Yes, I have heard these for decades on HF, many people have, but I think the wide spread use of waterfall displays have made them more obvious to listeners.
I am very certain these are not ionosondes of any kind. First, the signals are far to narrow banded to be useful ionosondes, even if you look at all of them as coming from one source you end up with too many gaps. Second, most ionosondes are well documented, as are their waveforms. In the case of the ionos.ingv.it sondes and plots Cornel posted, that source uses the INS-INGV ionosonde. Descriptions of the waveforms 16 bit complementary phase code can be found online…and it does not look like these things, and I think that one tops out at 20 MHz. No documented ionosonde has a waveform even remotely resembling these.
As for what they may be, I have no idea. I did once show an image of the signal to an engineer working with RF Induction heating, and he said they look something like what can be seen as a result of a low duty cycle pulsed RF Induction heating source, however he also said those are typically found below 4 MHz.
In my opinion they look incoherent and random with regard to amplitude and phase content. I think that makes them unlikely to be intentional transmissions other than byproducts of some operation / hardware. There is NO doubt they are fairly high power, I have received the same single transmission on multiple remotes located hundreds or thousands of miles apart before, but realistically that kind might be possible with fairly modest power levels. It does not take thousands of Watts, but only hundreds or maybe even tens.
T!
