HONOLULU -- The Honolulu Police Department had to go to its backup system Monday while they tried to determine what troubled its radio system.

The HPD radio system is reported to be back working in digital mode Monday evening. At around midday, police said they had to go a backup system.

"Today, the problem was with the city-owned microwave link that connects a lot of our radio repeaters to the station," HPD Assistant Chief Robert Prasser said. "When the officers transmit on 800 megahertz it goes to a repeater and comes to the ion by microwave link. That's what we had interference with today."

Sources told KITV 4 News that the system was totally down for up to 15 minutes Sunday and again Monday.

"When there's interference on the microwave link it comes out as electronic noise. So transmissions have to stop. We have a contingency plan. We went to that plan," Prasser said.

Communications were only cut off when the problem initially occurred, Prasser said.

The digital radio system cost $41 million and has had problems since it was installed.

Police officials insist the radio problems don't pose any threat to public safety even though on several occasions officers voices came across the radio as garbled electronic static.