BalloonSat Tracker 900 ISM

Overview | FCC | Risks | Assembly Instructions | Operating Instructions | Maintenance


The tracker is the critical flight element of any ballooning flight. This communication allows for the location of the device and other telemetry to be transmitted from the flight line to Earth.

Simple Operation

To operate the tracker, the operator needs 6 AA lithium batteries. The tracker will immediately operate if assembled correctly.

Product Components

  • The core component is the tracker circuit board which hosts the Digi XTend RF Module, an ISM 900MHz radio. The radio here is the MMCX Version.

  • The tracker has an attached dipole antenna. The dipole is the Nearson Inc. S152AH-915S with a 2dBi gain.

  • The power is supplied by 6 AA batteries. Alkaline batteries are only acceptable for testing, not flight. Lithium AA Batteries are required for balloon flight.

  • The tracker is provided as a Styrofoam container with the electronics system installed into black foam. The total size is 8in by 4in by 6in, and box dimensions can vary.

The tracker has firmware installed by RadioBro. This should not be modified.


The enclosed device complies with Part 15 of the FCC rules. Operation is subject to the following two conditions: (i.) this device may not cause harmful interference and (ii.) this device must accept any interference received, including interference that may cause undesired operation.

WARNING: This equipment is approved only for mobile and base station transmitting devices. Antenna(s) used for this transmitter must be installed to provide a separation distance of at least 30 cm from all persons and must not be co-located or operating in conjunction with any other antenna or transmitter.

Risk of Loss

Ballooning is a known rick environment which the flyer acknowledges by participating in the activity of flight. There exists a risk of payloads malfunctioning even with proper precautions being taken in manufacturing and pre-flight. Because this risk is known and probable, it is not possible to guarantee the success of this tracker.

Possible Known Risks

  • Damage at launch

  • Weather causing damage to electronics

  • Weather or human interruption of the receiving of GPS or transmitting of packets

  • Damage on landing

  • Landing location of the device on property not accessible to the recovery team

  • Tracker device failure due to software, hardware, or electrical

These risks are NOT warrantied by RadioBro in any way. RadioBro may provide support to the customer at its sole discretion.

Managing Risks

It is suggested that more than one tracking capability is installed on each balloon flight. A second tracker should be on another RF band (not 900MHz). This practice provides the most managed risk.

Payload Assembly

Packaging of the tracker is as important to the success of the tracker in flight.

Install the Batteries

Load the Battery Module

Install Insulation

Prepare the Radio

Install the Radio

Attach the Power Header

Notice the red light will be illuminated. The red light will turn off momentarily when the radio transmits.

Install the Lid

Attachment to Payload Line

The Styrofoam box can now be duck-taped to the payload line. Remember to expose the product label and attach information on the flyer including contact information. More duck tape does not make the payload stronger. Normally one wrap at the base and one wrap at the top of the payload is sufficient.


The tracker should loaded approximately 30 minutes before flight. The flight batteries should be installed at this time, and the system should be powered on. Attain a ground lock for at least 5 minutes before liftoff to ensure consistent packets. On landing, simply power off the payload.

Data Packet - Click Here

Serial Bypass

The BalloonSat ISM radio can be bypassed to work directly with the XTend radio as a data radio from your experiment.

Pin-out: Pin 1 GND, Pin 2 GND, Pin 3 RST (Pull to GND to disable MCU), Pin 4 TX, Pin 5 RX

Connector: The serial bypass receptacle is Molex’s C-GRID 5-pin 0705430004. Digikey Part WM4803-ND. Users should choose a compatible plug for this receptacle.

Programming: The XTend is programmed to use 4800 baud, Channel 0 in the XTend configuration tool. This is necessary for normal tracker operation.


  • Normal maintenance for this payload includes:

  • Replace the batteries for each flight

  • Inspect the radio for possible rust or contamination for each flight, especially after a multi-day flight.

  • Replace the Styrofoam container if it is damaged

Parts Replacement

Contact RadioBro for replacement information.

  • The radio is the Digi International XTend X09-MI

  • The antenna is the Nearson Inc. S152AH-915S

  • The circuit board is designed by Bill Brown and assembled by RadioBro

  • The Styrofoam container is from ULINE.