[Xastir-dev] LORA and interfacing

Sat Jul 31 12:58:18 PDT 2021

Steve,

I also have this model:
https://www.amazon.nl/DollaTek-LoRa32-SD-kaart-draadloze-module/dp/B07RXSKPBX/

The disadvantage is that it lacks the 8 Mbit PSRAM chip (which is on the 
T-beam) so the ESP32 is a bit short on memory for embedded python. (less 
then 1 MByte of RAM available).

Software development-wize, perhaps it makes more sense to turn the 
radio-device into just a dumb 'packet-modem', connect it to a 
single-board computer (say, a raspberry pi) and do all development 
overthere. That way you can run higher-level code, easily interface with 
the internet, connect other devices (e.g. a VHF/UHF packet mode), etc.

Last week, I found this python module for processing aprs message (*) 
which I think would be a good basis to do some experimental development 
for aprs-code.

I do like the sx1276 chip. It has a couple of nice features.

- as it also has a FSK modem, It might also be able to transmit POCSAG 
(paging) messages. If this works, we should be able to build a 
APRS-to-POCSAG gateway with just one piece of hardware: send a aprs 
text-message to a certain APRS node and it transmit that message as a 
POCSAG paging message.

I once wrote some code to create pocsag-message. (**)

- The automatic header-detection in lora is nice,
This means that if you send a packet with (say) a coding-rate of 4/8 to 
a lora-node configured with 4/5, the chip will still receive and decode it.

So, if you know that you are in area with bad APRS-over-lora coverage, 
you can switch to a coding-rate that provides better error-correction 
(like 4/8). Your packets will become larger (by 37.5 % in this case) but 
your packet might still arrive, which it might not have done with a 
coding-rate of 4/5.

Note that that bandwidth and Spread-Factor do need to match. If not, 
your packet will not be demodulated/decoded.

- Another nice thing is that, although the chip does have CRC-generation 
and CRC validation in silicon, it will still pass packets to the 
receiver, even if they fail the CRC check.
It will flag it as 'CRC error', but the code on application-level will 
still be able to retrieve it.
Most other radio-chips I have looked at so far do have do not do this 
and will silently drop that message.

This would allow for a nice lora "DX-ing" mode by implementing 
additional error-correction code on application-level.

Ah yes, there is also a GNU Radio implementation of the Lora PHY. (***)
I haven't tried it yet, so I do not know if it works but It would be 
interesting to experiment with this, e.g. tweaking the parameters even 
further to do even further DX.

I am not on Facebook.

I prefer mailing-lists for in-depth discussions. To get real-time help, 
...  I am on matrix / element.io which is an open-source and 
decentralized IM/voice/video service.
There are quite some open-source groups reachable via matrix, either 
directly on matrix itself or via bridges to IRC or some other IM protocol.

It's used the GNU Radio community.

(*) https://github.com/ampledata/aprs
(**) https://github.com/on1arf/pocsag
(***) https://www.epfl.ch/labs/tcl/resources-and-sw/lora-phy/

73
kristoff - on1arf

On 31.07.21 20:31, Steve wrote:
> I gave two of the TTGO units including a couple of Rnodes.
>
> I’m going to try a couple of the existing firmware options out there. Some
> are KISS based some are not. I like the possibility of using the wifi or
> Bluetooth with the TTGO with some of the APRS programs fir the phones.
>
> Seems for a mobile device, not have a extra board such as a PI might be
> nice… we’ll see!
>
> The TTGO can also be used for this:
> https://tinygs.com
>
> The Rnode guy is also implementing a MESH system but is only in the alpha
> stage. Beyond my ability.
>
> I’ll have to get back to you on Freq, I only got my TTGO going last night
> and didn’t bother to look!
>
> There is a LORA APRS group on Facebook, grin, that is mostly from Europe
> who have a lot of experience with this .
>
> Steve N0FPF
>
>
>
> On Sat, Jul 31, 2021 at 11:20 AM Kristoff <kristoff at skypro.be> wrote:
>
>> Steve,
>>
>>
>> Your project interests me too.
>>
>> We are using this hardware:
>> https://github.com/LilyGO/TTGO-T-Beam
>>
>> We are on 433.775 MHz, 150 KHz, SF12, 4/5
>> What frequency and what mode do you use?
>>
>>
>> The software comes from this project:
>> https://github.com/lora-aprs
>> But if the code of your project is standard arduino, it shouldn't be to
>> difficult to port it to ESP32.
>>
>> Apparently, there are also some high-altitude balloon projects that use
>> lora for their telemetry download.
>>
>>
>>
>> My personal interest is to use this for doing some software
>> experimentation, so I use micropython on the ESP32 (fast development)
>> and not the arduino code.
>>
>>
>>
>> 73
>> Kristoff - on1arf
>>
>>
>>
>>
>> On 31.07.21 20:05, Steve wrote:
>>> I connected it to my 10 db Omni antenna at home right at the base to
>>> minimize the loss.
>>>
>>> I was impressed that it was heard around some of the hills in west
>> seattle .
>>> I have plans to put a IGate at a high point around the end of the summer.
>>>
>>> I also found a small bi- directional amp too.  Boost it to a watt or two.
>>> Just don’t want to kill the receive sensitivity. Around $60.
>>>
>>> It’s all in the antenna.
>>>
>>> Steve N0FPF
>>>
>>>
>>> On Sat, Jul 31, 2021 at 10:59 AM Tom Russo <russo at bogodyn.org> wrote:
>>>
>>>> On Sat, Jul 31, 2021 at 10:35:44AM -0700, we recorded a bogon-computron
>>>> collision of the <stevewa206 at gmail.com> flavor, containing:
>>>>> I have interfaced the Rnode Lora device. It does Kiss and used a PI 3.
>>>>> Pretty straight forward.
>>>>>
>>>>> https://unsigned.io/projects/rnode/
>>>>>
>>>>> I was able to do a client and a IGAte.
>>>> That is pretty cool!
>>>>
>>>> --
>>>> Tom Russo    KM5VY
>>>> Tijeras, NM
>>>>
>>>>    echo "prpv_a'rfg_cnf_har_cvcr" | sed -e 's/_/ /g' | tr [a-m][n-z]
>>>> [n-z][a-m]
>>>>
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