Popular Science Monthly 



153 



How Germany's Secret Service Wireless 

 Stations Are Being Weeded Out 



THAT there are secret service wireless 

 stations of Germany in and about our 

 large cities and important harbors, there is 

 not the slightest doubt. At the time the 

 merchant submarine "Bremen" was to 

 arrive from Germany, it will be remem- 

 bered, German agents prepared moorings 

 for her at New London, Connecticut. 

 Neither the Government wireless stations 

 nor our commercial stations received any 

 communications from this submarine. Evi- 

 dently, secret stations, whose messages we 

 could not hear, must have kept in touch 

 with her. 



These stations, we can rest assured, have 

 not dismantled, but are working now. 

 They await only the opportunity to report 

 the sailing of a Europe-bound ship to a sub- 

 marine waiting offshore. Unquestionably, 

 such a menace must be weeded out. Our 

 Government has not been idle. According 

 to reliable information, it has already 

 located several of these stations. The 

 problem is not an easy one, and is one 

 entirely of wireless engineering. 



William Dubilier, one of our most 

 prominent experts, believes that the Ger- 

 mans manage to keep their antennas con- 

 cealed by stringing them inside high non- 

 metallic structures; as, for instance, a 

 hollow wooden flagpole. Though but 

 one wire could be strung inside a flag- 

 pole, what would be lost in antenna 

 efficiency could be partly compensated 

 for by the increased power of the station. 

 Of course, these spies would not be 

 compelled to use an aerial at all. They 



could use a close circuit system having two 

 grounds. But this is not likely. The 

 other method is more efficient and lends 

 itself to better selectivity. 



From the antenna concealed in the flag- 

 pole, the spies could run the aerial lead 

 directly through the roof and into the 

 garret of the building, without exposing it. 

 These instruments, we can take it for 

 granted, are the best that German money 

 can buy. The operators obtain their 

 unusual selectivity probably by the use of 

 a double heterodyne or ultra-ultra system. 

 That is, they superimpose a number of 

 oscillation circuits one upon the other 

 between the exciting transformer and the 

 aerial and ground connections. The various 

 ways in which each of these many circuits 

 can be tuned are almost unlimited. The 

 waves such a system would send out could 

 be efficiently received only by a receiving 

 system of similarly complex configuration. 

 The usual station which has not these 

 superimposed circuits could not receive 

 the signals distinctly. 



These facts give some idea of the task 



our wireless engineers are up against. 



First, they must obtain a circuit which will 



receive these secret signals — a most difficult 



task which would involve the finding of 



the exact number of the superimposed 



circuits and the exact configurations! 



Second, they must locate the stations with 



some sort of direction-finder using this 



type of circuit. The methods used with 



these finders would then be similar to 



that explained in a previous article on 



the direction-finder, on page 232 of the 



February 191 7 issue of the Popular 



Science Monthly. 



The Germans conceal their aerial in the hollow of the flag pole. Their complex waves 

 can be received only by submarines and other stations fitted out likt themselves 



