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Show (Edited by Q. DousUj W.rdrop. Editor of Radio Merchandising. , , , v -z. Transformers I Grounds LoJ JLA-L -Ifcru I Kzy tfrr. t5t Fig. 1 Hook-Up for Double Ground, Spark Transmitter. While the regular form of radio communication com-munication has been widely used in boy scout encampments, there are limitations limi-tations which restrict its use to those scouts mora advanced In the art. For instance, the wave-length regulations must be rigidly adhered to, and special licenses must be secured before the sets may be placed in operation. The "air" cannot be used Indiscriminately for fear of causing serious Interference with receiving sets for which the messages mes-sages are not Intended. There Is another form of communication communi-cation which Is suitable for scout camps and which Is deserving of wider application. The double ground system sys-tem has been little used In this country, coun-try, although it was of Immense value to the front line of the French army during the World war. The transmitter transmit-ter is so simple and well known as to require little explanation, for Its most Important unit Is the well-known spark coll. This Instrument has fallen Into disrepute In radio to a great extent, not only because of its gruff and uncertain un-certain tone, but also on account of the poor tuning- qualities of sets using spark coils. But with the double ground hook-up there Is no tuning required, re-quired, and since It Is useful primarily for slow speed communication the low note Is no obstacle. In Fig. 1 appears the hook-up for a double ground transmitter. The terminals ter-minals of the spark coll are placed a fraction of an Inch apart and a wire run out In each direction, where contact con-tact Is made with the ground. The longer these two wires, the greater will be the possibilities for distant communication, although If they are about fifty feet each code conversation may be carried on over distances not exceeding one-half mile. If Insulated wire is used it may be strung on the ground, although if It Isn't insulated It Bhould be kept a foot or two off the ground by wooden stakes. The grounds may be In the form of Iron pipes about four feet long driven deep into the earth ; the better the contact, of course, the better will be the results. In fact, a short strip of chicken wire, burled a foot or two beneath the soil, Is Ideal for the purpose. No connection should be made to piping systems, for that would destroy the possibilities of longer long-er distance. In Fig. 1 is shown a sample receiving circuit. There Is no tuning required, an that is needed being an audio-frequency amplifier. WD-11 tubes may easily be used, with two dry cells for lighting the filaments. This arrangement arrange-ment Is Indicated, and a single rheostat Is nsed. The receiving arrangements ere identical with those of the transmitting trans-mitting system as far as the ground wires are concerned. There is an unusual advantage in the double ground arrangement In that It Is directional. Fig. 2 shows a tyt-cal tyt-cal arrangement of double ground outfits out-fits at a boy scout camp. There are, let us assume, one headquarters station sta-tion and four outposts. The headquarters headquar-ters station Is equipped with four grounds, forming two double grounds, o El o & j ) fi-0ri m. I 0"gl0. , gr Fig. 2 Arrangement of Transmitting Stations. with a doyble pole, double throw witch connected so that either may be used. First, suppose outpost "A" to be sending. On account of the high resistance re-sistance of the soli between the two grounds of station "A," the electric currents must of necessity spread out materially in passing between one of A's grounds and the other. There is a considerable difference of voltage between be-tween the two grounds, as any scout who happens to get his hands on the secondary terminals will testify! Therefore, between grounds 3 and 4 of the "HQ" station there will also he a difference of voltage, on account of the weak currents set up by station "A." The further "HQ" Is from "A," the weaker will he the currents, and the response in the telephone receivers correspondingly weaker. But suppose "HQ" were to switch over to grounds 1 and 2. What would happen then? Since 1 and 2 are both on the same line to "A," there will be no difference of voltage and hence no signal in the telephones. tele-phones. How convenient! But with grounds 1 and 2, station "HQ" Is all set to receive from station "O," whose signals were excluded in the first case. "HQ" and "D" might, therefore, be carrying on a conversation, conversa-tion, and at the same time "A" and "B" could start up and exchange some messages without bothering the other two at all. Of course, It Is necessary to use the compass quite accurately, as scouts are trained to do, In placing the grounds. |