New Britain herald., 1922-11-28
WOULD USE RADIO
 IN MINE DISASTERS
ReSCuaFs and EntOmbed Could
 Then Communicate


 municatIoa between FesegsrP on the
 surface and miners enLembed,in mInet
 following fires and e1plosio1s, is a
 hope held out by tho United Htatea
 Bureau of Mines, to lessen the hoTiHort
 and losses Of mine disasters PreliKn.
 mary tests conducted by the Bureau,
 with the cooperation Of, a great cleo.
 trical manufacturing concern, in an
 experimental mine at Bruceton, Penn
 sylvania, already have resulted in a
 degree of success
 While these experiments have so
 far failed to develop any practical
 method of using wireless waves for underground communication, never theless says Il publication of the Mine Bureau. they indicate clearly that eloctromagnetie waves may be
 made to travel through solid strata. In tho Bruceton experiments signals were heard distinctly through fifty feet of coal strata, although the audi bility fell off rapidly ns the distance was increased, The absorption of loss Of Intensity with distance is very great for the short wave lengths used in these tests. Longer wave lengths are known to suffer less absorption and may possibly be found practically ef- fectIve under certain conditions. Tests Conducted.
 In this connection it is interesting Co note tests conducted by the Unit ed States Bureau of Standards. in sdropping wireless antennae down deep unused oil wells to underlying rock strata, in order to send the wireless impulses through the rock instead of through the air. The results; 1t is believed. may be the same as pro- jecting the antennae upward into the air strata ..,' -
 The desirability of substituting the wireless system of communication for tho present telephone systems in use in mines is evident in consider ing that rock fall or explosion, by breaking wire connections can put the entire system out of order.
 Tho mine telephone has been per fected to such an extent that it is giving satisfaction in most mines where the wiring is we'll insulated, the Bureau of Mines announcement con tinues. Very often the telephone can not be depended upon eon account of falls of rock, grounding due to worn l insulation or extreme dampness. In the event 2of disaster it frequently | happens that the mine telephone sys- tenn is put out of commission by the | agency that causes the disaster, at the | very time when 1t is most urgently l needed. On this account the mining 1 industry is interested in any kind of telephone system that can Do count ed upon in an emergency. Many re- quests have been received by the Bureau of Mines to devise means of | utilizing wireless methods for this purpose.
 Preliminary Experiments.
 The preliminary experiments con sisted first in receiving signals from without the mines by means of 8 re- ceiver located inside the mine and sec .ond, both @nding and receiving mes sa ges underground through the strata. It was found that with receiving in atrunient set Aat point 100 feet un- derground. signals sent from station KDKA, of the Nesting mouse Electric md Manufacturing com pany, at East Pittsburgh, is miles away, could be
 
 the receiving station used in the mine n this test was a 6-inch bore-hOle ex- tending from the surface, lined with iron pipe and containing electric light wires which extended therefrom through the mine. The presence of these wires. according to the experi- menters, evidently. assisted greatly in the reception Of the signals, for when tho receiving set was carried to an- nther point in the mine removed from Wires and track the signals were barely audible through fifty feet of cover. The fact that signals were de-#I tected 1t all. however, even though faintiy, was declared sufficient evi- dence of transmission through ground t0 encourage further experimenting.
 m sending waves underground transmitter WAS used in such a n1ar- nef as to send out continuous waves of 200 to 300 metres length. On ao- count of tho limited time at disposal no attempt was made to modify the in such manIser as to pro- dnes waves Of greater length. x n all experiments the vertical an- tennae were found to give better re- suits. The horizontal afltennae gave raeticaIi5 mo reception. N loop of a. l single turn was used with fair results An these experiments were tried with a wave length of 200 to 800 metres, except the reception from KDKA. which was aB0 metres.
 Strata Lie Horizontal.
 The strata at Elle experirae mine Iie almost horizontal The direction Df strata. it was said, may have some Influence on the transmission of ra- 1io waves, but the present experi- nents gave no conclusive evidence on Ehia point No doubt the degree of eetness Of the strata influence the z transmission of radio waves, it was z exported. The mine used is a conn4 H dry mine, but the over- N burden is damp and R small stream # water is continually flowing from H .he mine. This overburden consists H ,hfsfIy of soil and soft shale The tI workings of the mine 'dilssy hof ofsasitAi ne foot vein of N coaI and the transnitas ' .inss and rAeanfion inelk4a fha mine q