While in the Los Angeles area for work, I was picking up some of the many VHF P-25 frequencies being used throughout the southern end of the state by the CBP wide area system. This system is technically separate, but fiscally part of the Integrated Wireless Network (IWN). These are not trunked, but likely a vote-scan system used mainly by CBP Field Operations and Border Patrol. I have noted what is probable use by other agencies as well, such as Coast Guard and likely ICE.
I was checking what I was hearing against what I think is a pretty good source for the area, the SoCal Fedcom Blog, http://socalfedcom.blogspot.com. Among some of the updated frequencies, there is a reference to something the blog author is referring to as the MCS or Marine Common System. I would presume this refers to a common radio system for CBP, Coast Guard and other agencies working the various maritime operations.
Here are the frequencies noted as being part of the MCS:
162.6250 MHz, N820 - common input
171.3250 MHz, N820 - Mt. Solidad repeater
172.0625 MHz, N820 - Santa Ynez repeater
172.7125 MHz, N820 - San Pedro repeater
Reports indicate a fourth repeater located on San Nicolas Island, but the frequency is unconfirmed.
I'm still researching and trying to find more information on this system.
UPDATE!
While searching early one morning in LA, I found 171.1875 MHz, N820 active with encrypted voice. This might be the missing San Nicolas Island repeater, as I had a nice marine layer working the day I found this!
