Official Website of AMSAT INDIA

These Projects have been designed and developed by the technical team at AMSAT INDIA. The designer of
the linear transponder and Cubesat comm system is Ganesan, VU3GEK . The projects are currently at various stages of
redesign and testing.

U/V Linear Transponderhomebanner3
SPECIFICATION

  • TYPE : Linear (MODE-B) transponder
  • UPLINK : 70cm (435.250 MHz)
  • DOWNLINK : 2m (145.900 MHz)
  • IF : 21.4MHz
  • RF POWER : 1.5 w PEP at 12v dc / 3 w PEP at 28v dc
  • BANDWIDTH : 50 kHz
  • Communication : CW, AM, SSB & FM
  • BEACON : CW pre-programmed message beacon on 145.950MHz (~20mW)
  • SENSITIVITY : –106dBm for max Power output
  • WEIGHT : ~1kg
  • SUPPLY : 12VDc
  • 28V Dc for final power amplifier (for 3 w)
  • DIMENSION : 180mm × 120mm × 30mm

Payload General Specification

block-diagram

Cubesat Communication sub system1img


Functional Description

The Cubesat communication system is designed to provide the space segment part of a space link for nano and Pico‐satellites by means of a half‐duplex UHF transceiver operating in the amateur radio 70cm band. The internal interface is an I2C bus /CAN allowing command and data exchange with the Com board via a simple protocol. All packets framing plus the optional Viterbi encoding/decoding is performed by the Com‐system so only the raw data packets need to be transferred over I2C bus/CAN allowing for swift integration both of the hardware and the communication protocol. Vital housekeeping measurement points are sampled at user‐defined intervals and stored for retrieval via the I2C bus/CAN. An FM Morse beacon is activated when the system is idle which may Morse any combination of the housekeeping elements in human readable format.The Communications Satellite depends on a reliable onboard COM system in order to accomplish the primary technical mission: Establish two‐way communication. A COM system has been designed with respect to the Cube Sat concept, the hardware fits onto a, 8.7[cm] x 8.7 [cm] PCB and the weight and power consumption is kept on a minimum. COM consists of a microcontroller, a modem and a radio. The software has been designed and low level functions have been implemented and tested with success. This includes transmitting data on the radio at baud rates of 1200, 2400 and 4800[bps] with FFSK/GMSK modulation

RF Specifications

Transmitter specifications:

  • Frequency : 435.250MHz
  • Output power : 1Watt
  • Spurious transmissions : < 0.025μW (except 2nd and 3rd harmonic)
  • TX‐on delay : < 5ms
  • Modulation : FM
  • Frequency response : 1 Hz … 6kHz (‐3dB)
  • Modulation voltage : 1Vss (350mVrms) for 3kHz deviation
  • Distortion : <2% at 3kHz deviation
  • Current consumption : <10μA
  • Temperature range : ‐30°C … +70°C
  • Temperature stability : <±12ppm

Receiver specifications:

  • Frequency : 435.250MHz
  • Sensitivity : ‐120dBm for 1200 baud detection Threshold (e.g. ‐118dBm for 2400 baud with FEC)
  • Image frequency : ‐65dB
  • Adjacent channel : ‐60dB
  • Blocking : 50dB
  • RSSI : Calibrated to 1dB accuracy
  • RX‐on delay : <5ms
  • Modulation : FM
  • AF output voltage : 250mVss (90mVeff) at 3kHz deviation
  • Distortion : <2% at 3kHz deviation
  • Temperature range : ‐30°C … +70°C
  • Temperature stability : <±8ppm

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