Stratux FLARM I/O upgrade for USA - 978/1090/915Mhz?

[SoaringScholar]

Hi there!
After a recent near-miss with a powered-plane during a sailplane soaring flight, I'm revisiting my few-year-old Stratux 2 build from my powered flying and want to add FLARM Rx & Tx capability for glider use in the USA. I've been reading on this Github and Dross Aviation's website but have a few questions about implementation for USA. It's been years since I built this stratux and haven't messed with the software config since, so i'm trying to remember how this all should work...

Questions:

1. For USA FLARM I/O integration, would I want a 915Mhz TTGO T-Beam or T-motion for Tx + antennae (2x...one for TTGO Tx and one for SDR Rx)?

• It appears that FLARM uses 915 +/- 12Mhz in the USA per their website
• All the discussions I've seen mention use of the 868Mhz components for FLARM I/O, which makes sense for EU, but I want to double check to make sure that I need different hardware for US.
• I've also seen comments about 868Mhz having better range capability, but not sure why or if that applies to US use.

2. Is it possible and/or beneficial to attempt to keep 978Mhz, 1090es, and add FLARM In/Out? I'm worried about missing traffic that is only on 978Mhz, if I only run 1090es and Flarm.

• It looks like most of the builds only maintain 1090es for ADS-B, and convert the 978mhz SDR and swap antenna to the FLARM band antenna.
• Reading the Compatible Hardware section, It seems like this might be feasible if you replace the UBlox8 USB GPS Module with the TTGO. Meaning that the 4 USB ports on the RPi 3B would be filled by:

1. 978Mhz SDR
2. 1090Mhz SDR
3. FLARM 915Mhz SDR
4. FLARM TX (TTGO T-Beam/T-Motion)
   The goal would be a Build Example 3 but potentially with 978Mhz Rx as well.

3. What would I need to do from a software configuration standpoint to adjust the latest EU Stratux release for use in the USA (915MHz SDR assignment, etc)?

• I'm using XCSoar as my EFB, which it looks like the latest build (Stratux Europe Edition 1.6r1-eu026) now supports via NMEA output? Anything special to configure here?
• Assign the SDR's to the correct protocol (i found this discussion post from b3nn0 which suggests that this is fairly simple now in latest releases)
• Anything else?

For reference, my existing Stratux 2 Build Components:

Component	Link
Stratux AHRS 2.0 - Sensors and Fan Controller/Raspberry Pi ICM-20948+BMP280	https://www.amazon.com/gp/product/B06ZZCHBHT/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1
Stratux GPYes 2.0 u-blox 8 GPS unit	https://www.amazon.com/gp/product/B0716BK5NT/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1
Raspberry Pi 3 Model B Motherboard	https://www.amazon.com/gp/product/B01CD5VC92/ref=ppx_od_dt_b_asin_title_s01?ie=UTF8&psc=1
Stratux Case with Fan, White ABS	https://www.amazon.com/gp/product/B072ND582W/ref=ppx_od_dt_b_asin_title_s01?ie=UTF8&psc=1
SummitLink ADS-B High Gain Antenna 1 x 978MHz 1 x 1090MHz for DIY ADS-B Raspberry Pi Building Kit	https://www.amazon.com/gp/product/B01KBYHY3K/ref=ppx_od_dt_b_asin_title_s01?ie=UTF8&psc=1
Stratux 1090ES & UAT Radio - Low Power v2	https://www.amazon.com/gp/product/B01M69X5XI/ref=ppx_od_dt_b_asin_title_s02?ie=UTF8&psc=1
Kingston Canvas Select 16GB microSDHC Class 10 microSD Memory Card UHS-I 80MB/s R Flash Memory Card Adapter (SDCS/16GB)	https://www.amazon.com/gp/product/B079H6PDCK/ref=ppx_od_dt_b_asin_title_s02?ie=UTF8&psc=1

New components I'm thinking of for upgrade:

Component	Link
LILYGO & SoftRF TTGO T-Motion S76G Lora Chip LORA 868/915/923Mhz Antenna GPS Antenna USB Connector Development Board - 915MHz [Would replace Stratux GPYes 2.0 u-blox 8 GPS unit]	https://www.aliexpress.com/item/4000579732931.html?spm=a2g0o.cart.0.0.1e9e3c00wKreTe&mp=1
915MHz LoRa Gateway Antenna Omni 5dbi Gain SMA Male Connector 2 PCS	https://www.amazon.com/dp/B091PRHPTJ?psc=1&ref=ppx_yo2_dt_b_product_details
HiLetgo BMP280 BMP280-3.3 High Precision Digital Atmospheric Barometric Pressure Atmospheric Pressure Sensor	https://www.amazon.com/gp/product/B01ICN5QPU/ref=crt_ewc_img_dp_1?ie=UTF8&smid=A30QSGOJR8LMXA&th=1
3rd SDR - Stratux V2 or NooElec Nano2/3
3D printed case to support T-motion & additional antennae
Latest release of Stratux EU Edition configured for US use?

Thanks a bunch for your work & support!

[b3nn0]

1. Yes, IIRC Flarm is 915Mhz in the US.
2. Yes I think it makes sense to have 978Mhz reception. There is no UAT in Europe (mostly), so the conversion makes sense - you however will want to add instead of replace.

Now more generally speaking:
There is one issue with all of this: The SDR-Based reception in Stratux currently only supports the European frequency band (868Mhz). So you can not use an SDR right now to receive on 915Mhz. It's only a software limitation, but it is a limitation.
However, since you probably don't care about all the other protocols on 868Mhz that we decode, I think you should be fine with only using the RX/TX Data from a T-Beam or T-Motion. Yes, it's a bit less sensitive than the SDR, but not worse than a commercial unit either. Enough for a glider for sure.

So if I were you, the only thing I would do is replace the GPS with either a T-Beam or T-Motion running SoftRF firmware (it comes preinstalled). There are pros and cons for both..
T-Beam:

• Far better GPS (but the T-Motion one is usable too. It had issues in earlier revisions, but from what I hear it's fine now)
• Stratux EU case fits it
• Easier to configure
  But:
• It will create a second wifi hotspot for configuring it, so you now have two (you want to connect to the Stratux one of course)
• it's a bit larger (but tbh, once you factor in the huge USB plug on the T-Motion, the difference is negligable)

Regarding XCSoar: it was working perfectly fine in earlier EU versions too. But the last version also brings support for XCSoar's AHRS (which is mediocre at best...)

Regarding your component list:

• You don't really need the BMP280. Your AHRS module already has one and IMO it's not needed on the T-Beam/T-Motion. The protocol primarily uses GPS altitudes anyway and Stratux will convert accordingly.
• Skip the Nooelec SDR since it can only be used for 868Mhz right now
• the "official" Stratux EU case fits the T-Beam, but I'm sure you can find cases on thingiverse that fit the T-Motion
• You can just use the latest EU or EU-US version. Note that you will want to have OGN disabled and UAT enabled. The toggles are only meaningful for SDR devices. Traffic data from the T-* will be used no matter the setting.

Hope that answers everything. You can also ping me in Slack if something isn't clear.

[bboo1010]

Thanks b3nn0. Exactly the thread I was looking for.

I am in a similar boat like Alex but in Canada. I am interested to add OGNTP transmit and receive functions to my two yr old Stratux. I installed the latest EU version of the code‚ enabled UAT‚ disabled OGN and it is working beautifully. I can't thank you enough for this initiative.

From what u described above and what I read in SoftRF pages‚ I think replacing my GPYES GPS with a T-Motion would be my best option. My current case will require minimum mods to fit a T-Motion.

However I am not clear about a few things:

1. If I use T-motion with softRF‚ I can get the OGNTP transmit option but will stratux also receive the 915 band OGNTP targets from it and send them to Foreflight?
2. I have a T-Beam board too but in 868 version instead of 915. Lilygo Rep said the frequency can be changed by changing a value in utilities.h file in arduinoLora libraries and flashing the firmware with it (besides installing a 915Mhz antenna). Instead of doing that if I follow the steps described in Stratux wiki for T-Beam for letting Stratux flush the T-Beam firmware‚ can that be configured for 915?
3. I couldn't quite understand where in softRF I can configure my aircraft's Tail Number. Is it something that I need to do by registering at OGN website or is there a software setting for that in Stratux Eu?

[b3nn0]

1. Yes
2. No. In SoftRF, IIRC, you can just set the frequency in the web interface, no? The OGN-Tracker firmware that comes with Stratux can only do 868Mhz. If you want OGN-Tracker, but with 915Mhz, you'd have to compile the firmware yourself, changing the DEFAULT_FreqPlan in OGN Trackers config.h. (SoftRF is just a bit more runtime-configurable than OGN-Tracker)
3. AFAIK, SoftRF doesn't allow doing that. Don't ask me why, it seems like a very basic feature to me, but the SoftRF dev for some reason doesn't want it.IIRC, there was a fork that added the option to do so, but not sure if that is still maintained (or where it could be found).

[VirusPilot]

1. see above
2. see above
3. if you are familiar with Arduino, just modify line 167 of SoftRF.ino: ThisAircraft.addr = <your ICAO>; and compile/upload

[bboo1010]

Thanks b3nn0‚ VirusPilot. Much appreciated.
I never worked on Arduino but I will try a few tutorials and give that a shot. Hopefully wont have to bother u guys too much with silly questions along the way. :-)

[alexanderdross]

Regarding the case: I currently design a case which fits for a RPI3b + T-Beam + T-motion + 0,96" status display.
Hope I have the first version out in 3 weeks