Groundstation workshop : A Flashback By : Deepika Thakur

Groundstation Workshop Contents Overview of Communication subsystem Overview of Ground station Overview of Payload Overview of Social Goal Introduction to Yagi and its characterisation Introduction to 4NEC2 Doubts and Queries Groundstation Workshop 2/17/2019

Overview of Communication subsystem Receiver Antennae Uplink Onboard Transmitter Groundstation Workshop 2/17/2019

Overview of GS A typical GS for Pratham will have the following hardware: 4 Antennae: 2 for signal demodulation and 2 for payload purposes Low Noise Amplifiers and VHF/UHF Receiver A rotor or a stand to mount the antennae Tracking software for satellite tracking AD8302 for measuring polarisation of the incoming signal A computer for data storage Groundstation Workshop 2/17/2019

Overview of Payload Main goal is to measure TEC Faraday rotation phenomenon TEC Map of India Tomography Need of TEC Need of Social goal Groundstation Workshop 2/17/2019

Overview of Social Goal Aim of social Goal Groundstation workshop Virtual labs Groundstation Workshop 2/17/2019

Introduction of Yagi A yagi antenna consists of the following elements a) Director b) Reflector c) Folded dipole or feed element The impedance of the Yagi should be matched to 50 ohms for it to transmit effectively This is achieved using a balun of length λ/4. The antenna is simulated and optimised using the 4NEC2 software Groundstation Workshop 2/17/2019

Antenna parameters Beamwidth Gain Directivity F/B ratio Bandwidth Efficiency Polarisation purity Groundstation Workshop 2/17/2019

Antenna characterization Instruments needed Impedance measurement Process of characterisation Groundstation Workshop 2/17/2019

4NEC2 Widely used software for Yagi simulation Can be freely downloaded from the net Groundstation Workshop 2/17/2019

THANK YOU Groundstation Workshop 2/17/2019

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 Oscillator Power Amplifier Antenna

Beacon Receiver We are using a Monopole Antenna to transmit and a yagi antenna to receive. Antenna LNA Circuit Comp.

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 It is industrial grade. It is operational over a frequency band of 405MHz to 470 MHz and is tunable. It’s power requirements are low. It supports packet data transmission. Maximum bitrate is 156.2 kBps which is much higher than our requirements.

Constraints on Antennae 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. Groundstation Workshop 2/17/2019

Monopole Antenna 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 Groundstation Workshop 2/17/2019