Justin K5EMContinuing discussing these funny shapes in my waterfall from the other site and cross-posting from my bsky. Sometimes when looking at HF waterfalls, we see these funny blips that change frequency quickly and make shapes that looks like tilted "S"s or some have said fishhooks. What are they? Let's figure it out!
Depending on where you are and the time of day, you may see or hear a whole lot of these or none at all. They may be super loud, right at the noise floor, or somewhere in-between. They may be there all the time or fade in and out. Some come and go in a second or two, others last 5 second or more.
Are they ionosondes, or "sounders" that measure the height of the different layers of the ionosphere? Definitely not, as sounders tend to change frequency very linearly with time.
My first experience with them was during the T88WA DXPedition in Palau in 2022. The sunspots were picking up so 10m was open, and we were there making contacts as the sun came up everyday. The first clue was the timing. They would start at 8AM local time, and we would tend to hear them on 10m (28MHz). At 9AM local, more would appear. The cacophony they made sounded like a Star Wars light saber battle.
The timing leads to an industrial or commercial application. Sure enough, when I got home I started doing some research, and others had received these signals as well. They are likely 27MHz high frequency welding machines for vinyl and polyurethane. They should be operated in a shielded room...
So, back to hearing them in Palau. We can only guess that we were hearing the startup of manufacturing lines one ionospheric hop away in Indonesia or Vietnam. These are just guesses, as these signals reflect and refract off the ionosphere and could be coming from significant distances at times.
Want to hear these for yourself? Pick a websdr or kiwisdr somewhere around 3000km from where plastic products are manufactured, and have a listen between 26 and 28MHz. If the sun is up and the production lines are running, you might catch something!
http://vk2ggc2.ddns.net:8074/
http://vk2ggc2.ddns.net:8074/
Thanks to the operators of the VK2GGC SDR for the ability to create some of the images above by listening in on the other side of the world. The rest were heard and screenshotted on my RX-888 MKII SDR here in Seattle on a rainy afternoon. Antenna was a 40m EFHW about 20ft off the ground, and these were likely coming in from Asia or Central/South America based on the band conditions at the time.
