They may most likely be using the same DPL as they use on their primary channel. I can't figure out why 3 departments are using that same frequency in such close proximity to each other. Concord, Tewksbury and Watertown are pretty darned close to each other. Another example is Newton's F1 is Salem's F1, Salem's F2 is Winthrop's F1. And you got Wakefield and Brookline utilizing the same primary frequency. Mightily crowded in the Boston area.