Underground Radio Propagation

[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.