User-Definied Data Format¶

The APRS protocol defines many different data formats, but it cannot anticipate every possible data type that programmers may wish to send. The User-Defined data format is designed to fill these gaps. Under this system, program authors are free to send data in any format they choose.

The data in the AX.25 Information field consists of a three-character header:

{ APRS Data Type Identifier.

U A one-character User ID.

X A one-character user-defined packet type.

The APRS Working Group will issue User IDs to program authors who express a need.

[Keep in mind there is a limited number of available User IDs, so please do not request one unless you have a true need. The Working Group may require an explanation of your need prior to issuing a character. If only one or two data formats are needed, those may be issued from a User ID pool].

For experimentation, or prior to being issued a User ID, anyone may utilize the User ID character of { without prior notification or approval (i.e. packets beginning with {{ are experimental, and may be sent by anyone).

Important Note: Although there is no restriction on the nature of user- defined data, it is highly recommended that it is represented in printable 7-bit ASCII character form.

Bytes:

This is envisioned as a way for authors to experiment and build in features specific to their programs, without the danger of a non-standard packet crashing other authors’ programs. In keeping with the spirit of the APRS protocol, authors are encouraged to make these formats public.

The following list contains all of the User IDs and packet types as of April 2020. There is currently no mechanism in place to reserve a code and avoid conflicts.

HEADER AUTHOR DESCRIPTION

{BT KB3UKS For BRICSAT Telemetry

{BP KB3UKS For BRICSAT Pictures

{Dx WB2OSZ Direwolf software TNC

{Fnn WB4APR nn is a 2 byte descriptor of MITEL GPS data formats

{HT WB4APR For HAM-Trail reporting devices (tbd)

{ID WB4APR RFID tags

{K1 WB4APR "K" for Keps and "1" for NASA One line.

{K2n WB4APR For NASA two line elements. "n" is line 1 or 2.

{KY KI4YLJ For KYSAT (University of Kentucky)

{Q1 WB4APR For QIKcom-1 data

{Q2 WB4APR For QIKcom-2 data

{Sx ZL4FOX for SARTrack a SAR specific set of protocols

{TP WB4APR Telemetry for PCSAT2 Solar Panel Experiments

{TU WB4APR Telemetry for PCSAT2 Solar Panel Experiments

{x1 J Bennet for WX

{x2 J Bennet for WX

Generally, all formats using this method will be considered optional. No program is required to decode any of these packets, and must ignore any it does not decode. However, it is possible that in the future some of these formats may prove to be of sufficient utility and interest to the entire APRS community that they will be specifically included in future versions of the APRS protocol.