252 BELL SYSTEM TECHNICAL JOURNAL 



small currents in the grounding wires at the terminals. Waves 

 which approach longitudinally build up currents in the line wire 

 as they proceed along it and cause relatively large currents in the 

 grounding wire at the distant end. By building such a line so that 

 it points towards the transmitting station and attaching the receiving 

 set at the end most distant from the transmitter it is possible to 

 obtain a considerable degree of directivity. Further development of 

 this simple basic antenna system is obtained by attaching to it various 

 balancing arrangements. Or by combining several antennas together, 

 it is possible still further to improve the directional characteristics. 



In order to determine how much advantage could be obtained by 

 the use of wave antenna systems, the British Post Office constructed 

 one at their receiving station in England and the use of one at River- 

 head, L. I. was borrowed by the telephone company from the Radio 

 Corporation of America. Measurements taken over a considerable 

 period of time showed that the signal-to-noise ratio on a good system 

 of combined wave antennas was about ten times as great as that on a 

 simple loop antenna. This was very gratifying since it meant that by 

 the use of wave antennas the transmission would be improved just as 

 much as if the transmitting station power had been multiplied 100 

 times. 



At the receiving end quite aside from the special nature of the 

 directive antenna systems, the amplifying and detecting apparatus 

 must be of a character suited to the amplification and detection of 

 single sideband-carrier eliminated signals. In order to detect signals 

 of this kind it is necessary that a carrier be resupplied to the signal 

 before detection. This is done by means of a local oscillator. Thus 

 the signal actually supplied to the detector dififers from the ordinary 

 signals such, for instance, as are used in broadcasting, only by the 

 fact that one of the sidebands is missing. This is of no importance 

 since the complete signal may be detected from the carrier and one 

 of the sidebands. The actual apparatus being used at the American 

 receiving station is similar to the modulating apparatus employed at 

 the transmitting end for producing a single sideband in that the 

 process at the receiving end is substantially reversed. By means of a 

 double detection type receiving set having a beating oscillator fre- 

 quency of about 90 kc, the 60 kc. incoming sideband is reduced to 

 approximately 30 kc. in the first detection. It is then passed through 

 filters, amplified and has added to it the carrier frequency. The 

 second detection brings it back to voice frequency and after further 

 amplification it is ready to go on to the wire line to the terminal. 



A third way in which it is possible to avoid the effects of static is 



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