Amateur High |Altitude Balloon (HAB) Launches – W4OVH Field Day 2025

One Field Day bonus is an educational project. At one of the planning meetings, we decided to do a balloon launch with a radio package as our educational project. We has done one before, but with disappointing telemetry. Bruce, KN4GDX, took the project on again for 2025.

Payloads Planning and Testing

Two amateur payloads were planned and prepared for the Field Day 2025 launch. Launch was planned for ~1500 on June 28 at the field day W4OVH site; and actually occurred at about 1530. The following description covers the planning, launch activities and tracking of the two payloads.

The first payload, from Zachtek, was similar to the 2024 HAB payload launch, which worked while testing, but unfortunately did not produce track files after launch. For 2025 it was also a WSPR payload, this time programmed for the 20 meter band. In this photo, the payload is sitting next to its 20 meter dipole antenna. Power is supplied by two 5 volt solar panels, seen edge-on here, and backed up with two 2.7 volt super capacitors, in series, which are seen here as the large components on the board. At launch, the payload was suspended between the two 17 foot legs of the 20 meter dipole.

The lower board in this view is the second payload, from QRP Labs. The board contains an APRS payload which transmits through a 50 cm antenna on the 2 meter APRS frequencies. The antenna is attached downward from the board; and the GPS receiver is on the upper edge of the board.

The power source and physical attachment in the final configuration was similar to the WSPR board and included an “A frame”, formed from some scrap plastic, two solar panels, power wiring and one 5.5v super capacitor.

Programming the payload’s on-board computer was done with the Arduino IDE using a payload board-specific application. The on-board application is fairly complex because it has to control APRS transmissions depending on its geographic area. To meet this requirement, the GPS signals received by the payload determine the location and either alter the APRS frequency based on the country, or turn off APRS completely. In the event a payload reaches an altitude where a long distance “floating” condition is met, this feature is required by the ITU.

Each payload, at completion weighed about one ounce, including GPS receivers and antennas. The antennas were made from 28 gauge insulated stranded wire. The WSPR payload transmits at about 20 milliwatts; and the APRS payload transmits at about 500 milliwatts. WSPR is tracked on either PSK Reporter, or WSPR.net. WSPR is a “weak signal” format that can also be heard using WSJT-X software and appropriate receivers. APRS is normally tracked by global APRS receiver stations on VHF and reported as APRS-IS on the internet at APRS.fi.

Both payloads were tested during construction and just prior to launch at the Field Day site. During construction, the WSPR payload was tested using standard HF receivers and the WSJT-X WSPR application. The APRS payload was tested initially with a handheld APRS radio; then also tested in proximity to the W4VA APRS receiver to assure the signal was being reported in the APRS-IS system. on the internet.

Balloon Planning and Testing

In both 2024 and 2025, hydrogen gas was our preferred lifting medium with several balloon options. Hydrogen has become the preferred gas for many amateur and scientific uses due to being cheaper, and also having about twice the lift for a given volume. During the last few years, helium gas expense and availability has driven both government scientific and amateur balloon launches to hydrogen. Due to hydrogen’s flammability, extra precautions are taken with handling and filling. Gil, KN4OZH, and Byron, AK4XR, were instrumental in procuring the hydrogen ahead of time; and then supporting the filling processes for both balloon types.

Our balloon options included both 48 and 72 inch latex, and 32 inch mylar. These options have very different filling conditions with the latex neck about one inch in diameter, and the mylar neck about ¼ inch in diameter. To enable control of the hydrogen fill process, Bruce made a two part apparatus for matching the hydrogen gauge/valve assembly to both types of apertures.

There is no simple way to “weigh” a filled balloon to test its lift capability, while attached to the hydrogen source. In both cases, through some trial and error, we were able to fill both latex and mylar balloons to approximately the desired lift as tested with a gram/Newton scale. Our preferred net lift was 10 to 20 grams. The final latex balloon lift was closer to 30 grams so it was a bit of a “rocket” at launch. The mylar balloons – we used two, was closer to 5 grams, with expansion space in the mylar – which is preferred, and was a much slower ascent. Under some conditions, a mylar launch of a pico sized payload may achieve a “float” condition in the jet stream. Ours, unfortunately did not. Maybe next time. Floaters are sometimes achieved with mylar, but are usually planned and launched with a specific type of balloon which has a large volume and is relatively expensive at over $100, just for the balloon.

Payload Tracking

Our APRS payload was tracked almost immediately by Cat, KM4PBD, after launch and was tracked throughout it’s flight by a number of APRS receivers in the National Capitol region. It achieved close to 30,000 feet altitude and descended near the Annapolis High School. One of Bruce’s friends who does regular launches with Horus payloads (UHF, USB with 4FSK modulation) lives near the landing site and spent some time looking for the balloon/payload, but without success. He believes it landed in a heavily wooded area.

The WSPR payload tracking was not evident immediately, but was in fact tracked by a large number of stations across the US, Canada and Europe. The flight was fairly short, about 70 minutes, due to the rapid ascent, supposed balloon rupture at high altitude, and descent in the Alexandria area.

We all want to thank Bruce, Gil and Byron for their efforts in planning and executing our 2025 amateur balloon launches.

There is a slideshow below. Wait for a bit for the next slide.