obstacle and enters the second warning zone, the VHF radio transmits an audible warning describing the obstacle. (a) Radiodetermination (radar) frequencies. Frequencies authorized under § 87.475(b)(7) of this part are available for use by an AVWS. The frequency coordination requirements in § 87.475(a) of this part apply. (b) VHF audible warning frequencies. Frequencies authorized under § 87.187(j), § 87.217(a), § 87.241(b) and § 87.323(b) (excluding 121.950 MHz) of this part are available for use by an AVWS. Multiple frequencies may be authorized for an individual station, depending on need and the use of frequencies assigned in the vicinity of a proposed AVWS facility. Use of these frequencies is subject to the following limitations: (1) The output power shall not exceed -3