47 CFR § 90.689 - Field strength limits.
(a) For purposes of implementing §§ 90.689 through 90.699, predicted 36 and 40 dBµV/m contours shall be calculated using Figure 10 of § 73.699 of this chapter with a correction factor of −9 dB, and predicted 18 and 22 dBµV/m contours shall be calculated using Figure 10a of § 73.699 of this chapter with a correction factor of −9 dB.
(b) The predicted or measured field strength at any location on the border of the EA-based service area for EA licensees must not exceed 40 dBuV/m unless all bordering EA licensees agree to a higher field strength. In the event that this standard conflicts with the EA licensee's obligation to provide co-channel protection to incumbent licensees pursuant to § 90.621(b), the requirements of § 90.621(b) shall prevail.