Application of Printing Telegraph to Long-Wave Radio Circuits*

Abstract

This paper describes certain arrangements which have been used for start-stop printing teleW"aph 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. P R INT I NG telegraph equipment,' because of its speed, accuracy and convenience in transmitting intelligence, has become recognized 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 teletypewriter equipment over wire circuits in anyone of several electrical forms. As in earlier telegraph practice the signals are frequently transmitted as d-e impulses. More recently alternating currents of voicefrequency and of higher frequency have been employed.! In employing radio frequencies for operating teletypewriter equipment where the operating impulses are no longer guided by a wire circuit, new problems and new conditions arise, which are essentially those of radio telegraph 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.