Popular Science Monthly 



449 



to use them directly in the circuit (or 

 shunted by an extremely high resistance) 

 while receiving. 



How the Call Signals Are Made 



In taking up code practice over such a 

 telegraph line, the usual wireless methods of 

 calling and signing should be followed. 

 Since every radio telegraph station has 

 certain identifying call-letters assigned to it 

 by the Government, the two practice 

 stations should select call letters. Let us 

 suppose that the left-hand station chooses 

 the call signal KSW and the right-hand 

 station KUR; these groups of letters will 

 designate the corresponding station and 

 that one only. 



Having arranged the line and apparatus 

 so that every pressure of the sending key at 

 either station may be heard as a correspond- 

 ing short or long buzz or tone in the tele- 

 phones at the other, the sending of messages 

 may be begun. The time for the first trial 

 having been set, both students should be at 

 their instruments, and listening to the 

 telephones. Let us assume that it has 

 been arranged that KUR, the right-hand 

 station of Fig. 5, shall signal first. The 

 operator there will follow the International 

 calling method and first send the "atten- 

 tion" signal, dash-dot-dash-dot-dash, two 

 or three times as shown in Fig. 6. This is a 

 general signal which precedes transmission 

 of radio messages, and is merely to catch the 

 attention of the receiving operator. Hav- 

 ing signaled attention, the call letters of the 

 station desired are now formed three times 

 in succession : KSW KSW KSW, as is also 

 shown in Fig. 6. This part of the call 

 serves to notify the operator at KSW that 

 he is wanted by some other station. The 

 next part of the call is the French word 

 "de," meaning from, which is immediately 

 followed by the thrice repeated call letters 

 of the sending station : KUR KUR KUR. 

 At the close of this signature, which 

 indicates the name of the station from 

 which the call is sent out, the operator 

 makes the finish signal, dot-dash-dot-dash- 

 dot and then signals the letter "K." 

 These two characters used in this way 

 mean: "I have finished sending and will 

 listen immediately. Please reply." 



Answering the Call Signal 



The operator at the other station, upon 

 hearing this call, realizes that KUR desires 

 to open communication with him. There- 

 fore he sends an acknowledgment of the call 



signal and an invitation to transmit, in 

 accordance with Fig. 7. This consists of 

 the attention signal sent twice or three 

 times, the signal letters of the calling 

 station (KUR) sent three times, the word 

 "de" (from), his own signal letters (KSW) 

 three times, "K" several times (meaning 

 "go ahead"), and the finish signal. The 

 first operator, at KUR, then knows that the 

 second station KSW is ready to receive the 

 messages to be sent, and proceeds to 

 transmit them. In the course of a message 

 the sending operator occasionally makes a 

 mistake; noting this, he at once stops 



The usual wireless method of calling and 

 signaling should be taken up in code practice 



sending and signals a question mark dot- 

 dot-dash-dash-dot-dot, then repeats the 

 previous word correctly and continues with 

 his message. If a receiving operator fails 

 to receive the entire message correctly, in 

 his following period of sending he requests a 

 repetition of the words missed. This is 

 usually done by sending the last word 

 received correctly and following it by 

 several question marks (dot-dot-dash-dash- 

 dot-dot) and the next word correctly 

 received. If the receiving operator gets 

 correctly everything sent to him, he signals 

 "R" (meaning "Received Correctly") sev- 

 eral times at the beginning of his next 

 period of transmission. Thus complete 

 conversations are carried on and acknowl- 

 edged or corrected. The detailed form of 

 sending commercial messages is somewhat 

 more complicated, but the simpler method 

 just outlined will prove ample for practice 

 work. 



The practice messages should at first be 

 made up of words including only the letters 

 of the first three groups of Fig. 2, in last 

 month's article. As soon as all of these 

 letters are perfectly familiar and easily 

 recognized when their Morse sounds are 

 heard, the remainder of the alphabet may 

 be memorized and worked into the code 



