Page:Popular Science Monthly Volume 88.djvu/326

 Recent Radio Inventions

New Patents on Wireless Instruments By A. F. Jackson

��AMONG the most interesting pat- ents of 1915 is No. 1139226, is- sued to E. Raymond-Barker, for a system of radio-telegraphy using two wave-lengths for transmission of a sin- gle message. Instead of sending Morse signals in which the dots and dashes are distinguished by the diflference in dura- tion of impulses, this method uses sig- nals all of the same impulse length but distinguishes between dots and .dashes by sending each at a different wave frequency. That is to say, only short signals which cor- respond in length to ordinary Morse dots are sent, but these are emitted at two different wave lengths, one of which is for dots and one for dashes.

Figure 1 shows the way in which the invention may be applied to a Poulserr transmit- ter. Here the pow- er lines G supply energy to two oscillat- ing arcs, F F, through suitable imped- ances. The central contacts or levers of two telegraph keys A and Ai are con- nected in the shunt oscillating circuits of the two arcs, and serve to con- nect the arcs either to radiating reso- nant circuits C D or to non-radiating resonant circuits Ci Di. Consider- ing the operation :

���Fig. 1. Raymond-Barker double- wave transmitter

���Fig. 2. Telephonic Receiver for double- wave system

��\\'hen neither key is depressed both arcs are connected to their non-radiating cir- cuits through contacts H H, and gener-

��ate in these circuits oscillations of dif- ferent wave lengths. If it is desired to send a dot the left-hand key is depress- ed ; this connects the left-hand arc to the antenna, and waves of a certain length (say 3,000 meters) are radiated. If a dash is to be sent, the right-hand key is pressed for an instant, and for that time the right-hand arc is connected to the antenna and allowed to radiate waves of its different wave length (say 4,000 me- ters. Thus combi- nations of dots and dashes correspond- ing to the letters of the Morse code are transmitted.

At the receiving station it is 'neces- sary to pick up signals on either wave length and to indicate that one represents dots and the other dashes. Fig. 2 shows one way in which this may be done : The receiving antenna Bi is connected to two parallel tuned primary circuits, C^ D^, one of which is tuned to the "dot wave" and the other to the "dash wave." Each primary has coupled to it a tuned secondary C6 which acts upon a tikker detector Pi with telephone P and stopping condenser D6. One telephone is held to each ear of the operator and the dots dis- tinguished from the dashes by not- ing which 'phone A simpler way of

��gives the response

distinguishing the dots and dashes is by

adjusting the tikker-interrupter speeds

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