Some years ago now I set the transmit power of my Time Capsule to 25%, yet with various updates to the Airport Utility, the ability to reset that to something different was lost. The result? I crippled wireless network.
The solution in the past was to continue using Airport Utility 5.6, but with the upgrade to Mavericks and Yosemite, this was impossible.
Thankfully someone came up with a solution that, via a launcher that injects old system libraries upon opening, Airport Utility 5.6.1 can be used in Mavericks!