FCC Report 10/7: AM Interference Protection Changes Proposed
The FCC has proposed a rulemaking for changes to the protected contours of AM stations.
The agency states the first group of proposals are designed to preserve some of Class A AMs wide coverage areas while relieving more local stations of their current obligation to protect Class A stations from interference with the goal to allow smaller stations to better cover their communities at night. The new proposal states that in daytime hours Class A AMs are protected to their 0.5 mV/m daytime groundwave contour, from both co-channel and first-adjacent channel stations. The FCC is also seeking comment on a pair of proposals for both critical-hours and nighttime protection. The first critical hours proposal says Class A’s are afforded no protection from other AM stations, while the second keeps the same 0.5 mV/m groundwave contour as the daytime proposal. For nighttime protection, option one says there may be no overlap between a Class A AM station’s 0.5 mV/m nighttime groundwave contour and any interfering AM station’s 0.025 mV/m 10 percent skywave contour (calculated using the single station method), while the second offers Class A AM stations are protected from other AM stations in the same manner as Class B AM stations are protected, that is, interference may not be increased above the greater of the 0.5 mV/m nighttime groundwave contour or the 50 percent exclusion RSS NIF level (calculated using the multiple station method).
The FCC still intends to change Class B, C, and D stations to return to the pre-1991 0 dB daytime 1:1 protection ratio for first adjacent channels, change second adjacent channel groundwave protection to match the current levels for third adjacent channel protection, and eliminate third adjacent channel groundwave protection while changing the daytime protected contour to the 2.0 mV/m contour.
The full notice of proposed rulemaking can be read here.