Covenant communications jammer
From Halopedia, the Halo wiki
Covenant communications jammers are a piece of technology used by the Covenant. On August 23, 2552, during the Fall of Reach, SPARTAN-B312 assisted in destroying several of the jammers in New Alexandria that were blocking a signal to UNSC Command.
Jammers appear to operate by blocking out particular COM frequencies; while UNSC command could not receive or transmit radio orders to forces in New Alexandria, short-range communications were possible even at close range to the jammers.
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