Short definitions of the terms used across K3DPT tools. Click a heading to deep-link.
Automatic Dependent Surveillance, Broadcast. Aircraft transponder extension that broadcasts position, altitude, and velocity on 1090 MHz (most aircraft) or 978 MHz (some US general aviation). Mandatory for most US controlled airspace since 2020. See [[adsb-overview]].
Automatic Identification System. Maritime equivalent of ADS-B. Ships transmit position, course, speed, and identifying info on VHF channels 87B / 88B. Required for all commercial vessels over 300 GT and all passenger ships. See [[ais-overview]].
Daily quasi-linear average of geomagnetic disturbance. Companion to the [[#k-index]]. Higher means stormier; HF propagation degrades. See [[hf-propagation]].
American Radio Relay League. The US national association for ham radio. Publishes the ARRL Handbook (the canonical RF engineering reference for hams) and runs many of the contests and awards programs.
A radio-licensed station's unique identifier. US amateur callsigns follow patterns like W1AW (1x2), K3DPT (1x3), KC2ABC (2x3) where the digit indicates the call district at first licensing. FCC ship and aircraft radio licenses use W and K prefixes too (WDK9654, WDB6535). UK uses G, France F, Germany DL, and so on per ITU prefix block assignments.
Course Over Ground. The actual direction a vessel or aircraft is moving across the surface (or through the air), accounting for wind and current. Can differ from [[#heading]] when crosswinds or currents push the vehicle sideways.
DX Century Club. The ARRL's award program for contacting (working) operators in 100 or more different DXCC entities. There are 340 active DXCC entities and another 29 deleted ones (East Germany, Czechoslovakia, USSR, etc.) that count for DXers who worked them before they were removed.
A specific political or geographic area on the ARRL DXCC list. Mostly maps to countries but with carve-outs for things like Alaska and Hawaii being separate from the lower 48, and for inhabited islands isolated by ocean (Pitcairn, etc.).
Federal Communications Commission. The US regulator that issues radio licenses, allocates spectrum, and enforces interference rules. Publishes its full licensing database (ULS) as a free public download, which is what powers most of K3DPT's data.
Federal Aviation Administration. The US aviation regulator. Publishes the Aircraft Registry as a free public download (MASTER + ACFTREF + ENGINE tables). K3DPT uses this to overlay registration data on live ADS-B traffic.
Pressure altitude in hundreds of feet, used above 18,000 ft in the US (and 3,000-6,000 ft transition altitudes elsewhere) to give all aircraft a common altimeter reference. FL370 = 37,000 ft pressure altitude.
Global Maritime Distress and Safety System. The international framework of HF and VHF distress and calling frequencies (4125, 6215, 8291, 12290, 16420 kHz voice plus DSC variants) plus NAVTEX, EPIRB, and SART beacons that vessels use for emergency communication. See maritime frequencies.
The band of twilight following Earth's [[#terminator]]. Special to ham operators because long-haul HF propagation on the lower bands is unusually good in the brief window where two stations share the grey line. See [[greyline-and-terminator]].
The direction the bow or nose is pointing. Often differs from [[#cog]] when current or wind pushes the vehicle sideways. AIS transmits 511 when heading is not available.
International Civil Aviation Organization. The UN agency that sets international aviation standards, including the [[#icao24]] addressing scheme and the squawk-code reserved values.
The 24-bit (6 hex character) aircraft address used by Mode S transponders and ADS-B. Assigned permanently to the airframe by the registering country. US range is A00000-AFFFFF. See [[adsb-overview]].
Unwanted mixing products produced when two or more signals enter a non-linear stage. Third-order IMD (2*F1 ± F2, 2*F2 ± F1) is closest to the originals and hardest to filter out. The reason repeater coordinators have to think hard about co-located transmitters. See [[harmonics-and-intermod]].
A permanent 7-digit identifier assigned to commercial ships by the International Maritime Organization. Unlike [[#mmsi]], it does not change when the vessel is reflagged or sold, so it is the right key for tracking a vessel's history across owners.
3-hourly index of geomagnetic disturbance, 0-9 logarithmic scale. Higher means stormier; HF propagation suffers, especially through the auroral oval. See [[hf-propagation]].
The grid square system every ham operator uses to encode location compactly. A 6-character grid like FN20cd locates you to within 5-9 km. See [[maidenhead-grid]].
Maritime Mobile Service Identity. 9-digit number assigned by the vessel's flag state and used as the primary key in AIS broadcasts. US MMSIs are in the 366-369 range. The MMSI joins live AIS to static FCC ship registration. See [[ais-overview]].
The air traffic control transponder protocol that [[#adsb-b]] sits on top of. Older aircraft can have a Mode S transponder (gives ATC its ICAO24 and altitude) without ADS-B Out (would also give position).
The highest frequency that bounces off the ionosphere for a given path. Above the MUF the signal escapes into space. See [[hf-propagation]].
The acknowledgement card or electronic confirmation hams exchange to confirm a contact. "QSL?" means "do you confirm?". A "QSL card" is the physical postcard mailed to confirm.
Hams' shorthand for "my location." From the original Q-code list.
Solar flux at 10.7 cm wavelength, measured in solar flux units (sfu). High SFI means high ionospheric ionization, which means the higher HF bands open up. See [[hf-propagation]].
Speed Over Ground. The actual speed of a vessel or aircraft over the Earth's surface, in knots. Differs from airspeed (for aircraft) or speed-through-water (for vessels) by the current or wind component.
A 4-digit octal code transmitted by an aircraft's Mode S transponder, assigned by air traffic control. Reserved codes: 1200 (VFR US), 7000 (VFR Europe), 7500 (hijack), 7600 (radio failure), 7700 (emergency), 7777 (military intercept). See [[adsb-overview]].
The moving line on Earth's surface separating day from night. The band of twilight following it is the [[#greyline]]. See [[greyline-and-terminator]].
Universal Licensing System. The FCC's public database of all non-broadcast US radio licenses. Free daily download. Most of K3DPT's data comes from ULS: amateur licenses, microwave point-to- point, land mobile private (public safety + industrial), ship radio service, coast stations.