Homemade Esp32 gps tracker / NO sf8 and above


I have an esp32 gateway connected on a 8dBi collinear antenna. I am testing my gateway with another esp32 which is on the top of my car and whitch sends position indefinitely going trough sf7 to sf10 (antenna 3dBi).
Evering works fine and I reach a distance of 3.6 km with sf7 very easily.
For the other sf values, I can only reah 500…800m.
Do you have an expanation ?
is it due to these cheap boards ?
is it because the car is moving ?

thank a lot for your answers !!!

What happens when you stop the car ?

What software are yoiu using on the Gateway and the node ?

This is the same with car stopped.

node software bas on 2015 Thomas Telkamp and Matthijs Kooijma
gateway : 2016, 2017 Maarten Westenberg version for ESP8266

Do you have something better to propose ?

Thank you.

20190504_171615 20190504_171636%20(1) IMG-20190609-WA0003
The gateway is just below the antenna. Here you can see an imst that I borrowed from a friend but normaly it is an esp32

SF and antenna type makes a big difference.

The higher the SF the better range and also the type of antenna on your car.

I would check that your antenna connection SMA or uFL is good.

I found that going to SF12 and providing a good ground plane for the antenna significantly improves range.

Nice work, is the enclosures 3D printed?

yes every thing is 3d printed.
I like very much my shark antenna.

what could be better than the roof of the car as a ground plane ?

Yes, I would have expeted that my results would have been better with higher SF and here it is just the reverse !?!
Why ? If I reach 3.6 km with SF7, it means that my antennas are so bad than that, no ?
My range should be better with sf8 and above
Indeed, I do not like the very tiny coax provided with the esp32. I plan to replace it with a rg316.

I think the overall setup should be ok if functioning at SF7. Only a question - who knows - did you wait sufficient time at high SF? Because duty cycle limitations allow no more than one packet every 2-3 minutes at SF12.

1 Like

You are correct about the roof as a ground plane.

I would look at antenna, coax, connectors.

I usually have another antenna, a 1/4 wave that I can swap out so I can confirm it’s not problems with the coax, connectors.

So you modified the node software to ensure that it actually did transmit repeatadly on SF7 to SF10 ?

How long did you set it up to cycle between the range of SF7 to SF10 ?

What checks did you have to ensure the node actually did transmit ?

The node transmit from sf7 to sf10 continiously with a delay of 2s between ecah SF. after SF10 it restarts at SF7.
It works because this procedure is ok for small range.
I borrowed an imst880 from a friend and with the same antenna setup I had good range capabilities with high SF. Now, as I am back to esp32 as gateway, I only get good result with SF7

That software as I recall, uses a single RFM95 and hops around spreading factors using CAD to detect whether there are signals.

I would strongly suspect the issue you are seeing is an artefact of the ‘proof of concept’ way in which the software attempts to act as a multi spreading factor gateway on a single RFM95.

1 Like

LoRaTracker nailed it, I did not consider the gateway limitations . In the past I had a couple of ESP32 / ESP8266 single channel gateways and the SF hopping feature has never been really reliable (in the documentation a shorter range is also mentioned). Consider also that sending every 2 seconds is almost impossible (not only for duty cycle, but also because after sending the system is waiting for RX1 and RX2).

Try to lock both at SF12.

I should have more clear : I do not send something every 2s but I wait that a transmission is totaly finished before waiting 2s and considering start a new one at a different SF.
A complete cycle from SF7 to SF10 take about 2 min.

Ok, anyway to test range lock it at SF12; from the readme, “The CAD functionality comes at a (little) price: The chip will not be able to receive very weak signals as the CAD function will use the RSSI register setting of the chip to determine whether or not it received a signal (or just noise). As a result, very weak signals are not received which means that the range of the gateway will be reduced in CAD mode.”

(by the way, which RSSI and SNR do you have at SF7, 3.6km?)

RSSI : 120 +/ 2
SNR : I have to dig in my datalog
Good idea, I will try with fix SF on the gateway side.

you are at the limit, so likely CAD is the reason.