The struggle for the range of telephone communication before the invention of the audion Lee de Forest

Abstract

The increase in the range of laying telephone lines at the beginning of the 20th century raised the issue of high-quality telephone signal transmission for scientists and engineers. The innovative technology for solving the problem was based on the “Heaviside condition”. AT&T engineer George Campbell, who received a patent for the design of load coils, was engaged in this task. He demonstrated that a telephone line loaded with coils can transmit clear voice signals twice as far as unloaded telephone lines. At about the same time, Columbia University professor Michael Pupin dealt with this problem, who also received a patent for a similar concept in priority over Campbell's application. As a result, load coils became known as “Pupin coils”. Ironically, Campbell lost the patent priority battle. The proposed innovation eliminated time delays and distortions in the signal, thereby significantly increasing the transmission speed.