In the realm of Amateur Radio, APRS (Automatic Packet Reporting System) serves as a vital tool for real-time tactical digital communication and mapping. APRS allows radio amateurs to transmit their GPS coordinates, weather reports, and messages, facilitating situational awareness during emergency situations or everyday activities. While APRS traditionally relies on radio waves for communication, the integration of APRS with the internet, known as APRS-IS (Automatic Packet Reporting System-Internet Service), has opened up new possibilities and functionalities.

qAC – Packet was received from the client directly via a verified connection (FROMCALL=login). The callSSID following the qAC is the server’s callsign-SSID.
qAX – Packet was received from the client directly via a unverified connection (FROMCALL=login). The callSSID following the qAX is the server’s callsign-SSID. This construct is in addition to the TCPIP*/TCPXX* construct currently in place. TCPXX and qAX have been depricated on APRS-IS.
qAU – Packet was received from the client directly via a UDP connection. The callSSID following the qAU is the server’s callsign-SSID.
qAo – (letter O) Packet was received via a client-only port, the FROMCALL does not match the login, and the packet contains either a ,I or qAR construct where the indicated IGate matches the login.
qAO – (letter O) Packet was received via a client-only port and the FROMCALL does not match the login.
qAS – Packet was received from another server or generated by this server. The latter case would be for a beacon generated by the server. Due to the virtual nature of APRS-IS, use of beacon packets by servers is strongly discouraged. The callSSID following the qAS is the login or IP address of the first identifiable server (see algorithm).
qAr – Packet was received indirectly (via an intermediate server) from an IGate using the ,I construct. The callSSID following the qAr it the callSSID of the IGate.
qAR – Packet was received directly (via a verified connection) from an IGate using the ,I construct. The callSSID following the qAR it the callSSID of the IGate.

One of the key components enhancing APRS-IS is the implementation of the “q-construct.” This construct adds several capabilities to the internet APRS transport mechanism, thereby improving efficiency, security, and compatibility. In this article, we’ll delve into the intricacies of the q-construct and its significance within the APRS community.

APRS-IS Entry Identification

The q-construct provides APRS-IS with robust entry identification capabilities. By utilizing specific codes such as qAC, qAX, and qAU, packets received from clients via various connections—verified, unverified, or UDP—are properly labeled, ensuring accurate tracking of packet origins.

Support for Future Authorization Algorithm

In anticipation of evolving security needs, the q-construct lays the groundwork for supporting future authorization algorithms. This forward-looking approach ensures that APRS-IS remains adaptable to emerging security standards and protocols, safeguarding the integrity of the system against potential threats.

Loop Detection and Automatic Protection

Efficient network management is crucial in preventing packet loops and ensuring smooth data flow. The q-construct addresses this by supporting loop detection mechanisms and automatic loop protection. These features minimize network congestion and maintain the stability of APRS-IS operations.

Compatibility and Server-Side Implementation

A significant advantage of the q-construct is its compatibility with existing IGate and client software. Whether packets are generated by servers or clients, the q-construct ensures seamless integration and interoperability across the APRS-IS network. Moreover, implementing the q-construct primarily requires server-side support, simplifying deployment and minimizing client-side modifications.

Understanding q-Construct Codes

The q-construct introduces a range of codes for both server-generated and client-generated packets. From qAS indicating packets from servers to qAI for trace packets, each code serves a specific purpose, enhancing clarity and facilitating efficient packet management.

In conclusion, the q-construct represents a pivotal advancement in the evolution of APRS-IS, offering enhanced functionality, security, and compatibility. By incorporating this construct into the APRS infrastructure, operators can optimize their digital communication capabilities while ensuring the reliability and integrity of APRS-IS operations. As technology continues to evolve, the APRS community can rely on the adaptability and robustness of the q-construct to meet emerging challenges and requirements in the dynamic landscape of amateur radio communication.



An amateur radio operator, Royal Signals veteran, jack of all trades and master of none.

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