Started earlier this morning on all channels actually. I tweeted about this issue and shortly afterwards, their was a still and box at 42nd Halsted and had many communication issues. From my understanding of the system, I would guess some of the receiver sites weren't making a connection with the consoles at the OEMC and this was occurring on all the channels. They were performing radio checks with the companies this evening and as a result of their findings that many of the portables were inoperable, a fire company will be dispatched on all EMS runs for safety of the crews.