Aeronautical Frequency Notification, FCC Form 321

Multichannel Video Programming Distributors (MVPDs) provide their programming over a closed system and, thus, may use all frequencies to do so. They must, however, prevent leakage of those signals from the system and guard against and minimize any harm to aeronautical communications should leak occur. Part of the regime for protecting aeronautical frequencies from interference and resolving interference is notification of the Commission of use of those frequencies and that proper frequency offsets and other precautions are taken. Form 321 is used for this purpose. Under 47 CFR 76.1804, an MVPD shall notify the Commission before transmitting any digital signal with average power exceeding 10-5 watts across a 30 kHz bandwidth in a 2.5 millisecond time period, or for other signal types, any carrier of other signal components with an average power level across a 25 kHz bandwidth in any 160 microsecond time period equal to or greater than 10−4 watts at any point in the cable distribution system on any new frequency or frequencies in the aeronautical radio frequency bands (108-137 MHz, 225-400 MHz). The notification shall be made on FCC Form 321.

The latest form for Aeronautical Frequency Notification, FCC Form 321 expires 2028-07-31 and can be found here.