Popular Science Monthly 



301 



The primary 3 is coupled to secon- 

 daries 4 and 5, with their corresponding 

 detectors 8, 14, and stopping condensers 

 12, 18, in the usual manner. The leads 

 from the condensers 12, 18, which ordi- 

 narily go direct to telephone receivers, 

 are in this case carried to the two pri- 

 mary windings of a telephone trans- 

 former. These two coils, 10 and 16, op- 

 pose each other's effects upon the sec- 

 ondary 20, which has in series with it 

 the telephone receivers 21. This trans- 

 former is adjustable, so that either of 

 its primaries may be caused to induce 

 stronger signals in the secondary than 

 will the other. 



The operation of the device may be 

 considered in connection with a condi- 

 tion assuming simultaneous sending by 

 two wireless stations, one nearby and the 

 other distant. Suppose that with an or- 

 dinary receiver the strong signals from 

 the nearer station practically drown out 

 those coming from a distance, and yet 

 that it is desired to read messages on 

 the weaker waves. With the apparatus 

 of this patent the receiving operator 

 would adjust one of the detectors, say 

 8, to a sensitive condition in which it 

 would respond well to the weak signals. 

 The other detector, 14, is then adjusted 

 to receive only the strong signals. Thus 

 there are set up telephone currents in 

 primary 10 from both stations, that from 

 the distant one being much weaker than 

 that from the interfering set, and tele- 

 phone currents in the opposite direction 

 in coil 16, these latter being only from 

 the interfering station. Since the sen- 

 sitiveness of detector 14 has been re- 

 duced, the interference currents in 16 

 will be weaker than those in 10. By 

 loosening the coupling between 10 and 

 20, the signals from the interfering sta- 

 tion will oppose in their magnetic effects 

 on the secondary, and so produce no re- 

 sponse ; if it has not been necessary to 

 weaken the coupling too far, the signals 

 from the distant station should still be 

 heard. 



Thus, if detector 14 is of the type 

 which requires a certain fairly large cur- 

 rent before it gives any response, and 

 if the difference in signal intensities is 

 not too great, some very advantageous 

 interference reducing effects may be 

 had. 



A Cheap Ground Clamp 



A hose clamp can be purchased at any 

 hardware store at two for five cents and 

 a binding post taken fnjm the zinc side 

 of an old dry battery. A hole is then 

 drilled in the hose clamp and the post 

 soldered fast. 



Insulators can be made by taking a 

 broomstick, sawed into 4 inch or 5 incli 



Strain insulator made from 

 a broom stick 



lengths and having a screw eye put in 

 each end. Baked and thereafter boiled 

 in paraffine these make first-class strain 

 insulators. To prevent splitting, a hole 

 should be drilled in each end a trifle 

 smaller than the screw eye and then 

 filled with glue. The screw eye should 

 have a coarse thread. The tough hard- 

 v/ood holds the eyes so they will stand a 

 heavy strain. Two coats of black as- 

 phaltum make them resemble hard rubber. 



Crystal Detector Hints 



WHEN the best results are to be ob- 

 tained, the crystal should be 

 mounted in a fusible alloy. This can be 

 easily made by melting equal parts of 

 ordinary fuse wire and tinfoil and add- 

 ing a little mercury. 



In selecting pieces of galena the parts 

 that are very shiny and have the most 

 vein will be found to be the most sensi- 

 tive. When breaking galena do not hit 

 the mineral one hard blow : tap it three 

 or four times lightly with a liammer, 

 breaking it into square pieces, and there 

 will be no waste. 



With silicon or ferron as a mineral, 

 use a gold wire having a sharp point. A 

 fairly heavy pressure may be used, and 

 results in a firmer adjustment. The re- 

 sistance of a crystal is great, and there- 

 fore as small a piece as possible should 

 be used. 



Different combinations of minerals 

 will often work better than one mineral. 

 Galena and graphite, silicon and graphite, 

 zincite and bornite. or chalcopyrites 

 (perikon), ferron and silicon, and galena 

 and tellurium will all work better in 

 combination than alone. 



