A. Pulse Modulation Studies

The present study of the interference problem in certain types of pulse modulation was first outlined in the Progress Report of October 15, 1947. Some of the basic phenomena resulting from interference between two pulsed carriers were discussed and illustrated in the last progress report. The work has continued, with emphasis on experimental analyses of common and adjacent channel interference; although this has been done by means of a pulse-duration modulation system, many of the results are applicable also to pulse-position modulation or more generally to any type of pulse modulation which involves only time modulation of the pulse edges. Theoretical considerations have accompanied much of the experimental work. The following items have been covered: (1) A mathematical derivation has been made of the time shift suffered by a desired-signal pulse edge as a result of interference. This has been expressed as a function of the phase difference between carriers and of the ratio of their amplitudes. Linearly rising and falling pulse edges were assumed. From this, the average effective noise time shift has been evaluated, based on the random nature of the phase difference between carriers. The results have been modified to apply to the exponentially shaped pulse edges and take into account the slicing level used in detecting the time position of the pulse edges. (2) A qualitative theoretical analysis has been carried out with the object of predicting the types of disturbances resulting from interference under various conditions. Common and adjacent channel as well as two-path inter-