858.7125 was first licensed by Clarkstown in 1993 and was in use for years for their MDT system. They eventually switched to Verizon's network, rendering the 800 MHz frequency silent.
As the rest of the county's police departments were starting to migrate over to the 700 MHz system, Clarkstown decided that having an existing 800 MHz repeater gave them an advantage as far as being able to maintain their own backup to the county system that would operate using the 700/800 MHz APX radios they were already deploying.
So, they converted the Quantar repeater from data to voice, and wired up their APX consolette so that it would multi-cast on the 700 MHz talkgroup and 858.7125 whenever they keyed from the consoles. They also enabled a console patch between the two resources.
CPD operates natively on 700 MHz, although on rare occasion you might hear a radio accessing the 800 MHz repeater directly. All of their radios have 858.7125 programmed in for backup purposes should there be a trunked system failure.
No, there are no significant coverage issues for them. The New City RF subsite was activated in Sept of 2015, which increased the signal in the area by quite a bit.
In the end, it's just easier to leave it setup as a multi-cast so that if there's a problem on 700 MHz, they're already transmitting on 800 MHz without having to do anything else. Also, while maybe not their intention, it also makes it easier and cheaper to monitor them on 800 MHz FDMA than it does on 700 MHz TDMA for those without APX subscribers. Which of course allows for interop with outside agencies such as Westchester's aviation unit, which I don't believe has 700 MHz TDMA capability yet.
