318 BELL SYSTEM TECHNICAL JOURNAL 



connections to New York and a suitable terrain for antenna construc- 

 tion. The first of these factors required a location along one of the 

 main telephone trunk routes in Maine and the second, since we had 

 decided upon the use of a wave-antenna ^^ for reasons which will be 

 given in the following section, demanded a rather large and reasonably 

 fiat land area available for pole-line construction. A location, al- 

 though not altogether ideal, was decided upon near Houlton, Maine, 

 about six miles from the Canadian border. 



Choice of Receiving Antenna Systems 



The number of fundamental types of receiving antennas that may 

 be employed for long-wave reception is quite definitely limited. In 

 fact all of the known practical receiving antennas may be considered 

 as falling into one of three principal classes of structure; i.e., the 

 vertical antenna, the loop or coil antenna, and the wave-antenna. 

 The selection of the proper receiving antenna system quite evidently 

 becomes a problem — first, of choosing the best type of antenna from 

 one of these three classes and, second, of choosing a particular antenna 

 structure in the class which is found to be best. 



The factors governing the choice of a receiving antenna are as 

 follows: 



1. Directional Discrimination Against Static. Inasmuch as the 

 signal to be received has a definite average value, the receiving system 

 can only better the circuit in the amount that it improves the signal- 

 to-noise ratio. A directional antenna system afi^ords a means of 

 reducing the received noise in relation to the desired signal.^- ^* The 

 directional characteristics of the principal antenna types are shown 

 in Fig. 5. 



A measure of the directional discrimination of the various antenna 

 types is the Noise Reception Factor (abbreviated NRF) which is 

 defined as the ratio of the total noise current received from the antenna 

 in question to that received from a vertical antenna under the condi- 

 tions of continuous, constant distribution of noise sources about the 

 antenna and of equal output currents for signals from the direction 

 of maximum receptivity. The back end NRF is the noise reception 

 factor for the arc between 90 degrees and 270 degrees from the direc- 

 tion of maximum receptivity. 



On this basis, the choice rests quite unmistakably with the wave- 

 antenna. 



2. Transmission- Frequency Characteristic. Since the receiving an- 

 tenna is to be used on a system for communication by speech, necessi- 



^* H. H. Beverage, C. W. Rice and E, W. Kellog, "The Wave Antenna," Trans. 

 A. I. E. E., 42, 215; 1923. 



