We launched again on Monday, September 20th, 2021, from our usual spot in the Berkeley Marina. The launch party was Martin W6MRR and Robert K6RGG, and the launch time was a bit later than usual at 11:30am Pacific time (1830 UTC). The picoballoon did not wake up on launch day. After our previous halfway around the world picoballoon, we were a bit dismayed to have another failed launch.

But the following day it woke up! The picoballoon was meandering out in the Pacific Ocean in gridsquare CL79, somewhere between 9,900 and 11,100 meters (32.5k to 36.5k feet). While this is higher than most of our previous picoballoons, our ideal altitude is above 11,100 meters, which is higher than most bad weather but still in the jetstream.

Something was definitely wrong with the tracker, because on Tuesday Sept 21st we only received a total of 7 packets from KFS and KPH (pdf). These two stations have have huge antennas right on the California coast near San Francisco, with excellent receivers. I ran a Hysplit prediction ...

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At the beginning of Week 3 of Launch 10, we were getting excited that this balloon might circumnavigate the globe. The prediction made from the middle of Egypt showed strong winds would take the balloon to the West Coast within 5 days, maybe even crossing the -122 degree longitude line of our launch site before heading back out to sea.

Flight Results

Unfortunately, the picoballoon only survived two more days in the Middle East. In a situation eerily similar to W6MRR-17, a single packet was received from the ground in southwest Uzbekistan near the Turkmenistan border. The altitude reported was less than 900 meters (encoded in the WSPR power field as 0 dBm or 1 mW). Maybe the tracker was stuck in a tree, or just laying on the ground, we will never know. The single packet from the ground was received by Jari Perkiömäki OH6BG in Finland, approximately 3,700 km away.

This picoballoon made it all the way from gridsquare CM87 to MN10. The center of MN10 is 63 degrees East longitude, which means that the balloon traveled ...

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After the previous three picoballoons did not turn on, we were really struggling to launch another. Was it worth it to build trackers, inflate balloons, and get up early to launch a balloon that never turned on? Luckily, we powered thru and launched another picoballoon on Saturday, Sept 4th, 2021, from our usual spot in the Berkeley Marina.

The team met at 9am, which is a bit later than usual. It was still very cloudy, so the actual launch didn't happen until 9:50am Pacific time (1650 UTC). The launch party was Martin W6MRR, Rob NZ6J, and Robert K6RGG.

The tracker was released in full sunlight without getting wet in the bay.

Predictions

Running HYSPLIT predictions on the morning of the launch, the trajectory of the balloon was really dependent on what altitude the balloon finally reached. Lower altitudes, such as the red line at 9,000 meters, showed the balloon spinning in circles around the western United States. If we could reach 10,000 meters, the balloon had a good chance of reaching the Atlantic Ocean within 3 days ...

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With the lessons learned from the failed previous launch, we decided to launch again the next weekend, August 28th, 2021. The launch party was Martin W6MRR, Justin, Robert K6RGG, and myself KF6ZEO. We launched again from the northwest corner of the Berkeley Marina.

Our major lesson learned from the previous launch failure was there should be no fog or clouds at the launch site. Fog or clouds can condense on the balloon surface or tracker electronics, weighing down the picoballoon so it falls out of the sky. In addition, any winds or downdrafts associated with clouds can push the balloon into the ground.

This morning there was no fog or clouds, but the smoke from the Caldor and Dixie fires meant the sun was a beautiful burnt orange color as I was heading to the launch site. You could barely see San Francisco from the Berkeley Marina.

The winds felt very calm when we were ready to launch, and there was no wind ripples on the surface of the bay. But looks can be deceiving, and the very light breeze ...

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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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I've been spending a lot of time recently listening to WSPR beacons. The recent picoballoons that I have launched all used WSPR for to transmit their location and altitude. WSPR is a great for solar-powered picoballoons because the transmit power is on the order of 10 dBm (10 milliwatts), which is extremely low.

One night, I was just passively watching the WSPR decodes while doing other things on my shack computer. Every once in a while, I would notice a WSPR beacon that was outside of the 200 Hz WSPR band, and therefore wasn't decoded by WSJT-X. I thought this was interesting, who was transmitting out of the band? The transmissions seemed to always be on the high side.

This waterfall plot shows the 200 Hz WSPR decoding band as 1400 to 1600 Hz, denoted by the green bar at the top. You can see the signal marked with the red arrow is just above this band. This signal is also tilted slightly to the left, indicating that as the transmitter heated up, the frequency decreases by a few Hertz ...

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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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