‘A’ antenna and other demos
and two microwave antennas (not in operation). Both standard antennas
are linked with four IntelSat Satellites out of 24. These all are
Cassegrain Antenna or Gregorian antenna.
Standard ‘A’: Main purpose is International
Calls, Internet Connection for NTC, and Occasional TV for NTV. Its
diameter is 16.4m and largest in Nepal.
Standard ‘B’: There are two standard
antennas. Used mainly for VSAT network. Their diameters are 11m and
9m. Placed for 66º E satellite. Consists of
In Sagarmatha Earth Station, multiplexer are used for Occasional
TV, VSAT communication and Telecommunication.
STM Multiplexer: This multiplexer is used in VSAT
PCM Multiplexer: Used for telecommunication.
REP: Multiplexer used for telephone system. (Now-a-days
not in operation or replaced).
DTX 240E System:
The function of the respective units:
PSK MODEM: Used for satellite communication using
PSK technique. Few years ago MODEM used BPSK (Binary Phase Shift Keying)
technique but due to newer invention of modulation technique Sagarmatha
Station uses QPSK (Quadrature Phase shift keying) and 8PSK(Eight Phase
Shift Keying) technique. This leaded to minimize the bandwidth to
be used in transponder and cost for communication is gradually decreasing.
SDM-309 Satellite MODEM: MODEM used for VSAT communication.
Used TDMA technique in the earth station.
DVB Digital Video Modem: MODEM used for occasional
TV used by NTV (Nepal Television).
N × 64Kbps Modem: Extensively used for Internet
Access by NTC.
6. OCCASSIONALV TV EQUIPMENTS OF NTV
Digital Video MODEM (DVB 3030)
RCS-11 Redundancy switch
Audio Video Distribution Amplifier
Digital Baseband patch for occasional TV
Video patch and TV Test Signal generation
TV sound monitor and webform monitor.
Solid State Power Amplifier
Extended Range DC Power Supply (0-60V and 20A).
7. DTX-360 Ethernet HUB for VSAT
Can be called as the heart of the VSAT network. Signal
coming from any VSAT station from remote place is received by this HUB station and transmitted to desired place for
efficient communication. Internet access, Local and International
telephone calls are sent from remote village via VSAT antenna to main
earth station and here HUB receives the signal and transmits to the
satellite for communication. Efficient communication is possible in
Sagarmatha Earth Station by utilizing DAMA technology
and dedicated technology in this HUB. E.g. Due to use VSAT technology
internet access in Base camp of Mount Everest has been made possible.
8. Antenna Steptrack Controller
Used to operate in different modes of antenna. It is fully automated
system and software oriented control system. Controller works according
to values of Look Angles i.e. Azimuth and Elevation.
Azimuth is measured eastward (clockwise) from geographic north to
the projection of satellite path on a (locally) horizontal plane at
the earth station. Elevation is the angle measured upward from the
local horizontal plane at the earth station to the satellite path.
Operated by 7200 Antenna Control Unit, which is fully software oriented
8PSK: Eight Phase Shift Keying
ADPCM: Adaptive Differential Pulse Code Modulation
AM: Amplitude Modulation
BPSK: Binary Phase Shift keying
CDMA: Code Division Multiple Access
CELP: Code Excited Linear Prediction
DACCS: Digital Access Cross Connect System
DAMA: Demand Assigned Multiple Access
DBS-TV: Direct Broadcast Satellite Television
FDMA: Frequency Division Multiple Access
FM: Frequency Modulation
GEO: Geo-Stationary Earth Orbit
GPS: Global Positioning System
GPRS: Global Positioning Radio System
IF: Intermediate Frequency
IntelSat: International Telecommunications Satellite
ITU-T: International Telecommunications Union
LHCP: Left Hand Circular Polarization
LEO: Lower Earth Orbit
LNA: Low Noise Amplifier
MEO: Medium Earth Orbit
NTC: Nepal Telecom
PCM: Pulse Code Modulation
PSK: Phase Shift Keying
QPSK: Quadrature Phase Shift Keying
RHCP: Right Hand Circular Polarization
SCPC: Single Channel Per Carrier
SSPA: Solid State Power Amplifier
TDMA: Time Division Multiple Access
TTCM: Telemetry, Tracking, Command and Monitoring
VSAT: Very Small Aperture Terminal
I heartly thank Nepal Telecom, Kathmandu, Nepal for
providing me a week to complete my 'In-Plant Research in Satellite
Communication' on 23rd -30th May 2007 at the Sagarmatha
Earth Station, Balambu, Kathmandu, Nepal. I am grateful to Mr. Mithilesh
Chandra Jha (Senior Engineer) for giving me his precious time to complete
research on Sagarmatha Satellite Earth Station as a technical advisor.
Without his technical guidance this research program wouldn’t
have been completed in time. I’m equally thankful to Mr. Birendra
Gongol (Station Manager) for giving me opportunity to study each and
every instruments involved in ground to satellite communication. I
would like to thank Mr. Lok Raj Paneru (Senior Engineer) for his technical
guidance. I’m equally thankful to all the staffs of Station
for giving me chance to study sensitive parts of station. I would
like to thank Nepal Telecom and Nepal Telecom Training Centre for
giving me oppurtinity to study each and every sections of a Sagarmatha
Earth Station. I sincerely thank to Mr. Dipeen Dhakal, Pulchowk Engineering
College, Kathmandu, Nepal for his guidance in analysis of different
List of Refrences
 Timothy Pratt, Charles Bostian, Jeremy Allnutt. Satellite
Communication, Wiley Student Edition (2006).
 Handbook of communication, Tata Mc-Graw Hill Edition (2005)