KC.SHARMA

BASICS OF SATCOM-2

Satellite Block DiagramTransponder - the frequency conversion and amplification part of the satellite

Satellite Frequencies and TranspondersUplink - The signal from the earth antenna to the satellite.

Downlink - The signal from the satellite to the earth station

Low Noise Amplifier(LNA)-amplifies the uplink signal

Frequency Converter-converts the incoming signal to the downlink frequency.(The uplink and downlink signals must differ to avoid conflicts with each other.

High Power Amplifier(HPA)-Amplifies the signal to be rebroadcast.Satellite Frequencies and Transponders (contd.,)

The difference between the uplink and downlink frequency is called the deltaFrequency Assignments For Satellite Systems

Inroutes And Outroutes

Comparison of C-band and Ku-band C-bandIn the U.S.A., C-band requires an FCC license for each site

C-band is commonly used for satellite transmission outside of the U.S.A.

Ku-bandWith very heavy rain,fog, or clouds, the received signal strength falls and the noise increases.

Antennas for Ku-band can be smaller than for C-band

Bandwidth Allocation Methods One user is assigned the entire available bandwidth for an infinite amount of time.Allocates a finite amount of bandwidth to one user for an infinite amount of time.

Bandwidth Allocation Methods ( contd.,)Allocates the entire available bandwidth to one user for a finite amount of time.Allocates a small amount of bandwidth to one user for a short amount of time, allowing many users to share the same bandwidth.

Example of FDMASPECTRUM ANALYZER SCREEN

Example of TDMASPECTRUM ANALYZER SCREENFrequency

Frame In a TDMA SystemNote : Bursts need not be in sequential orderA frame is a time segment that contains data. ( 45msec in ISBN)

A burst is a data transmission on an inroute

Bursts can contain either user data or control data

Slotted AlohaEach burst must begin on one of the time divisions (slots).

Any bursts that occur at the same time will collide. These bursts must then be transmitted.

Basic Block Diagram Of An Earth StationThe baseband equipment provides interfaces that allow space link/user protocol conversion.

The IF subsystem performs modulation/demodulation

The RF subsystem performs IF/RF conversion and signal amplification.

POLNET HUB EQUIPMENT11 Mtr Antenna 2KW HPA (1+1) Low Noise Amplifier(1+1) UP Converter (1+1)Down ConvertorAntenna Control UnitDehtdratorTDMA Base band Equipment - 5 networksSCPC Base band equipmentSCPC NMS 1+1TDMA NMS- 1+1 (2 sets)

POLNET HUB EQUIPMENT

Exchange VOIP Box 2 nos.Gatekeeper PCAudio Broadcast PC/MessagingRouterX.25 SwitchUPS30 KVA 3phase30 KVA 1 phase20 KVA 1 phase

2 KW HPA (1+1)

Frequency 5.925 GHz to 6.425 GHzPower O/P- 2000 WattsMain Components- 2 Amplfiers 2 Power Suplies Change over switch Wave Guide Switch Dummy loadAmplifier- TWT 2 KwAC Power input 440 V 3 PhaseCooling- Forced Air cooling

11 Meter Antenna11M Parabolic Reflector with Cassegrian feed & SubreflectorFrequency of Operation Trans 5.925-6.425 GHz Receive 3.7-4.2 GHzGainTransReceive54 dB51 dBVSWR1.3:1Power Handling Capacity5KWCross Polarisation 30 dBPolarisation- Linear as well as circularNo. of ports 4 ports

11 Meter Antenna (cont.)Antenna Diameter11.0 MAntenna TypeCassegrainReflector Construction24 Panels Stretched formedAluminiumMountElevation over AzimuthElevation5 to 90 degAzimuth 90 continuous or180 in two sectorsPolarisation AdjustmentManual +/- 90 deg

11 Meter Antenna (cont.)Antenna Travel rateAzimuth 0.01 deg/sec0.02 deg/sec (high speed settingElevation0.01 deg/sec0.02 deg/sec (high speed setting

EnvironmentalOperational:70 Km/hrSurvival200 Km/hr

Antenna Control Unit (ACU)Function:- To Keep the antenna pointed towards the satellite at all times by continuosly tracking the beacon signal and rotating the antenna in elevation & azimuth direction automatically/manually in case of any fall in the beacon signal. The unit can also be used toShift from one satellite to another satellite.

Main ComponentsControllerPDU(Power Distribution Unit)Elevation Actuator with motorAzimuth Actuator with MotorLimit Switches for Azimuth & Elevation

Antenna Control Unit (ACU) Cont.. Elevation Decoder (For Converting mechanical movement into degrees in digital form)Azimuth Decoder (For Converting mechanical movement into degrees in digital form)Block Down Convertor ( For down converting beacon signal coming from satellite into L-band and giving to controller)Operates on single phase AC power and motors operate on 3 phase 440V AC power.

Antenna can be rotated manually in small steps. A command for long movement can be given and antenna will move to that location. The geographical position of various satellites can be stored in memory of controllers.

Antenna Control Unit (ACU) ContBoth the elevation & Azimuth motors have settable fast & slow speeds.

The antenna is protected against any damage during motion by the limit switches which switches OFF the motors.

The antenna can be rotated manually in Azimuth as well as Elevation by using handle in case of failure of ACU.

DEHYDRATORDehydrator is used to pump dry air into waveguide in trans path & maintain a constant air pressure inside the whole section of waveguide. This prevents the ingress of moisture into the waveguide and avoid any arcing which may take place due to high power.

Maintenance free sealed unit operates on 230 volts AC power supply.

UPCONVERTORIt is used in the transmit chain

It converts IF signal to RF signal in C-Band

Input Freq.70+18 MHzOutput Freq Settable between 5925-6425MHz

Two Upconvertors connected in 1+1 configuration

Both are connected to changeover switch in hotstandby Configuration.

UPCONVERTOR (contd..)The output of all basebend equipments in IF range is combined and given to IF input of Upconvertor.

The RF output is given to HPA

The upconvertor & switch operate on 230V AC supply.

DownconvertorIt is used in the Receive chain

It converts RF signal to IF signal in C-Band

Output Freq.70+18 MHzInput Freq Settable between 5925-6425MHz

Two Dnconvertors connected in 1+1 configuration

Both are connected to changeover switch in hotstandby Configuration.

Downconvertor (contd..)The output of LNA in RF range is given to RF input of Dnconvertor.

The IF output of downconvertor is given to all Baseband equipments as IF input.

The Dnconvertor & switch operate on 230V AC supply

TDMA BASE BAND EQUIPMENTConsists of 5 separate & independent TDMA networkEach network has two racks i.e. Base band rack & IF subsystem rack Base band rack consistsNetwork Control Clusters (1+1) also called NCC2LAN SLIM (1+1) X25 SLIM (1+1)IF Subsystem rack consist ofUMOD (1+1)BCD (10+2)

NCC2 controls all the functions of the network. It also interfaces with NMS.

TDMA BASE BAND EQUIPMENTVoice is transmitted using VOIP and LAN SLIMDATA is transmitted using LAN SLIMMessaging is done using X25 SLIMInterconnection between different network for voice & LAN data is done at LAN SLIM & LAN hub. Voice Call switching between different network is done using Gatekeeper.

Interconnection for messaging is done at X25 LAN SLIM and X.25 switch.

SCPC BASEBAND EQUIPMENTSCPC is full mesh single hop hub based satellite communication system with DAMA facility.DAMA is a software installed at NMS.OCC(Outbound control Channel) is continuously transmitted from hub at 58.5MHz. All the remotes are tuned to this frequency all the time. All the information from the hub is transmitted on OCC to remotes.

Two nos. of ICC (Inbound Control Channels) are provided. The remotes have to transmit their information/ request on this channels to hub.

OCC & ICC are called control channels. Total of 6 control channels are provided at hub, 3 are operational and 3 are standby at all times.

TDMA NMSThere are total 5 TDMA networks.One NMS can control 3 networks. Therefore 2 NMS in (1+1) configurations are provided(total 4 machines). The NMS is on Compaq DS-10 machineThe operating system is UNIX.Configuration/monitoring is done from NMS.NMS can remain OFF during normal operation.

SCPC NMSOne NMS in 1+1 configuration is provided.

The operating system & hardware is same to TDMA NMS.

The NMS is required to be ON all the time as DAMA function is installed at NMS,

Call by call Frequency allotment for all DAMA circuits is done by NMS besides the monitoring & controls.

OTHER SUBSYSTEMSGatekeeper PCAll the IP packets pertaining to voice communication from remotes are brought to hub and given to gatekeeper. These packets are then routed to respective remotes.

X.25 SwitchThe routing of messaging between different networks on TDMA is done by this.

Exchange One no. of BPL make IDX 250 model exchange has been installed at Hub for POLNET voice communication.

POLNET HUB EQUIPMENT11 Mtr Antenna 2KW HPA (1+1) Low Noise Amplifier(1+1) UP Converter (1+1)

Exchange UPS30 KVA 3phase30 KVA 1 phase20 KVA 1 phase

Frequency 5.925 GHz to 6.425 GHzPower O/P- 2000 Watts

11M Parabolic Reflector with Cassegrian feed & SubreflectorFrequency of Operation Trans 5.925-6.425 GHz Receive 3.7-4.2 GHz

Antenna Diameter11.0 MAntenna TypeCassegrainReflector Construction24 Panels Stretched formedAluminiumMountElevation over Azimuth

Antenna Travel rateAzimuth 0.01 deg/sec0.02 deg/sec (high speed settingElevation0.01 deg/sec0.02 deg/sec (high speed setting

Function:- To Keep the antenna pointed towards the satellite at all times by continuosly tracking the beacon signal and rotating the antenna in elevation & azimuth direction automatically/manually in case of any fall in the beacon signal. Elevation Decoder (For Converting mechanical movement into degrees in digital form)Azimuth Decoder (For Converting mechanical movement into degrees in digital form)

Both the elevation & Azimuth motors have settable fast & slow speeds.The antenna is protected against any damage during motion by the limit switches which switches OFF the motors .Dehydrator is used to feed dry air into waveguide in trans path & maintain a constant air pressure inside the whole section of waveguide. This prevents the ingress of moisture into the waveguide. It is used in the transmit chainIt converts IF signal to RF signal in C-BandInput Freq.70+18 MHzOutput Freq Settable between 5925-6425MHzTwo Upconvertors connected in 1+1 configurationBoth are connected to changeover switch to providehot The output of all basebend equipments in IF range is combined and given to IF input of Upconvertor.Consists of 5 TDMA networkEach network has two racks i.e. Base band rack & IF subsystem rack Voice is transmitted using VOIP and LAN SLIMDATA is transmitted using LAN SLIMMessaging is done using X25 SLIMInterconnection between different network is done at LAN SLIM & LAN hub.

SCPC is full mesh single hop hub based satellite communication system with DAMA facility.DAMA is a software installed at NMS.OCC(Outbound control Channel is continuously There are total 5 TDMA networks.One NMS can control 3 networks. Gatekeeper PCAll the IP packets pertaining to voice communication from remotes are brought