Wireless data link (telemetry)

Stuart France

Active member
Does anyone out there have experience and a working design to transmit data from a cave entrance through the odd bunch of fir trees or through a leafy canopy of hardwoods and maybe around a very slight ground obstruction due to the curvature of the hillside over a distance of hundreds of metres?  Power consumption doesn't matter as it will only be powered up when the sensor side wants to send a digital message, maybe once a day.

I have already tried Zigbee modules (the high power ones) but these are 2GHz and hopeless except on a clear line of sight.  I got about 600m from Penwyllt with one of these transmitting "hello world" into a laptop inside the small common room - perfect line of sight but behind a glass window.  We then tried the hill road above OFD1 across the valley to the cafe at Craig y Nos country park which is a kilometre through air only and just got it to work on a line of sight that didn't involve any trees provided that a stainless steel dogbowl was used as a 'parabolic' reflector behind the Zigbee whip antenna.  No dog bowl = no hello world.

I'm thinking I ought to be trying VHF instead, as low a frequency as possible.  For instance the 'new' 168MHz band for which there are modules.  Has anyone tried these and got something to work well, e.g. with a PIC driving it?
 
yes lora will probably do it.
dev boards available from china can to p2p (probably what you want) 868 Mhz but optimised for small data / long distances
 

nickwilliams

Well-known member
Does it have to be wireless? This would be easily and cheaply done by fibre optic cable if the terrain was such that a cable could be hidden in it.
 
given the requirements its the perfect use case for a lora network you can get a dev board with a microcontroller on board and range is often measured in 10's of km from mw of power.

 

Stuart France

Active member
There is no mains power and no mobile phone coverage at some sites of interest.  Any solution must run on Duracell type batteries for 6-12 months at a time and be cheap and simple to develop.

Perhaps I've misunderstood, but LoRa seems not to fit that scenario well?  In the absence of a commercial 5G network to connect to, it implies setting up a private LoRa network with all that entails like servers/gateways and lots of power and a container like a building to put it in?

From my own Zigbee experiments, I'm not convinced that ballpark GHz devices will transmit data through forestry or on not-quite line-of-sights.  To quote from a LoRa module manual I've just read:

"You have to be aware that radio link quality and performances are highly dependent of environment. Better performances can be reached with: outdoor environment with no obstacles, no high level radio interference, at least 1 meter above the ground.  Radio performances are degraded with: obstacles: buildings, trees, inner buildings environments, wireless band usage by other technologies.  Radio communication are usually killed with bad topographic conditions.  It is usually not possible to communicate through a hill, even very small."



 
stuart yes you have missed some tricks with lora.
Its perfect for what you want. It can either be deployed in an infrastructure way or as a p2p system between 2 nodes.
have a look at https://hackaday.com/2017/10/24/lora-is-the-network/
or send me a message if yoru interested in finding out some more
 
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