Bell Telephone Laboratories - Type-O Carrier System
October 1952 Radio-Electronics

October 1952 Radio-Electronics [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

Always creating and pushing the leading edge of communications technology, Bell Telephone Systems and their research group, Bell Telephone Laboratories, frequently ran full-page promotions in many types of magazines, from electronics industry publications like the 1952 issue of Radio-Electronics, to domestic rags like Woman's Day and Better Homes and Gardens. In this instance, Bell Labs was justifying its continued use of the original open-wire telephone line distribution systems using poles with individual pairs rather than the newer multi-pair cables that carried sometimes hundreds of circuits in the space of a few square inches of cross-section, and in a protective sheath that guarded against signal interference and weather degradation. An entire volume of the Bell System Technical Journal (BSTJ) was published on the Type−O (open wire) Carrier System in the same year this ad appeared. It basically came down to economics based on the fact that so many thousands of miles of the old lines in existence performed adequately well, and new technology allowed two or more circuits to co-exist on the same twisted pair.

Bell Telephone Laboratories: Open-Wire Lines

Same wires - many more voices

Connecting new multi-voice system to open-wire lines, near Albany, Georgia. With new system, 150,000 miles of short open-wire telephone lines can be made to carry up to 16 simultaneous messages economically.

Much of your Long Distance telephone system works through cable but open-wire lines are still the most economical in many places. Thousands of these circuits are so short that little would be saved by using elaborate carrier telephone systems which are better suited for long-haul routes. But a new carrier system ... the Type O designed especially for short hauls ... is changing the picture. It is economical on lines as short as 15 miles. With Type O thousands of lines will carry as many as 16 conversations apiece.

Type O is a happy combination of many elements, some new, some used in new ways. As a result, terminal equipment takes up one-eighth as much space as before. Little service work is required on location; entire apparatus units can be removed and replaced as easily as vacuum tubes.

Moreover, the new carrier system saves copper by multiplying the usefulness of existing lines. For telephone users it means more service ... while the cost stays low.

Repeater equipment is mounted at base of pole in cabinet at right, in easy-to-service position. Left-hand cabinet houses emergency power supply. System employs twin-channel technique. transmitting two channels on a single carrier by using upper and lower sidebands. A single oscillator serves two channels.

Bell Telephone Laboratories

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Posted September 1, 2022