Repeater Planning Series Vol. 3: “The Six Most Common Mistakes" [Contains Stupidity]

[intermod]

Mistake #3: Fail to Communicate with Existing (Incumbent) Repeater Licensees

You fail to coordinate access codes with the other repeater owners on your channel and install your repeater anyway.  The incumbent(s) become unhinged and pissed off.  You also fail to realize that some repeaters use multiple access codes (for different user groups), and may also be using unmatched code pairs on the repeater uplink and downlink (i.e., repeater access/uplink uses 141.3 Hz, but its downlink uses 85.4 Hz).  While this can be closely related to Mistake #2 described earlier, it’s also possible you are using one of the incumbent's codes.  You could have attempted to contact the incumbent and ask whether they were using any of your proposed codes (via mygmrs.com, over their repeater, or by reading their Morse code repeater ID and getting their address through the FCC website).

Or - you could have researched the codes in use the traditional way: purchasing one of the essential tools used by repeaters owners for decades, called the "CTCSS/DCS decoder".  Also, many new radio models will automatically decode and display downlink codes when set correctly.