FCC OVERVIEW on AM Screenings:
The FCC requires that the AM stations be notified of any proposed construction of nearby towers or other structures that might distort the AM stations pattern. The current FCC regulations require coordination anytime construction is within 1.0 kilometers of a Non-directional broadcast station and 3.0 kilometers of a directional broadcast station. This requires "measurements" at the site. RSI Note: The FCC is no longer specifying the type of measurements required. Normally, the station's directional monitoring points will suffice, or a few measurements on the Non-directional pattern of the station be used. But measurements do need to be taken both before (pre-) and after (post) the construction. Call RSI to ensure compliance with federally mandated standards.

Why does the FCC require this screening?

Interference between cellular towers and standard broadcast (AM) radio antenna systems is becoming increasingly common. The solution to these problems is often complex and, since the AM band at 540 to 1710 kHz is so far removed from other frequencies, non-AM broadcast technical personnel are often not familiar with the demands of lower frequency technology. If the mast or tower on which the cellular antennas are mounted is a significant portion of a wavelength in the AM broadcast band there will be mutual coupling between the new tower and the AM broadcast towers. This mutual coupling in the AM broadcast towers induces RF voltage in the cellular tower. Then the induced RF voltage will lead to significant RF current at the AM broadcast frequency and the new tower will radiate power at the AM frequency and effectively becomes a parasitic element of the AM station array, changing the pattern.