Glossary

Revision as of 11:09, 29 August 2009

APRS Glossary

A

• Announcement - An APRS message that is repeated a few times an hour, perhaps for several days.
• APRS - Automated Packet Reporting System
• APRS Data - The data that follows the APRS Data Type Identifier in the AX.25 Information field and precedes the APRS Data Extension.
• APRS Data Extension - A 7-byte extension to APRS Data. The Data Extension includes one of Course/Speed, Wind Direction/Wind Speed, Station Power/Antenna Effective Height/Gain/Directivity, Pre-Calculated Radio Range, DF Signal Strength/Effective Antenna Height/Gain, Area Object Descriptor.
• APRS Digipeater Path - A digipeater path via repeaters with RELAY, WIDE and related aliases. Used in Mic-E compressed location format.
• APRS Data Type Identifier - The single-byte identifier that specifies what kind of APRS information is contained in the AX.25 Information field.
• APRS-IS - APRS-Internet System
• Area Object - A user-defined graphic object (circle, ellipse, triangle, box and line).

B

• Base 91 - Number base used to ensure that numeric values are transmitted as printable ASCII characters. To obtain the character string corresponding to a numeric value, divide the value progressively by decreasing powers of 91, and add 33 decimal to the result at each step. Printable characters are in the range !..{. Used in compressed lat/long and altitude computation.
• Bulletin - An APRS message that is repeated several times an hour, for a small number of hours. A General Bulletin is addressed to no-one in particular. A Group Bulletin is addressed to a named group (e.g. WX).
• Bulletin Identifier - A single digit 0-9 that identifies a particular bulletin.

D

• Destination Address field - The AX.25 Destination Address field, which can contain an APRS destination callsign or Mic-E encoded data.
• DF Report - A report containing DF bearing and range.
• DGPS - Differential GPS. Used to overcome the errors arising from Selective Availability.
• digi - short for "digipeater"
• digipeater - A station that relays AX.25 packets. A chain of up to 8 digipeaters may be specified.
• Digipeater Addresses field - The AX.25 field containing 0–8 digipeater callsigns (or aliases).
• DX Cluster - A network host that collects and disseminates user reports of DX activity.

F

• findu - a web site at http://www.findu.com which collects APRS data from APRS-IS and can answer queries on the database. Also, generically, the Internet aspect of APRS, though there are many other useful APRS sites

G

• gate - short for IGate
• GPS - Global Positioning System. A //GPS receiver// uses signals from satellites to determine its position. For APRS use, the GPS receiver will then send the location information to a TNC for transmission by radio

H

• ham - a person who uses amateur radio. The origin of the nickname is obscure
• hop - when a digipeater repeats a packet, it's considered a "hop." If a second digi receives the packet from the first digi and retransmits it, that counts as a second hop

I

• IGate - Internet Gateway, a radio and computer setup for receiving packet data via radio and sending those packets to the Internet (via APRS-IS)

P

• packet - a bundle of data (like an APRS user's call sign and location, or a weather station's report on conditions) plus a path and other information, represented as a set of bytes in a computer or transmitted via radio as a series of rapidly-changing tones
• path - a specification of the path a packet should take through the digipeater system. Can be explicit (using the callsigns of the intended repeaters and the ultimate destination) or symbolic, like "WIDE2-2" which digipeaters will interpret to mean "repeat twice."

T

• TNC - Terminal Node Controller. A device which can control a radio and transmit computer data (like a user's call sign and GPS position information) using a series of rapidly-changing tones

V

• Voice Alert - is a way of setting up an APRS station to notify you if other active stations come into simplex voice range
• VTG Received Sentence - A standard NMEA sentence, containing the receiving station’s course and speed.

W

• WIDE - A generic APRS digipeater callsign alias, for a digipeater with wide area coverage.
• WIDEn-N - A generic APRS digipeater callsign alias, for a digipeater with wide area coverage (N=0-7). As a packet passes through a digipeater, the value of N is decremented by 1 until it reaches zero. The digipeater keeps a record of each packet (or its FCS) as it passes through, and will not digipeat the packet again if it has digipeated it already within the last 28 seconds.
• WPT Sentence - A standard NMEA sentence, containing waypoints.
• WX - Weather.