. The Bell System technical journal . -quencies than at the high frequencies, in approximately the samedegree as the line had less attenuation. To make up for certaincumulative irregularities an equalizer was built and added to theoverall circuit. The net result was a transmission path which hadapproximately zero loss over the whole band which it was desired touse from 60 kc. to 1000 kc. as shown in Fig. 3. 440 BELL SYSTEM TECHNICAL JOURNAL Another complicating factor is, however, involved, as is the casewith all long wire circuits, namely, the variation encountered withchanges in temperature.
. The Bell System technical journal . -quencies than at the high frequencies, in approximately the samedegree as the line had less attenuation. To make up for certaincumulative irregularities an equalizer was built and added to theoverall circuit. The net result was a transmission path which hadapproximately zero loss over the whole band which it was desired touse from 60 kc. to 1000 kc. as shown in Fig. 3. 440 BELL SYSTEM TECHNICAL JOURNAL Another complicating factor is, however, involved, as is the casewith all long wire circuits, namely, the variation encountered withchanges in temperature. The loss in a 10-mile repeater section variesmaterially from summer to winter. If the cable is hung overhead,this variation is about as shown in Fig. 4 and amounts to a change ofabout ± 7 per cent in the attenuation. If the line is buried under-ground at the normal depth used for telephone cables, the actualvariation is about one-third as much. Automatic transmission regu-lators were developed to compensate for these changes. These. 200 400 600 800 1000 1200 1400 FREQUENCY IN KILOCYCLES PER SECOND 1800 2000 Fig. 2- -Attenuation per mile of the New York-Philadelphia coaxial cable,proportion of that attenuation due to conductance losses. Also the regulators depend, for their operation, on the transmission of a pilotchannel. At each point where it is desired to regulate the transmission,the pilot channel is selected by a very narrow band filter and itsamplitude used to control an automatic device which changes the gainof the repeater until the amplitude of the pilot at the output of therepeater reaches a certain predetermined value. The regulators onthe New York-Philadelphia circuit have operated with such accuracythat it has been unnecessary to make manual adjustments to takecare of temperature changes. COAXIAL CABLE SYSTEAI FOR TELEVISION TRANSMISSION 441 The repeaters used along this route were novel in that most of themwere placed in small iron boxes located at convenient po
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