[Xastir-dev] interface xastir to aprs-over-lora

[Jason Winningham]

lots of good information in Tom’s response.

The answer depends on what your goal is. A fully integrated LoRa APRS network bridged/routed to a standard AX.25 network would be a challenge.  Doable, but certainly not trivial. If the goal is to use LoRa to import data from the oft-maligned “dumb tracker” or some sort of sensor for display in xastir, the problem is a bit simpler.

I haven’t used LoRa, but I have used Xbee 900MHz data radios in a way that sounds similar toy what you are describing.

These xbee radios are point-to-point or broadcast.  I configure dumb trackers (for tracking rockets) in broadcast mode, and the code is written to time-slot the transmissions to avoid collisions. The digital side of the radio is a simple serial interface. The tracker prints a TNC2 format string to the radio, which is received by the ground station radio and transmitted via RS232 to an xastir port configured as a "serial TNC”.

The TNC2 format has the advantage of being human readable, so I can hand a radio+usb/rs232 adapter to a student with a windows laptop and a simple terminal program, and they can easily see the coordinates in the position report. Not as nice as a map, but in the past everyone had HyperTerm on a windows laptop, and putty is a free substitute. It is also possible to use multiple receivers, e.g. a simple dipole on one receiver and a yogi on another, to allow for different distances. This is helpful since the distance can change quite quickly during a rocket’s flight.

Getting this data retransmitted (digipeated) is problematic because digi software is not designed to accept TNC2 format packets for multiple legitimate reasons.  In my attempt to accomplish this I experimented with modifying the code of a popular digi software	package whose name escapes me at the moment. The modification was not as simple as I understood the author to imply, and I lost the hardware where that code lived.


If you are starting from the ground up and have digipeating to an AX.25 network as a requirement, I’d probably use a KISS mode packet. If you requirements, like mine, are a bit simpler, TNC2 may do the job.

-Jason




> On Jul 23, 2021, at 11:17 AM, Kristoff <kristoff at skypro.be> wrote:
> 
> Hi all,
> 
> 
> A quick question.
> 
> A few people in our local radioclub have become interested in aprs over lora, mainly using the LilyGo T-beam devices. This is in essence an ESP32 running arduino-code + a 'lora32' module (which is a clone of of the sx1276).
> I have been tinkering with the kit, mainly using micropython to get to understand the sx1276 chip.
> 
> So,
> If I would would want to use that device as an interface for xastir, what would be the most easy way to do this?
> 
> I guess just use the serial interface and create some kind of "bridge" between the serial packets and the Lora "air-interface"?
> 
> What is the difference between the "Serial TNC", "Serial KISS TNC" and the "Serial Multi-Port KISS TNC"?
> Where can I find the documentation for this?
> 
> Or does this already exist?
> 
> 
> Note, I am on linux (of course :-) )
> 
> 
> 
> 
> BTW.
> I have been discussion with a fellow ham on the use of 'UART pass-through' devices on LoRa. These are very simple, once they are configured, you just send data and receive data as it is a transparent serial path, ... except that it is 'multicast'.
> 
> What would be the best way to connect this kind of device to xastir?
> 
> 
> Many thanks in advance.
> 
> Kristoff - on1arf
> 
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