Commercially-available radiolocation devices?

[boxofrocks]

Hi all,

I'm new to this forum, hopefully this is the right place to post this.

I'm researching a cave system located in a rather remote area overseas and someone recently turned me towards the idea of using some sort of radiolocation device to connect a cave survey to the surface topography. The original idea was to use emergency avalanche transcievers to do this, but from what I've read online, this has had somewhat lacklustre results for others. The low-frequency transistor/receiver setups published in CREG and written about by David Gibson seem more fit-to-purpose, but the homemade nature of them is a little daunting to someone with no electrical engineering experience, as is the notion of trying to transport one on a long-haul international trip. I've tried looking into personal safety locators used in the mining industry but haven't found anything available for individual purchase.

So, does anyone know of any commercial devices, available for individual purchase, that could be used as radiolocators?

I'd also love to hear about radiolocator devices, homemade or otherwise, that are relatively idiot-proof and could feasibly survive a long plane ride in checked baggage. Any and all advice is helpful here.

Thanks!

 

[wellyjen]

Welcome to the forum.
I am not a mining, or civil engineer, but I'd suggest that the reason there are few/no commercial versions is that mining and civil engineers don't need them. Their tunnels are designed around humans and can be easily surveyed using conventional techniques with much longer survey legs than is typical in caves. Much lower opportunity for cumulative errors to build up that would necessitate a radio fix. The channel tunnel broke through many decades ago, with errors between the British and French side teams measured in cm. That happened below the sea bed, so radiolocation wouldn't have been practical anyway.

I've built two locators for my clubs over the decades to published designs in the UK caving press. Both worked for what we wanted them. They were used in the UK and not taken abroad, to my knowledge. I'd reckon any locator electronics and antenna that is robust enough to survive caving trips will be plenty tough enough to survive a flight and the airport baggage throwers at each end.

 

[Leclused]

commercial devices are hard to find.

do a search on Arcana on this forum or Google and you will find some usefull info.

I’m not sure if there are arcana devices around in the UK

 

[LJR]

The mining industry in general does not use this technology. Any man (or vehicle ) locator works with a wifi or radio network laid out within the mine. No reference to the surface at all. This is usually by reflector / booster points around the mine or a leaky feeder cable along roadways.
These systems are moved about depending on the current working areas. Usually access into worked out or abandoned parts of working mines are required to be fenced off and access prohibited to the workforce.

 

[cavingbiker]

Try looking at https://bcra.org.uk/creg/index.html
The page has a lot of links that could be of use to you.

 

[Relict]

My survey buddy has built an outfit over the last year. We got the wire for the antenna hoops in the UK but I believe he used a US design which gave source links for the components. He is good at this stuff unlike me, though I had success in construction of a reliable underground signalling system. We normally use Disto underground and Moasure to link surface sites. His superb construction of this radio locator gives us the ability to confirm sites reliably by closing the loop between the surface and underground survey stations. We are really happy with the device and I guess if you find someone with interest in electronic self build projects they would probably want to help you.

 

[Stuart France]

What sort of depth of rock is thought to be between your cave and the surface directly above? Obviously there are 'serious issues' with signal strength loss the further the transmitter-receiver are apart since magnetic moment reduces by the distance cubed, not distance squared as with light illlumination. Also an error in levelling the underground transmitter loop (or the regularity of its windings) will introduce a displacement of the apparant surface position directly above the transmitter (the so-called Ground Zero) as determined by the surface person using the receiver set.

You need to ask "has it any hope of working well enough - if at all" before building something.

I've lent my gear to the Forest of Dean people, possibly permanently - we'll see, as they're in the Second Entrance business. The distances they're interested in measuring are of necessity quite short and thus any Ground Zero positioning error there would be insignificant.

 

[wormster]

Sounds like you need to build a set of Brian Prewer's Gunterphones. We used it in St Cuthbert's Swallet moons ago.

COTS underground radio location kit is as rare as rocking horse poo!

 

[wellyjen]

What sort of depth of rock is thought to be between your cave and the surface directly above? Obviously there are 'serious issues' with signal strength loss the further the transmitter-receiver are apart since magnetic moment reduces by the distance cubed, not distance squared as with light illlumination. Also an error in levelling the underground transmitter loop (or the regularity of its windings) will introduce a displacement of the apparant surface position directly above the transmitter (the so-called Ground Zero) as determined by the surface person using the receiver set.

You need to ask "has it any hope of working well enough - if at all" before building something.

I've lent my gear to the Forest of Dean people, possibly permanently - we'll see, as they're in the Second Entrance business. The distances they're interested in measuring are of necessity quite short and thus any Ground Zero positioning error there would be insignificant.

Both sets I built were to answer the question when we reckoned a place underground was close to the surface, but we were not confident exactly where, or how deep, due to cumulative errors from a survey with lots of legs in convoluted passage. Places where the inverse cube law wasn't an issue. It's a situation where they are an ideal solution.

 

[Leclused]

With an arcana tool you will be able to pin-point the spot. We used it several times in France in one of our projects. We were able to found the spot to make an entrance post-sifon. Divers placed the sending part under a chimney and the spot was picked up on the surface. Location was correct and the depth of 8m was calculated. We dug a entrance there and since then that became the main entrance for the non-diver cavers.

Also see the following thread where you can see some pictures of last summer where we did another pin pointing. Ferret finder

 

[wellyjen]

With an arcana tool you will be able to pin-point the spot. We used it several times in France in one of our projects. We were able to found the spot to make an entrance post-sifon. Divers placed the sending part under a chimney and the spot was picked up on the surface. Location was correct and the depth of 8m was calculated. We dug a entrance there and since then that became the main entrance for the non-diver cavers.

Also see the following thread where you can see some pictures of last summer where we did another pin pointing. Ferret finder

I do like the idea of suspending the transmitter from a tripod, so it is at a true vertical. Also much more compact with the ferrite core than others I've seen/made, so easier to transport underground.

 

[Leclused]

I do like the idea of suspending the transmitter from a tripod, so it is at a true vertical. Also much more compact with the ferrite core than others I've seen/made, so easier to transport underground.

Suspending it from a tripod would indeed even be better. But it's always a trade-off of how much you want to carry This tool doesn't take to much room and has been transported in dry-tubes through several siphons without problems.

 

[Stuart France]

Oh dear. Suspending a thing from a tripod and hoping it will hang perfectly vertical underneath depends on the perfection of building the thing in a vertically symmetrical way, i.e. its centre of gravity is in the middle of its vertical axis line. Imagine a rod with a string attached symmetrically at one end from which it is suspended. It should hang vertical. Now glue a penny to one side of the rod at its bottom end, or indeed its top end, or anywhere else along it. It does not hang vertically any more.

One way or another your wire windings need to be formed perfectly symmetrically and equally tightly wound, like a factory-made coil, and all other aspects need to be such that they do not shift its centre of gravity off the axis on which the thing is hung. This calls for a lot of care.

 

[ChrisB]

I was thinking that the benefit of the tripod would be that before going to the cave, you could set up the receiver directly above the tripod (and as high as practical), using a plumb bob, hang the transmitter from the tripod and adjust ('calibrate') it by adding weights to get the strongest signal. Hanging the transmitter from the tripod in the cave would result in vertical transmission.

I wouldn't be concerned about the robustness of a home-built device on a flight, but I'd be more confident of taking a lump of electronics through airport security if had a manufacturer's label saying what it was for.

 

[traff]

Oh dear. Suspending a thing from a tripod and hoping it will hang perfectly vertical underneath depends on the perfection of building the thing in a vertically symmetrical way, i.e. its centre of gravity is in the middle of its vertical axis line. Imagine a rod with a string attached symmetrically at one end from which it is suspended. It should hang vertical. Now glue a penny to one side of the rod at its bottom end, or indeed its top end, or anywhere else along it. It does not hang vertically any more.

One way or another your wire windings need to be formed perfectly symmetrically and equally tightly wound, like a factory-made coil, and all other aspects need to be such that they do not shift its centre of gravity off the axis on which the thing is hung. This calls for a lot of care.

Sounds very dismissive.
0.1deg at 100m depth is just 17cm on the surface.

 

[Stuart France]

If you can construct, presumably at home, and then align a hand-made transmitter coil to 0.1deg accuracy in a cave then I'd really like to know how you do it.

There are 360 degrees in a circle. So you're talking about 1 part in 3,600 error, all done by hand. Impressive or what?

 

[Stuart France]

Oh dear, again. Hanging a transmitter off a tripod in a cave and then measuring the "strongest signal" depends on where the person doing the "strongest measurement" is standing (in the cave or on the surface) and the orientation of their receiver antenna, which is presumably swinging around in their hand - and if not and under another tripod then it has the same sources of error as anything does hung under tripod.

Assessing a max/min on the surface assumes that you already know (or think you know) where Ground Zero is, which is the very thing you actually don't know and you are trying to discover.

 

[wellyjen]

It's no different from having to carefully level the more traditional in the UK horizontal transmitter coil underground with a spirit level and packing stones. The accuracy depends a lot on how well this is done. Similarly for the surface team finding the direction of weakest and strongest signals at different places and triangulating the position and depth.

 

[ChrisB]

Hanging a transmitter off a tripod in a cave and then measuring the "strongest signal"

I think you're quoting me there? I wasn't suggesting doing that in the cave, I meant setting up the tripod directly under the receiver in something like a stairwell, with the receiver directly above. Then tune the transmitter to point vertical. The tripod enables the setup to be replicated in cave.

 

[Stuart France]

I couldn't agree more with wellyjen: some kind of semi-rigid frame around the transmitter coil which is supported by handy stones found lying round and levelling it with a spirit level is how it is often done. This does not detract from the fact that you cannot do the above accurately to even 1 degree, and it in no way factors out asymmetry in the way the transmitter coil was wound and fitted to its frame and the contruction of the frame itself - bits of plastic or wood etc.

If you are trying to tune an antenna coil in a cave, and I've actually done that and after practicing it beforehand, you need to consider the minimum not maximum signal level. The human ear is very good at determining when a signal vanishes as compared to when it reaches its loudest/strongest. Indeed this is basic to radiolocation: it all depends on no longer hearing the signal, i.e. its minimum not maximum level.

In the case of a wide null, you need to interpolate to find the middle angle within an arc that spans the least you can hear either side of the true null position. Tuning a coil with an oscilloscope on a lab bench can be done by looking for maxima as an oscilloscope is very clear about that, but in the caving scenario, you listen for minima not only because of the physics of magnetic fields but also the capability of the human ear.