Communication and Ground Station 12 October 2008

Agenda Comm. Work and Requirements Beacon Telemetry Link Budget General Decision Ground 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. Ground Station: Which can receive signals We don’t have UPLINK

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.

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

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 OscillatorPower AmplifierAntenna

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

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

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

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

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.

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

Decision making Requirements Capture report Selection of components Testing of components Review by the team

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

Modulation Technique. The three key parameters of a carrier wave are its amplitude, it’s phase and it’s 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.

Modulation Tecniques Analog Modulation Amplitude modulation Frequency Modulation Digital Modulation Frequency Shift Keying Amplitude Shift Keying Phase shift Keying Pulse modulation

Modulation Parameters. The selection of a particular modulation technique depends upon the following parameters: a) Data Requirements b) Availability of Modules c) Minimum SNR d) Minimum Bandwidth required e) Intersymbol Interference

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

Carrier Wave Frequency The carrier wave frequency was to be selected keeping in mind the following parameters a) Availability of frequency bands b) Payload Requirements c) Availability of modules d) Interband Interference and noise We selected the Amateur band of and the 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.

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.

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.

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

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.

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 a) It is industrial grade. b) It is operational over a frequency band of 405MHz to 470 MHz and is tunable. c) It’s power requirements are low. d) It supports packet data transmission. e) Maximum bitrate is kBps which is much higher than our requirements.

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.

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

Ground station Requirements The ground station equipment can be divided into the following : a) Pre-pass Components b) Real Time Components c) Post-pass Components

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

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

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

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

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

For Beacon and TEC Crossed Yagi LNAPolarizationLNA Power Divider Polarization Beacon Circuit Beacon Signals Block Diagram

For Beacon and TEC Contd. Crossed Yagi LNAPolarizationLNAPolarization FSK Signals Block Diagram

Cost Analysis ComponentsQuantityCost ($) LNA4320 Crossed Yagi2100 OOK circuit1100 Power Divider1100 Extra80 Total700

Ground Station for Beacon YagiLNACircuit

Cost Analysis ComponentsQuantityCost ($) LNA180 Yagi250 OOK circuit1100 Extra70 Total300

Thank You