Looking for a super rugged antenna


#1

Hello everyone,

I’m in search of an antenna (868MHz) which allows cars to drive over.
My LoRaWAN node will be installed in driveways and maybe even streets.

If anyone knows a manufacturer that makes rugged antennas or a webshop that sells these, it would be greatly appreciated!

Thanks in advance


(Lachlan Etherton) #2

Hi Bert. You would have to look at a solution which has flex to it, maybe a rubber type. I’ve seen them before, some even for 915MHz which is close enough to 868MHz that they should work, however I have never found a place where they are for sale.

That being the case, I am interested as well in where they are available.

I do have a question and that is if the antenna is near the node, how are you protecting the node from being run over. Is the node built into the ground or underground or something else?


#3

The node itself will be installed underneath a manhole cover.
I want to monitor the water level.


(Lachlan Etherton) #4

This is a use case I’ve been thinking of doing as well. Let me take a look.


(Lachlan Etherton) #5

I would suggest to perhaps rename your forum post to something like “Transmitting LoRaWAN signal from Manhole Cover” or “How to Transmit Signal from Manhole” as it seems to me that the not only do you have to find a durable antenna, you also will have to work out how to get a reliable connection. This is because the elevation is really low and you have a huge metal plate, being the cover right where the antenna is. As metal is a conductor of electricity and magnetism it absorbs electromagnetic waves (radio waves), reducing the strength of the signal and as a result decreasing the distance of a connection.

Before you are to invest resources and purchase antennas, I would first check to make sure that the location where you want a connection to reach will do so by simply placing a node with a normal antenna on the ground near the intended deployment location. Also, if you can source a cover similar to the one where mounting is intended, perhaps try testing a node on one.

If you can get a signal which is strong enough, I would make the assumption that this your best case scenario for a ground mount and begin looking at antennas. If you are unable to get a signal, I would start looking at potential mounting points. As a manhole cover is generally on a road or footpath, a light pole could be nearby where an antenna could be mounted. Perhaps some waterproofed wiring feeding up to the antenna might work in this case.

If the signal is strong enough, there are two antennas I would begin looking at:

Flexible PCB Antenna
These are generally about as thick as a few sheets of paper. My gut feeling is that even though you could place this flat on the ground, I don’t think you would get a connection due to the elevation on top of the fact that the cover is made of metal, unless you could place the antenna on the road or path surface.

Flexible Whip Antenna
This is probably your best bet in my opinion. These have a solid metal base, which would have to be protected somehow, but the top is made of a flexible rubber which surrounds the metal inside that can bend.

I would also consider where this antenna is going to be mounted. If it is on a road, is it in an intersection where would it likely be driven over or is it in the middle of a lane where the only time it would be driven over would in an overtaking situation? Better yet, is the mounting location in the middle of a one way road where it would rarely, if at all, be driven over? The less time it will be driven over the better and would mean that you have some chance of it working for an extended period of time.

Do note that I am still trying to understand about antenna theory and my logic is based on common sense rather than hard facts or experience.


#6

My first thoughts indeed pcb antennas. There are also several pcb antennas available. Perhaps you can mill a slot in the top of the manhole cover and the node at the bottom and pour the pcb antenna into resin.


#7

I have done some measurements underneath some manhole covers by lowering a node down into the sewer.
I also measured the signal just above the surface of the manhole cover.
The signal just above the cover is 20dBm stronger than the one underneath the cover.
Some of these manhole covers are located just on the edge of our gateways, which means that I am not able to get a connection if the antenna is below the cover.
My only option in these places is to install the antenna above the cover.

I like your suggested antennas. My only concern at the moment is finding an enclosure that is capable of housing the antenna. This means that it has to be made out of plastic, as metal acts like a Faraday cage.
I found these parking sensors online: http://www.libelium.com/products/smart-parking/
The housing that these parkings sensors use would be perfect for me.


(Robert Goss) #8

You might try looking at Pulse antenna, they make custom water meter antennas, most of the water meter companies use manhole antennas, I have bought some on ebay, see the Itron antenna also.
Opti


#9

Thank you for your suggestion.
I have found a couple of antennas that might work!