1090 MHz Mode S “extended squitter” transponder

An Aircraft Transponder for the Experimental Aviation Community to meet the 2020 FAA ADS-B mandate.

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In 2020 all experimental aircraft will be required to update their transponders to meet the new ADS-B out requirement. Many of the commercial available options are very expensive so I thought I would give rolling my own a shot.

RF Front End

  • 250 Watt Peak Pulse Transmitter @ 1090 MHz
  • 1030 MHZ Receiver
    • Modulation PAM and DPSK
  • 1090 MHz Receiver
    • Modulation PPM
  • 978 MHz UAT Receiver 
    • Modulation FSK

Avionics Instrumentation 

  • WAAS GPS Source
  • Pressure Altitude 

Communication Buses

  • GDL90 (RS422)

Power Supplies

  • SWMPS 6v
  • SWMPS 50v
  • LDO 5v
  • LDO 3.3v


  • ATSAMC21E ---> Panel MCU
  • ATSAMC21G ---> Radio MCU


  • Monochrome OLED 1.54"

  • 1 × ATSAMC21E Arm MCU
  • 1 × ATSAMC21G Arm MCU

  • Assembled the first set of boards

    SN:10112410205/01/2018 at 19:27 0 comments

    Well, some errors where discovered in the first set of board, but I should still be able to use them for code development.

  • First Boards Arrive.

    SN:10112410204/16/2018 at 15:04 0 comments

    Got the boards back from fab, now just need to populate them. The two board cover all the digital logic, now just need the RF stuff, basically the hard part. A couple of careless mistakes on the large board but it should be fine, nothing to worry about at the moment. 

  • Avionics Board v0

    SN:10112410204/12/2018 at 16:40 0 comments

    Well I finished out the layout for the avionics board. Hopefully have it back from fab next week. 

View all 3 project logs

Enjoy this project?



L wrote 06/18/2023 at 02:59 point

any news?

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Julspower wrote 01/23/2022 at 23:27 point


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Chris wrote 07/20/2020 at 16:20 point

I am a licensed pilot.  If I can be of any help on testing or verifying some equipment please let me know how I can be of assistance. 

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SN:101124102 wrote 10/21/2020 at 03:03 point

I am also a licensed pilot but thanks for the offer. 

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L wrote 03/14/2019 at 05:39 point

I'm interested in you project ,and can help you to do something.

sorry , I cant find any RF part on your PCB, not here?

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SN:101124102 wrote 03/14/2019 at 06:09 point

The RF is a separate board, that needs Dk contorlled substrate, hence not fr4. The RF is done in keysight ADS so unless you have that software you can not really use it. I did the rest in Kicad. Also since the board has a 250 watt transmitter I am not keen on posting prototype work since tx in that band and power is a major fine and legal problem if its not working correctly. Interfering with aircraft operations is looked down upon in the law. I have a coupled dummy load to prevent broadcasting in the clear. Also you probably need to have pilot licence/A&P to operate one legally even for testing. 

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lalalandrus wrote 03/11/2019 at 23:21 point

any progress on this project? do you require any assitance to seeing this project to completion?

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SN:101124102 wrote 03/12/2019 at 01:07 point

Yes I need more hours in the day. I have been busy with work/life and its taken time away from this project. I am doing the next iteration of the RF section now. The digital side of the boards need another rev, some changes I want to make work ease of assembly by hand, like no qfpn. 

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