Arduino LoRa GitHub library errors

[Steve]

Has anyone got any thoughts on this:

I'm using the Arduino LoRa GitHub library (sandeepmistry) to implement PITS LoRa on the Pi Pico

I have a couple of Picos + RFM96 set up using the send and receive examples from the repository. 

All seems to work OK when higher data rates are used (low and medium spreading factors and wide and medium bandwidths) - but errors with low data rates.

For example SF10 + 20.8KHz works fine as does SF11 + 41.7KHz  (anything faster than this works fine too):

but errors with SF11 + 20.8KHz or SF12 with 41.7KHz (anything slower than this fails too) :

As you can see the first few characters come though fine.

Coding Rate does not seem to affect this issue.

I'm literally only changing the SF and Bandwidth values to get the error or not.

I get the same sort of errors if using the PITS gateway to receive (although only the leading $$ is decoded correctly).

At first I thought it might be something to do with the Low Data Rate Optimize flag - but this seems to be being set correctly.

Thoughts?

    Steve G8KHW

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[David Akerman]

Can you check the frequency offset between Tx and Rx?  The Rx side will have that in a register and presumably there's a library function to read it.

Offsets between Tx and Rx have a greater effect with lower bandwidth transmissions.

Dave

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[Steve]

Good point - It was about 500Hz:

SignalBandwidth = 20800, SpreadFactor = 11, symbolDuration =100, lodon = 1
LDO flag = 1
Received packet '$$Xpi5,75,20=⸮4;7?|72,47353 1 ⸮97R0$3⸮⸮`x|0T>"4uN(⸮' with Frequency error 488' with RSSI -76
Received packet '$$Xpi5,75,2=:⸮4<76|72(⸮⸮353 1 ⸮94R8$3⸮⸮`x⸮0T>"9⸮N(~' with Frequency error 523' with RSSI -76
Received packet '$$Xpi5,7<,20:⸮4<7?72,>7353 1 ӫ⸮97R8$3⸮⸮`x|0T>"9⸮N(:' with Frequency error 559' with RSSI -79
Received packet '$$Xpi5,75,20:⸮4<7670,⸮735⸮

    Steve

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[David Akerman]

500Hz is plenty low enough, so it's not that.

It does have the feel of an LDO issue as the start of the packet gets through and then it deteriorates.

Can you try the same code on another LoRa module (especially the Rx side)?

And is this 434 or 868MHz bands?

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[Steve]

Thanks Dave.

More info:

I'm using some 868MHz modules at mo (I have some 434MHz ones on order)  - most of the testing has been at 868MHz but:

I have an old 434MHz Mode 0 (SF11, BW20.8KHz EC4:8 LDRO ) tracker - I fired up (the 868MHz modules will receive 434MHz but are very deaf - as they have no connection to the SX12xx LF port).

That works OK - the Pico/Arduino RX code spits this out:

SignalBandwidth = 20800, SpreadFactor = 11, symbolDuration =100, lodon = 1

LDO flag = 1, Frequency = 434317000
Received packet '$$X1,145,11:38:50,51.97291,1.37100,2,10,3,3.25,00*0AC5
' with Frequency error 16' with RSSI -133
Received packet '$$X1,155,11:41:44,51.97303,1.37108,23,9,3,3.23,00*46D6
' with Frequency error -15' with RSSI -133
Received packet '$$X1,157,11:42:18,51.97304,1.37103,18,10,3,3.25,00*18C7
' with Frequency error -6' with RSSI -133
Received packet '$$X1,159,11:42:54,51.97304,1.37100,14,10,3,3.24,00*3F3A
' with Frequency error -9' with RSSI -133

So it looks to be some form of problem with the transmitter end - although both TX & RX are set up identically in terms of Explicit/Implicit, SF, BW, CR and LDRO

I'll maybe swap the TX and RX and see if that helps and what the 434MHz modules bring.

    Steve

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[David Akerman]

Interesting.  I asked about 434/868 because back when I started with these I set up a Tx/Rx pair with 868 modules, using a fairly low bandwidth (sorry I don't remember the settings) and I couldn't get them to reliably link.  I don't remember the symptoms but they could well be what you are seeing.  When I switched to a higher bandwidth it worked fine.  When I replaced them with 434 modules and used 434-ishMhz it worked fine.  I didn't investigate any further.

Dave

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