Live Oscilloscope Frequency Converter

Heinrich Hertz did not set out to name a unit. In 1887 and 1888, working at the Technical University of Karlsruhe, he built a primitive spark-gap transmitter and a wire-loop receiver and confirmed experimentally what James Clerk Maxwell had proposed mathematically in 1864: electromagnetic waves propagate through space at the speed of light. He measured wavelength by moving the receiver until standing waves formed. He died in 1894 at 36, having no idea his name would soon be on every radio, every clock, every CPU.

Nikola Tesla had already moved electromagnetism out of the lab. His 1888 polyphase AC patents licensed to George Westinghouse made the "War of Currents" possible against Edison's DC. Westinghouse's engineers settled on 60 Hz to minimize flicker in carbon arc lamps and to match available gear ratios. AEG in Germany independently chose 50 Hz a few years later. Both choices froze permanently the moment millions of synchronous motors, transformers, and clocks were calibrated to them.

The unit "hertz" was formally adopted by the International Electrotechnical Commission in 1930, replacing "cycles per second" (cps). The change rolled out slowly. American radios still printed "mc" (megacycles) into the 1960s. The CGPM ratified Hz as an SI derived unit in 1960. The redefinition of the second in 1967 - in terms of 9,192,631,770 periods of cesium-133 radiation - made every other frequency calibration ultimately traceable to a single atomic standard.

The FCC was created in 1934 to allocate frequencies. Before that, US broadcasters squatted on whatever they could detect; collisions were constant. The International Telecommunication Union (ITU) coordinates globally - which is why an 88-108 MHz radio sold in any country can receive any FM station in any other country. The bands ELF through EHF in our classifier banner are ITU-defined.

WiFi was unlocked by the FCC's 1985 decision to permit unlicensed spread-spectrum use of the 902-928 MHz, 2.4 GHz, and 5.8 GHz ISM bands. The 2.4 GHz band was previously allocated to microwave ovens; the same frequency that heats water just happens to be absorbed by it, which is why your microwave is a Faraday cage. WiFi 6E in 2020 opened up 6 GHz; WiFi 7 in 2024 extended to multi-link operation.

The Web Audio API arrived in browsers in 2014, finally letting JavaScript synthesize sound directly without plugins. The OscillatorNode you trigger when you click "Play" on this page is a real-time DSP graph node running in the audio thread, gapless and sample-accurate. Combined with WebGL and SVG, it means the browser can now demonstrate an oscilloscope and a tone generator with no install, no plugin, and no driver.

That is what this tool celebrates - not a dropdown form, but a phosphor-green CRT sweeping a sine wave whose color, audibility, and ITU band update as you drag. Hertz never saw this. He would have loved it.