He created the first cathode-ray tube oscilloscope and detailed a fundamental source of random interference with information traveling on wires, now called Johnson–Nyquist noise.

[3] Johnson received a PhD in Physics at Yale University in 1917, after which he went to work for Western Electric in their engineering department, primarily studying ionized gases.

[5] Jonathan Zenneck had proved the possibility of creating visible waveforms electronically using a Braun tube, but it was not reliable due to power and noise interference.

This was commercialized by Western Electric in 1924 as the Cathode-Ray Oscillograph[7] and attracted a wide array of interest from the mainstream press when it was used to show the waveforms of recorded voice.

In sworn testimony to the U.S. patent office in 1949, Johnson reported "...although the modulation index of 11 per cent is not great,...the useful output power is substantial...it is in principle operative as an amplifier".