COAXIAL CABLE SYSTEM FOR TELEVISION TRANSMISSION 439 



a lead sheath about J"^" in diameter as indicated in Fig. 1. Two 

 coaxial units were provided because, for long distance telephone 

 operation four-wire operation is preferable, one coaxial being employed 

 for transmission east to west and the other west to east. Each coaxial 

 unit is made up of a 13-gauge inner conductor on which hard rubber 

 disks have been placed at intervals of ^ of an inch. The outer 

 metallic tube is made up of 9 overlapping copper tapes so designed 

 that they form essentially a solid copper tube about 20 mils in thickness 

 and .267" in inside diameter. 



The transmission loss of this circuit as a function of frequency is 

 shown on Fig. 2 together with the portion of the attenuation that is 

 contributed by conductance losses. Inasmuch as the intention is to 

 use these conductors at very high frequencies, a high grade insulating 

 material was used with the result that the conductance losses are small. 



Fig. 1 — Section of the New York-Philadelphia coaxial cable. 



It should be noted that the attenuation increases very nearly as the 

 square root of the frequency. 



In order to transmit high frequencies over long distances, a great 

 deal of amplification is obviously required. The New York-Phila- 

 delphia cable was initially equipped to handle a band of one million 

 cycles. Its overall attenuation at a million cycles is approximately 

 600 decibels. In order to reduce this to a usable amount 10 repeater 

 points were provided at intervals of about 10 miles each having an 

 amplification at the top frequency of about 60 decibels. These 

 repeaters were so designed that they provided less gain at low fre- 

 quencies than at the high frequencies, in approximately the same 

 degree as the line had less attenuation. To make up for certain 

 cumulative irregularities an equalizer was built and added to the 

 overall circuit. The net result was a transmission path which had 

 approximately zero loss over the whole band which it was desired to 

 use from 60 kc. to 1000 kc. as shown in Fig. 3. 



