I recently acquired a Digital Communications Inc. DCI-146-4H band-pass filter. This is a 4-pole cavity filter for the 2 meter Amateur radio band, with a pass band of 144 to 148 MHz. Physically it's about 12" long, 6" high, and 3" deep, and is very light. The connectors are UHF SO-239.

I purchased this band-pass filter for operating Summits On The Air (SOTA) radio events. Operating 2 meters FM simplex on the top of mountains is a lot of fun, but many SOTA mountains also have high-powered broadcast transmitters, public safety repeater systems, etc. These strong transmitters cause desensitization in receivers, and I can't hear other stations unless they are very strong. This type of band-pass filter removes all out-of-band signals, but won't remove any in-band transmitters like amateur radio repeaters.

Close-In Performance

The datasheet (local pdf) shows the insertion loss at around 0.4 dB. I measured this at about 0.7 dB, and the extra loss was probably the short RG-58 jumpers and RF adapters I used.

Zooming out a bit, rejection at 151 MHz is approximately 20 ...

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In July 2023 another work trip took me to Hokkaido, Japan. I stayed in Obihiro, a city of about 165,000 people. I brought along a RTL-SDR dongle and mag-mount antenna, and if I had some free time, I would try and decode nearby radiosondes.

From my earlier trip back in September 2022, I knew there was radiosondes launched from Sapporo twice a day. However, it was unclear if the Kushiro autolauncher had been replaced after the fire.

After tracking the radiosondes in Hokkaido, I would travel to Tokyo for a few days and try and track them in the city, labeled "Tateno" in the above map.

Tracking Hardware

The equipment I use is very simple but effective, just a RTL-SDR Blog v3, a mag-mount antenna, laptop, and car power supply.

Pro tips for using this mobile setup:

• Have someone else drive the car, or pull over whenever viewing the laptop.
• Use a short USB extension cable instead of plugging the RTL-SDR dongle directly into your laptop. This prevents torque on the laptop's USB port.
• Use a car DC-DC converter ...

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After my visit to Fairbanks, Alaska back in July 2022, I chatted with a friend who lives in Fairbanks. He agreed to host a radiosonde receiver at his house just north of town. Since I wasn't traveling to Fairbanks again in 2022, I shipped him all the parts necessary for the installation.

This station is the standard Raspberry Pi and RTL-SDR Blog v3 that I have been shipping around to Houston and other sites. radiosonde_auto_rx runs inside a docker container, which makes it trivial to install and update the software. For remote monitoring and control, wireguard is the way to go.

Antenna

My go-to antenna for radiosonde receiving is a quarter-wave ground plane antenna. They are super easy to build, very inexpensive, and work better than commercially-made antennas.

But a home-made quarter-wave vertical antenna has one major flaw: ice. Ice buildup on the elements will not only cause it to detune, but there is also a potential for mechanical failure. Hardware store 14-gauge copper wire just isn't strong enough to hold up ice.

Since Fairbanks gets a lot of snow ...

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A recent work trip brought me to Hokkaido, Japan. Taking a look at Sondehub beforehand, I noticed a few radiosonde launch sites on the island. My work would bring me closest to the Kushiro radiosonde launch site, so maybe if I had some free time I could go watch a launch.

Research

Before leaving for the trip, I contacted Shaun JH1HNB/KJ6VGQ, who was uploading radiosonde data to Sondehub. Shaun lives in Tokyo, and has written some blog posts about his experiences.

Shaun gave a presentation (pdf) in February 2022 to the Tokyo International Amateur Radio Association. The presentation was about using radiosonde_auto_rx or a rdzTTGOsonde to receive radiosondes.

I also did some research on the Japan Meteorological Association's radiosonde webpage (pdf), which has a lot of information about the program. Their online map showed that this site uses an autolauncher, but doesn't indicate which type of radiosonde is launched.

Since radiosonde_auto_rx can receive all three of the types of radiosondes that are launched in Japan, I felt confident that I could receive any radiosonde that was taking measurements.

Kushiro ...

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With the release of WSJT-X 2.3.0 in September 2020, Steve Franke K9AN, Bill Somerville G4WJS, and Joe Taylor K1JT included a two new digital protocols called FST4 and FST4W. These two digital modes are the next evolution in low-power and long distance digital communications. These modes use four-level Gaussian frequency-shift keying (4-GFSK) modulation, which has smooth transitions between the four tones. This modulation is a bit easier to decode than regular WSPR, which uses 4-FSK modulation that has abrupt tone changes.

FST4 is designed for keyboard-to-keyboard QSOs (similar to FT8), and FST4W is designed for beacon transmissions like the regular WSPR protocol that we use for picoballoons. The time periods for a single transmission are 120, 300, 900, and 1800 seconds, with longer periods requiring less SNR for decoding.

In Spring 2022, Rob Robinett AI6VN included FST4W decoding in Version 3.0 of the wsprdaemon software, which is what I run for WSPR decoding at my home in San Francisco and in Inuvik, NWT. That's cool, I thought. I can just "check the box" in the configuration file ...

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I recently set up a Weak Signal Propogation Reporter receiver in the town of Inuvik, NWT. I was there in the beginning of June 2022, just as the world was opening back up from the COVID-19 travel restrictions.

I thought Inuvik would be an interesting place, as it's at 68 degrees North latitude, which is above the Arctic Circle. During the summer, the sun never sets from May 25th to July 19th. In the winter, the sun doesn't rise from Dec 6th to Jan 5th. But the sun does get close enough to the horizon to have civil twilight, where the sun is less than 6 degrees below the horizon, so it's not completely dark all the time in the winter.

From an RF perspective, I thought this would be a really interesting location for several reasons. What happens to HF propagation when the D layer is always present? Would 20 meters be alive all summer long? Conversely, what happens in the winter when it's only the E and F layers?

Hardware

The hardware for this receiver is almost identical ...

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On the last day of my recent trip to Fairbanks, Alaska, I finished up work a bit early and headed to the airport to see a radiosonde launch. Looking at satellite imagery before my trip, the launch location has a few buildings so I thought it might be a manually-launched site like Inuvik or Newfoundland.

However, when I arrived, through the fence I saw a Vaisala AS41 autolauncher, just like my local radiosonde launch site across the bay in Oakland, California. No one to talk with this trip.

I arrived just before 3pm local time (2300 UTC), and the autolauncher was beeping away, indicating that the balloon was filling with hydrogen. I set up my mobile radiosonde_auto_rx station, with a mag-mount antenna and RTL-SDR dongle. Running the software inside a docker container makes it easy to install and update.

The radiosonde was turned on and transmitting on 405.3 MHz inside the autolauncher, but the expected launch at 2300 UTC came and went with nothing happening. Interesting, maybe something was wrong? My local Oakland station launches at exactly 1100 and ...

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Back in October 2021, the excellent team behind Sondehub added several features to the map. They added launch site locations, grabbed from the official NOAA database. Clicking on a particular launch site allowed a user to generate a weeks worth of flight predictions based on the most recent GFS run. Cool!

The red lines on this prediction map of Oakland show the next 14 launches (7 days). As with any prediction of the future, the further out you go the worse the prediction.

Reverse predictions (pdf) were also added, for predicting where a radiosonde was launched from. This feature would have been very helpful when I was trying to find the Monterey Bay launch location.

Scrolling around the new map, I saw a launch site just east of Houston, Texas. I knew some people that lived in Houston, so I sent them a radiosonde receiving station. The hardware was almost identical to the Santa Cruz station, except that this station is entirely inside a home. No weatherproof case was needed, which is great because I didn't really want to figure ...

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Now that the pandemic has tapered off a bit, I took another short trip up to Inuvik, NWT. While I was up there, I visited the Environment Canada Weather Station, and participated in a radiosonde launch.

The big news out of Inuvik during this trip was that the road from the airport to the town has been paved! The road is much smoother, and I don't need to worry about windshield cracks every time a big truck passes.

Since my 2016 visit, the site has been upgraded with modern equipment. The old Electrolyser Corporation hydrogen generator was replaced with a Proton Hogen unit, all housed in a modern building with explosion-proof light switches, electrical outlets, etc.

I arrived just before the Midnight UTC launch, and Chris already had the balloon inflated and was working on the radiosonde transmitter. As I saw in Newfoundland, Canada has transitioned to the Graw DFM-09 radiosonde.

To my surprise, he actually let me release this radiosonde. This was my first radiosonde release, and it's very similar to a bursting HAB release. One interesting aspect of ...

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The San Francisco Radio Club organized another Summits on the Air event on 23 April 2022. For this "Simul-SOTA" event, there was 11 amateur radio operators activating 9 summits around the Bay Area. Steve W1EGG made a handy map with who was activating each peak:

I activated Vollmer Peak, which is at the southern end of Tilden Park in the hills above Berkeley. Parking at the trailhead was easy in the morning, but by the time I left parking was nonexistent.

The hike up was short, and the views were excellent. I could clearly see Mt. Tamalpais across the bay, which was activated by Vlad K6VVP.

A lot of the other peaks that were activated that morning were visible from from the top, including my previous activated San Pedro Mountain.

HF Radio

This was my first HF activation. I borrowed a Xiegu G1M radio, which is a small QRP SDR. I also borrowed a lithium power pack, and a 49:1 balun for an End-Fed Half Wave antenna. I cut a piece of two conductor zip-cord 33 feet long, which ...

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