As many as 100 police officers were unable to communicate with each other Monday night in downtown Oakland during Obama's speech at a fundraiser at the Fox Theater, the San Francisco Chronicle reported.
"The guys downtown couldn't talk to one another," said Barry Donelan, head of the Oakland Police Officers Association.
The radio system, installed a year ago, has been a frequent problem for the police force, leaving officers' digital radios prone to blackouts across the city, officials said.
"It's touch and go every day with this system," Donelan said. "It just happened that one of the antennas went down when the president of the United States was here."
On Monday, a cooling system in one radio tower malfunctioned, causing "severe" communications problems after 10 p.m., said Sgt. Chris Bolton. The problem was identified around 12:30 a.m. Tuesday but wasn't fully restored until about 6 p.m.