1220 THE BI:LL system TECHXICAL journal, NOVEMBER 1954 



1 1 



^5 700 



E5 500 



y?: o 



y O 200 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 8 — Base band width per channel versus frequency for a 2" diameter pipe 

 (one-mile waveguide length). 



and optically aligned so as to provide a waveguide straight within about 

 \i," over its entire length. The philosophy behind this installation was 

 the familiar one of providing for experimental purposes, as close to the 

 ideal line as possible so that deviations could be created in a controlled 

 manner. The inside diameter is about 4.73", chosen to obtain the de- 

 sired theoretical loss of about 2 db per mile at 9,000 mc, where measuring 

 equipment was readily available. The difference between the major and 

 minor inside diameters of the pipe was in the range 0.005" to 0.008" at 

 the ends of the sections which averaged 20 ft in length. At the time this 

 work was initiated, in 1946, generators of higher frequencies which would 

 permit the use of smaller waveguides had not yet become available for 

 use in this research. 



Tests were conducted on this line using a technique due to A. C. Beck,^ 

 and involving the layout of equipment shown in Fig. 10. Short bursts of 

 RF energy approximately ^.fo microsecond in duration, were injected 

 into the line at intervals of about three hundred microseconds. Except 

 for two small holes through which to couple to the transmitter and 



