Interconnexion of frequency-division and time-division multiplex transmission systems

Multichannel transmission systems are of two general types: frequency-division multiplex (f.d.m.) and time-division multiplex (t.d.m.). In order to interconnect a t.d.m. system with an f.d.m. system, it is not necessary to demodulate each channel to audio frequencies. An amplitudemodulated t.d.m. signal can be converted to f.d.m. by gating it to a bank of band-pass filters, each passing one harmonic of the pulse repetition frequency (p.r.f.). The output of these filters are connected to a common path to provide an f.d.m. signal. An f.d.m. signal can be converted to t.d.m. by separating the channels with band-pass filters and sampling the output of each filter with a pulse occupying a different position in the t.d.m. cycle. The sampled outputs are connected to a common path to provide an amplitude-modulated t.d.m. signal. It is necessary, however, for the carrier frequencies of the f.d.m. system to be harmonics of the p.r.f. of the t.d.m. system. It is shown that resonant-transfer can be used to reduce energy losses in the conversion and so eliminate amplifiers. This has been demonstrated experimentally.