Page:Popular Science Monthly Volume 91.djvu/811

 Popular Science Monthly

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��ber of the message, the "check" or number of words, and the hour in (8) are given in figures, the hour being followed by "am" or "pm." Sometimes the signature letters of the sending operator are merely written on the blank and not transmitted, but this omission may give rise to confusion be- tween the number of the message and the "check."

A Specimen Message

Let us consider a typical message to be transmitted from Philadelphia (call letters NAI) to New York (call letters WHB), on commercial matters, and sent by an opera- tor at Philadelphia who has adopted the letters XM as his personal identification signature — letters or "sign." This might be as follows:

��3, 1917,

��Philadelphia, Pa., Nov Filed 11:03 a. m To James Doherty,

Equitable Building, New York. Express twelve thousand item seven drawing eight two.

Duncan.

As sent out by the Phila- delphia operator, assuming it to be the fifth message sent to New York that day, it would be as given below. Each section is given separately, so that it may be compared with the list of parts just stated:

"Dash-dot-dash-dot-dash

RADIO

Philadelphia

5

X M

14

THIRD

1 103 a m

Dash-dot-dot-dot-dash

James Doherty Equitable Building Newyork

Dash-dot-dot-dot-dash

Express twelve thousand item seven drawing eight-two

Dash-dot-dot-dot-dash

Duncan

Dot-dash-dot-dash-dot

Taking up these lines in sequence, we find first the attention signal and then the prefix. This is followed by the station's name, spelled out, and by the number of the message (namely, 5). Next come the operator's sign and the check, or number of words in the message. It is difficult to see just how the specimen message contains fourteen words until one knows that the

���Radio waves sent in all directions from several sta- tions may overlap and create consider- able "interference"

��check includes the words in the address, text and signature (according to "cable count") and notes that names of cities such as New York and New Orleans and states such as West Virginia are counted as single words in addresses but as two words when they appear in the text. The rest of the message should be perfectly clear without further explanation, though it may be noted that no relays or via's, and no route for addressing appear in such a simple transmission as that assumed for this example.

Sending Messages in Sequence

When the sending sta- tion has several messages to transmit to the same receiver, the operator may follow with the second and third immediately after the first; it is not a good plan to send too many in se- quence without giving the receiving station an oppor- tunity to acknowledge and ask for any corrections or confirma- tions which may be necessary. After sending one or two messages the sending operator should "sign off" with his station call and make the "go ahead" signal "K"), after which the receiv- ing station will call and send "R R R" if he has received everything correctly or "???" to indicate repetitions desired. The method of indicating partial repetitions necessary to fill in doubtful words or phrases was indicated in the September arti- cle, and need not be given again here. When all messages in both directions have been transmitted and satisfactorily received, the Dot-dot-dot-dash-dot-dash, which 'finished," is sent out by both

��signal means ' stations.

Complicated as all this may seem to the beginner, it is a system of communication which is quickly learned and which contains little or nothing that is not essential when many different stations are involved in the traffic system. Naturally enough, when two plants (such as Sayville and Nauen) communicate with each other exclusively it is possible to eliminate a large part of the preamble. Messages may be sent without confusion by giving nothing but the num-

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