I use a similar method to ofd8001. For consistency I always assign QKs to sites starting at 71. I assign each nearby site its own QK so I can turn each one on or off at will. Usually that's 2 or 3 nearby sites, maybe as many as 5. Then for a big statewide system I'll assign the distant sites in groups by area. So the 7 sites in the south valley all get QK 75 for example, and the 9 sites in the central part of the state are all QK 76, etc. These are sites that are too far away to receive from my home, but I keep them in the radio so that when I travel I can unlock a bunch of sites at once for a given area.
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