01What's that signal?
The short version: Search everything in this guide by what you noticed - "plane on a flight tracker", "phone says SOS only", "scanner went silent", "antenna on a light pole", "clock set itself" - and jump to the explanation. Below it, the spectrum chart lays every band in this guide on one ruler, from the time signal that sets radio-controlled clocks to the 5G millimeter waves.
Signal lookup
140 things you might notice
The spectrum on one ruler
Each bar is a band covered in this guide, placed on a logarithmic scale so that kilohertz and gigahertz fit on the same line. Tap a bar for what lives there, where the rule applies and the source.
Spectrum ruler
68 bands on one line
Tap or focus a band to see what uses it.