158 



Popular Science Monthly 



come. It has also been demonstrated 

 that the best signal-tone frequency for 

 working through static interference is 

 about 1000 per second, which is in the 

 neighborhood of the second C above 

 middle C on the musical scale. This 

 frequency of 1000 has now been selected 

 as standard for nearly all radio trans- 

 mitters. 



An Artificial Static Producer 



It follows, then, that to get practice in 

 reading signals through static we must 

 have (in addition to the buzzers which 

 produce the Morse signals themselves) 

 some device which will imitate the sounds 

 of static. The simplest way in which an 



s 



S.M 



"Wi 



FI&.25 



One way to associate the buzzer telegraph 

 line and the stray-maker for practice work 



idea of atmospherics can be secured is 

 shown in Fig. 23, where a telephone re- 

 ceiver T is connected in series with a 

 battery B and a coarse file F. The loose 

 end of the wire from the telephone re- 

 ceiver, W, may be rubbed along the rough 

 surface of the file. The telephone will 

 reproduce irregular rough and scratchy 

 noises corresponding closely to some 

 types of strays. 



The file arrangement is scarcely uni- 

 form enough in action to use for regular 

 practice, and so it will be well to make up 

 a "static producer" or "stray maker" of 

 the sort shown in Fig. 24. A wooden 

 base X has mounted upon it a block Y 

 and two drilled standards, S' and S^ 

 These standards aui)port a shaft upon 

 which is fastened a brass disk or wheel 



BW, about }/2 in. thick and 3 in. in diame- 

 ter. One end of the shaft carries a pulley 

 P which permits the disk to be rotated 

 slowly by belt B, a clockwork or back- 

 geared motor being used as a source of 

 power. The circumferential surface of 

 the disk is roughened by cutting irregular 

 diagonal V's across it with a sharp saw- 

 file, so that its surface somewhat re- 

 sembles an exceedingly coarse and rasp- 

 like file. On the block Y is pivoted a 

 soft copper wire W, about No. 12 in size, 

 one end of which is bent up to rub upon 

 the surface of the roughened disk at the 

 contact point C. The other end of the 

 wire extends out away from the disk, and 

 a small lead weight W is fastened upon 

 it so that the pressure of contact at C may 

 be varied by sliding the weight back and 

 forth along the wire. 



If the terminals of the battery and tele- 

 phone in Fig. 23 are connected with the 

 disk and the wire of Fig. 24, so that the 

 three elements are in simple series con- 

 nection, and if the disk is then slowly 

 turned, the telephone will produce sounds 

 like those set up by static. By varying 

 the speed of rotation (which must always 

 be slow — not more than about one revolu- 

 tion per second) and by changing the 

 number of dry cells in the battery, 

 almost any type of static can be imitated. 



Connecting the Stray-Maker with the 

 Telegraph Line 



Now arrange the stray-maker in such a 

 way that its imitation static can be 

 impressed upon the buzzer telegraph line 

 previously described. Thus, one static 

 producer will afford practice to all the 

 students using the line, and practice can 

 be had in the actual exchange of messages 

 under various conditions of atmospheric 

 interference. 



Fig. 25 shows one way of associating the 

 buzzer telegraph line and the stray- 

 maker SM. The left-hand portion of the 

 figure represents any one of the stations 

 along the line, and comprises the tele- 

 phone T, the buzzer Z, the battery B, the 

 key K and the ground connection which 

 have been described in earlier articles. 

 At any one of these stations (though pref- 

 erably one near the middle of the line) the 

 stray-maker may be installed by con- 

 necting it as shown in the right-hand part 

 of Fig. 25. i2 is a resistance of about 



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