The Duga-3 radar is found within the 30km exclusion zone surrounding the Chernobyl nuclear disaster. Originally the first functional Soviet over-the-horizon radar in operation from 1976 to 1989. This radar array was used as an early warning network to alert the Soviets if the USA where to launch ballistic missiles against them.
Unlike a traditional radar which uses microwaves and can only see to the horizon c8 miles an over-the-horizon radar uses shortwave systems that reflect their signals off the ionosphere for very long-range detection. The Duga-3 was apparently able to cover distances as far as the central states of the US.
The signal was so strong it interrupted commercial signals as far as Europe causing issues with radios and televisions!