KC0YA-11 GPS/APRS System

The payload after the flight of EOSS-103

The GPS/APRS module was built by Steve Osborne, KC0YA. More photos of this system are available here.


The GPS/APRS system uses an Alinco DJ-C5 transceiver. The output signal is transmitted at around 300 milliwatts.

This system is frequency agile and can be set to work on any 2 meter (144 MHz - 148 MHz) or 70 centimeter (440 MHz - 450 MHz frequency. Of course, we will follow band plans and place the signal on an appropriate frequency. Usually the transceiver is set to 144.340 MHz. But, check the flight announcement page for the frequency. We might move to the national APRS frequency (144.390 MHz), or perhaps some other packet freq.

The GPS/APRS system is use primarily as a beacon for Tracking and Recovery teams and an APRS position beacon and digipeater for tracking purposes.

This payload includes a full KPC3 Plus TNC Packet station. It is possible to Digipeat through the payload however, it is requested that you adhere to the policy set for each individual flight. 

A beacon will identify this package as "EOSS Flight XX" where XX represents the flight number. You can ascertain the callsign of the packet station from this beacon. We set the alias to "EOSS" for all flights.

Beacons are usually NOT given any paths in the unproto addressing. That is, we only set UNPROTO to APRS to indicate an aprs packet. This may change depending on our use of the National APRS frequency.

The signal from this payload is received by several I-Gate stations along the front range of Colorado and forwarded into the APRS-IS internet APRS system.


This payload will sometimes download telemetry strings. See the KC0YA Telemetry Page for info on how to decode this data.


Normally we do NOT encourage digipeating. If we have decided to support it for an individual flight check out the digipeating page for info on how to work the station.


Because this payload is often flown to enable Tracking and Recovery personnel to coordinate their recovery operations. Many of the T&R teams are equipped with APRS and they WILL BE digipeating through the payload. This operation offers the Recovery Coordinator the opportunity to see the dispersal of his or her team members on an APRS display. At an altitude of 90,000 feet this payload sees LOTS of territory (see General Coverage). If all packet stations listening to the APRS data were also beaconing out their positions using the payload as a digi we might get anywhere from dozens to (potentially) hundreds of digipeated packets. This would significantly impair the beacon's own ability to beacon out the payload's position and would also decrease the frequency of digipeated packets from the Tracking and Recovery team members. 

Also, since the vast majority of packet stations on the ground will not be able to hear each other, there is a strong likelihood that individual stations will be causing unintended packet collisions at the airborne packet station, thus reducing the ability of Tracking and Recovery team members to benefit from the APRS capabilities of this payload.

Onboard Systems:

Generally, the GPS/APRS system shown here uses an Alinco credit card transceiver (visible in the picture) connected to a KPC3 TNC and a GPS board. 

The full NMEA GPS data strings are transmitted. These usually include $GPGGA, $GPRMC, and $GPGSA. See the NMEA FAQ for details on each string. An APRS formatted position string is NOT transmitted by this payload. However, most modern APRS software will properly decode and plot this type of data.