For some time, you can hear a strange sound on the band. Ever thought about what it is?
Well, it's called Over-The-Horizon-Radar. The OTH which you are hearing now on the band is from Iran.
Over-the-horizon radar, or OTH (sometimes also beyond the horizon, or BTH), is a type of radar system with the ability to detect targets at very long ranges, typically up to thousands of kilometres. Several OTH radar systems were deployed starting in the 1950s and 60s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems instead. OTH radars have recently been making something of a comeback, as the need for accurate long-range tracking becomes less important with the ending of the Cold War, and less-expensive ground based radars are once again being looked at for roles such as maritime reconnaissance and drug enforcement (Source : WikiPedia)
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