PRoject of OIT Electric-Rocket-Engine Onboard Small Space Ship

Communication Subsystem

Specification of transmission method

All communications are scheduled to be executed in the frequency of 430MHz.

Subsystem Block diagram

Components

Transmitter and receiver(Nishi RF Lab. Custom made module)

This module transmits AX.25 packet (telemetry data) to the ground station by FM method with speed of 1200bps via the dipole antenna. This module also transmits Morse codes (beacon signal) to the ground station. As for the receiver function, this module receives FM signal (command) and send AX.25 packet to TNC in communication controller.

Communication controller(UNISEC Custom made module)

Overview of communication controller

The communication controller mediates on-board computer and the Nishi RF Lab. module. Functions of this unit are follows;
1. Capsulation of AX.25 packet (Terminal Node Controller)
2. Modulation and demodulation of binary FSK (BFSK) data
3. Configure the phase lock loop and frequency, PTT of Nishi RF Lab. module

Antennas
In this satellite, the same frequency, 430MHz band is used for the transmission and the reception. Thus one antenna is installed in the satellite. As for installation antenna type, now we are concerning some antennas.
1. Half wavelength dipole antenna
  This type antenna is widely used for ultra small satellite systems. However, half wavelength of used frequency is longer than satellite's size. Thus, to use of this type antenna, it should be folded at launch or shortening antenna size by using coils.
2. Inverted L antenna
  Inverted L antenna is a kind of l/4 monopole antenna. It has the structure bent at the angle of 90 degree on the way of the element of the monopole antenna. Though the performance inferior to the monopole antenna, it has feature of modest attitude. The performance decreases to approaching to about the feeding point by the part of bent. Moreover, it is necessary to match it so that impedance may shift greatly from 50 ohm.