Wireless Work in Wartime 



VI. — Atmospheric or static interference, and 

 how to secure practice in operating through it 



By John L. Hogan, Jr. 



WHEN the student has learned to 

 send and receive correctly, and 

 has had sufficient practice in 

 reading wireless messages through artificial 

 "station" interference, he is ready to take 

 up the most important (and perhaps most 

 difficult) problem that confronts the radio 

 operator. This is the copying of received 

 messages in spite of the interfering 

 sounds produced by natural electrical 

 disturbances, and called "static," "atmos- 

 pherics," "X's" or "strays." 



The December article described simple 

 ways to practice reading messages when 

 interfering sounds corresponding to un- 

 desired signals from some external radio 

 station are heard. The four earlier in- 

 stalments of this series outlined the work 

 necessary to learn the Morse code and the 

 sending and receiving of messages. This 

 article takes up the study of atmospheric 

 interference, its effects, and the reduction 

 of harmful results from it. 



In the first place, we must examine the 

 differences between strays and signals. 

 These differences are, fortunately, usually 

 well defined. First we shall consider the 

 very practical distinction depending upon 

 the fact that strays or static in general 

 produce irregular noises at the receiver, 

 while radio signals may be made to 

 produce musical tones. 



In the December article it was pointed 

 out that practice enabled the receiving 

 operator to distinguish between the sig- 

 nals heard from two stations, so that 

 messages from one of them could be 

 written out even though both were send- 

 ing at the same time. The more skilful 

 the receiving operator, the more closely he 

 is able to concentrate, and the nearer alike 

 the two signal sounds may be without 

 producing interference. The two distinc- 

 tions usually relied upon are pitch and 

 intensity; if the signal tones are equally 

 strong, there must usually be a con- 

 siderable difference in their pitch or 

 frequency if one is to be read "through" 

 the other. If the interfering signal is 



much weaker than that from the com- 

 municating station, not so great a differ- 

 ence in pitch is necessary in order that the 

 receiving operator may concentrate upon 

 the desired dots and dashes. 



Static Noises and Signal Tones 



As has been indicated, since strays 

 usually set up irregular noises rather than 

 tones at the receiver, the operator there is 

 usually able to concentrate upon the 

 messages he wants to receive and to ignore 

 the^ interference because of the difference 

 in sound. Static sounds are of various 



Simple method of producing a static and a more 

 elaborate model for obtaining same resiilts 



kinds; they have been described as hissy, 

 scratchy, or rattly, and as resembling 

 frjdng or bubbling noises. They vary in 

 character from time to time, and are often 

 much louder than the signals it is desired 

 to receive. Static sounds are almost 

 never musical in character, in even the 

 smallest degree. Since the signals from 

 radio stations may be made either musical 

 or non-musical (as has been known for 

 some years), and of almost any pitch, it 

 follows that by choosing clear musical 

 tones the difficulties of reading messages 

 through static noises are largely over- 



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