Low Band Radio Interference. From Private Wireless Forum, Posted by Bill Brownlow

NY DOT reports they have been experiencing severe interference issues with their low band radios and have found the culprit  to be high efficiency fluorescent ballasts. They have narrowed it down to the ballasts that are commercial grade and that operate at multiple voltages (120-277V). The ballasts that had that operated strictly on 120V did not cause issues. They believe it comes from the switching power supply that allows for multi-voltage use and they have tested ballasts that are single voltage (120V) and they do not cause harmful interference.

NTDOT has contacted a few manufacturers (Sylvania, Philips, GE) and they have stated that they have heard of very few interference issues and they are trying to consolidate product and stop manufacturing single voltage ballasts. The noise can be as high as -80 dbm from 30-80Mhz. The manufacturers state that these ballasts meet FCC Part 18 rules (Industrial and commercial). NYDOT would like the other low band users out there to be aware of this.