. The Bell System technical journal . transmitting directional filter while the upper sideband is sup-pressed. It is apparent from Fig. 16 that the received sideband coming in onthe line from the distant repeater or terminal is operated upon by thefilters in a reverse manner from that described above for the trans-mitted sideband. The incoming frequencies are directed through thereceiving directional filter to the demodulator, where modulation withthe original carrier reproduces the voice frequencies together with 182 BELL SYSTEM TECHNICAL JOURNAL Other modulation products. The desired voice-f
. The Bell System technical journal . transmitting directional filter while the upper sideband is sup-pressed. It is apparent from Fig. 16 that the received sideband coming in onthe line from the distant repeater or terminal is operated upon by thefilters in a reverse manner from that described above for the trans-mitted sideband. The incoming frequencies are directed through thereceiving directional filter to the demodulator, where modulation withthe original carrier reproduces the voice frequencies together with 182 BELL SYSTEM TECHNICAL JOURNAL Other modulation products. The desired voice-frequency band is thenseparated from these products by the receiving low-pass filter. In addition to performing the function of selecting desired and re-jecting undesired currents, a filter, if operating in parallel with anotheras in the case of the directional filters or the line filters, should offer ahigh impedance to the transmitted currents of the other and thusprevent an excessive drain of these currents. Since these filters are. Fig. 17—Filter (with cover cut away) showing general method of assembly. designed for operation in parallel, either filter operated without theother would have somewhat different electrical characteristics. The economies and reduction in size of these filters as compared tothose of the Type D system are due to several factors. Improvedpaper condensers having the required stability are used. Compared tomica condensers, these condensers are less costly and smaller for agiven capacity. Moreover, at a very slight increase in cost papercondensers are used which will withstand 1000-volt line surges. Mostof the condensers of the Type D system were designed for only 500-voltprotection. New types of coils with molybdenum permalloy cores having thenecessary stability and low hysteresis losses are employed instead of NEW SINGLE CHANNEL CARRIER TELEPHONE SYSTEM 183 the air core solenoidal coils used in the Type D system. Since thesenew coils have less dissi
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