202 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



frequencies of 525 to 150,000 cycles, all originating from eight basic 

 channel frequencies. 



The potential capacity of this system is enormous. If nine wide- 

 band, high-speed carrier channel terminals were assigned to each of 

 the 32 voice channels, we would have 288 channels over which we 

 could operate the 4-channel Multiplex. This would give us 1,152 

 Multiplex channels, each operating at 66 words per minute, a total 

 of 76,032 words per minute in each direction over the entire carrier 

 system. 



In case we should get both feet clear off the ground and assign 

 a 36-channel Varioplex system to each of the 288 high-speed carrier 

 telegraph channels, we could get 10,368 sending and receiving Tele- 

 printer circuits for subscriber service. 



If the narrow-band telegraph channel terminals were used on the 

 32-voice channel carrier system, we would have 512 sending and receiv- 

 ing positions at each terminal. 



During the first stage of the modernization program, a number of 

 2-channel Multiplex circuits will be established between the larger 

 offices. These will operate at 66 words per minute, or a line frequency 

 of 33 cycles per second. In the ultimate, plans are to discontinue the 

 use of the Multiplex with its complicated equipment and use nothing 

 but Teleprinter circuits, as the simplicity and flexibility of this type 

 of equipment will more than offset the high load capacity of the 

 Multiplex. 



Radio relay stations will be spaced from 20 to 50 miles apart, de- 

 pending upon the topography of the land. The location will also 

 depend upon the availability of satisfactory commercial power and 

 will be near good roads. The height of the open steel towers will 

 range from 60 to 120 feet, as it seems advisable that the transmitted 

 beam clear any obstacle by 30 to 50 feet. 



A small cabin 12 feet square and 9 feet high will be mounted at the 

 top of the tower. Windows which will be transparent to the micro- 

 waves will be provided. Several materials are available for this use, 

 such as plexiglass, laminated bakelite, but tests indicate that impreg- 

 nated fiberglass cloth has the lowest loss for the high-frequency waves. 

 Ice on an open reflector apparently does little harm, while wet snow 

 will cause a large drop in signal strength. Provisions will be made to 

 house a total of four reflectors with their accompanying high-fre- 

 quency oscillator circuit cabinets in each tower. 



A sturdily constructed concrete building about 16 by 30 feet will 

 be located at the base of the tower. It will be heated in the winter and 

 ventilated in the summer in order to keep the humidity as low as 

 possible. 



The balance of the radio equipment and a reserve power plant will 



