OTH radars are strategic military equipments that basically allow the operator to “see” beyond the horizon trough the means of ionospheric reflexion that allows HF signals to propagate all over the globe. Regular radars use signals in the GHz regions (better for detection of smaller objects) and are only good for direct visibility, that is why sometimes OTH radars were replaced by more expensive “flying radars” more commonly known as AWACS, but as the Cold War has ended armies are folding back to the cheaper technology and the OTH radard operating in HF are spotted more and more oftenly by amateurs. More details on the OTH Wikipedia page, if you are courious.
Such a signal could be recieved today in Bucharest between 27.480500 MHz and 27.499500 MHz at a S9 level, with a type of pattern I haven’t seen before. Feel free to check out the video and to see how it looks on my SDR transciever.