Dragino LDDS75 Connection problems

Good morning Central European time.
I am writing this post because I am having problems with my Lora Node which unfortunately I cannot solve on my own.
I have an LDDS75 sensor from Dragino which is normally used about 350m away from the gateway.
Currently, it is a little closer to my location (50m to gateway behind a brick wall).
The problem I have is that the uplink messages only arrive “sporadically” or the sensor is in a join request loop from time to time.
I hope to get to the bottom of this problem with your help and get the sensor to send regularly again. I have lowered the uplink interval for testing purposes.
I will attach some pictures to this post, but I don’t know what is helpful for you so I have to rely on you. Please feel free to ask if something is missing. The gateway is mine so I can also share information about it. Please let me know if there is data that is Private".

LoRa Node Settings and Facts:

  • The Lora node is a Dragino LDDS75 ultrasonic sensor with 868MHz.
  • The SNR of the sensor is between “-2 / -12”.
  • The RSSI of the sensor is “-90”.
  • The sensor is set to “Europe 863-8700 MHz (SF9 for RX2 - recommended)”.
  • Data rate according to the dashboard: SF12BW125
  • Regional Parameters: “RP0001 regional Parameters 1.0.3 revision A”.
  • FPort: 2
  • These are uplink gaps of between 30 minutes and 7 hours.

Gateway Settings and Facts:

  • The gateway is a Mikrotik LH8 with “Mikrotik LoraWan - Omni Antenna 824-960 MHz”.
  • Channel plan “EU 868”.
  • The gateway has many CRC errors.


As you can see the RSSI and the SNR vary a lot. You can also see that there are gaps where no data is changing at all. These Gaps are times when there are no uplinks.

In this picture, you can see the join loop I mentioned before. In this example, the uplinks are coming every 10 Minutes (for testing!).
But also as mentioned before there are often times where there are no uplinks for several hours.

This picture shows the last uplink you can see in the picture before in the Gateway.

This picture shows that there are a lot of CRC errors i don’t know what these are.

Right when I was writing this post there was one dropped uplink. This is the message in the Gateway (I think). There is only this message.
The next one is after 1 minute and is only a confirmed up

So this is where I’m stuck an don’t know what I should do next.
If there is anything you need to understand this problem feel free to ask!

Thank you very much in advance!

It looks like your device has the DevAdr 260Bxxxx and there are some other devices around using (or trying to use) your gateway.
Maybe the signal of your node is disturbed by other devices in the vicinity using the LoRa-frequencies.

Do you have the possibility to listen what is going on between 865MHz and 870MHz? It could make sense to look for strong signals ±10 MHz.

The frequency range used by LoRaWAN may be used by many other applications, it is for ISM-usage.

btw all the CRCs of your device seem to be ok, I would not care about the negative CRC-check of unknown devices.
I see many negative CRC-checks in my gateways too. They seem to be caused by non LoRaWAN devices.

Thanks for your answer.
There is a small DVBT antenna for ADSB around the gateway. But that’s at 1080MHz. Im using it for flightradar.
That shouldn’t be a problem, right?
How would I test whether there is such a signal in +/-10?
Is there a measuring device?
Without paying a lot of Money.

ADSB should not be a problem because it’s receive only (hopefully you don’t transmit ADSB-signals).
The measuring device you are looking for is a spectrum analyser or a SDR-receiver. The cheapest solution is a RTL-SDR stick.
The signals with negative CRC you are seeing are coming from devices using the Semtech-chipset for LoRa but not for LoRaWAN. This signals are discarded by the LoRaWAN-gateways.

That’s what I thought. But I wanted to mention it because of the small distance between these two antennas.

I just bought an “Nooelec NESDR SMArt v4”USB RTL-SDR Kit to lock If there are some of the mentioned frequencies.

I hope to learn something about the RF Environment around me and maybe find something which is disturbing LoRa.

Are your node set for acknowledgement of uplinks?

I don´t understand exactly what you mean with that.
You mean my nodes get an downlink if my Gateway got the Payload?

Yes are it set for confirmed uplinks?

no, your nodes get a downlink if the data were received by TTN.
But use this feature only very seldom, it’s better not to use it. Every successful uplink to TTN will be followed by a downlink to your node, during this time your gateway is deaf and blocks the frequency.

I now have the RTL-SDR. after. What should
I look for? At the moment I haven’t seen anything that would be particularly noticeable. But I have to admit I have no clue what to do with it.

Are you in the city or country side?

City interference more likely than country side.

Are you in a hilly area of flat, if hill area on top of hill or in valley?

Terrain can shield you a lot rom RF interference.

I would investigate

  1. Antennas on the gateway and node, make sure all connections are good and the connectors match. What gateway are you using?
  2. Check the internet connection to the gateway, is that stable?
  3. Power supply to the gateway.
  4. Check all the settings on the gateway and node.
  5. Any high power around? (HV transmission lines, big electrical motors…)

What I would do:
Switch off the gateway, disconnect it’s antenna and connect the antenna to the SDR-stick. Pay attention to the SMA-connectors, sometimes they use R-SMA (the connector fits, but the inner conductor is not connected).

Next scan the frequency-range between 800 MHz and 900 MHz to find out wether there are strong signals. A continuous scan with “peak-hold” could make sense.

As I already said, the gateway seems to receive your node without CRC-errors, I would ignore all the other nodes trying to use your gateway.

Well i did not figure out how to really get this to work. I connected the USB to the antenna and started the program. I have to admit i do not understand exactly how to interpretate it. So I hope you can.
In the picture i used FM. I know this is the kind of modulation and Lora is usin CSS so the modulation does not fit. Is this for the test crucial?
I also made pictures from all the other modulations if needed.

The problems still exist and they got worse when put the node back to the original position.
About 250-300m from the gateway and only a few trees in the way.
The RSSI and SNR still lock very good to me.

Screenshot (14)
Screenshot (13)

Hello, I’m still having a lot of trouble with this node.
But I’m pretty sure it’s not a problem with the above-mentioned SNR and RSSI because both are pretty good.

As mentioned before, the only Gateway that is within reach is mine, so i can see what is happening on the Gateway side of things.

Recently, I logged both “Live Data” tabs with “verbose” enabled and noticed something.
As far as I know, I did not see everything i should have seen.
I could see that the node and the gateway are having trouble for about 45 seconds, in which the node is sending numerous “join requests” along with Join Accept messages and so on.

I would like to share the JSON with you guys, but I’m not sure what i need to delete to keep private data private. Maybe someone can answer this so i can share the JSON without deleting important stuff for troubleshooting.

Thank you in advance.

Nothing, everything in it is publicly transmitted in plain text at some point in the Join / Uplink cycle.

You need to keep your Keys - both LoRa & API - safe, that is all.

Okay then.
There is one additional problem…
Both JSONs are a few thousand lines long. (I cleared the chat before the uplink, so it only should be one uplink)
Is it still ok to post this in here?

Nope. Click on the line you want to share and it will open up on the right hand side - copy & paste that.

Not sure it will help - if the gateway is transmitting the join accept, then the problem lies with your device hearing it.

But im not sure which part of the log could be relevant for you.

What could be the cause of my node not hearing the accept? The uplink RSSI and SNR are good so whatt could be the problem here?

If the Join Request RSSI is between -100 to -60 and SNR is above 5 you are in a perfect place.

Looking at the prior posts you may benefit from getting a different device to check with. And if that’s no joy, try a different gateway. This is the only way to eliminate the possibility the device (or potentially the gateway) is not working as intended.