An Experimental Multichannel Pulse Code Modulation System of Toll Quality + Electron Beam Deflection Tube For Pulse Code Modulation

L. A. Meacham and E, R. W. Sears
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See this blog post for context. Pulse Code Modulation offers attractive possibilities for multiplex telephony via such media as the microwave radio relay. The various problems involved in its use have been explored in terms of a 96-channel system designed to meet the transmission requirements commonly imposed upon commercial toll circuits. Twenty-four of the 96 channels have been fully equipped in an experimental model of the system. Coding and decoding devices are described, along with other circuit details. The coder is based upon a new electron beam tube, and is characterized by speed and simplicity as well as accuracy of coding. These qualities are matched in the decoder, which employs pulse excitation of a simple reactive network.


There are other coding schemes possible without "A/D converters". One is called "delta modulation", and was used to encode audio. Delta modulator works as follows: there is an integrator (can be RC circuit), a comparator, and a D-flipflop. The flipflop is clocked at ~100KHz. Flipflop output is fed to the integrator (as +/- voltage). Comparator compares instantaneous voltage of audio to the integrator voltage, and is sent to the "D" input of the flipflop. circuit constantly "chases" audio voltage with the integrator. The output is the 100KHz binary stream. Decoding requires simply another integrator of RC circuit. Circuit was used (in conjunction with psudo-noise generator) to prevent eavesdropping on transmitted audio.
4 weeks ago
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