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Communication and Ground Station

Agenda. Comm. Work and RequirementsBeacon TelemetryLink BudgetGeneral DecisionGround Station. Communication Work . Beacon: Low bit rate device on the satellite which is functional for the entire lifetime of the satellite. Telemetry Data: High bit rate (1.2kbps) Monopole for downlink of data.

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Communication and Ground Station

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    1. Communication and Ground Station 12 October 2008

    2. Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground Station

    3. Communication Work Beacon: Low bit rate device on the satellite which is functional for the entire lifetime of the satellite. Telemetry Data: High bit rate (1.2kbps) Monopole for downlink of data. Ground Station: Which can receive signals We dont have UPLINK

    4. Communication Requirements Both the antennas onboard must be transmitting linearly polarized radio signals. 2 independent crossed yagi antennas at ground stations to receive data and measure their polarization. Low cost ground station for other universities to measure polarization.

    5. Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground Station

    6. Beacon It is device which transmits low power signal by an omni-directional antenna which help us to locate our satellite Beacon circuit is not connected to OBC OOK transmitter and receiver at 437MHz and transmission power 0.4 Watt. Transmitter

    7. Beacon Contd. Receiver We are using a Monopole Antenna to transmit and a yagi antenna to receive.

    8. Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground Station

    9. Telemetry We are using Monopole 2 (another antenna) used for data transmission. Contact time: 13 15 min Data rate: 1.2 kbps Over India; we will transmit Position Data and transmit stored data of last 24 hrs over IITB GS. Modulation: FSK

    10. Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground Station

    11. Link Budget At what power we should transmit our signals so that we will definitely receive it? Through Link Budget Analysis Estimate various types of losses for example : Ionosphere losses, atmospheric losses, polarization losses, pointing losses etc.

    12. Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground Station

    13. Decision making

    14. Communication parameters Modulation Carrier Wave Frequency On Board Antennae Transmitter Circuit Protocol of Transmission

    15. Modulation Technique. The three key parameters of a carrier wave are its amplitude, its phase and its frequency all of which can be modified in accordance with a low frequency information signal to obtain the modulated signal. Modulation Techniques can be broadly divided into 3 categories Analog Modulation and Digital Modulation and Pulse modulation.

    17. Modulation Parameters.

    18. Frequency Shift Keying We decided to go ahead with frequency shift keying as it has the following characteristics : Spectrally Efficient Moderate value of Eb/No Modules Readily Available Low intersymbol interference as compared to FM.

    19. Carrier Wave Frequency The carrier wave frequency was to be selected keeping in mind the following parameters Availability of frequency bands Payload Requirements Availability of modules Interband Interference and noise We selected the Amateur band of 433-437 and the 400-405 band as the former is an amateur band and hence it is easy to get modules and sanctions for that band and the latter is a band reserved for Ionospheric studies which is what our payload deals with.

    20. Onboard Antenna An antenna is a transducer designed to transmit or receive electromagnetic waves. As we had done away with uplink the selction of the transmitting antennae, both the telemetry and the beacon, was a very critical decision for the team.

    21. Antenna parameters Moderate to High Gain Moderate Beamwidth Linear Polarization For payload purposes Polarization Purity Ease of Fabrication Characteristic length to be of the order of satellite dimensions.

    22. Monopole Antennae We chose the monopole over the other antennae because: Being Omnidirectional it reduces the constraints on attitude control It produces a linearly polarized beam. High polarization purity can be obtained by careful design of the antenna. The length of the antenna is comparable to the satellite dimensions It is easy to fabricate . The loss in gain can be compensated by using a directional antenna on the ground station

    23. Transmitter Circuit Parameters. Industrial grade . Low power requirements in accordance with the power budget. Wide bandwidth covering our operational range. Minimum and Maximum Bitrate should cover our requirements Compatible with AX.25 protocol.

    24. CC1020 We selected this circuit mainly because it had been used earlier in a student satellite and hence had some space heritage. The other parameters of CC1020 are It is industrial grade. It is operational over a frequency band of 405MHz to 470 MHz and is tunable. Its power requirements are low. It supports packet data transmission. Maximum bitrate is 156.2 kBps which is much higher than our requirements.

    25. Protocol It is a standard practice in communication systems to use a protocol for the transmission of data. The protocol tells the user regarding the start and end of the data stream and enables the end user to correct the data in case it has become corrupt due to noise or interference.

    26. AX.25 The AX.25 protocol is a standard protocol used by the amateur radio enthusiasts and is robust enough for our purpose.

    27. Ground station Requirements The ground station equipment can be divided into the following : Pre-pass Components Real Time Components Post-pass Components

    28. Pre pass Components Nova Tracking Software We have selected this software as it is compatible with the rotor interface.

    29. Real Time Components Crossed Yagis G5500 Rotor LNA Power Dividers Receiver for both the beacon and the telemetry data

    30. Post Data Requirements Signal strength Analysers for payload purposes Data storage and analysis equipment Computers

    31. Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground Station

    32. Ground Station

    33. Ground Station Contd. Communication horizon: -30 to 30 deg Location: GG Building terrace Tracking accuracy: 1 degree Yagi 2 independent crossed yagis at 405MHz and 437MHz FSK Circuit OOK circuit

    35. For Beacon and TEC

    36. For Beacon and TEC Contd.

    37. Cost Analysis

    38. Ground Station for Beacon

    39. Cost Analysis

    40. Thank You

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