Balloon Launch at Field Day

W4OVH Amateur Balloon Payload Experiment – Field Day, 2024

Our W4OVH team of radio experiment enthusiasts launched an amateur radio high altitude balloon (HAB) payload on Field Day, June 22. Our first ever launch attempt zoomed into the blue sky trailing a lengthy HF antenna. To the amazement of the small group of spectators, the balloon and payload headed toward an uncertain fate. How did we get here?

 

Background
The earliest known hydrogen gas balloon launch, according to Wikipedia, took place near Paris in 1783. One of the spectators in attendance was Benjamin Franklin. The balloon, fashioned in rubberized silk, was about 13 feet in diameter. The hydrogen was generated by pouring sulfuric acid over iron, then delivered into the balloon via lead pipes. You can read the details on Wikipedia. The launch was successful, but the landing at a rural site about 20KM distant prompted an attack by local peasants involving knives and pitchforks.

There are many types of amateur balloon payloads and launching techniques with helium or hydrogen gas providing the balloon’s lifting force. Latex and mylar balloons are commonly used. The most common payloads are APRS (VHF packet) and HF WSPR. APRS payloads operating on VHF are tracked via the global APRS receivers and reported on the APRS network and the radio amateur Sondehub website (amateur.sondehub.org).

Payloads using WSPR are tracked by the global HF WSPR receiver network and reported on the WSPR.net tracking site. The Sondehub site provides mapping and payload information on both APRS and WSPR payloads, as well as additional payload methods.

Another payload of interest to many radio amateurs is the Horus payload system. Fewer HABs carry this payload, but it provides an interesting challenge to set up the proper equipment. The Horus payload typically transmits on 430 MHz using Four Frequency Shift Keying (4FSK).

Tracking is done with the Horus application and a UHF receiver using USB mode. The Horus application decodes the packet information from the 4FSK modulation. HAB location and payload parameters are provided by the Horus application to the  amateur.sondehub.org  website for viewing and tracking. So far, this is a rare HAB approach, but is growing in popularity. LoRa 433MHz or 900MHz is another new technology that is, or will soon be, employed in HAB payloads. As LoRa stations proliferate, this method may become common.
Tracking amateur HABs is a great learning experience and meshes nicely with the NOAA HAB tracking hobby.

Back to our experiment
In preparation for Field Day, 2024, John, KG4NXT, asked if I would be willing to take the lead on an OVH-sponsored HAB payload launch. I accepted the challenge and provided the payload, while John, Byron, AK4XR, and Gil, KM4OZH, worked out details of procuring hydrogen and a storage to balloon delivery apparatus for the launch.

John also took on the onerous task of coordinating with the FAA to advise of our launch. Our HAB/payload was well within the size, weight and tensile strength limits of FAA regulations.

Our balloon was a latex 36 inch style which was adequate to provide lift for the payload. The payload, weighing approximately one ounce, was comprised of an HF WSPR transmitter (in kit form), weighing approximately 10 grams; and a wire dipole suitable for 30M WSPR transmission, at about 20 grams. Power was provided by two solar panels soldered to the transmitter kit in an inverted “V” configuration designed to provide good access to the sun angle as the payload rotates in its suspended state.

The transmitter board includes two super-capacitors to help maintain power, when the solar panels cannot, due to sun angle or clouds. No batteries are involved in this design.  Programming the payload with call sign and WSPR frequency and other parameters is a simple matter of running the free application and a USB connection with the host computer.

The vendor for our payload was Zachtek (zachtek.com). Zachtek provides a number of aerial and terrestrial WSPR solutions for amateur hobbyists. Our payload included integrated GPS and the WSPR reporting included the six-element grid square.

 

The overall length of the OVH HAB was nearly 50 feet; and that’s primarily due to the length of the vertically oriented 30M dipole – comprised of two approximately 23-foot legs. The wire I used for the  antenna was ~ 30-gauge coated copper wire. This wire has adequate strength to carry the very lightweight payload.

Prior to FD24 I built a test, or prototype version of the ultimate flight unit and verified the operation and WSPR reception of the flight configuration. On field day, the flight unit WSPR transmission was verified again prior to launch.

So, the question arises, how do you figure out the ballon size, hydrogen load, and other factors that contribute to a successful launch?

I did some tethered experimenting using the prototype payload and large mylar balloons with helium. I was able to get a tethered payload up in the air long enough to verify proper power and operation through WSPR receptions.

Unfortunately, tethering a balloon in even ‘calm’ conditions leads to trees capturing the balloon; and that’s what happened in my case. Testing provided confidence our FD24 flight unit, using a hydrogen balloon, should be successful.

The remaining calculations involve obtaining adequate lift to enable ascent at a reasonable rate. Hydrogen lift is dependent, to first order, on the volume of the balloon. So, the final net lift is the hydrogen lift minus the weight of the balloon and payload. Our balloon was about one ounce, and the payload was also about one ounce. When filling the balloon we measured the resulting lift force using a 1 Newton, or 100 gram, scale.

The Launch
Our launch team, with several helpers to manage the long antenna legs, was successful in avoiding several HF antenna wires at the launch site; and rapidly ascended at several meters per second. The rapid rise and wind-borne track resulted in the OVH experimental balloon payload disappearing from sight.

Shortly after launch we noted tracking from several WSPR receivers, but no additional reception was reported beyond the first half hour after launch. The fate of W4OVH HAB is unknown. The payload carried my phone number in the event it was recovered.

So far, there have been no calls.

Maybe there’s another HAB launch in our W4OVH future?

Bruce Crandall, KN4GDX.