Should I increase the SF or Power rate

End Devices (Nodes) LMIC
1

Good day,

I have a gateway and two nodes in a Apple tree (orchard)
The first node is at about 900m from the gateway and the second is about 1km from the gateway.
The first node is at about 430m and the second at 435m (alittude)
Finally the first is close the leaft of the tree (just not above) and the second node has a more clean space around.

Both of the node use SF 7 with transmission power of 14. I am usinf lmic-arduino library

LMIC_setDrTxpow(DR_SF7,14)

The gateway receive the data from the second node, but NOT from the first node, which is closer. I was a bit suprise because the node have a distence of only 1km.

I wonder if I should increase the Spreading factor or the transmission power?

I once experience some transmission with SF7, SF8, SF9, SF10, SF11 and I will try with SF8 or 9. But I wonder, if it would be better to keep SF7 and increase the transmission power.

What do you suggest?

Thank a lot

2

you can try changing the node antenna first for a better one

(0#90)

3

Are both nodes line of sight to GW? Any obstructions or sources of interference? I would switch the two nodes and see if problem follows node or if 2nd node shows problem or even reduced performance in node 1 location. If so next step would be as Borroz suggests replace (try swap round antennas on the nodes 1st?) antenna…

Also you mention height of nodes…height of gateway? Is there any terrain masking getting in the way?

4

Is it legal for you to increase the power beyond 14dBm ?

5

And for reference each increase in SF number is the equivalent of increasing power by 2.5dBm. Packets take longer to send of course.

6

Hello, thank for your reply.
Yes both node are line of sight of the GW.

Is it legal for you to increase the power beyond 14dBm ?

That a good observation. I remember I red something about it.

you can try changing the node antenna first for a better one

I finally solved my problem. SF7 works fine.
I first tried with differen SF without sucess.
Then, I t changed the antena but it did not fix the problem
I finally changed the SMA to uFL adaptator which fix the problem. May be that part was defect. No idea, but since the Gateway receive the data from node1.

Thank for your suggestion

1 Like
7

Between SF7 and SF12 there is a 12.5dB link margin improvenment. To match that in a power increase would have needed an increase from 14dbm (25mW) to 26dBm (200mW), … sheesh … that is good enough for sensors in Earth orbit.

Since the problem is now ‘fixed’ do tell us what the RSSI and SNR are now reporting for the ‘fixed’ system, very useful information for us all …

1 Like
8

Hello, TTN console show me this for the last transmission

{
“time”: “2018-06-28T20:06:35.00547569Z”,
“frequency”: 867.1,
“modulation”: “LORA”,
“data_rate”: “SF7BW125”,
“coding_rate”: “4/5”,
“gateways”: [
{
“gtw_id”: “eui-b827aaaaaaaaa”,
“timestamp”: 3648089747,
“time”: “2018-06-28T20:06:34.952693Z”,
“channel”: 3,
“rssi”: -114,
“snr”: -2.5,
“latitude”: 46.,
“longitude”: 6.,
“altitude”: 400
}
],
“latitude”: 46.,
“longitude”: 6.,
“altitude”: 400,
“location_source”: “registry”
}