Force downlink to use a different SF

Gateways
1

Summary
I have a class C device running on an instance of TTS Cloud. Uplinks from device are using ADR SF12. I can see an option to set the RX2 downlink to SF12, but as this is a class C device I’m not using RX2.

In the End Device > Settings > Network Layer > Frequency Plan I have set SF12 for RX2, but in the Live Data view I still see the following

      "rx2_data_rate": {
        "lora": {
          "bandwidth": 125000,
          "spreading_factor": 9,
          "coding_rate": "4/5"
        }
      },

Is there a way I can confirm/alter the SF used for downlinks

Hardware
Milesight UG65 gateway / mClimate 16ASPM relay module

2

Somewhat of a meta request to want to change a value for something you can’t use.

Have you looked at the CLI options?

You should be aware that the LA prohibit the regular use of SF11 & 12. This may have some bearing on the use of SF12 for Class C.

Your other ISM band users in the area would love you to get another gateway to get uplinks down to SF10 and your current gateway will keep its duty cycle reputation intact as well!

3

I did get a ‘succesfully processed data message’ in the live data with the following

    "settings": {
      "data_rate": {
        "lora": {
          "bandwidth": 125000,
          "spreading_factor": 12,
          "coding_rate": "4/5"
        }
      },
      "frequency": "867700000",
      "timestamp": 1274019690,
      "time": "2025-07-31T17:18:58.112284898Z"

So looks like this isn’t where I can fix this, think the problem is purely down to signal strength, device is showing RSSI -136, SNR -22.25 . Looks like I need to relocate one of my gateways

4

Indeed, that’s what the SF does - it increases range at the expensive of airtime and, for Class A devices, battery life.

Generally, as you have discovered, when on the edge at SF12, the situation corrects itself or the slightest bit of breeze/dumper-truck/rain blocks comms which leads to much wailing & nashing of teeth and sometimes inquisitions.

5

That is to be expected, settings in the UI only take effect when the device rejoins.

You will need to use the cli (and find the right setting) to change the settings for a running session.

However given your rssi values you won’t be able to have reliable data exchange. Just last week I had to to decommission a device with the SF12 rssi values in the same range where I encountered gaps in data of several hours. No option to place a gateway closer to the device due to lack of power in the nature reserve so the device has been removed as it wouldn’t work reliably.

6

Thanks guys, I will relocate a gateway, I have 2 on site so should be pretty simple to test

1 Like
7

PS you are actually almost always using RX2. The devices uses the RX1 frequency and settings only during the RX1 window and will be listing with the RX2 setting all of the time (when not transmitting).

8

good to know, thanks

9

The default behaviour is to send all downlinks on Rx2 for Class C devices, except downlinks that carry Network MAC commands or in certain cases when a situation caused the Class C downlink to fail scheduling.