My suggestion would be encrypted frequency hopping which is typical of Military organisations and such like.
Probably something along these lines: "More blatant [intruders] are the repeat offenders, such as the “Chinese foghorn” heard by over-the-horizon (OTH) radars on several frequencies in the exclusive Amateur Radio 20-meter allocation, as well as on 15 and 40 meters." http://www.arrl.org/news/not-all-intruders-on-ham-bands-are-illegal-but-a-lot-of-them-are
Very interesting signal. You can see the sync as the rolling phase tone. I’ll vote for the transmitted signal of a bi-phase, ground based Radar-like system. Im not aware of any NATO systems that use that signal scheme tho.
