HORIZONTAL RHOMBIC ANTENNAS 147 



the broadest arrangements under the prescribed conditions. This 

 statement is based on a large number of calculated directive diagrams, 

 for various frequencies, and has been substantiated by operating tests. 

 Also, in certain applications, as with ultra-short waves where the 

 direction of wave propagation is substantially horizontal (A = 0), the 

 derived equations place no restrictions on the antenna size. 



Experimental Checks of Directivity Calculations 



One method employed for experimentally checking the calculations 

 of directivity was by means of a model small enough to permit con- 

 tinuous rotation of the antenna in respect to a fixed wave-direction. 

 A simple transmitter and a double-detection receiving set, which 

 employed a calibrated intermediate frequency attenuator, both 

 operating at about four meters, were utilized for this work. Even at 

 these wave-lengths, the physical dimensions of the antenna were rather 

 large so that it was necessary to build an antenna smaller in wave- 

 length dimensions than is usually recommended for commercial 

 installations. As previously stated, any antenna for regular service 

 would be designed for its own specific conditions, so that this antenna is 

 not to be taken as a recommended design. However, this fact had no 

 bearing on the results of these tests, for there was no intention of using 

 this movable antenna for any purpose other than experimentally 

 checking the directivity equations. 



A photograph of the test installation is shown in Fig. 11. The 

 antenna wires were mounted on a lattice work cross of light weight 

 wood suspended by a system of ropes from two wooden poles. This 

 permitted the hoisting of the entire antenna system to any height up to 

 several wave-lengths, and rotating it to any desired angular position. 

 The antenna is shown in more detail in the photograph of Fig. 12. It 

 was constructed of two space-tapered wires in parallel, spaced in order 

 to lower the antenna impedance to permit the matching of the open- 

 wire transmission line which was attached to one end. Each element 

 was three and a quarter wave-lengths long. The receiving set was 

 placed in a small push-cart at the other end of the transmission line so 

 that the line length did not need to be changed with antenna move- 

 ments. An antenna of this size had a measured gain of fourteen 

 decibels over a half-wave horizontal dipole at the same height. 



The horizontal plane directive pattern was experimentally de- 

 termined by measuring the antenna angle and signal output at each 

 maximum and minimum and at fixed angles on the major lobe, as the 

 antenna was rotated about its vertical axis. The pattern measured 



