. The Bell System technical journal . w vflOO i-sOCO/—i I TO OTHER CHANNELS TO OTHER CHANNELS TO OTHER CHANNELSTO OTHER CHANNELS. TO OTHER CHANNELS TO OTHER CHANNELS Fig. 1 at the terminals. In the balanced system this separation is accom-plished by means of a three-winding transformer or hybrid coil to-gether with a balancing artificial line such as is used with a voice-frequency repeater. In the grouped system, different carrier fre-quencies are used for transmission in the two directions and theirseparation at the terminals is effected by means of suitable band-pass filters. These two syste
. The Bell System technical journal . w vflOO i-sOCO/—i I TO OTHER CHANNELS TO OTHER CHANNELS TO OTHER CHANNELSTO OTHER CHANNELS. TO OTHER CHANNELS TO OTHER CHANNELS Fig. 1 at the terminals. In the balanced system this separation is accom-plished by means of a three-winding transformer or hybrid coil to-gether with a balancing artificial line such as is used with a voice-frequency repeater. In the grouped system, different carrier fre-quencies are used for transmission in the two directions and theirseparation at the terminals is effected by means of suitable band-pass filters. These two systems are shown diagrammatically inFig. 1. The balanced system has the advantage that for each channel The general principles of carrier-current telephony are described at considerablelength in a paper by Messrs. Colpitis and Blackwell which was published in VolumeXL of the Journal of the Institute. CARRIER-CURRENT COMMUNICATION 639 the same carrier frequency may be used for transmission in both direc-tions so that there may be as many channels as there are separatecarrier frequencies. On the other hand, the wire circuit must
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