448 



Popular Science Monthly 



another part of tre nouse, there will always 

 be the temptation to call from one "sta- 

 tion" to the other and to make corrections 

 in that way instead of depending strictly 

 upon the Morse signals. Only by relying 

 upon the line and Morse signals exclusively 

 can the best practice be had. 



An excellent system of connections for a 

 practice line is shown in Fig. 5. For each 

 station there are needed a buzzer, dry cells, 

 telegraph key, and telephones. Almost 

 any sort of buzzer or telephones will do, 

 though it is better to get a buzzer which 

 gives a high musical tone and to use tele- 

 phones of the usual wireless type. The 

 small buzzers which can be purchased from 

 any electrical sup- 

 ply store have fairly 

 high tones and are 

 very good. There 

 are special "wire- 

 less" test buzzers 

 made, which have 

 three connection 

 points and which 

 are designed to give 

 a very high and 

 clear tone of about 



the same sound as that produced by a 

 modern radio-telegraph station. This is 

 the best type to buy. The preferred tele- 

 phones are of high resistance (about 2000 

 ohms total) and consist of two "watch- 

 case" earpieces mounted upon a headband 

 which automatically holds them in place 

 and so leaves both hands of the operator 

 free for sending, writing out the message 

 being received, or adjusting his apparatus. 

 An advantage of buying both the buzzer 

 and the telephone of the sorts used in 

 regular wireless telegraph work is that both 

 may be used later on when radio-telegraphy 

 itself is taken up. 



Wiring the Two Stations 



The diagram, Fig. 5, shows how the two 

 buzzer telegraph stations are to be con- 

 nected. First the dry cells and the key are 

 connected in series across the two ordinary 

 terminals of the buzzer, marked I and 2 in 

 the figure. Then the binding post I is con- 

 nected to earth, and a wire is attached to 

 the contact post near the buzzer armature, 

 marked 3 in the figure. This wire is con- 

 nected with one terminal of the telephones. 

 To make sure that everything is in good 

 shape at either station, the remaining 

 terminal of the telephone may be con- 

 nected with the ground, so placing the 



In answering a call at the other station ac- 

 knowledgment of the call is sent in return 



receivers in series between terminals I and 3 

 of the buzzer. If the adjustments and 

 wiring are correct the buzzer will operate 

 whenever the key is pressed, and the tone of 

 the buzzer will be reproduced loudly in the 

 telephone receivers. If the tone is so loud 

 that it becomes annoying, a resistance of 

 several hundred ohms may be connected 

 across the telephones as shown in the left 

 hand station of Fig. 5. If this resistance is 

 variable, as it is in a potentiometer used 

 with radio receivers, the loudness of the 

 sound in the telephone may be made any- 

 thing desired by adjusting the resistance so 

 that any chosen portion of the line current 

 will be shunted around the winding in the 

 "by-pass" circuit. 

 Assuming that 

 both stations have 

 been set up and 

 adjusted to operate 

 properly, it is only 

 necessary to con- 

 nect the outer ter- 

 minals of the two 

 telephones by 

 means of a line 

 wire. This line 

 wire may be of almost any kind since it 

 carries very little current. Any copper 

 wire may be strung from one station to the 

 other; it need not be larger than No. 30, 

 and does not require careful insulation 

 unless the distance is large. When the two 

 stations are set up completely, as in Fig. 5, 

 pressure of either key should result in a 

 corresponding clear signal tone in both 

 telephones. If it does not work out in this 

 way, go over the circuits in detail and be 

 sure that they are correctly connected and 

 sufficiently well insulated. The earth or 

 ground connection may be made by wrap- 

 ping a bare wire around a scraped water or 

 gas pipe, or a steam radiator. For con- 

 venience the ground lines may be discarded 

 and a second line run between posts 3 of the 

 two buzzers. 



The diagram shows the variable shunting 

 resistance at only the left-hand station; 

 obviously the same plan may be used at 

 both ends if the signals are too loud. The 

 incoming signals are likely to be somewhat 

 weaker than those made by the buzzer at 

 the home station when sending, but if the 

 line wire is of sufficient size and well enough 

 insulated this difference in intensity should 

 cause no trouble. Under some particularly 

 poor conditions it may be found necessary 

 to shunt the telephones while sending and 



