Notes on the tools and the data behind them. One topic per concept, enough to use the tool without looking it up somewhere else.

• ADS-B overview (live aircraft tracking)How ADS-B works, what ICAO24 and Mode S mean, squawk codes, and the FAA registry join.
• AIS overview (live ship tracking)Maritime AIS basics, MMSI numbers, Class A vs Class B, and what every field on the live ship panel means.
• DX cluster and spotting networksA global federated telnet network where operators report ("spot") interesting contacts in real time. The grapevine of HF.
• Greyline and the terminatorWhy HF bands open up at sunrise and sunset, and what the grey line on the globe means.
• Harmonics and intermodulationWhat harmonics and IMD products are, how to predict them, and how the FCC regulates spurious emissions.
• HF propagation and solar indicesHow to read SFI, K-index, A-index, MUF and turn them into "which band right now."
• Maidenhead grid squaresThe world location system every ham radio operator uses. 6-character grids pin a QTH to within a few km.
• Maritime frequenciesHF maritime mobile nets, GMDSS distress channels, US VHF marine channels, and where to pull weather underway.
• Radio modes & what they look likeA field guide to the ham + commercial modulation modes you see on K3DPT, with a small spectrum sketch for each so you know what to look for on a waterfall.
• GlossaryShort definitions of every term, callsign convention, and acronym used across K3DPT tools.