A MULTIPLE UNIT STEERABLE ANTENNA 



377 



critical to one section of the network (67.5 microseconds) and always 

 to two sections. The angles were determined from the calibration 

 curve reproduced in Fig. 28. The phase readings observed on the 

 monitoring oscilloscope were recorded to within ±10 degrees and the 

 earth angles determined by them are liable to be in error by one degree 

 (possibly 1.5 degrees) apart from the ambiguity due to the multiple 

 lobe characteristics of the MUSA. At this wave-length, the major 

 lobe of the unit rhombic antennas is broad, the first null occurring at 

 58 degrees, so that two angles had to be considered possible. 



The multiple hop picture is illustrated in Fig. 29. Here the delay 



40 80 120 160 200 240 280 320 360 



PHASE SHIFTER READING, 02 



Fig. 28 — Calibration curves of the Holmdel MUSA for 49.1 meters, giving the 

 angle of the principal lobe as a function of phase advance 4>i (Fig. 3). Note that 

 the sense of the phase shift depends upon the beating oscillator frequency. The 

 curves are calculated for a velocity ratio v = 1/0.933. 



referred to the ground wave is expressed in terms of earth angles h and 

 «, the number of hops or ionosphere reflections. The height h and 

 angle h are also related through n as shown in Fig. 29. Using the first 

 relation, the curves of Fig. 30 were drawn; using the second relation, 

 points corresponding to various heights were located on the curves. 

 For the Holmdel-Halifax circuit d is 643 miles (1030 kilometers) 

 making ^ = 9° 21'. Corresponding to each measured angle there is a 

 delay (referred arbitrarily to the ground wave which, of course, was 

 not received) and a layer height, for each of the modes or orders. 

 Both angles together yield a delay difference which is to be compared 

 with the measured value. 



