Multiplex Employing Pulse-Time and Pulsed-Frequency Modulation

A microwave communication system giving two-channel voice transmission over a single carrier is described. Diplexing is accomplished by the use of two types of modulation, rather than by time or frequency division. One channel is transmitted by a form of pulse-time modulation using 1-microsecond pulses at a mean repetition rate of 10 kc, and the other channel by frequency modulation of the pulsed microwave carrier (FM burst). The addition of the pulsed-FM channel requires no additional carrier power or change of duty cycle. Cross talk is negligible. The double system is applicable to most of the common forms of pulse-time modulation. Time-division techniques are as applicable as in systems employing pulse-time modulation alone. If a time-division index of n is employed, i.e., that necessary to give n channels in a straight pulse-time time-division multiplex system, the employment of the diplex system described gives 2n channels. Compared to a straight pulse-time time-division system giving 2n channels, the double-modulation system results in economies in synchronizing equipment, and provides a better signal-to-noise ratio on the pulse-time portion of the system, but requires some additional bandwidth.