Thanks for the info, all. I might have gotten closer on my own had I looked up the frequencies matching Med 21, 22, and 23, all being patched in the Baltimore City trunking system....I usually have those two talkgroups locked out, though, and simply have Med 1 through 10 programmed conventionally...
I'll go out on a limb and assume that all those voice channels in use around these parts are using PL 167.9?
All MIEMSS Region III (Baltimore City, Baltimore County, Harford County Howard County, Anne Arundel County, Carroll County, and Cecil County) use PL 167.9 on the MIEMSS UHF system.
I'm not 100% sure I understand what you mean by "the frequencies matching Med 21, 22, and 23, all being patched in the Baltimore City trunking system."
Those jurisdictions having their own EMRC consult talk groups on their respective trunked systems aren't patched to Med channels. They are patched directly to the consulting hospital using tie-lines or microwave intercom. This is a common misconception. In other words, Med 4 (463.075) is completely independent of Baltimore County's trunked system talk group 224 (despite the fact that it is given the label of "Med-4"). Two separate units could use those two separate mediums to consult with two separate hospitals simultaneously. They are not "patched" together to complete a call.
The only med channels/talk groups that are "patched" are the "CALL" channels/talk groups:
MIEMSS Call-1 (a.k.a. Med-9, 462.95)
Baltimore City talk group A-5 CLL21
Baltimore County talk group 221 CALL-1
Harford County talk group A-6 CALL-301
Carroll County talk group 2 EMRC-1
Howard County talk group E-1 CALL-1
Anne Arundel talk group 3-F CALL-1
Cecil County talk group 3 EMRC
And in reality, they aren't even really "patched" together. They are slaved together so that one operator can monitor traffic on all the systems via one port on the console. You won't hear traffic from one jurisdiction on another county's system.
So since each county has 2 consult talk groups, and you add the two Region III UHF med channels, there could be 16 simultaneous consults occurring in Region III.