the "Russian Woodpecker" was an over-the-horizon radar, and had a nasty habit of coming up on various frequencies that were in use elsewhere. although i remember hearing it often on frequencies that weren't in use as well, so i don't think it's frequency selection was always with the intent of jamming, but it may have been used as a jammer from time to time... there was also a US version that used a frequency modulated sweep at about a 20hz rate, but it locked out SW broadcast and ham bands, so it wasn't well known. i do remember being an RTTY operator in the Army, and having it come up on our net frequency one night...
the OP is from France, and the CEPT is where he should look first.