The VUARClipse Project

Amateur Radio on the Vanderbilt University Eclipse Balloon


During the solar eclipse on Aug. 21, 2017, Vanderbilt University will launch a weather balloon from Nashville, Tennessee as part the NASA Eclipse Ballooning Project.  The balloon will include two cameras for livestream video and high-resolution still images, and an atmospheric sensor package.


In addition, the Vanderbilt University Amateur Radio Club (VUARC), with station call sign AA4VU, will fly three items in the balloon payload:

·      a crossband VHF / UHF FM voice repeater

·      an APRS tracking unit

·      a VHF CW beacon


The AA4VU Balloon Repeater

The balloon carries a custom VHF-to-UHF crossband FM repeater constructed using two Baofeng handheld transceivers and a Raspberry Pi 3 computer running the OpenRepeater software package.  The repeater transmits in the 70 cm UHF amateur radio band (448.800 MHz) at an output power of 1 watt.


For ham operators outside the Nashville area, the repeater can be worked at the following frequencies:


VHF uplink:  146.420 MHz (tone 123.0 Hz)

UHF downlink:  448.800 MHz


A radio capable of crossband operation (2 meters / 70 cm) can be used to work the repeater, or else two separate radios can be used (one to transmit at 146.420 MHz, and the other to receive at 448.800 MHz).  Most dual band transceivers, including inexpensive Baofeng transceivers (readily available for purchase online), can be programmed for crossband operation if needed.


For better results, higher transmit power and a directional 70 cm / 2 meter antenna can be used at longer ranges from the balloon repeater.  Arrow Antenna offers some excellent handheld high-gain antennas that can be used for working repeaters in balloons or orbiting satellites.


Hams living within 15 to 20 miles of the Vanderbilt University campus will have a second option for contacting the balloon repeater.  By using the AA4VU campus repeater on the top of the Vanderbilt University Medical Center, and adding a second UHF-to-VHF crossband repeater, the VUARC has created intermediate relays so that hams will be able to contact the balloon repeater using standard mobile or handheld transceivers.


UHF uplink (only in Nashville):  446.500 MHz (tone 123.0 Hz)

UHF downlink (only in Nashville):  443.800 MHz


Note that these two frequencies are not a standard UHF repeater split (i.e. ± 5 MHz), so your radio will need to be programmed appropriately prior to the eclipse.


The APRS Tracker

The balloon includes a TrackSoar APRS tracker transmitting at 144.390 MHz to provide updates on balloon location, altitude, and velocity during flight.  The APRS data from the balloon, along with an interactive graphic of the flight track, will be available on this web page on the day of the flight.


The VHF CW Beacon

The balloon also carries a MicroHunt transmitter broadcasting at 50 mW signal at 146.565 MHz.  Listen for “AA4VU BALLOON” in Morse code for 30 seconds, then 30 seconds of silence before repeating.  This beacon provides a means of locating the balloon in case of failure of the APRS tracker or the balloon’s Iridium satellite datalink, but will also be used to test the limits of ultra-low power VHF propagation during the flight.


The Balloon Flight

The balloon will be launched from the Vanderbilt University campus between 30 to 60 minutes before totality (occurring at 1:27 p.m. CDT in the Nashville area).  Based on previous test flights, the balloon should travel to an altitude of approximately 90,000 feet (17 miles) before bursting, after which the payload will return to earth by parachute to land somewhere east of Nashville.  Total mission time from launch to touchdown should be less than three hours.


Below is the geolocation track from the Aug. 8 test flight, showing a flight similar to what is expected on Aug. 21.  Note the back-and-forth movement of the balloon as it rises and falls through the jet stream in the upper troposphere.



As the balloon rises in altitude, the potential range of the amateur radio equipment on board will increase as the radio horizon (the maximum distance for line-of-sight VHF / UHF radio transmission) increases.  Below are figures showing the calculated radio horizons for 10, 30, 50, 70, and 90 thousand feet.  Actual propagation distances may be somewhat greater or smaller, depending on atmospheric conditions and terrain.



The Aug. 21 eclipse will provide an opportunity for hams throughout the eastern United States (and possibly much further away) to make a contact through a high-altitude balloon repeater.  It can also be an opportunity to introduce and educate people about amateur radio, and to show them what is possible with low power, long distance communication.