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OGNbase (OGNSXR) APRS format.txt
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Format of APRS messages from OGNbase ground stations
Source: https://github.com/glidernet/ogn-aprs-protocol
This version last edited to fit OGNbase MB139: May 22, 2024
OGNbase is alternative OGN ground station technology using simple low-power hardware based on the ESP32 "system on a chip". OGNbase also offers the "relay" mode of operation, where the "remote" station is located at a high point for good reception of signals from aircraft, and the "base" station (also a simple ESP32-based device) is located where there is internet access. The two stations communicate via radio. The remote station may run on a small solar panel, and automatically enters a very-low-power "sleep" mode at night, when there is no traffic, or when its battery is depleted. Source code, compiled binaries and documentation are here: https://github.com/moshe-braner/Open-Glider-Network-Groundstation
The "tocall" OGNSXR was chosen for OGNbase, to distinguish it from the common SDR-RTL based systems. The ESP32 boards currently used include a radio chip from the Semtech sx12__ series. This hardware/software combination can only listen to one frequency at a time, and decodes only one protocol at a time - the one transmitted by FLARM and compatible devices.
Traffic messages
These messages are in a similar format to those sent by OGSDR stations, but some of the data fields are not available and therefore skipped. Here are two examples, the first uses a FLARM device ID, the second an ICAO aircraft ID with a 2-bit CRC error corrected:
FLR1EFCCC>OGFLR,qAS,K2B9:/172500h4432.07N/07306.44W^000/000/A=000646 !W72! id061EFCCC +039fpm -2.1rot 28.0dB gps3x5
ICAD23456>OGFLR,qAS,K2B9:/172500h4432.07N/07306.44W^000/000/A=000646 !W72! id06D23456 +039fpm -2.1rot 6.0dB 2e gps4x9
These examples report an aircraft from the time 172500h located at 44 32.07N and 073 06.44W at altitude 646 climbing at 39 fpm and turning left. For more information about this type of message see: http://wiki.glidernet.org/wiki:ogn-flavoured-aprs
SoftRF (from version MB09k) in flying aircraft can forward radio packets from other aircraft. OGNbase reports relayed traffic to OGN in one of two formats, selectable via its configuration:
ICAD23456>OGFLR,qAS,K2B9:/172500h4432.07N/07306.44W^000/000/A=000646 !W72! id06D23456 +039fpm -2.1rot 15.0dB relayed
ICAD23456>OGFLR,qAS,relayed:/172500h4432.07N/07306.44W^000/000/A=000646 !W72! id06D23456 +039fpm -2.1rot 15.0dB
The second format avoids including the range of relayed packets in the station's range statistics. (The dB SNR reported for relayed packets is for the reception at the station of the relayed packet.)
Station position message
These messages are in the standard format, but using the "tocall" OGNSXR. For example:
K2B9>OGNSXR,TCPIP*,qAC,GLIDERN0:/000627h4353.05NI07215.22W&/A=000692
Station status messages
The data fields in OGNbase station status message vary between messages, depending on the operational status of the stations - both the "remote" and "base" stations when using the "relay" method. An example of the most common status while fully operational and with the base station using the exact UTC time data sent from the relay station (for correct frequency hopping):
K2B9>OGNSXR,TCPIP*,qAC,GLIDERN0:>183602h vMB101-ESP32-OGNbase 3.8V 55/min 2/3Acfts[1h] 10sat time_synched 180_m_r_uptime
Where the fields are:
183602h time stamp
vMB101-ESP32-OGNbase software version and type of hardware
3.7V battery voltage (in remote relay station if used)
55/min traffic packets received in the last minute
2/3Acfts[1h] number of unique aircraft heard from in the last hour (visible/total)
8sat number of GNSS satellites received (in remote relay station)
time_synched the base station is receiving GNSS time from the remote relay station
180_m_r_uptime the remote relay station has been "up" for roughly 180 minutes
Here are annotated status messages with varying formats:
K2B9>OGNSXR,TCPIP*,qAC,GLIDERN0:>194557h vMB101-ESP32-OGNbase 3.8V 9sat time_synched 1155_m_r_sleep
- the remote relay station will soon go to sleep for 1155 minutes
K2B9>OGNSXR,TCPIP*,qAC,GLIDERN0:>170017h vMB101-ESP32-OGNbase time_not_synched 1017_m_sleep
- the base station will soon go to sleep for 1017 minutes (optionally following the remote)
- expect no status messages while it sleeps
K2B9>OGNSXR,TCPIP*,qAC,GLIDERN0:>195343h vMB101-ESP32-OGNbase time_not_synched 9_m_uptime
- the base station has been "up" for 9 minutes
- the base station is not receiving GNSS time from the remote relay station
- the remote station is either still sleeping, or has not acquired a GNSS fix yet
K2B9>OGNSXR,TCPIP*,qAC,GLIDERN0:>183602h vMB101-ESP32-OGNbase 3.8V 0/min 0/0Acfts[1h] 10sat time_synched 0_m_r_uptime
- the remote relay station has been "up" for less than 10 minutes