DIRECTIVITY STEERING FOR FADING REDUCTION 



201 



Fig. 5 — -Mechanical layout of the steerable horizontal rhombic antenna. 



quency wobbled carrier from the transmitting station. By beating 

 this frequency-wobbled carrier with a local fixed frequency, a wobbled 

 audio note was obtained after detection. This audio output was im- 

 pressed on the horizontal plates of a cathode ray tube, after being 

 amplified by an audio amplifier. This produced a horizontal spot de- 

 flection on the tube screen which was directly proportional to the 

 field strength of the signal. The vertical plates had a locally adjusted 

 sweep circuit voltage impressed on them to produce vertical spot de- 

 flections. The sweep frequency was synchronized with the wobble 

 rate so that the extreme upper and lower deflections occurred at the 

 same instant as the respective upper and lower frequencies of the 

 wobble. Figure 6 indicates the cathode ray picture of a signal with- 

 out selective fading while that of Fig. 7 shows a severe case of selective 

 fading. It is apparent that general fading was revealed by the hori- 

 zontal collapse of the rectangle of Fig. 6. 



It is an interesting fact that upon the first appearance of the cathode 

 ray figure, with the wobble rates employed, it is a horizontal line mov- 

 ing up and down, but after a few seconds, the traced solid figure stands 

 out clearly, due to the persistence of vision. 



One of the surprising results of experience with this system was 

 that, at times of severe fading, eight or ten depressions were occasion- 

 ally seen within a sweep of a few hundred cycles. 



For comparison purposes, there were two complete outfits, as de- 

 scribed, with their cathode ray tubes mounted side by side. One outfit 



