A Study of Reception from Synchronized Broadcast Stations

The present paper gives the practical results of an extensive analysis of the detection of two modulated waves of identical carrier frequency. It is shown that the total effects of time delay in the program distribution circuits, differences in circuit elements in the two transmitters, and differences in path lengths of the two signals in traveling from their respective transmitters to the receiving point, may all be expressed in terms of two fundamental angles, γ and β. γ is the phase angle between the two carriers at the receiving point, and β is an angle determining the relation between the side frequencies received from the two stations. At any given point there will be a different value of β for each modulation frequency. Analyses in terms of β and γ yield quantitative descriptions of the distortions present in the rectified wave. From these results it is possible to determine how the distortions vary from point to point in space and upon what significant quantities they are dependent. Experimental work has been carried out in the laboratory which confirms the results of the theoretical analysis and which shows in a striking manner the effects of small time delays on the quality of the received signal. This work agrees with theory in showing that time delays, of the order of 200 microseconds, may be responsible for serious distortion, and that a delay as small as 50 microseconds requires a 2:1 carrier ratio to prevent distortion.