Application of Printing Telegraph to Long- Wave 

 Radio Circuits * 



By AUSTIN BAILEY and T. A. McCANN 



This paper describes certain arrangements which have been used for 

 start-stop printing telegraph operation over a transatlantic long-wave radio 

 channel and also describes results obtained from certain tests of long-wave 

 teletypewriter transmission from Rocky Point, L. I., to Rochester, N. Y. A 

 prediction of year-round results is obtainable by correlation of these test 

 data with year-round noise measurement data taken at Houlton, Maine, in 

 connection with transatlantic telephone service. 



PRINTING telegraph equipment,^ because of its speed, accuracy 

 and convenience in transmitting intelligence, has become recog- 

 nized as a very useful method of telegraphy on wire circuits. It 

 seems important, therefore, to determine something of the possible 

 utility of present types of teletypewriters on radio circuits. 



It is common practice to transmit the signals for operating tele- 

 typewriter equipment over wire circuits in any one of several electrical 

 forms. As in earlier telegraph practice the signals are frequently trans- 

 mitted as d-c impulses. More recently alternating currents of voice- 

 frequency and of higher frequency have been employed.^ In employ- 

 ing radio frequencies for operating teletypewriter equipment where the 

 operating impulses are no longer guided by a wire circuit, new prob- 

 lems and new conditions arise, which are essentially those of radio tele- 

 graph transmission. For this reason, it is desirable to review briefly 

 the conditions under which radio telegraph systems are operated. 



In manual-sending aural-receiving practice for radio telegraphy it 

 has been customary to utilize, at the receiving end, only a marking 

 tone or sound which is received during intervals corresponding to the 

 time that the sending key is depressed. In transmitting signals from 

 an arc transmitter, a signal of a different frequency is sent out during 

 the spacing periods in order to simplify the keying process, but this 

 spacing signal is not utilized at the receiving end. For aural reception 

 the necessary and sufficient requirement is that the marking tone be 

 distinguishable through the noise. Using ear receiving it is possible to 

 distinguish the signal under a wide variation of conditions because of 

 the ability of the ear to accomodate itself to variations in signal level 

 and in signal-to-noise ratio. 



* Presented at Sixth Annual Convention of I. R. E., Chicago, Illinois, June 4-6. 



1931. 



601 



