After a short break from the previous launch, we launched again on the morning of Saturday August 14th, 2021. The launch party was Martin W6MRR, Robert K6RGG, and myself KF6ZEO. We launched again from the northwest corner of the Berkeley Marina.

Martin W6MRR had made some changes to the tracker PCB layout to try and mitigate GPS RFI issues, but since none of the standard layout changes made were helping at all, we decided to use an older board design that flew previously. We also decided to bring two trackers. Each tracker was identical electronics and balloon inflation, just different callsigns.

Robert K6RGG brought his drone again and took some great video of both launches.

Launches

After powering on and checking the tracker for the first picoballoon, it was launched at 8:25am. WSPR callsign was W6MRR.

A few minutes after the first launch, we had tied the second tracker to the balloon and we were waiting for a lull in the breeze. The second balloon was released at 8:35am. WSPR callsign was KF6ZEO. Unfortunately, the lower dipole wire ...

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After the dissappointing results from the last balloon, we decided to respin the boards to try and fix this GPS self-interference problem. We also decided to add a low-pass filter to try and keep the WSPR transmitter harmonics out of the GPS band. The new boards did not arrive in time for the Memorial Day weekend, so we decided to launch anyways.

After a day delay due to strong winds and high altitude clouds, we launched on the morning of Sunday May 30th 2021. The weather was beautiful. The launch party was Martin W6MRR, Robert K6RGG, and myself KF6ZEO. We launched again from the northwest corner of the Berkeley Marina.

The winds were gusting to 5 knots or so, and we had to wait for a few minutes for a lull in the winds to release the picoballoon. Even a very slow wind can make the balloons bend over almost to the ground. We released the picoballoon just after 8 am local time (1500 UTC).

Robert K6RGG took a video of the preparation and launch sequence:

Just after launch, I ...

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After the fourth launch, Martin W6MRR respun the tracker board to try and fix some GPS lock errors. Unfortunately, the new layout did not fix the self-interference, but we decided to launch the new tracker board anyways on Saturday May 22nd, 2021. The launch party was Rob NZ6J, Martin W6MRR, Robert K6RGG, and myself KF6ZEO.

This time, Rob NZ6J brought a 20m receiver and speaker so we could actually verify the tracker was transmitting before letting it float away. While we didn't have any software to actually decode the packets, we were able to see that the transmitter on the radio S-meter. This is more of a nice-to-have, as the tracker board also has an LED that lights up when transmitting. The transmitter output power is a fixed 10 mW, and the altitude of the balloon is encoded in the "power" field of the WSPR packet according to this chart:

The WSPR callsign of this balloon was again W6MRR, and using the aprsWsprBridge.py script, was piped into the APRS network using the callsign W6MRR-16.

Launch

The big change we ...

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The next Saturday after the third launch, Martin W6MRR, Robert K6RGG, and Rob NZ6J got together at the Berkeley Marina and launched another picoballoon. I was away on a much-needed vacation.

Since the last launch didn't get above 9000 meters, Martin spent extra time measuring the payload and lift of the balloon. To go around the world, it's important that the balloon has enough lift to rise above weather that may push the balloon down, or coat it with water or ice.

Here's the mass breakdown of this balloon, with the same tracker electronics as the previous launch:

Item	Mass
2 solar cells & carbon fiber stick	5 g
Beacon PCB w/supercaps	7 g
Upper wire	1.5 g
Lower wire	0.9 g
Total payload	15.24 g

The two balloons weighed 71 grams, and after filling with hydrogen had a net neck lift of 23 grams, for a total free lift of 8 grams. This lift should give the balloon a final altitude of 11,500 meters (~38,000 ft), which is above any weather.

Since longevity of ...

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On the morning of Saturday April 10, 2021, members of the San Francisco High Altitude Balloon group launched another picoballoon from the Berkeley Marina. Launch location was the south tip of Shorebird Park, and the launch party was Martin W6MRR, Robert K6RGG, Peter W6DEI, and myself.

Balloon Hardware

The hardware was very similar to the previous launch. The one big change this time was that the APRS 144.39 MHz transmitter was removed. This 500 mW transmitter took a lot of power, and sometimes RFI would lock the processor up bad enough that the balloon needed to power off completely before it would reset. The only transmitter on this balloon was WSPR on 14.0956 MHz.

Output power of WSPR transmitter is only 10 mW. Since the WSPR protocol only includes a Maidenhead gridsquare and not altitude, we encoded the altitude using the Power field in the WSPR protocol. This is described more by ZachTek (PDF). This chart shows the different Power values corresponding to the altitude bands.

Software

The ground software to post the WSPR packet on the APRS ...

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As part of the San Francisco High Altitude Balloon group, Martin W6MRR has been experimenting with picoballoons. Picoballoons are different than regular amateur radio balloons in that are designed to be neutrally buoyant at around 40k feet. This requires payloads that are much lighter than traditional balloons, and different balloon materials that won't stretch or break. This altitude was picked because it is above airplanes and weather, but still in the jetstream, where they can float around the world in a matter of weeks. Our goal is to circumnavigate the globe at least once.

Picoballoons use either Mylar or plastic material in their construction. More traditional Amateur radio balloons, like from our previous launch use latex, which expand dramatically at altitude, then bursts. Latex balloons also break down under ultraviolet light, and are much more expensive than plastic balloons.

Early picoballoon launches just used 2m APRS for sending position information. However, the APRS frequencies in Europe and the rest of the world are different than the North American standard of 144.390 MHz, so balloons that crossed the Atlantic needed ...

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