Yeah, I saw that one active tonight. I have been watching that radar / sounder for close to a year now, trying to figure out where and who.
Because of when I see it, and who else sees it, I suspect eastern side of the Pacific, not yet ruled out South America.
Because of how infrequent it sounds, often much more than 30 minutes between activity, I suspect a sounder or atmospheric radar of some kind, not one meant to track man made objects.
It sometimes uses an interesting waveform. It is LFMCW (Linear Frequency Modulated CW) however using a triangle wave modulation. Most HF radars, almost all others in recent years, use a sawtooth wave when they are LFMCW. The one notable oddball is the new Russian 29B6 Container radar. It uses LFMOP (Linear Frequency Modulation On Pulse), essentially a sawtooth wave with interruptions (dead time) between each sweep, so it is not CW.
The one you are talking about has also used another very interesting waveform, it had an interrupted sweep, but unlike traditional interrupted sweeps it was not stopped at one end or the other, but in the middle. I only saw it used one time, for one stepping cycle. I am not 100% sure it is the same system, but there were some strong indicators it was. I have a video of it here:
https://www.youtube.com/watch?v=436kdnSgjjM
I will put up a vid of the more "normal" waveform for this system in the future, I have several I/Q recordings of it, just need to pick out the best to use. The "normal" waveform is interrupted LFMCW, but with the initial sweep starting mid freq, instead of at the high or low freq, again, unusual.
T!
