Wednesday, August 24, 2016

How do you build a 1U Cube-Sat Linear transponder using SDR / DSP technology with limited Power?

How do you build a 1U Cube-Sat Linear transponder using SDR / DSP technology with limited Power?



Requirements:

Satellite requirements.
  1. Linear Transponder 70cm (437Mhz) up-link and S band (2.4GHz or 1.2Ghz down) Down-link (Bandwidth ? 250Khz on 70cm ?)
  2. Satellite Low Earth orbit (LEO) altitude between 650 kilometers. We need this so we can calculate path loss and RF power and antenna gain requirements.
  3. Available Power 1.5W for transponder from Solar panels and battery system.
  4. Telemetry mode? CW / AX25 / AFSK 9k6 /....  
    1. UHF Beacon recomendation.
      • UHF Beacon interval:  about 55 seconds
      • UHF Transmit power: ~ 1 W
      • AFSK AX25 1k2 and fallback of CW 10WP 
  5. Satellite antennas for 70cm ? and (Polarization ?) 
  6. Satellite antennas for 2.4Ghz / 1.2Ghz and (Polarization ?) 
  7. Telemetry Requirements ? (ID, Temperature, Power in, Power out, Battery left, Transponder Mode status, Antenna Status, Satellite Orientation, ........)
  8. Inter board Connector Specification (PC/104 communication)
  9. OBC, SOLAR,charger,Orientation and Battery from existing Satellite ?
  10. 1 U Cube-Sat Space frame from existing Satellite (10x10x10) 1kg
  11. DSP 10 to 14Bit A/D /D/A Dynamic range. what is good enough ?
  12. PCB Board size details PC104 with cutouts for wire.
  13. Space frame and Solar panel frame and Antenna deployment. (out of scope)
  14. Solar panels. (Out of Scope)
  15. Power regulator and Charge regulator and Battery. (out of Scope)
  16. Orientation controls. (out of scope) (Stabilization)
  17. RF Linear Transponder using SDR / DSP. (70cm up 2.4Ghz or 1.2Ghz down)
  18. OBC (In scope ARM M4 or possibly A9) (FreeRTOS)
  19. Inter board communication standard.

 Out of Scope for now:

  1. Space frame, Solar panels and panels frame.
  2. Solar panels
  3. Power regulator and Charge regulator and Battery.
  4. Orientation controls.
In scope for now:

  1. Linear Transponder using SDR / DSP. (ARM Processor possibly not FPLG due to power constraint.)
  2. Telemetry TX
  3. Command control RX

Block diagram.


Transponder SDR transmitter. (Down-link 145.9?? MHz USB) (not confirmed) (250Khz)


Telemetry transmitter

  • Estimated TX full power for beacon and transponder (300 mW) when Sat is in sunlight.
  • When satellite is in eclipse low power of about (30mW). 

Transponder SDR receiver. (Up-link 435.??? MHz LSB ) (not confirmed) (250Khz)


  • Estimated maximum TX up-link power of 5 watts with a 7 dBi gain antenna. 

Beacon / Telemetry

Here are several DDS signal generators I'm looking at:

  1. AD9833  0 - 12.5 Mhz 
  2. AD9850  0 - 50 Mhz
  3. AD9851  0 - 70 Mhz 
  4. Si5351    0 - 150 Mhz
  5. Si5351A 0 - 290 Mhz
  6. AD9959  0 - 500Mhz
  7. AD9952  0 - 500Mhz Practical max 160Mhz depending on patern
Ref : Examples code for the STM32f4  and AD9850  https://zissisprojects.wordpress.com/2015/01/24/stm32-f4-discovery-and-ad9850-dds/

1.2Ghz band plan for Downlink





TX

  1. https://github.com/F5OEO/rpitx
  2. http://ebrombaugh.studionebula.com/radio/txdac/index.html
  3. https://www.etherkit.com/rf-modules/si5351a-breakout-board.html
  4. http://www.simplecircuits.com/files/Download/QEX_release.pdf
  5. http://www.amrad.org/projects/sdr/
  6. https://myriadrf.org/projects/rdk/
  7. http://www.eevblog.com/forum/projects/the-sdr32-a-stm32-based-software-defined-radio/
  8. http://www.stm32-sdr.com/styled/index.html  (PSK)
  9. https://wiki.analog.com/resources/eval/user-guides/ad-fmcomms2-ebz/software/baremetal?rev=1395324588#code_size_information ( AD9361 NON OS Drive)
  10. https://github.com/GomSpace/libcsp (Cubesat Space Protoco)
  11. https://github.com/robots/APRS  (STM32 APRS code)
  12. https://michaldemin.wordpress.com/2012/02/27/cheap-afsk-tnc/  (AFSK stm3  2)
  13. https://github.com/athirasubhash/AX25MODEM (AX25 for STM32)
  14. www.analog.com/en/education/education-library/videos/3845680080001.html (Video Analog devices)
  15. https://datasheets.maximintegrated.com/en/ds/MAX2837.pdf  (IQ front end Maxim)
  16. https://www.maximintegrated.com/en/products/analog/data-converters/analog-front-end-ics/MAX5863.html (A/D and D/A MAXIM)
  17. https://github.com/mossmann/hackrf/blob/master/firmware/common/max2837.c (max2837 c Library)
  18. http://www.g4jnt.com/DDSVHFBeaconDriver.pdf  (DDS beacon generation)

Possible def tools.

  1. GNU radio
  2. Math lab
  3. ARM DEV board tools. (How to setup Eclipse for Arm development)
  4. Real time OS https://istarc.wordpress.com/2014/08/04/stm32f4-behold-the-project-wizard/
  5. Installing FreeRTOS on STM32F4 https://istarc.wordpress.com/2014/07/10/stm32f4-deploy-freertos-in-under-10-seconds/
Ref :

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