338 BELL SYSTEM TECHNICAL JOURNAL 



referred to one rhombic antenna. With the object of predicting 

 the performance of larger systems, the performance of the experi- 

 mental system is examined in great detail and compared with 

 theory. 



I. Introduction 



T?OR more than a decade, point-to-point short-wave radio services 

 -^ have employed directional antennas both in transmitting and 

 receiving. Transmitting antenna directivity results in increased field 

 intensity at the receiving location and receiving antenna directivity 

 discriminates against noise. Both directivities improve the signal-to- 

 noise ratio of a given circuit and permit operation under more adverse 

 transmission conditions. Arrays of simple antennas as well as ex- 

 tensive configurations of long wires have been used to produce these 

 directivities in both the vertical and the horizontal planes. 



Antennas in present use on the longer circuits, such as the New 

 York-London telephone facilities, represent about the limit of fixed 

 directivity. Further increase or ' ' sharpening ' ' of the directivity would 

 seriously encroach upon the angular range of directions which are 

 effective in the propagation of waves from transmitter to receiver. 

 The vertical angle range useful in transmitting and receiving short 

 waves is considerable. The horizontal range is appreciable although 

 considerably less than the vertical range. To confine the principal 

 antenna response to only a portion of these ranges penalizes the circuit 

 when that portion is inelTective. 



Much experience and considerable statistical data have been ob- 

 tained which determine this useful range of directions for the New 

 York-London circuits, and antennas have been designed in conformity 

 with these results. However, too much weight must not be given to 

 statistical results which indicate, for instance, that ninety per cent of 

 the time the effective angles are, say, in the range from ten to twenty 

 degrees. For, if the remaining ten per cent includes much of the time 

 that has been lost with existing facilities, an antenna designed for a 

 ten- to twenty-degree response may really be of no value, or even 

 detrimental as a means of extending the usefulness of the circuit. 

 Owing to the great variability in conditions on the north Atlantic 

 path and to the relatively small amount of significant data which has 

 been accumulated during times when gain is most needed it might be 

 detrimental to carry fixed directivity further than present practice 

 has adopted.^ 



^ One way of attacking the problem of obtaining increased antenna gain has 

 been proposed by John Stone Stone in U. S. Patent 1,954,898. This patent relates 

 to fixed antennas but has certain features, such as delay equalization, in common 

 with the system to be described in this paper. 



