Recently, I have been using an SDR to frequently detect a strange signal in the 8MHz-12MHz frequency band (as shown in the figure below). The signal appears as a spring-like shape on the waterfall plot (see the figure below for details).
Upon observation, the signal repeats with a cycle of approximately 40-45 seconds. When using the USB mode and setting the bandwidth to 10 kHz for decoding, the sound resembles that of rapidly blowing bubbles.
I searched online and found a signal that was extremely similar to it —sigidwiki - ROTHR Both the waterfall plot and the audio features show a high degree of correlation. However, I'm not sure if they are the same signal because, according to the description, ROTHR has some connection with the US military, which is somewhat ambiguous. What do experienced HAMs think about this? What kind of signal is it actually?
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