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.

[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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