1. Groundstation workshop : A Flashback
By : Deepika Thakur

2. 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

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

4. 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

5. 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

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

7. 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

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

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

10. 4NEC2 Widely used software for Yagi simulation
Can be freely downloaded from the net
Groundstation Workshop
2/17/2019

11. THANK YOU
Groundstation Workshop
2/17/2019

12. 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

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

14. 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.

15. 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 kBps which is much higher than our requirements.

16. 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

17. 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