. BSTJ 1: 2. November 1922: Application to Radio of Wire Transmission Engineering. (Espenschied, Lloyd) . of the voice circuitwhich tends to prevent this sing-around action. Actually, there is alimitation in the degree of balance which can be realized between the APPLICATION 0I: WIRE TRANSMISSION TO RADIO 131 telephone line and the balancing network, especially if the telephoneline is to be switched at a nearby central office, and this factor, to-gether with the margin of safety which is required between the oper-ating condition and the singing condition, prevents the radio channelsfrom being
. BSTJ 1: 2. November 1922: Application to Radio of Wire Transmission Engineering. (Espenschied, Lloyd) . of the voice circuitwhich tends to prevent this sing-around action. Actually, there is alimitation in the degree of balance which can be realized between the APPLICATION 0I: WIRE TRANSMISSION TO RADIO 131 telephone line and the balancing network, especially if the telephoneline is to be switched at a nearby central office, and this factor, to-gether with the margin of safety which is required between the oper-ating condition and the singing condition, prevents the radio channelsfrom being operated much better than the zero equivalent. Thiswhole matter of realizing in practice an adequate transmission equiva-lent, will be appreciated to be an especially difficult problem in thecase of marine radio telephony, where the connection is switchedfrom one vessel to another at varying distances. It should be noted further, with reference to two-way operation,that the difficulty of effecting simultaneous sending and receivingat a station arises primarily from the large attenuation which must be. TWO WAV RADIO CIRCUS Fig. 5 overcome and the resulting large ratio between the energies trans-mitted into and received from the ether. The receiver must be pre-vented from being overloaded by the home transmitter and this,in general, requires that there be provided between the high frequencyside of the transmitter and that of the receiver, a transmission losscomparable in size to that obtaining over the radio circuit itself. Thisseparating transmission loss is ordinarily provided (a) by fre-quency-selecting circuits (tuned circuits and filters), the sending andreceiving transmissions being placed on different frequencies; (b) bybalance, as when using the blind spot of a loop-antenna receiver,and (c) by spatial separation between sending and receiving points,where the large step-off loss is used to advantage. 132 BELL SYSTEM TECHNICAL JOURNAL
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