. Bell telephone magazine . ductor crystals. This concerted ef-fort produced, in a relatively shorttime, a device that for nearly a quar-ter of a century has been a house-hold word: the transistor. The di-minutive successor to the vacuumtube has in turn spawned a vastfamily of solid state devices, amongthem diodes developed at Bell Lab-oratories which can generate radiowaves at extremely high frequen-cies—the millimeter waves neededfor a waveguide. Indeed, the systemas it now comes out of the labora-tory is based almost entirely on solidstate devices and technology. Waveguide utilizes PCM This
. Bell telephone magazine . ductor crystals. This concerted ef-fort produced, in a relatively shorttime, a device that for nearly a quar-ter of a century has been a house-hold word: the transistor. The di-minutive successor to the vacuumtube has in turn spawned a vastfamily of solid state devices, amongthem diodes developed at Bell Lab-oratories which can generate radiowaves at extremely high frequen-cies—the millimeter waves neededfor a waveguide. Indeed, the systemas it now comes out of the labora-tory is based almost entirely on solidstate devices and technology. Waveguide utilizes PCM This technology includes thetransmission technique known aspulse code modulation with regen-erative repeaters. PCM was chosenfor use with the waveguide for threeprincipal reasons: it is a ruggedmodulation technique, relativelyunaffected by undesired modes insystems like waveguide; it is wellsuited to intermixing voice, compu-ter data, Picturephone or televisionsignals; and it can be designed toprovide great accuracy in the ov
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