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First off, the three counties do not share one single system. Outagamie and Winnebago do but Brown has it's own. Location and what you use for an antenna will make all the difference in hearing one of these systems or not. I'm in New London and I can't hear Brown county at all. Or Winnebago's control channel for that matter. I can hear traffic from Winnebago county on Outagamie's control channel, however.
Where are you located and what are you using for an antenna? Also, have you programmed it by hand or have you used Sentinel?