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Over-the-Horizon Radars Causing Widespread Interference on 40 Meters


Over-the-horizon (OTH) radars continue to plague various amateur radio bands. Those operating on exclusive ham radio allocations have been complaining for years, but military systems have a blanket waiver to use amateur radio frequencies. The latest edition of the International Amateur Radio Union Monitoring System (IARUMS) newsletter reports that a radar in northern Iran — likely military — has been operating 40 meters (6978 – 7022 kHz). Several Russian and Chinese OTH radars have become mainstays in the ham bands. While these sort of signals are operating on exclusive amateur radio allocations, the International Telecommunication Union (ITU) Convention essentially gives military stations free reign in the spectrum. Article 48 says, “Member States retain their entire freedom with regard to military radio installations.” Member states are countries that have agreed to follow the Convention, and that is not a given.

The Convention goes on to say, however, “Nevertheless, these installations must, so far as possible, observe statutory provisions relative to giving assistance in case of distress and to the measures to be taken to prevent harmful interference [emphasis added], and the provisions of the Administrative Regulations concerning the types of emission and the frequencies to be used, according to the nature of the service performed by such installations.”

According to IARUMS, the Iranian OTH radar was centered on 7000 kHz using amplitude modulation on pulse (AMOP) at 81 sweeps per second. Recordings of military transmissions are available on the SIGIDWIKI signal identification site.

The South African Amateur Radio League (SARL) News reported this week that radio amateurs in Europe and South America have reported major interference from Russian OTH radar stations on several parts of 40 meters — with 12 kHz-wide signals. The radar transmissions have been heard on 7064, 7109, 7170, and 7190 kHz.

Several European IARU member-societies have already sent complaints to their respective telecommunications regulators.




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