Popular Science Monthly 



will be noted that the buzzer-sounds from 

 each of the three stations possess a certain 

 individuality, and that the identity of a 

 sending station can be established even 

 before the operator has given his station 

 call, merely by noting the signal-tone 

 character. If three of the same make or 

 model of buzzers are used, the tones may 

 sound very much alike, and it may be 

 difficult to tell by tone which station is send- 

 ing. If three different sizes or types are 

 used, however, the signal tones are likely to 

 be widely different. It is this variation in 

 signal tone which makes possible the reduc- 

 tion of station interference by the operator's 

 concentration on the sounds themselves. 



Fig. 17 shows a sig- 

 nal station of the 

 buzzer telegraph line. 

 The buzzer Z\ has the 

 telegraph key K\ and 

 battery Bi connected 

 across its binding 

 posts, so that when 

 the key is pressed the 

 buzzer will operate. 

 The left-hand binding 

 post, which is con- 

 nected with the vi- 

 brating armature, is 

 made fast to the earth 



connection; and the contact-adjustment 

 post is connected with the line wire through 

 a pair of head-telephones of approximately 

 1000-ohms resistance. These telephones 

 may be shunted by a variable resistance of 

 about the same value, for the purpose of 

 weakening the signals heard. The resist- 

 ance is not usually necessary, however. 

 The line wire may be extended in either 

 direction to reach as many stations as de- 

 sired, within reasonable limits of number 

 and distance. Each station is connected as 

 shown in Fig. 17, and the system is such 

 that signals produced by pressing the key at 

 any station are heard simultaneously in the 

 telephones at all the other stations. 



Using One Station to Make Interference 



Obviously, such a system resembles a 

 group of radio stations in many particulars. 

 If there are more than two stations on the 

 line, it is possible to arrange for one of them 

 to interfere while the others are attempting 

 to exchange messages. By choosing the buz- 

 zer pitch of the interfering station so that it is 

 different from that of the sending station, 

 the easiest interference condition is created. 

 By gradually adjusting the interfering note 



*-- G 



Fig. 19 and 20. A typical buzzer of the iron 

 frame type and a method of adjustment 



957 



to a sound closer and closer to that of the 

 sending station, the difficulty of receiving is 

 continually increased and practice in con- 

 centrating on one note to the exclusion of 

 others is secured. 



A better way to develop systematically 

 the power to eliminate or reduce station 

 interference by tone selection is to install at 

 one of the buzzer-telegraph line stations an 

 equipment such as shown in Fig. 18. Here 

 the left-hand portion represents the usual 

 buzzer sending and receiving outfit, con- 

 nected as in Fig. 17. The telephone shunt- 

 ing resistance is. not shown, but may be 

 added if found necessary. The right-hand 

 portion of the diagram shows the inter- 

 ference makfer, which 

 consists' mainly of a 

 second buzzer Z 3 hav- 

 ing its own battery 

 B 3 and a sending key 

 or sending machine S 

 connected across its 

 terminals. From the 

 contact-adjustment 

 post to the left-hand 

 (armature) binding 

 post is connected a 

 high resistance R 2 , 

 which should have a 

 value of at least 1000 

 ohms. A sliding contact on this resistance 

 is connected with the line wire. 



This interference-maker will produce 

 interference signals whose strength, tone 

 and occurrence are under control, and may 

 be arranged so as to operate automatically. 

 When first set up, it will be noticed almost 

 immediately that sliding the contact along 

 R 2 changes the strength of the interfering 

 signal at all the stations on the line, and 

 that the more resistance is cut-in between 

 the line wire and the ground, the louder the 

 signals are. In practicing, it is a good plan 

 to start with fairly weak interfering signals, 

 and then gradually to increase their 

 strength until they are as loud as or louder 

 than the messages it is desired to receive. 



Varying the Tone of the Buzzer 



The adjustment of the interfering or 

 sending signal tone has been mentioned 

 several times, but specific methods of 

 making this adjustment have not been 

 shown. In Fig. 19 a typical buzzer of the 

 iron-frame type is illustrated. This is use- 

 ful for this sort of work because of its 

 cheapness and reliability. The mechanical 

 arrangements vary in detail according to 



