WiFi LoRa V2 : LoRa issue with the new CE version

aimesavouret · December 19, 2019, 10:18am

Hi,

Recently I have noticed that there are some changes on the WiFi LoRa V2 module.

I have some issues with the new one (CE version). I use the WiFi LoRa V2 within a gateway which works in RX only. The LoRa devices which send the data use a SX1272 chip (TX only).

If I download the same software, I can see that the new WiFi LoRa V2 (CE version) doesn’t received the frames. I have checked to change the spreading factor on both side but it doesn’t work. I have updated the software and board libraries but there was the same issue.

I have the same issue on the 5 samples ordered in November but no problem on the samples ordered in May.

As you can see, there are some hardware changes and the RF filters are impacted.

After I have tried the example OLED_LoRa_Receiver and OLED_LoRa_Sender at 868MHz and the results were strange.

Sender = November version / Receiver = November version
-112dBm (RF_PACONFIG_PASELECT_RFO at 14dBm)
-27dBm(RF_PACONFIG_PASELECT_PABOOST at 14dBm)

Sender = May 2020 version / Receiver = November 2020 version
-66dBm (RF_PACONFIG_PASELECT_RFO at 14dBm)
-32dBm (RF_PACONFIG_PASELECT_PABOOST at 14dBm)

Sender = November 2020 version / Receiver = May 2020 version
-120dBm (RF_PACONFIG_PASELECT_RFO at 14dBm)
-30dBm(RF_PACONFIG_PASELECT_PABOOST at 14dBm)

The RFO mode doesn’t work correctly on the new version but I don’t understand why.

Have you some ideas to solve my issue ?

My main problem is that my gateway doesn’t work with the new version of WiFi LoRa V2 (CE version), the module doesn’t see the frames from my LoRa devices.

Thanks !

Supporter · December 19, 2019, 2:07pm

In previous versions, we connected the RFO and PA_BOOST pins together through a 0R resistor. However, when CE certification was performed, the accuracy of the RF signal was assessed, and when RFO and PA_BOOST were connected together, the SX1276‘s internal circuit has an impact on the impedance matching of the entire system, so in the CE version, we have eliminated the resistance on the RFO.

Can you use the PA_BOOST pin as the output path?

aimesavouret · December 21, 2019, 9:33pm

No problem to use PA_BOOST, you should indicate this change in the software library because it is written that we can choose between PA_BOOST or RFO (see the OLED_LoRa_Sender example).

The schematic on your website doesn’t correspond to the CE version, can you share the new schematic ? I could do a quick checking.

My issue is that my node which use a SX1272 is “invisible” for the CE version. But I don’t have any issue with the older WiFi LoRa V2 by using the same firmware. I have some new interesting results, the test was performed with the example OLED_LoRa_Receiver and OLED_LoRa_Sender.

Node = My SX1272 device
Old = Older WiFi LoRa V2
New = WiFi LoRa V2 (CE version)

The TX frequency is fixed at 868.000 MHz and I check the frequency window in which the message is correctly received.

CONFIG 1
SpreadingFactor = 11
SignalBandwidth = 125E3
CodingRate4 = 5

Node (TX) & Old (RX) : RX frequency window 867.970 to 868.025 MHz -> Center frequency = 868.998 MHz (OK about -2 KHz shift)
Node (TX) & New (RX) : RX frequency window 867.930 to 867.985 MHz -> Center frequency = 867.957 MHz (NOK about -40 KHz shift)
Old (TX) & New (RX) : RX frequency window 867.945 to 868.000 MHz -> Center frequency = 867.962 MHz (NOK about -40 KHz shift)
New (TX) & Old (RX) : RX frequency window 868.000 to 868.055 MHz -> Center frequency = 868.027 MHz (NOK about +30 KHz shift)
New (TX) & New (RX) : RX frequency window 867.980 to 868.035 MHz -> Center frequency = 868.007 MHz (About +7 KHz shift)

CONFIG 2
SpreadingFactor = 7
SignalBandwidth = 125E3
CodingRate4 = 8

Node (TX) & Old (RX) : RX frequency window 867.985 to 868.015 MHz -> 868.000 MHz (OK no shift)
Node (TX) & New (RX) : RX frequency window 867.970 to 867.990 MHz -> Center frequency = 867.980 MHz (NOK about -20 KHz shift)
Old (TX) & New (RX) : RX frequency window 867.970 to 868.005 MHz -> Center frequency = 867.987 MHz (NOK about -15 KHz shift)
New (TX) & Old (RX) : RX frequency window 868.000 to 868.020 MHz -> Center frequency = 868.015 MHz (NOK about +15 KHz shift)
New (TX) & New (RX) : RX frequency window 867.980 to 868.030 MHz -> Center frequency = 868.005 MHz (About +5 KHz shift)

As you can notice, my node is not invisible if I change the frequency of the CE version. My issue seems to be due to a frequency shift between the node and the new WiFi LoRa V2. I had no shift with the old WiFi LoRa V2 but I have up to 40 KHz with the new one.
You can notice also that the old WiFi LoRa V2 is close to the limit and could be invisible for the new WiFi LoRa V2. I don’t have perfomed test with bandwidth below 125 KHz but the issue should appear more often.

I am quite worried because it seems to be an hardware issue. You need to check your RF filters and your center frequency on the new WiFi LoRa V2 and compare to the old one.

Have you a test report regarding the CE certification ?