Bell Telephone Laboratories - Traveling Wave Tube
November 1957 Radio-Electronics

November 1957 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.

Contrary to the claim in this Bell Telephone Laboratories promotional piece from a 1957 issue of Radio-Electronics magazine, according to the Wikipedia entry for the traveling wave tube (TWT) was invented in 1931 by Andrei "Andy" Haeff while he was working as a doctoral student at the Kellogg Radiation Laboratory at Caltech. His original patent, "Device for and Method of Controlling High Frequency Currents," was granted in 1936 (US2064469A). Bell gives credit to Dr. Rudolf Kompfner. The TWT's wide bandwidth, 500 MHz in this case - was heralded as a major breakthrough for supporting the rapidly growing microwave relay network spanning the country, vastly increasing the number of concurrent telephone connections. By that time (1957) transcontinental video broadcasts were also being made thanks to the system. It would still be half a decade before satellites (e.g., Telstar) would be available for long distance communications.

A Great Amplifier Tube is Perfected for Telephony

A new transcontinental microwave system capable of carrying four times as much information as any previous microwave system is under development at Bell Laboratories. A master key to this development is a new traveling-wave tube of large frequency bandwidth.

The traveling-wave amplifying principle was discovered in England by Dr. Rudolf Kompfner, who is now at Bell Laboratories; the fundamental theory was largely developed by Labs scientist Dr. John Pierce. Subsequently the tube has been utilized in various ways both here and abroad. At the Laboratories it has been perfected to meet the exacting performance standards of long distance telephony. And now for the first time a traveling-wave tube will go into large-scale production for use in our nation's telephone systems.

The new amplifier's tremendous bandwidth greatly simplifies the practical problem of operating and maintaining microwave communications. For example, in the proposed transcontinental system, as many as 16 different one-way radio channels will be used to transmit a capacity load of more than 11,000 conversations or 12 television programs and 2500 conversations. Formerly it would have been necessary to tune several amplifier tubes to match each channel. In contrast, a single traveling-wave tube can supply all the amplification needed for a channel. Tubes can be interchanged with only very minor adjustments.

The new amplifier is another example of how Bell Laboratories research creates new devices and new systems for telephony.

Left: A traveling-wave tube. Right: Tube being placed in position between the permanent magnets which focus the electron beam. The tube supplies uniform and distortionless amplification of FM signals over a 500 Mc band. It will be used to deliver an output of five watts.

Bell Telephone Laboratories

World Center of Communications Research and Development

Posted May 3, 2022