Science: P.T.M.

A new system of radio transmission, called Pulse Time Modulation, has been announced by International Telephone and Telegraph Corp. Outstanding advantage of P.T.M.: its ability to send a number of voices—or musical programs, for that matter—over a radio channel which heretofore could handle only one.

In the diagram above, P.T.M. is sending 24 telephone conversations. The trick is done by allowing each conversation only part-time on the air. A cathode-ray tube acts as a multiple switch. Inside it, a scanning ray revolves like a clock hand, 8,000 times per second. Arranged like the numbers of the clock are 24 contacts, each connected...

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