The contacts should be gone over 

 frequently with very fine sandpaper, as a 

 poor contact is liable to cut down the 

 efficiency of the receiver to no small extent. 

 The left contact-screws are adjusted to 

 touch the springs when the key is depressed 

 while the right hand pair are to make 



IS 



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Popular Science Monthly 159 



Loading Coil in Series with 

 the Secondary 



WHEN a low resistance detector is 

 used, it is a good plan to tune the 

 secondary circuit by using a comparative- 

 ly small inductance coil and a large con- 



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Detail of the parts that enter into the 

 construction of the magnetic break key 



contact when the armature has come back, 

 and to break the contact when it has been 

 drawn to the magnets. 



A little experience will make it possible 

 to get an adjustment where there is no 

 sparking at the contacts and no noise in 

 the telephones. 



I doubt if anyone, after using a key such 

 as described, will ever willingly go back to 

 the old clumsy aerial switch. 



H L 



denser, for then the current flow is a maxi- 

 mum and the voltage is quite low. For 

 high resistance detectors the reverse is 

 true. Increased efficiency with such de- 

 tectors as the audion can frequently be 

 secured by inserting a loading coil in series 

 with the secondary, and correspondingly 

 reducing the capacity of the tuning con- 

 denser. This applies the highest possible 

 voltage to the grid. 



An Emergency Form for Winding 

 Motor Fields 



RECENTLY my rotary spark-gap, no- 

 . volt A. C. motor burned out one of 

 its fields. As I was in a hurry to use it I 

 tried a quick method of rewinding the coil 

 by driving a series of nails into a wood 

 face-plate on a small lathe and winding 

 the wire on them. After winding the coil 

 I bent the nails together so that the coil 

 could be slipped off. — Edward McClure. 



Effect of the Moon and Season on 

 Wireless in the Tropics 



WHILE stationed in the tropics for 

 several years as a wireless operator, 

 I observed that in the periods of a full 

 moon, or thereabouts, the atmospheric 

 interferences are slight and the ether seems 

 to carry the wireless waves with less ab- 

 sorption than when the moon is in its 

 quarter periods, or thereabouts. With a 

 full moon, and using the same receiving set, 

 I could receive from stations that were 

 about 200 miles farther away than those 

 which could be heard when the moon was 

 in its first or last quarter. Also, during the 

 winter months from about the first of 

 December to April, there seemed to be bet- 

 ter atmospheric conditions.-#-J. M. Cohen. 



