TELEGRAPHY — HILLIS 201 



at both reflectors. The resultant signal variation is well within the 

 limits of the FM receiver and excellent results have been obtained. 



The present explanation is that during periods of perfect calni 

 there is a stratification of either temperature or humidity or both 

 which will refract the transmitting signal causing a multipath re- 

 ception at the receiving parabola. 



Studies indicate that the initial installation cost and annual ex- 

 pense of operation of a microwave relay system will be less than that 

 of a land line, especially if the capacity of the microwave system is 

 fully utilized. Very little time will be required for installation of the 

 towers and they can be moved without too much trouble. Relocat- 

 ing any stretch of land line is a long-drawn-out operation, with 

 numerous interruptions to service. 



These and many other advantages led the Western Union to ini- 

 tiate a comprehensive experimental program for the use of micro- 

 waves for commercial telegraphy. A patent license agreement was 

 entered into with the Radio Corp. of America in July 1944 for use of 

 the necessary radio circuit patents. Similar arrangements have also 

 been made to use the Armstrong method of frequency modulation. 



The design of the radio equipment has been rapidly developed from 

 what were essentially radar techniques to those that will meet the 

 requirements of telegraphy by the Victor Division of the Radio Corp. 

 of America at Camden, N. J. The telegi-aph company's engineei-s 

 have developed the high-capacity WN-2 carrier system which will be 

 used in conjunction with the microwave beam system. 



The Western Union carrier which feeds into the radio transmitter 

 will consist of 32 voice channels, each of which may carry either 

 16 narrow-band telegraph channels, a telephone, or a facsimile cir- 

 cuit. The 16 narrow-band telegraph channels are in two groups of 8, 

 each of which has a frequency spread of 525 cycles for channel 1 to 

 1,575 cycles for channel 8. By means of a frequency translator, iden- 

 tical terminal equipment is used for the second group, which, after 

 translation in frequency, appears as a band from 2,025 cycles to 3,075 

 cycles. Thus the two groups fill a voice channel that has a band width 

 of approximately 300 to 3,300 cycles. This means that only eight basic 

 telegraph channels are required. Sixty-four duplications of each of 

 the eight channels will be used for the entire carrier system instead of a 

 total of 512 channel terminals, each having a different frequency. 

 This is made possible by the frequency translator or varistor, a simple 

 copper oxide or crystal rectifier. 



The output of each of the 32 voice bands will be identical but, again 

 by using the frequency translator, each voice band has its output 

 translated so that they may be "stacked" one above the other in the 

 frequency spectrum, and at the carrier system output there will be 



