Does anyone know what these are? They are like whistlers but are on higher frequencies. They only come in when daytime skip is present, and very in frequency / intensity, and have fade. Did some searching but so far nothing?
IQ file...
13-45-05_27160000Hz.wav
The Iq file was recorded in December if that means anything?
I call these "hooks" or "sweepers". I have heard them for decades, but the proliferation of waterfalls in hobby use make them much more evident.
These signals are often attributed to industrial processes, such as RF welding. I can say for sure I have looked at several pieces of RF welding gear and can confirm that, in operation, they do emit signals similar to those. It is often tempting to say "yeah, but how big a signal should an industrial process make?" Keep in mind that many of these kinds of welders run to 10's of kW of welding power.
In the US the welders might have pretty tight specifications to meet. However, I have noticed that when the skip is in from various locations, Asia and South America, I can turn my beam in those directions and see many, many, more of these signals over a much wider range of frequencies.
First set of two images taken when skip was in to South America. The second set of two images were taken when the skip was in to Asia.
Here is an image with the antenna pointed 320 degrees, away from South America. South American skip was in at the time, but my antenna is pointed away from South America, about 320 degrees true.
Here is an image take 2 minutes earlier, with the antenna pointed towards South America, about 140 degrees true. You can see that the sweepers are much stronger and more numerous.
Below is a different set, on a different day, taken when the skip was in from Asia. The first image is taken with the antenna pointed away from Asia, at about 140 degrees true.
The second image is with the antenna pointed towards Asia, about 320 degrees true.
T!