Underground LoRa device - Page 1
Forum section: electronics / projects

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 10, 2020, 08:57:50 pm
content: Hi!I'm working on a school project where I have to have a sensor underground. The sensor data is not relevant, the thing is that I need to use LoRa.I know that antenna performance is much worse underground.What are the ways that I can make this work? What type of antenna should I use? Can a PCB antenna solve this?The thing is that the sensor must be level with the ground. So the antenna can be level with the ground, but can't stick out.P.S. I'm not an antenna expert, so please I need as much detail as possible. Research papers are welcome too.

author: sam[PS]
author_rank: Contributor
timestamp: March 11, 2020, 04:28:46 am
content: what king of ground are we talking about ?

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 11, 2020, 09:49:11 am
content: Asphalt or concrete

author: TomS_
author_rank: Frequent Contributor
timestamp: March 11, 2020, 10:54:31 am
content: It must be possible, but probably frequency dependent to some extent.The water meter for my house is "underground", and the water company simply drives around the streets to get readings.The meter itself is not much bigger than an orange, so no extensive external antenna.I say "underground" because it's about 1 meter down in a bit of tube with a little hatch on top, so not buried, but not exactly out in the open either. This is on the footpath so the hatch is surrounded by asphalt (in this case), and 5-10 metres from the road itself.I don't know what frequency it uses.

author: Marco
author_rank: Super Contributor
timestamp: March 11, 2020, 10:56:52 am
content: What's the depth? Where's the receiving antenna?Don't make people pull information like pulling teeth ...

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 11, 2020, 12:50:04 pm
content: I'm using a ceramic antenna at 868MHz. Antenna is:https://export.farnell.com/johanson-technology/0868at43a0020e/antenna-ceramic-868mhz/dp/1885493The gateway for testing will be positioned on top of a building, the sensor will be infront of the building.Imagine something like having a gateway on top of the house and the sensor where the road is. So around 10m distance, nothing fancy.The depth is like I said, 1cm max, because the sensor is level with the ground.

author: Styno
author_rank: Regular Contributor
timestamp: March 12, 2020, 08:47:22 am
content: I have 868MHz LoRa sensors ~10cm below ground level under a heavy plastic street lid, the signal is picked up by gateways several km's (and sometimes over 10 km's) away. But the antenna's for these gateways are mounted high: ~25 m above ground, that is crucial for providing long range coverage.The sensors use small omnidirectional helical antenna's. In my experience, pcb antenna's require more tuning, have often blind spots and require a lot of pcb space (but that depends on the application).

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 12, 2020, 12:14:33 pm
content: This is good news.If I put those helical antennas, but vertically (like in this photo:https://www.thethingsnetwork.org/forum/uploads/default/original/2X/7/70f6609cf0ce2e940240d8388d99a372b849efea.png) would it make it worse than a pcb antenna?