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BELL SYSTEM TECHNICAL JOURNAL 



direction is maintained although, as would be expected, the directivity 

 becomes less sharp as the wave-length is increased in respect to the 

 antenna dimensions. 



note: GROUND CANCELLATION 15 IGNORED 



Fig. 21 — -Plan view directive diagram. 



Due to the variability of the wave directions in the vertical plane, 

 this desirable direction is not well defined. As the wave-length is in- 

 creased, a broadening characteristic counteracts the possibility of losing 

 signal due to the optimum direction of the characteristic moving slightly 

 upward. 



Antenna Coupling Circuit 



A two-wire transmission line has been used as the connecting link 

 between the antenna and the coupling circuits at the receiver. With 

 this arrangement, the circuits must be carefully balanced against ver- 

 tical waves to obtain local noise reduction and to avoid reradiation 

 losses from the transmission line. This is not difficult for a single fre- 

 quency but if the coupling circuits are to maintain this balance for a 

 range of frequencies, very careful designing of the coupling circuits is 

 required. 



The present practice is to place these coupling circuits in an ele- 

 vated position directly at the antenna terminals to reduce the necessity 

 for finical balancing adjustments. These circuits are connected to the 

 receiver through a concentric pipe transmission line with its accom- 

 panying low loss, freedom from "pick-up," and substantial weather- 

 proof construction. Multipeaked coupling circuits have been devised 

 so that no readjustment is required over quite a frequency range. 



Measured Performance 

 From the inception of our short-wave experience, we have been 

 accustomed to compare the performance of antennas with a half-wave 

 vertical antenna. The lower end of this standard of comparison is near 



