&quot;The Duga systems were extremely powerful, over 10 MW in some cases, and broadcast in the shortwave radio bands. They appeared without warning, sounding like a sharp, repetitive tapping noise at 10 Hz, which led to it being nicknamed by shortwave listeners the Russian Woodpecker.&quot;<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Duga_radar" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Duga_radar</a><p><a href="http:&#x2F;&#x2F;www.brogers.dsl.pipex.com&#x2F;Wpecker5.html" rel="nofollow">http:&#x2F;&#x2F;www.brogers.dsl.pipex.com&#x2F;Wpecker5.html</a>