12/01/2021

In October, the International Amateur Radio Union (IARU[1]) Region 1 Monitoring System (IARUMS[2]) newsletter reported on the continuing run of over-the-horizon radar (OTHR) troublemakers that often cause severe interference on amateur radio bands - primarily in IARU Regions 1 and 3 but are audible in the rest of the world. Now, another threat is looming, IARU Region 1 says[3].

IARU Region 1 has cited a report by Alpha Defense India that the Defence Research and Development Organisation (DRDO[4]) premier radar development laboratory is working on an OTHR system to keep a close eye on Chinese movements in the Indian Ocean region. The system design has already been completed, according to the report. The prototype stage comes next.

According to the report, the radar prototype is to have two different types of radar arrays - a log-periodic wire antenna array and a broadband monopole antenna array. It is believed that the log-periodic antenna array will be used to determine the best maximum usable frequency (MUF), which is known to depend on current conditions in the ionosphere and the sunspot cycle. The monopole antenna will consist of a 32-element array. The actual system will be developed after extensive testing and evaluation, but the report gave no timeline or completion date.

"OTHRs often massively interfere with amateur radio," the IARU Region 1 report said, citing the well-known Russian "Contayner" OTHR, an OTHR at the UK base in the Republic of Cyprus, and others in Iran and China. "They are present daily on several frequencies within the exclusive amateur radio HF bands," IARU Region 1 said.

The best-known Chinese OTHR - called "Foghorn" because of its distinctive sound - has signals at varying sweep rates that occupy 10 kHz of spectrum. The IARUMS newsletter reported other OTHRs occupying 160 kHz of bandwidth with 10 scan-per-second rates.

"Depending on propagation, some familiar broadcast stations were also audible almost daily in Europe, including Radio Ethiopia on 7110 kHz with an often very strong signal," the newsletter also reported.

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[1] http://www.iaru.org/
[2] https://www.iaru-r1.org/
[3] https://www.iaru-r1.org/
[4] https://www.drdo.gov.in/

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