DIY Mode S Transponder for ADS-B 2020 Mandate

[oahupilot]

So the 2020 ADS-B out requirement is getting closer and the cost of many systems is just painful on the wallet. So I figure why not role my own, because how hard can it be ;D.

Going with a two part setup featuring a remote head for pilot input while the rest of radio can be installed where ever in the plane. The design includes an altitude encoder, waas gps, 978 Mhz UAT receiver, 1030/1090 transceiver @250 watts peak. Serial connection support CAN Bus and GDL-90(RS232) format.


I should have my first set of boards back from OSHpark in the next two weeks. Working on finishing up the layout for the Main digital board, hopefully finish that by the weekend.

 

[oahupilot]

Just a pic of a quick mock up I did with for the panel mount and the most expensive chip of the design the $250 Power Amplifier.

 

[oahupilot]

WOW Avionics Data Buses are the most unorganized, non-coherent mess ever. Every vendor uses a different protocol and data frame. Some people use CANBUS (MGL), other uses RS-485/422 (Garmin)or RS-232.

Its almost like they want to be sure you can only use their equipment exclusively. :

 

[oahupilot]

Main Avionics board is only 100 mm by 60 mm, will definitely get it smaller in after testing. A lot of stuff on here is more to be make it easy to test and do development. The large headers will be gone and replaced with just whats needed and smaller pitch connections. So that board is now off to the fab shop, should be in next week. So all the digital stuff has been layed out, now on to the real fun stuff the RF front end layout and tuning.

 

[oahupilot]

PCBs have arrived! Time to bust out the tweezers and populate the board. Few things I need to correct on the main board, but not worried about it at the moment. hopefully get these assembled over the next few days.

 

[oahupilot]

Its so ugly . Testing some things for the RF.

 

[oahupilot]

Well started to put some boards together and found out I goofed on the footprint for some components, thats what I get for using the prebuilt libraries. Going to make due with them till I get the code worked out , after that onto the a new round of boards.

 

[oahupilot]

The component costs will more than likely increase by 25% due to trade tariffs.

Working on a revised version of the boards, hopefully get it done shortly. Also getting a vector network analyzer, which will help me test out the transmitter board.

 

[oahupilot]

Update.

I may ditch the ADS-B in portion of the due to complexity and cost that imposes on the t/r switch design. I can use a quarter wave transformer printed on the pcb instead of fancy mems switch or really expensive pin diode by skipping ADS_B in. Because the power amplifier has 250 Watt final output stage, you need alot of isolation to prevent the transmitter from cooking your receiver. I am currently evaluating switching from FR4 pcb material to rogers doriod to see if I can make small enough micro strip elements or if I need to go back to discrete SMD components.

More to come in the future if I get enough free time.

 

[Matthuntrr1448]

Update.

I may ditch the ADS-B in portion of the due to complexity and cost that imposes on the t/r switch design. I can use a quarter wave transformer printed on the pcb instead of fancy mems switch or really expensive pin diode by skipping ADS_B in. Because the power amplifier has 250 Watt final output stage, you need alot of isolation to prevent the transmitter from cooking your receiver. I am currently evaluating switching from FR4 pcb material to rogers doriod to see if I can make small enough micro strip elements or if I need to go back to discrete SMD components.

More to come in the future if I get enough free time.

Did anything ever happen with this? It's quite interesting.