Underground Radio Propagation

[pwdrive]

Something I have not researched, is anyone in the know about this subject?
Briefly I own a tunnel and some underground mine workings, Me and a few buddys explored and surveyed the tunnel and workings some years ago, we had no form of communication other than banging on the rock and shouting, if I/we ever go in there again I wouldn't mind a more effective means of communiction, there is lots of flowing water in there, country rock is Granite.

Lawrence.

[Steve_P]

This puts it fairly well.

http://nopr.niscair.res.in/bitstream/123...18-422.pdf

Basically, lower frequencies are better. Best around 6 Mhz.

Cheers,

Steve P.

[AlanBeckett]

Lawrence,

The preferred method of underground (Radio) Communications is 'Leaky Feader', eg http://www.gai-tronics.org.uk/products/rfm.htm.
I assume you're not a 'Gassy Mine' so you don't care about Intrinsic Safety etc.
The original Systems worked on the old (low) PMR Band - 60-80MHz?
The one above, which is getting a bit out of date now, works on the VHF PMR Band.
Modern Systems are UHF and are designed to carry Voice, Video, Ethernet, etc, etc.
Now for the bad news:-
The systems use a special co-ax cable which is designed to leak rf, which is why you have to insert a Repeater every 500m or so. As the cable is a 'Linear Bilateral Network', you hope, you can receive from it and transmit into it.
For I.S. reasons the power levels are low - typically 1mW at the drive end of the cable.
Designing a two way Repeater - the go and return channels are typically 10MHz apart - with power splitting, while maintaining a decent match and linearity in both directions, is interesting.
You do, of course, need hand-helds at the right frequency.

Through-the-ground Systems have been about for years, but to my knowledge no-one has ever really made them work consistently. They usually kept for Emergency situations when you haven't got much choice.

Alan

[pwdrive]

Thanks for the replies guys, both the link and the explanation, not looking to good then, out with the loud halers! Generally no explosive gas in granite mine workings unless some one has dumped tons of rubbish into them, we were allowed to smoke underground in the hardrock mines in Cornwall and Canada no problem (apart from smoking in itself!) apart from when charging or handling explosives, I am wondering if a pair of those cheap walkie talkies you can get without a license would amount to anything, I could do with the them down the woods anyway so my missus can let me know when the kettle has boiled.

Lawrence.

[Yorkie]

Some year ago, a well respected Leeds radio amateur, John Heys, of the White Roe Amateur Radio Club (designer of the White Rose ARS Receiver project), conducted a great deal of research into cave radio and designed transmitters and receivers which featured in RSGB's Radcom. There are some pics here, but no additional info:

http://whiterose.shacknet.nu/cave_radio.html

The British Cave Research Organisation claims to be one of the most advanced outfits of its kind in developing cave communications, and has an extensive website which might be of interest. You'll find the BCRA here:

http://bcra.org.uk/creg/

Hope that helps a bit Lawrence.

[pwdrive]

Thanks for that David.

Lawrence.

[AlanBeckett]

The problem with 'Through the Ground' Transmission is the strata, and to a lesser extent, the depth. In Limestone and not too deep, typical Caving situation, it can be fine, at least in the Surface to Undergound direction. Transmitting back to the surface is more problematic due to the limited power and Antenna size available. The problem in other Mines is that there is often metalliferous strata in the way, which I guess will be the case in your situation.

There are/were systems which attempted to 'shine' the signal down the Roadways - Tunnels in Media Speak. That works OK in reasonably straight Roadways, and you can put Repeaters at Junctions and turns. However, you still need PSUs at regular intervals. Again, in my very limited experience of Cornish Mines, the Roadways are anything but straight.

Alan

[pwdrive]

The problem with 'Through the Ground' Transmission is the strata, and to a lesser extent, the depth. In Limestone and not too deep, typical Caving situation, it can be fine, at least in the Surface to Undergound direction. Transmitting back to the surface is more problematic due to the limited power and Antenna size available. The problem in other Mines is that there is often metalliferous strata in the way, which I guess will be the case in your situation.

There are/were systems which attempted to 'shine' the signal down the Roadways - Tunnels in Media Speak. That works OK in reasonably straight Roadways, and you can put Repeaters at Junctions and turns. However, you still need PSUs at regular intervals. Again, in my very limited experience of Cornish Mines, the Roadways are anything but straight.

Alan

Hello Alan, you are correct in what you say, old tunnels/drives/roadways are anything but straight in Cornwall, the only straight tunnels/drives were the main crosscuts these were driven at various levels from the shaft at an angle of approx 90 degrees to the known direction of the various tin/copper lodes, once a lode was intersected and the assay values were proved economic then the lode would be driven on usually either side of that lodes intersection with the main crosscut, in narrow lode mining (mainly that in Cornwall) the tunnel/drive follows that strike of the lode however much it deviates from being straight. Typicaly the lodes would strike East West so the main crosscut from the shaft would be driven North South at various levels to intersect these lodes. The lodes obviously consist of metaliferous matter, principaly tin, copper, wolfram, iron pyrytes etc. When I worked down there the only electrical communication was from the shaft station up to the surface, one was a wind up telephone link which was connected to the banksmans hut and the other was the shaft signaling system which consisted of push buttons and bells connected from the differnet shaft stations and the winder house for signaling for the cage to be lowered/raised etc, both systems had accumilator backup. For "communicating" along a straight crosscut we had a simple homebrew/ad hoc arrangement using our cap lamps which usually consisted of shaking your head side to side for a "problem" or "no" and shaking your head up and down for "no problem" or "yes" I did at one point try to get some of the guys to learn a bit of basic Morse so we could tap out a basic message down the air or water pipes but it didn't catch on, they thought I was nuts!
As for direct transmission through mineralised granite strata I would think it would be pretty impossible, but I am no expert on that subject.
Just as a note I worked at Geevor tin mine also, they had a 3 Kv substation at the 1500 ft level, the transformers had to be specially constructed to fit the shaft compartment dimension in order for it to be lowered down in one piece.
One of the problems in the workings I have is that there is a large iron lode that cuts through one of the tunnels, I remember when we surveyed it that my compass bearings were way out as we approached it so that bit of the survey was a bit of guesstimation, in the end it all worked out ok and we were able to find the locations of the old capped and filled air shafts at surface within a few yards of the points noted underground on our survey, the survey was not scientific, just an offset compass, a grid map and a surveyors tape plus torch.
if we go down there again It would not warrant any expensive technical comms. kit.

Lawrence.

[AlanBeckett]

Just a last couple of comments 'cause I don't like the idea of you heading into a Pit with no communications.

In a lot of American Pits they send and receive rf over the Trolley wires - they use Trolley Pole Locos and little cars when they're well away from the face. It works reasonably well, so I suspect a single wire strung along the roadways should work. I don't know what frequency they use but I could find out.

You could use (effectively) a Telephone, either with a pair or a single wire and Earth. Actually a Telephone is a bit of an overkill unless you have a couple of 'Buttphones' handy. The usual method is to have a battery powered amplifier with a Press To Talk (PTT) switch. You clip it to the line or lines and press the switch to talk, using the LS as a Microphone, then release the switch and listen. Generally you need a simple Signal Detector when listening otherwise you'll flatten the batteries.

Alan

[Joe]

When I first read "Buttphones" I thought we were back to Morse!

- Joe