Attenuation
A VHF or UHF signal loses strength extremely quickly in rock. A few metres of limestone can do what kilometres of open air would not, and the loss gets worse as frequency rises. That is exactly the direction useful data rates lie in.
Technology
Why underground communication is hard, and what LoCave does about it.
The problem
Rock is very good at stopping radio.
No line of sight
Cave passages bend, pinch, drop and double back. Even where a signal would travel, there is rarely a straight path between two points for it to travel along.
Through-the-earth is slow
Very low frequency systems genuinely do pass through rock. They do it over modest depths, with substantial gear at both ends, and with no way to extend the link as the team moves. A line laid along the passage has none of those limits.
None of this is a criticism of the radios cave teams already carry. They work, within their limits. LoCave exists because those limits are reached quickly, and because a system that only comes out for a rescue is a system nobody has practised with.
The approach
Three link types, one network
LoCave does not try to beat physics. It splits the job in three: fibre between nodes where distance matters, LoRa radio (433 MHz) between nodes where fibre is not laid, and Wi-Fi where the people are.
Short-range radio, at each node
At a node the network becomes ordinary Wi-Fi. A caver’s phone joins it and opens the chat page the node hosts: no pairing ritual, no dedicated radio to train on, nothing extra to carry beyond what is already in a pocket. A sent message shows a tick once the gateway has it.
The range of any one node is a pocket, not a blanket. That is deliberate. Covering a chamber with short-range radio is cheap and dependable; covering a whole cave system with radio alone is neither.
Fibre, everywhere in between
Between nodes the signal runs on optical fibre wherever fibre has been laid. Fibre does not care about rock, water, bends or electrical noise, and it carries messages and data over far more distance than radio manages underground.
The cable is light enough to be paid out from a spool while the team moves in, and recovered on the way out. That is what turns it into a tool for a normal trip rather than a permanent installation somebody has to fund.
Node-to-node radio, where there is no fibre
Every node also carries a LoRa radio on the licence-free 433 MHz band, running LoCave’s own mesh protocol rather than LoRaWAN, so there is no network server to depend on. Two nodes with no fibre between them link over it automatically, and the same happens when a fibre is damaged. Fibre is the preferred link; radio is what lets the line be extended quickly and survive a break.
Radio between nodes is slower and shorter than fibre and needs the nodes placed within range of each other, which is what the node’s own deployment display is for.
How it works
The signal chain, end to end
- Handset — A caver’s phone joins the nearest node’s Wi-Fi and opens the chat page the node hosts.
- Node — The node takes the message off the air and puts it onto the line.
- Fibre line — The line carries it along the passage, over fibre where fibre is laid and node-to-node radio where it is not, past every bend, pitch and sump a phone’s signal could not.
- Surface gateway — At the entrance the line ends in a base node connected by USB cable to the gateway: a small computer that stores every message, shows the line on its own screen and passes the traffic to whatever network exists above ground.
- Surface and cloud — From there it reaches the surface team on the gateway’s screen, a Telegram group the gateway relays to, and the LoCave cloud dashboard, where the deployment can be followed and answered from anywhere with an internet connection.
Deployment
Laid as you go, not installed once
The deployment model is the part that changes what the system is for.
On the way in
The fibre spools out behind the lead caver. Nodes go in where coverage is wanted: a chamber, a junction, the top of a pitch. The node’s own display shows link quality as you walk, and tells you when to stop.
While you are there
The line is live as soon as the gateway sees it. Pushing deeper is a matter of more fibre and another node, not a new installation.
On the way out
The line comes back with you, or stays if the site is being worked repeatedly. Either way, nothing has been drilled into the cave.
What LoCave does not do
Publishing this matters more than a good specification sheet would. A team that finds a limitation underground has found it too late.
It is not a through-the-earth system — LoCave does not send a signal through solid rock. If there is no route for a cable — no connected passage, or one nobody is willing to pass — there is no link.
It does not replace a call-out plan — A communication line supports a rescue; it does not replace surface call-out arrangements, agreed return times, or the training and judgement of the people underground.
Coverage is where the nodes are — Coverage is where the nodes are. A caver away from any node’s Wi-Fi pocket is out of contact until they reach one. The nodes themselves talk to each other over fibre or, where no fibre is laid, over LoRa radio, which reaches further than a phone’s Wi-Fi but still needs the nodes placed within range of each other.
A cable is still a cable — Fibre is far tougher than it sounds and far lighter than copper, but it can be cut, crushed in a squeeze or pulled out by a rope. It is designed to be repaired in the field; it is not indestructible.
How can LoCAVE help you?
Send us the survey, the passage, or just the problem. We will tell you plainly whether LoCave is the right answer, including when it is not.